WIP: broken merge but need a git checkpoint

.github/stale.yml

@@ -1,10 +1,9 @@
 # Configuration for probot-stale - https://github.com/probot/stale
 daysUntilStale: 180
-daysUntilClose: 365
+daysUntilClose: false
 exemptLabels:
   - "critical"
+  - "never-stale"
 staleLabel: "stale"
-markComment: |
+markComment: false
-  I marked this as stale due to inactivity. → [More info](https://github.com/NixOS/nix/blob/master/.github/STALE-BOT.md)
+closeComment: false
-closeComment: |
-  I closed this issue due to inactivity. → [More info](https://github.com/NixOS/nix/blob/master/.github/STALE-BOT.md)

.github/workflows/backport.yml

@@ -2,9 +2,15 @@ name: Backport
 on:
   pull_request_target:
     types: [closed, labeled]
+permissions:
+  contents: read
 jobs:
   backport:
     name: Backport Pull Request
+    permissions:
+      # for zeebe-io/backport-action
+      contents: write
+      pull-requests: write
     if: github.repository_owner == 'NixOS' && github.event.pull_request.merged == true && (github.event_name != 'labeled' || startsWith('backport', github.event.label.name))
     runs-on: ubuntu-latest
     steps:
@@ -15,7 +21,7 @@ jobs:
           fetch-depth: 0
       - name: Create backport PRs
         # should be kept in sync with `version`
-        uses: zeebe-io/backport-action@v0.0.7
+        uses: zeebe-io/backport-action@v0.0.8
         with:
           # Config README: https://github.com/zeebe-io/backport-action#backport-action
           github_token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/ci.yml

@@ -4,10 +4,12 @@ on:
   pull_request:
   push:
 
+permissions: read-all
+
 jobs:
 
   tests:
-    needs: [check_cachix]
+    needs: [check_secrets]
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
@@ -20,28 +22,34 @@ jobs:
     - uses: cachix/install-nix-action@v17
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v10
-      if: needs.check_cachix.outputs.secret == 'true'
+      if: needs.check_secrets.outputs.cachix == 'true'
       with:
         name: '${{ env.CACHIX_NAME }}'
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     - run: nix --experimental-features 'nix-command flakes' flake check -L
 
-  check_cachix:
+  check_secrets:
-    name: Cachix secret present for installer tests
+    permissions:
+      contents: none
+    name: Check Cachix and Docker secrets present for installer tests
     runs-on: ubuntu-latest
     outputs:
-      secret: ${{ steps.secret.outputs.secret }}
+      cachix: ${{ steps.secret.outputs.cachix }}
+      docker: ${{ steps.secret.outputs.docker }}
     steps:
-      - name: Check for Cachix secret
+      - name: Check for secrets
         id: secret
         env:
           _CACHIX_SECRETS: ${{ secrets.CACHIX_SIGNING_KEY }}${{ secrets.CACHIX_AUTH_TOKEN }}
-        run: echo "::set-output name=secret::${{ env._CACHIX_SECRETS != '' }}"
+          _DOCKER_SECRETS: ${{ secrets.DOCKERHUB_USERNAME }}${{ secrets.DOCKERHUB_TOKEN }}
+        run: |
+          echo "::set-output name=cachix::${{ env._CACHIX_SECRETS != '' }}"
+          echo "::set-output name=docker::${{ env._DOCKER_SECRETS != '' }}"
 
   installer:
-    needs: [tests, check_cachix]
+    needs: [tests, check_secrets]
-    if: github.event_name == 'push' && needs.check_cachix.outputs.secret == 'true'
+    if: github.event_name == 'push' && needs.check_secrets.outputs.cachix == 'true'
     runs-on: ubuntu-latest
     outputs:
       installerURL: ${{ steps.prepare-installer.outputs.installerURL }}
@@ -60,8 +68,8 @@ jobs:
       run: scripts/prepare-installer-for-github-actions
 
   installer_test:
-    needs: [installer, check_cachix]
+    needs: [installer, check_secrets]
-    if: github.event_name == 'push' && needs.check_cachix.outputs.secret == 'true'
+    if: github.event_name == 'push' && needs.check_secrets.outputs.cachix == 'true'
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
@@ -76,11 +84,12 @@ jobs:
     - run: nix-instantiate -E 'builtins.currentTime' --eval
 
   docker_push_image:
-    needs: [check_cachix, tests]
+    needs: [check_secrets, tests]
     if: >-
       github.event_name == 'push' &&
       github.ref_name == 'master' &&
-      needs.check_cachix.outputs.secret == 'true'
+      needs.check_secrets.outputs.cachix == 'true' &&
+      needs.check_secrets.outputs.docker == 'true'
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3
@@ -88,9 +97,9 @@ jobs:
         fetch-depth: 0
     - uses: cachix/install-nix-action@v17
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - run: echo NIX_VERSION="$(nix-instantiate --eval -E '(import ./default.nix).defaultPackage.${builtins.currentSystem}.version' | tr -d \")" >> $GITHUB_ENV
+    - run: echo NIX_VERSION="$(nix --experimental-features 'nix-command flakes' eval .\#default.version | tr -d \")" >> $GITHUB_ENV
     - uses: cachix/cachix-action@v10
-      if: needs.check_cachix.outputs.secret == 'true'
+      if: needs.check_secrets.outputs.cachix == 'true'
       with:
         name: '${{ env.CACHIX_NAME }}'
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
@@ -100,7 +109,7 @@ jobs:
     - run: docker tag nix:$NIX_VERSION nixos/nix:$NIX_VERSION
     - run: docker tag nix:$NIX_VERSION nixos/nix:master
     - name: Login to Docker Hub
-      uses: docker/login-action@v1
+      uses: docker/login-action@v2
       with:
         username: ${{ secrets.DOCKERHUB_USERNAME }}
         password: ${{ secrets.DOCKERHUB_TOKEN }}

.github/workflows/hydra_status.yml

@@ -1,8 +1,12 @@
 name: Hydra status
+
+permissions: read-all
+
 on:
   schedule:
     - cron: "12,42 * * * *"
   workflow_dispatch:
+
 jobs:
   check_hydra_status:
     name: Check Hydra status

.gitignore

@@ -22,7 +22,7 @@ perl/Makefile.config
 /doc/manual/src/SUMMARY.md
 /doc/manual/src/command-ref/new-cli
 /doc/manual/src/command-ref/conf-file.md
-/doc/manual/src/expressions/builtins.md
+/doc/manual/src/language/builtins.md
 
 # /scripts/
 /scripts/nix-profile.sh
@@ -35,6 +35,7 @@ perl/Makefile.config
 /src/libexpr/parser-tab.hh
 /src/libexpr/parser-tab.output
 /src/libexpr/nix.tbl
+/src/libexpr/tests/libexpr-tests
 
 # /src/libstore/
 *.gen.*

.version

@@ -1 +1 @@
-2.9.0
+2.12.0

Makefile

@@ -8,6 +8,7 @@ makefiles = \
   src/libfetchers/local.mk \
   src/libmain/local.mk \
   src/libexpr/local.mk \
+  src/libexpr/tests/local.mk \
   src/libcmd/local.mk \
   src/nix/local.mk \
   src/resolve-system-dependencies/local.mk \
@@ -27,7 +28,8 @@ makefiles = \
 OPTIMIZE = 1
 
 ifeq ($(OPTIMIZE), 1)
-  GLOBAL_CXXFLAGS += -O3
+  GLOBAL_CXXFLAGS += -O3 $(CXXLTO)
+  GLOBAL_LDFLAGS += $(CXXLTO)
 else
   GLOBAL_CXXFLAGS += -O0 -U_FORTIFY_SOURCE
 endif

Makefile.config.in

@@ -1,4 +1,3 @@
-HOST_OS = @host_os@
 AR = @AR@
 BDW_GC_LIBS = @BDW_GC_LIBS@
 BOOST_LDFLAGS = @BOOST_LDFLAGS@
@@ -7,18 +6,20 @@ CC = @CC@
 CFLAGS = @CFLAGS@
 CXX = @CXX@
 CXXFLAGS = @CXXFLAGS@
+CXXLTO = @CXXLTO@
 EDITLINE_LIBS = @EDITLINE_LIBS@
 ENABLE_S3 = @ENABLE_S3@
 GTEST_LIBS = @GTEST_LIBS@
 HAVE_LIBCPUID = @HAVE_LIBCPUID@
 HAVE_SECCOMP = @HAVE_SECCOMP@
+HOST_OS = @host_os@
 LDFLAGS = @LDFLAGS@
 LIBARCHIVE_LIBS = @LIBARCHIVE_LIBS@
 LIBBROTLI_LIBS = @LIBBROTLI_LIBS@
 LIBCURL_LIBS = @LIBCURL_LIBS@
+LIBSECCOMP_LIBS = @LIBSECCOMP_LIBS@
 LOWDOWN_LIBS = @LOWDOWN_LIBS@
 OPENSSL_LIBS = @OPENSSL_LIBS@
-LIBSECCOMP_LIBS = @LIBSECCOMP_LIBS@
 PACKAGE_NAME = @PACKAGE_NAME@
 PACKAGE_VERSION = @PACKAGE_VERSION@
 SHELL = @bash@
@@ -30,6 +31,7 @@ datadir = @datadir@
 datarootdir = @datarootdir@
 doc_generate = @doc_generate@
 docdir = @docdir@
+embedded_sandbox_shell = @embedded_sandbox_shell@
 exec_prefix = @exec_prefix@
 includedir = @includedir@
 libdir = @libdir@

README.md

@@ -20,7 +20,7 @@ Information on additional installation methods is available on the [Nix download
 
 ## Building And Developing
 
-See our [Hacking guide](https://hydra.nixos.org/job/nix/master/build.x86_64-linux/latest/download-by-type/doc/manual/contributing/hacking.html) in our manual for instruction on how to
+See our [Hacking guide](https://nixos.org/manual/nix/stable/contributing/hacking.html) in our manual for instruction on how to
 build nix from source with nix-build or how to get a development environment.
 
 ## Additional Resources

boehmgc-coroutine-sp-fallback.diff

@@ -1,3 +1,35 @@
+diff --git a/darwin_stop_world.c b/darwin_stop_world.c
+index 3dbaa3fb..36a1d1f7 100644
+--- a/darwin_stop_world.c
++++ b/darwin_stop_world.c
+@@ -352,6 +352,7 @@ GC_INNER void GC_push_all_stacks(void)
+   int nthreads = 0;
+   word total_size = 0;
+   mach_msg_type_number_t listcount = (mach_msg_type_number_t)THREAD_TABLE_SZ;
++  size_t stack_limit;
+   if (!EXPECT(GC_thr_initialized, TRUE))
+     GC_thr_init();
+ 
+@@ -407,6 +408,19 @@ GC_INNER void GC_push_all_stacks(void)
+             GC_push_all_stack_sections(lo, hi, p->traced_stack_sect);
+           }
+           if (altstack_lo) {
++            // When a thread goes into a coroutine, we lose its original sp until
++            // control flow returns to the thread.
++            // While in the coroutine, the sp points outside the thread stack,
++            // so we can detect this and push the entire thread stack instead,
++            // as an approximation.
++            // We assume that the coroutine has similarly added its entire stack.
++            // This could be made accurate by cooperating with the application
++            // via new functions and/or callbacks.
++            stack_limit = pthread_get_stacksize_np(p->id);
++            if (altstack_lo >= altstack_hi || altstack_lo < altstack_hi - stack_limit) { // sp outside stack
++              altstack_lo = altstack_hi - stack_limit;
++            }
++
+             total_size += altstack_hi - altstack_lo;
+             GC_push_all_stack(altstack_lo, altstack_hi);
+           }
 diff --git a/pthread_stop_world.c b/pthread_stop_world.c
 index 4b2c429..1fb4c52 100644
 --- a/pthread_stop_world.c

configure.ac

@@ -147,6 +147,20 @@ if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
     LDFLAGS="-latomic $LDFLAGS"
 fi
 
+# LTO is currently broken with clang for unknown reasons; ld segfaults in the llvm plugin
+AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto],[Enable LTO (only supported with GCC) [default=no]]),
+  lto=$enableval, lto=no)
+if test "$lto" = yes; then
+    if $CXX --version | grep -q GCC; then
+        AC_SUBST(CXXLTO, [-flto=jobserver])
+    else
+        echo "error: LTO is only supported with GCC at the moment" >&2
+        exit 1
+    fi
+else
+    AC_SUBST(CXXLTO, [""])
+fi
+
 PKG_PROG_PKG_CONFIG
 
 AC_ARG_ENABLE(shared, AS_HELP_STRING([--enable-shared],[Build shared libraries for Nix [default=yes]]),
@@ -282,18 +296,28 @@ AC_CHECK_FUNCS([setresuid setreuid lchown])
 AC_CHECK_FUNCS([strsignal posix_fallocate sysconf])
 
 
-# This is needed if bzip2 is a static library, and the Nix libraries
-# are dynamic.
-case "${host_os}" in
-  darwin*)
-    LDFLAGS="-all_load $LDFLAGS"
-    ;;
-esac
-
-
 AC_ARG_WITH(sandbox-shell, AS_HELP_STRING([--with-sandbox-shell=PATH],[path of a statically-linked shell to use as /bin/sh in sandboxes]),
   sandbox_shell=$withval)
 AC_SUBST(sandbox_shell)
+if test ${cross_compiling:-no} = no && ! test -z ${sandbox_shell+x}; then
+  AC_MSG_CHECKING([whether sandbox-shell has the standalone feature])
+  # busybox shell sometimes allows executing other busybox applets,
+  # even if they are not in the path, breaking our sandbox
+  if PATH= $sandbox_shell -c "busybox" 2>&1 | grep -qv "not found"; then
+    AC_MSG_RESULT(enabled)
+    AC_MSG_ERROR([Please disable busybox FEATURE_SH_STANDALONE])
+  else
+    AC_MSG_RESULT(disabled)
+  fi
+fi
+
+AC_ARG_ENABLE(embedded-sandbox-shell, AS_HELP_STRING([--enable-embedded-sandbox-shell],[include the sandbox shell in the Nix binary [default=no]]),
+  embedded_sandbox_shell=$enableval, embedded_sandbox_shell=no)
+AC_SUBST(embedded_sandbox_shell)
+if test "$embedded_sandbox_shell" = yes; then
+  AC_DEFINE(HAVE_EMBEDDED_SANDBOX_SHELL, 1, [Include the sandbox shell in the Nix binary.])
+fi
+
 
 # Expand all variables in config.status.
 test "$prefix" = NONE && prefix=$ac_default_prefix

doc/manual/anchors.jq

@@ -0,0 +1,31 @@
+"\\[\\]\\{#(?<anchor>[^\\}]+?)\\}" as $empty_anchor_regex |
+"\\[(?<text>[^\\]]+?)\\]\\{#(?<anchor>[^\\}]+?)\\}" as $anchor_regex |
+
+
+def transform_anchors_html:
+    . | gsub($empty_anchor_regex; "<a name=\"" + .anchor + "\"></a>")
+      | gsub($anchor_regex; "<a href=\"#" + .anchor + "\" id=\"" + .anchor + "\">" + .text + "</a>");
+
+
+def transform_anchors_strip:
+    . | gsub($empty_anchor_regex; "")
+      | gsub($anchor_regex; .text);
+
+
+def map_contents_recursively(transformer):
+    . + {
+        Chapter: (.Chapter + {
+            content: .Chapter.content | transformer,
+            sub_items: .Chapter.sub_items | map(map_contents_recursively(transformer)),
+        }),
+    };
+
+
+def process_command:
+    .[0] as $context |
+    .[1] as $body |
+    $body + {
+        sections: $body.sections | map(map_contents_recursively(if $context.renderer == "html" then transform_anchors_html else transform_anchors_strip end)),
+    };
+
+process_command

doc/manual/book.toml

@@ -1,2 +1,7 @@
 [output.html]
 additional-css = ["custom.css"]
+additional-js = ["redirects.js"]
+
+[preprocessor.anchors]
+renderers = ["html"]
+command = "jq --from-file doc/manual/anchors.jq"

doc/manual/generate-manpage.nix

@@ -1,4 +1,4 @@
-{ command, renderLinks ? false }:
+{ command }:
 
 with builtins;
 with import ./utils.nix;
@@ -21,9 +21,7 @@ let
            listCommands = cmds:
              concatStrings (map (name:
                "* "
-               + (if renderLinks
+               + "[`${command} ${name}`](./${appendName filename name}.md)"
-                  then "[`${command} ${name}`](./${appendName filename name}.md)"
-                  else "`${command} ${name}`")
                + " - ${cmds.${name}.description}\n")
                (attrNames cmds));
          in

doc/manual/local.mk

@@ -1,5 +1,9 @@
 ifeq ($(doc_generate),yes)
 
+MANUAL_SRCS := \
+  $(call rwildcard, $(d)/src, *.md) \
+  $(call rwildcard, $(d)/src, */*.md)
+
 # Generate man pages.
 man-pages := $(foreach n, \
   nix-env.1 nix-build.1 nix-shell.1 nix-store.1 nix-instantiate.1 \
@@ -46,7 +50,7 @@ $(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli
 
 $(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/generate-manpage.nix $(bindir)/nix
 	@rm -rf $@
-	$(trace-gen) $(nix-eval) --write-to $@ --expr 'import doc/manual/generate-manpage.nix { command = builtins.readFile $<; renderLinks = true; }'
+	$(trace-gen) $(nix-eval) --write-to $@ --expr 'import doc/manual/generate-manpage.nix { command = builtins.readFile $<; }'
 
 $(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/generate-options.nix $(d)/src/command-ref/conf-file-prefix.md $(bindir)/nix
 	@cat doc/manual/src/command-ref/conf-file-prefix.md > $@.tmp
@@ -61,10 +65,10 @@ $(d)/conf-file.json: $(bindir)/nix
 	$(trace-gen) $(dummy-env) $(bindir)/nix show-config --json --experimental-features nix-command > $@.tmp
 	@mv $@.tmp $@
 
-$(d)/src/expressions/builtins.md: $(d)/builtins.json $(d)/generate-builtins.nix $(d)/src/expressions/builtins-prefix.md $(bindir)/nix
+$(d)/src/language/builtins.md: $(d)/builtins.json $(d)/generate-builtins.nix $(d)/src/language/builtins-prefix.md $(bindir)/nix
-	@cat doc/manual/src/expressions/builtins-prefix.md > $@.tmp
+	@cat doc/manual/src/language/builtins-prefix.md > $@.tmp
 	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp
-	@cat doc/manual/src/expressions/builtins-suffix.md >> $@.tmp
+	@cat doc/manual/src/language/builtins-suffix.md >> $@.tmp
 	@mv $@.tmp $@
 
 $(d)/builtins.json: $(bindir)/nix
@@ -92,12 +96,12 @@ doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
 	  if [[ $$name = SUMMARY ]]; then continue; fi; \
 	  printf "Title: %s\n\n" "$$name" > $$tmpFile; \
 	  cat $$i >> $$tmpFile; \
-	  lowdown -sT man -M section=1 $$tmpFile -o $(DESTDIR)$$(dirname $@)/$$name.1; \
+	  lowdown -sT man --nroff-nolinks -M section=1 $$tmpFile -o $(DESTDIR)$$(dirname $@)/$$name.1; \
 	  rm $$tmpFile; \
 	done
 	@touch $@
 
-$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/command-ref/conf-file.md $(d)/src/expressions/builtins.md $(call rwildcard, $(d)/src, *.md)
+$(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/custom.css $(d)/src/SUMMARY.md $(d)/src/command-ref/new-cli $(d)/src/command-ref/conf-file.md $(d)/src/language/builtins.md
 	$(trace-gen) RUST_LOG=warn mdbook build doc/manual -d $(DESTDIR)$(docdir)/manual
 
 endif

doc/manual/redirects.js

@@ -0,0 +1,330 @@
+// Redirects from old DocBook manual.
+var redirects = {
+  "#part-advanced-topics": "advanced-topics/advanced-topics.html",
+  "#chap-tuning-cores-and-jobs": "advanced-topics/cores-vs-jobs.html",
+  "#chap-diff-hook": "advanced-topics/diff-hook.html",
+  "#check-dirs-are-unregistered": "advanced-topics/diff-hook.html#check-dirs-are-unregistered",
+  "#chap-distributed-builds": "advanced-topics/distributed-builds.html",
+  "#chap-post-build-hook": "advanced-topics/post-build-hook.html",
+  "#chap-post-build-hook-caveats": "advanced-topics/post-build-hook.html#implementation-caveats",
+  "#part-command-ref": "command-ref/command-ref.html",
+  "#conf-allow-import-from-derivation": "command-ref/conf-file.html#conf-allow-import-from-derivation",
+  "#conf-allow-new-privileges": "command-ref/conf-file.html#conf-allow-new-privileges",
+  "#conf-allowed-uris": "command-ref/conf-file.html#conf-allowed-uris",
+  "#conf-allowed-users": "command-ref/conf-file.html#conf-allowed-users",
+  "#conf-auto-optimise-store": "command-ref/conf-file.html#conf-auto-optimise-store",
+  "#conf-binary-cache-public-keys": "command-ref/conf-file.html#conf-binary-cache-public-keys",
+  "#conf-binary-caches": "command-ref/conf-file.html#conf-binary-caches",
+  "#conf-build-compress-log": "command-ref/conf-file.html#conf-build-compress-log",
+  "#conf-build-cores": "command-ref/conf-file.html#conf-build-cores",
+  "#conf-build-extra-chroot-dirs": "command-ref/conf-file.html#conf-build-extra-chroot-dirs",
+  "#conf-build-extra-sandbox-paths": "command-ref/conf-file.html#conf-build-extra-sandbox-paths",
+  "#conf-build-fallback": "command-ref/conf-file.html#conf-build-fallback",
+  "#conf-build-max-jobs": "command-ref/conf-file.html#conf-build-max-jobs",
+  "#conf-build-max-log-size": "command-ref/conf-file.html#conf-build-max-log-size",
+  "#conf-build-max-silent-time": "command-ref/conf-file.html#conf-build-max-silent-time",
+  "#conf-build-repeat": "command-ref/conf-file.html#conf-build-repeat",
+  "#conf-build-timeout": "command-ref/conf-file.html#conf-build-timeout",
+  "#conf-build-use-chroot": "command-ref/conf-file.html#conf-build-use-chroot",
+  "#conf-build-use-sandbox": "command-ref/conf-file.html#conf-build-use-sandbox",
+  "#conf-build-use-substitutes": "command-ref/conf-file.html#conf-build-use-substitutes",
+  "#conf-build-users-group": "command-ref/conf-file.html#conf-build-users-group",
+  "#conf-builders": "command-ref/conf-file.html#conf-builders",
+  "#conf-builders-use-substitutes": "command-ref/conf-file.html#conf-builders-use-substitutes",
+  "#conf-compress-build-log": "command-ref/conf-file.html#conf-compress-build-log",
+  "#conf-connect-timeout": "command-ref/conf-file.html#conf-connect-timeout",
+  "#conf-cores": "command-ref/conf-file.html#conf-cores",
+  "#conf-diff-hook": "command-ref/conf-file.html#conf-diff-hook",
+  "#conf-enforce-determinism": "command-ref/conf-file.html#conf-enforce-determinism",
+  "#conf-env-keep-derivations": "command-ref/conf-file.html#conf-env-keep-derivations",
+  "#conf-extra-binary-caches": "command-ref/conf-file.html#conf-extra-binary-caches",
+  "#conf-extra-platforms": "command-ref/conf-file.html#conf-extra-platforms",
+  "#conf-extra-sandbox-paths": "command-ref/conf-file.html#conf-extra-sandbox-paths",
+  "#conf-extra-substituters": "command-ref/conf-file.html#conf-extra-substituters",
+  "#conf-fallback": "command-ref/conf-file.html#conf-fallback",
+  "#conf-fsync-metadata": "command-ref/conf-file.html#conf-fsync-metadata",
+  "#conf-gc-keep-derivations": "command-ref/conf-file.html#conf-gc-keep-derivations",
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+}

doc/manual/src/SUMMARY.md.in

@@ -26,21 +26,14 @@
     - [Copying Closures via SSH](package-management/copy-closure.md)
     - [Serving a Nix store via SSH](package-management/ssh-substituter.md)
     - [Serving a Nix store via S3](package-management/s3-substituter.md)
-- [Writing Nix Expressions](expressions/writing-nix-expressions.md)
+- [Nix Language](language/index.md)
-  - [A Simple Nix Expression](expressions/simple-expression.md)
+  - [Data Types](language/values.md)
-    - [Expression Syntax](expressions/expression-syntax.md)
+  - [Language Constructs](language/constructs.md)
-    - [Build Script](expressions/build-script.md)
+  - [Operators](language/operators.md)
-    - [Arguments and Variables](expressions/arguments-variables.md)
+  - [Derivations](language/derivations.md)
-    - [Building and Testing](expressions/simple-building-testing.md)
+    - [Advanced Attributes](language/advanced-attributes.md)
-    - [Generic Builder Syntax](expressions/generic-builder.md)
+  - [Built-in Constants](language/builtin-constants.md)
-  - [Writing Nix Expressions](expressions/expression-language.md)
+  - [Built-in Functions](language/builtins.md)
-    - [Values](expressions/language-values.md)
-    - [Language Constructs](expressions/language-constructs.md)
-    - [Operators](expressions/language-operators.md)
-    - [Derivations](expressions/derivations.md)
-      - [Advanced Attributes](expressions/advanced-attributes.md)
-    - [Built-in Constants](expressions/builtin-constants.md)
-    - [Built-in Functions](expressions/builtins.md)
 - [Advanced Topics](advanced-topics/advanced-topics.md)
   - [Remote Builds](advanced-topics/distributed-builds.md)
   - [Tuning Cores and Jobs](advanced-topics/cores-vs-jobs.md)
@@ -66,12 +59,23 @@
 @manpages@
   - [Files](command-ref/files.md)
     - [nix.conf](command-ref/conf-file.md)
+<!--
+- [Architecture](architecture/architecture.md)
+  - [Store](architecture/store/store.md)
+    - [Closure](architecture/store/store/closure.md)
+    - [Build system terminology](architecture/store/store/build-system-terminology.md)
+  - [Store Path](architecture/store/path.md)
+  - [File System Object](architecture/store/fso.md)
+-->
 - [Glossary](glossary.md)
 - [Contributing](contributing/contributing.md)
   - [Hacking](contributing/hacking.md)
   - [CLI guideline](contributing/cli-guideline.md)
 - [Release Notes](release-notes/release-notes.md)
   - [Release X.Y (202?-??-??)](release-notes/rl-next.md)
+  - [Release 2.11 (2022-08-25)](release-notes/rl-2.11.md)
+  - [Release 2.10 (2022-07-11)](release-notes/rl-2.10.md)
+  - [Release 2.9 (2022-05-30)](release-notes/rl-2.9.md)
   - [Release 2.8 (2022-04-19)](release-notes/rl-2.8.md)
   - [Release 2.7 (2022-03-07)](release-notes/rl-2.7.md)
   - [Release 2.6 (2022-01-24)](release-notes/rl-2.6.md)

doc/manual/src/advanced-topics/diff-hook.md

@@ -101,7 +101,7 @@ In particular, notice the
 `/nix/store/krpqk0l9ib0ibi1d2w52z293zw455cap-unstable.check` output. Nix
 has copied the build results to that directory where you can examine it.
 
-> **Note**
+> []{#check-dirs-are-unregistered} **Note**
 > 
 > Check paths are not protected against garbage collection, and this
 > path will be deleted on the next garbage collection.

doc/manual/src/advanced-topics/distributed-builds.md

@@ -12,14 +12,14 @@ machine is accessible via SSH and that it has Nix installed. You can
 test whether connecting to the remote Nix instance works, e.g.
 
 ```console
-$ nix ping-store --store ssh://mac
+$ nix store ping --store ssh://mac
 ```
 
 will try to connect to the machine named `mac`. It is possible to
 specify an SSH identity file as part of the remote store URI, e.g.
 
 ```console
-$ nix ping-store --store ssh://mac?ssh-key=/home/alice/my-key
+$ nix store ping --store ssh://mac?ssh-key=/home/alice/my-key
 ```
 
 Since builds should be non-interactive, the key should not have a

doc/manual/src/architecture/architecture.md

@@ -0,0 +1,79 @@
+# Architecture
+
+*(This chapter is unstable and a work in progress. Incoming links may rot.)*
+
+This chapter describes how Nix works.
+It should help users understand why Nix behaves as it does, and it should help developers understand how to modify Nix and how to write similar tools.
+
+## Overview
+
+Nix consists of [hierarchical layers][layer-architecture].
+
+```
++-----------------------------------------------------------------+
+| Nix                                                             |
+|                  [ commmand line interface ]------,             |
+|                               |                   |             |
+|                           evaluates               |             |
+|                               |                manages          |
+|                               V                   |             |
+|                  [ configuration language  ]      |             |
+|                               |                   |             |
+| +-----------------------------|-------------------V-----------+ |
+| | store                  evaluates to                         | |
+| |                             |                               | |
+| |             referenced by   V       builds                  | |
+| |  [ build input ] ---> [ build plan ] ---> [ build result ]  | |
+| |                                                             | |
+| +-------------------------------------------------------------+ |
++-----------------------------------------------------------------+
+```
+
+At the top is the [command line interface](../command-ref/command-ref.md), translating from invocations of Nix executables to interactions with the underlying layers.
+
+Below that is the [Nix expression language](../expressions/expression-language.md), a [purely functional][purely-functional-programming] configuration language.
+It is used to compose expressions which ultimately evaluate to self-contained *build plans*, used to derive *build results* from referenced *build inputs*.
+
+The command line and Nix language are what users interact with most.
+
+> **Note**
+> The Nix language itself does not have a notion of *packages* or *configurations*.
+> As far as we are concerned here, the inputs and results of a build plan are just data.
+
+Underlying these is the [Nix store](./store/store.md), a mechanism to keep track of build plans, data, and references between them.
+It can also execute build plans to produce new data.
+
+A build plan is a series of *build tasks*.
+Each build task has a special build input which is used as *build instructions*.
+The result of a build task can be input to another build task.
+
+```
++-----------------------------------------------------------------------------------------+
+| store                                                                                   |
+|                   .................................................                     |
+|                   :  build plan                                   :                     |
+|                   :                                               :                     |
+|  [ build input ]-----instructions-,                               :                     |
+|                   :               |                               :                     |
+|                   :               v                               :                     |
+|  [ build input ]----------->[ build task ]--instructions-,        :                     |
+|                   :                                      |        :                     |
+|                   :                                      |        :                     |
+|                   :                                      v        :                     |
+|                   :                               [ build task ]----->[ build result ]  |
+|  [ build input ]-----instructions-,                      ^        :                     |
+|                   :               |                      |        :                     |
+|                   :               v                      |        :                     |
+|  [ build input ]----------->[ build task ]---------------'        :                     |
+|                   :               ^                               :                     |
+|                   :               |                               :                     |
+|  [ build input ]------------------'                               :                     |
+|                   :                                               :                     |
+|                   :                                               :                     |
+|                   :...............................................:                     |
+|                                                                                         |
++-----------------------------------------------------------------------------------------+
+```
+
+[layer-architecture]: https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers
+[purely-functional-programming]: https://en.m.wikipedia.org/wiki/Purely_functional_programming

doc/manual/src/architecture/store/fso.md

@@ -0,0 +1,69 @@
+# File System Object
+
+The Nix store uses a simple file system model for the data it holds in [store objects](store.md#store-object).
+
+Every file system object is one of the following:
+
+ - File: an executable flag, and arbitrary data for contents
+ - Directory: mapping of names to child file system objects
+ - [Symbolic link][symlink]: may point anywhere.
+
+We call a store object's outermost file system object the *root*.
+
+    data FileSystemObject
+      = File      { isExecutable :: Bool, contents :: Bytes }
+      | Directory { entries :: Map FileName FileSystemObject }
+      | SymLink   { target :: Path }
+
+Examples:
+
+- a directory with contents
+
+      /nix/store/<hash>-hello-2.10
+      ├── bin
+      │   └── hello
+      └── share
+          ├── info
+          │   └── hello.info
+          └── man
+              └── man1
+                  └── hello.1.gz
+
+- a directory with relative symlink and other contents
+
+      /nix/store/<hash>-go-1.16.9
+      ├── bin -> share/go/bin
+      ├── nix-support/
+      └── share/
+
+- a directory with absolute symlink
+
+      /nix/store/d3k...-nodejs
+      └── nix_node -> /nix/store/f20...-nodejs-10.24.
+
+A bare file or symlink can be a root file system object.
+Examples:
+
+    /nix/store/<hash>-hello-2.10.tar.gz
+
+    /nix/store/4j5...-pkg-config-wrapper-0.29.2-doc -> /nix/store/i99...-pkg-config-0.29.2-doc
+
+Symlinks pointing outside of their own root or to a store object without a matching reference are allowed, but might not function as intended.
+Examples:
+
+- an arbitrarily symlinked file may change or not exist at all
+
+      /nix/store/<hash>-foo
+      └── foo -> /home/foo
+
+- if a symlink to a store path was not automatically created by Nix, it may be invalid or get invalidated when the store object is deleted
+
+      /nix/store/<hash>-bar
+      └── bar -> /nix/store/abc...-foo
+
+Nix file system objects do not support [hard links][hardlink]:
+each file system object which is not the root has exactly one parent and one name.
+However, as store objects are immutable, an underlying file system can use hard links for optimization.
+
+[symlink]: https://en.m.wikipedia.org/wiki/Symbolic_link
+[hardlink]: https://en.m.wikipedia.org/wiki/Hard_link

doc/manual/src/architecture/store/path.md

@@ -0,0 +1,105 @@
+# Store Path
+
+Nix implements [references](store.md#reference) to [store objects](store.md#store-object) as *store paths*.
+
+Store paths are pairs of
+
+- a 20-byte [digest](#digest) for identification
+- a symbolic name for people to read.
+
+Example:
+
+- digest: `b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z`
+- name:   `firefox-33.1`
+
+It is rendered to a file system path as the concatenation of
+
+  - [store directory](#store-directory)
+  - path-separator (`/`)
+  - [digest](#digest) rendered in a custom variant of [base-32](https://en.m.wikipedia.org/wiki/Base32) (20 arbitrary bytes become 32 ASCII characters)
+  - hyphen (`-`)
+  - name
+
+Example:
+
+      /nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1
+      |--------| |------------------------------| |----------|
+    store directory            digest                 name
+
+## Store Directory
+
+Every [store](./store.md) has a store directory.
+
+If the store has a [file system representation](./store.md#files-and-processes), this directory contains the store’s [file system objects](#file-system-object), which can be addressed by [store paths](#store-path).
+
+This means a store path is not just derived from the referenced store object itself, but depends on the store the store object is in.
+
+> **Note**
+> The store directory defaults to `/nix/store`, but is in principle arbitrary.
+
+It is important which store a given store object belongs to:
+Files in the store object can contain store paths, and processes may read these paths.
+Nix can only guarantee [referential integrity](store/closure.md) if store paths do not cross store boundaries.
+
+Therefore one can only copy store objects to a different store if
+
+- the source and target stores' directories match
+
+  or
+
+- the store object in question has no references, that is, contains no store paths.
+
+One cannot copy a store object to a store with a different store directory.
+Instead, it has to be rebuilt, together with all its dependencies.
+It is in general not enough to replace the store directory string in file contents, as this may render executables unusable by invalidating their internal offsets or checksums.
+
+# Digest
+
+In a [store path](#store-path), the [digest][digest] is the output of a [cryptographic hash function][hash] of either all *inputs* involved in building the referenced store object or its actual *contents*.
+
+Store objects are therefore said to be either [input-addressed](#input-addressing) or [content-addressed](#content-addressing).
+
+> **Historical Note**
+> The 20 byte restriction is because originally digests were [SHA-1][sha-1] hashes.
+> Nix now uses [SHA-256][sha-256], and longer hashes are still reduced to 20 bytes for compatibility.
+
+[digest]: https://en.m.wiktionary.org/wiki/digest#Noun
+[hash]: https://en.m.wikipedia.org/wiki/Cryptographic_hash_function
+[sha-1]: https://en.m.wikipedia.org/wiki/SHA-1
+[sha-256]: https://en.m.wikipedia.org/wiki/SHA-256
+
+### Reference scanning
+
+When a new store object is built, Nix scans its file contents for store paths to construct its set of references.
+
+The special format of a store path's [digest](#digest) allows reliably detecting it among arbitrary data.
+Nix uses the [closure](store.md#closure) of build inputs to derive the list of allowed store paths, to avoid false positives.
+
+This way, scanning files captures run time dependencies without the user having to declare them explicitly.
+Doing it at build time and persisting references in the store object avoids repeating this time-consuming operation.
+
+> **Note**
+> In practice, it is sometimes still necessary for users to declare certain dependencies explicitly, if they are to be preserved in the build result's closure.
+This depends on the specifics of the software to build and run.
+>
+> For example, Java programs are compressed after compilation, which obfuscates any store paths they may refer to and prevents Nix from automatically detecting them.
+
+## Input Addressing
+
+Input addressing means that the digest derives from how the store object was produced, namely its build inputs and build plan.
+
+To compute the hash of a store object one needs a deterministic serialisation, i.e., a binary string representation which only changes if the store object changes.
+
+Nix has a custom serialisation format called Nix Archive (NAR)
+
+Store object references of this sort can *not* be validated from the content of the store object.
+Rather, a cryptographic signature has to be used to indicate that someone is vouching for the store object really being produced from a build plan with that digest.
+
+## Content Addressing
+
+Content addressing means that the digest derives from the store object's contents, namely its file system objects and references.
+If one knows content addressing was used, one can recalculate the reference and thus verify the store object.
+
+Content addressing is currently only used for the special cases of source files and "fixed-output derivations", where the contents of a store object are known in advance.
+Content addressing of build results is still an [experimental feature subject to some restrictions](https://github.com/tweag/rfcs/blob/cas-rfc/rfcs/0062-content-addressed-paths.md).
+

doc/manual/src/architecture/store/store.md

@@ -0,0 +1,151 @@
+# Store
+
+A Nix store is a collection of *store objects* with references between them.
+It supports operations to manipulate that collection.
+
+The following concept map is a graphical outline of this chapter.
+Arrows indicate suggested reading order.
+
+```
+                      ,--------------[ store ]----------------,
+                      |                  |                    |
+                      v                  v                    v
+               [ store object ]     [ closure ]--,      [ operations ]
+                      |               |   |      |        |        |
+                      v               |   |      v        v        |
+           [ files and processes ]    |   | [ garbage collection ] |
+               /          \           |   |                        |
+              v            v          |   v                        v
+[ file system object ] [ store path ] | [ derivation ]--->[ building ]
+                  |        ^      |   |                         |
+                  v        |      v   v                         |
+             [ digest ]----' [ reference scanning ]<------------'
+              /      \
+             v        v
+[ input addressing ] [ content addressing ]
+```
+
+## Store Object
+
+A store object can hold
+
+- arbitrary *data*
+- *references* to other store objects.
+
+Store objects can be build inputs, build results, or build tasks.
+
+Store objects are [immutable][immutable-object]: once created, they do not change until they are deleted.
+
+## Reference
+
+A store object reference is an [opaque][opaque-data-type], [unique identifier][unique-identifier]:
+The only way to obtain references is by adding or building store objects.
+A reference will always point to exactly one store object.
+
+## Operations
+
+A Nix store can *add*, *retrieve*, and *delete* store objects.
+
+                [ data ]
+                    |
+                    V
+    [ store ] ---> add ----> [ store' ]
+                    |
+                    V
+              [ reference ]
+
+<!-- -->
+
+              [ reference ]
+                    |
+                    V
+    [ store ] ---> get
+                    |
+                    V
+             [ store object ]
+
+<!-- -->
+
+              [ reference ]
+                    |
+                    V
+    [ store ] --> delete --> [ store' ]
+
+
+It can *perform builds*, that is, create new store objects by transforming build inputs into build outputs, using instructions from the build tasks.
+
+
+              [ reference ]
+                    |
+                    V
+    [ store ] --> build --(maybe)--> [ store' ]
+                             |
+                             V
+                       [ reference ]
+
+
+As it keeps track of references, it can [garbage-collect][garbage-collection] unused store objects.
+
+
+    [ store ] --> collect garbage --> [ store' ]
+
+## Files and Processes
+
+Nix maps between its store model and the [Unix paradigm][unix-paradigm] of [files and processes][file-descriptor], by encoding immutable store objects and opaque identifiers as file system primitives: files and directories, and paths.
+That allows processes to resolve references contained in files and thus access the contents of store objects.
+
+Store objects are therefore implemented as the pair of
+
+  - a [file system object](fso.md) for data
+  - a set of [store paths](path.md) for references.
+
+[unix-paradigm]: https://en.m.wikipedia.org/wiki/Everything_is_a_file
+[file-descriptor]: https://en.m.wikipedia.org/wiki/File_descriptor
+
+The following diagram shows a radical simplification of how Nix interacts with the operating system:
+It uses files as build inputs, and build outputs are files again.
+On the operating system, files can be run as processes, which in turn operate on files.
+A build function also amounts to an operating system process (not depicted).
+
+```
++-----------------------------------------------------------------+
+| Nix                                                             |
+|                  [ commmand line interface ]------,             |
+|                               |                   |             |
+|                           evaluates               |             |
+|                               |                manages          |
+|                               V                   |             |
+|                  [ configuration language  ]      |             |
+|                               |                   |             |
+| +-----------------------------|-------------------V-----------+ |
+| | store                  evaluates to                         | |
+| |                             |                               | |
+| |             referenced by   V       builds                  | |
+| |  [ build input ] ---> [ build plan ] ---> [ build result ]  | |
+| |         ^                                        |          | |
+| +---------|----------------------------------------|----------+ |
++-----------|----------------------------------------|------------+
+            |                                        |
+    file system object                          store path
+            |                                        |
++-----------|----------------------------------------|------------+
+| operating system        +------------+             |            |
+|           '------------ |            | <-----------'            |
+|                         |    file    |                          |
+|                     ,-- |            | <-,                      |
+|                     |   +------------+   |                      |
+|          execute as |                    | read, write, execute |
+|                     |   +------------+   |                      |
+|                     '-> |  process   | --'                      |
+|                         +------------+                          |
++-----------------------------------------------------------------+
+```
+
+There exist different types of stores, which all follow this model.
+Examples:
+- store on the local file system
+- remote store accessible via SSH
+- binary cache store accessible via HTTP
+
+To make store objects accessible to processes, stores ultimately have to expose store objects through the file system.
+

doc/manual/src/architecture/store/store/build-system-terminology.md

@@ -0,0 +1,32 @@
+# A [Rosetta stone][rosetta-stone] for build system terminology
+
+The Nix store's design is comparable to other build systems.
+Usage of terms is, for historic reasons, not entirely consistent within the Nix ecosystem, and still subject to slow change.
+
+The following translation table points out similarities and equivalent terms, to help clarify their meaning and inform consistent use in the future.
+
+| generic build system             | Nix              | [Bazel][bazel]                                                       | [Build Systems à la Carte][bsalc] | programming language     |
+| -------------------------------- | ---------------- | -------------------------------------------------------------------- | --------------------------------- | ------------------------ |
+| data (build input, build result) | store object     | [artifact][bazel-artifact]                                           | value                             | value                    |
+| build instructions               | builder          | ([depends on action type][bazel-actions])                            | function                          | function                 |
+| build task                       | derivation       | [action][bazel-action]                                               | `Task`                            | [thunk][thunk]           |
+| build plan                       | derivation graph | [action graph][bazel-action-graph], [build graph][bazel-build-graph] | `Tasks`                           | [call graph][call-graph] |
+| build                            | build            | build                                                                | application of `Build`            | evaluation               |
+| persistence layer                | store            | [action cache][bazel-action-cache]                                   | `Store`                           | heap                     |
+
+All of these systems share features of [declarative programming][declarative-programming] languages, a key insight first put forward by Eelco Dolstra et al. in [Imposing a Memory Management Discipline on Software Deployment][immdsd] (2004), elaborated in his PhD thesis [The Purely Functional Software Deployment Model][phd-thesis] (2006), and further refined by Andrey Mokhov et al. in [Build Systems à la Carte][bsalc] (2018).
+
+[rosetta-stone]: https://en.m.wikipedia.org/wiki/Rosetta_Stone
+[bazel]: https://bazel.build/start/bazel-intro
+[bazel-artifact]: https://bazel.build/reference/glossary#artifact
+[bazel-actions]: https://docs.bazel.build/versions/main/skylark/lib/actions.html
+[bazel-action]: https://bazel.build/reference/glossary#action
+[bazel-action-graph]: https://bazel.build/reference/glossary#action-graph
+[bazel-build-graph]: https://bazel.build/reference/glossary#build-graph
+[bazel-action-cache]: https://bazel.build/reference/glossary#action-cache
+[thunk]: https://en.m.wikipedia.org/wiki/Thunk
+[call-graph]: https://en.m.wikipedia.org/wiki/Call_graph
+[declarative-programming]: https://en.m.wikipedia.org/wiki/Declarative_programming
+[immdsd]: https://edolstra.github.io/pubs/immdsd-icse2004-final.pdf
+[phd-thesis]: https://edolstra.github.io/pubs/phd-thesis.pdf
+[bsalc]: https://www.microsoft.com/en-us/research/uploads/prod/2018/03/build-systems.pdf

doc/manual/src/architecture/store/store/closure.md

@@ -0,0 +1,29 @@
+# Closure
+
+Nix stores ensure [referential integrity][referential-integrity]: for each store object in the store, all the store objects it references must also be in the store.
+
+The set of all store objects reachable by following references from a given initial set of store objects is called a *closure*.
+
+Adding, building, copying and deleting store objects must be done in a way that preserves referential integrity:
+
+- A newly added store object cannot have references, unless it is a build task.
+
+- Build results must only refer to store objects in the closure of the build inputs.
+
+  Building a store object will add appropriate references, according to the build task.
+
+- Store objects being copied must refer to objects already in the destination store.
+
+  Recursive copying must either proceed in dependency order or be atomic.
+
+- We can only safely delete store objects which are not reachable from any reference still in use.
+
+  <!-- more details in section on garbage collection, link to it once it exists -->
+
+[referential-integrity]: https://en.m.wikipedia.org/wiki/Referential_integrity
+[garbage-collection]: https://en.m.wikipedia.org/wiki/Garbage_collection_(computer_science)
+[immutable-object]: https://en.m.wikipedia.org/wiki/Immutable_object
+[opaque-data-type]: https://en.m.wikipedia.org/wiki/Opaque_data_type
+[unique-identifier]: https://en.m.wikipedia.org/wiki/Unique_identifier
+
+

doc/manual/src/command-ref/env-common.md

@@ -2,11 +2,11 @@
 
 Most Nix commands interpret the following environment variables:
 
-  - `IN_NIX_SHELL`\
+  - [`IN_NIX_SHELL`]{#env-IN_NIX_SHELL}\
     Indicator that tells if the current environment was set up by
-    `nix-shell`. Since Nix 2.0 the values are `"pure"` and `"impure"`
+    `nix-shell`. It can have the values `pure` or `impure`.
 
-  - `NIX_PATH`\
+  - [`NIX_PATH`]{#env-NIX_PATH}\
     A colon-separated list of directories used to look up Nix
     expressions enclosed in angle brackets (i.e., `<path>`). For
     instance, the value
@@ -44,7 +44,7 @@ Most Nix commands interpret the following environment variables:
     The Nix search path can also be extended using the `-I` option to
     many Nix commands, which takes precedence over `NIX_PATH`.
 
-  - `NIX_IGNORE_SYMLINK_STORE`\
+  - [`NIX_IGNORE_SYMLINK_STORE`]{#env-NIX_IGNORE_SYMLINK_STORE}\
     Normally, the Nix store directory (typically `/nix/store`) is not
     allowed to contain any symlink components. This is to prevent
     “impure” builds. Builders sometimes “canonicalise” paths by
@@ -66,41 +66,41 @@ Most Nix commands interpret the following environment variables:
 
     Consult the mount 8 manual page for details.
 
-  - `NIX_STORE_DIR`\
+  - [`NIX_STORE_DIR`]{#env-NIX_STORE_DIR}\
     Overrides the location of the Nix store (default `prefix/store`).
 
-  - `NIX_DATA_DIR`\
+  - [`NIX_DATA_DIR`]{#env-NIX_DATA_DIR}\
     Overrides the location of the Nix static data directory (default
     `prefix/share`).
 
-  - `NIX_LOG_DIR`\
+  - [`NIX_LOG_DIR`]{#env-NIX_LOG_DIR}\
     Overrides the location of the Nix log directory (default
     `prefix/var/log/nix`).
 
-  - `NIX_STATE_DIR`\
+  - [`NIX_STATE_DIR`]{#env-NIX_STATE_DIR}\
     Overrides the location of the Nix state directory (default
     `prefix/var/nix`).
 
-  - `NIX_CONF_DIR`\
+  - [`NIX_CONF_DIR`]{#env-NIX_CONF_DIR}\
     Overrides the location of the system Nix configuration directory
     (default `prefix/etc/nix`).
 
-  - `NIX_CONFIG`\
+  - [`NIX_CONFIG`]{#env-NIX_CONFIG}\
     Applies settings from Nix configuration from the environment.
     The content is treated as if it was read from a Nix configuration file.
     Settings are separated by the newline character.
 
-  - `NIX_USER_CONF_FILES`\
+  - [`NIX_USER_CONF_FILES`]{#env-NIX_USER_CONF_FILES}\
     Overrides the location of the user Nix configuration files to load
     from (defaults to the XDG spec locations). The variable is treated
     as a list separated by the `:` token.
 
-  - `TMPDIR`\
+  - [`TMPDIR`]{#env-TMPDIR}\
     Use the specified directory to store temporary files. In particular,
     this includes temporary build directories; these can take up
     substantial amounts of disk space. The default is `/tmp`.
 
-  - `NIX_REMOTE`\
+  - [`NIX_REMOTE`]{#env-NIX_REMOTE}\
     This variable should be set to `daemon` if you want to use the Nix
     daemon to execute Nix operations. This is necessary in [multi-user
     Nix installations](../installation/multi-user.md). If the Nix
@@ -108,16 +108,16 @@ Most Nix commands interpret the following environment variables:
     should be set to `unix://path/to/socket`. Otherwise, it should be
     left unset.
 
-  - `NIX_SHOW_STATS`\
+  - [`NIX_SHOW_STATS`]{#env-NIX_SHOW_STATS}\
     If set to `1`, Nix will print some evaluation statistics, such as
     the number of values allocated.
 
-  - `NIX_COUNT_CALLS`\
+  - [`NIX_COUNT_CALLS`]{#env-NIX_COUNT_CALLS}\
     If set to `1`, Nix will print how often functions were called during
     Nix expression evaluation. This is useful for profiling your Nix
     expressions.
 
-  - `GC_INITIAL_HEAP_SIZE`\
+  - [`GC_INITIAL_HEAP_SIZE`]{#env-GC_INITIAL_HEAP_SIZE}\
     If Nix has been configured to use the Boehm garbage collector, this
     variable sets the initial size of the heap in bytes. It defaults to
     384 MiB. Setting it to a low value reduces memory consumption, but

doc/manual/src/command-ref/nix-build.md

@@ -12,6 +12,12 @@
   [`--dry-run`]
   [{`--out-link` | `-o`} *outlink*]
 
+# Disambiguation
+
+This man page describes the command `nix-build`, which is distinct from `nix
+build`. For documentation on the latter, run `nix build --help` or see `man
+nix3-build`.
+
 # Description
 
 The `nix-build` command builds the derivations described by the Nix
@@ -47,16 +53,16 @@ All options not listed here are passed to `nix-store
 --realise`, except for `--arg` and `--attr` / `-A` which are passed to
 `nix-instantiate`.
 
-  - `--no-out-link`\
+  - [`--no-out-link`]{#opt-no-out-link}\
     Do not create a symlink to the output path. Note that as a result
     the output does not become a root of the garbage collector, and so
     might be deleted by `nix-store
                     --gc`.
 
-  - `--dry-run`\
+  - [`--dry-run`]{#opt-dry-run}\
     Show what store paths would be built or downloaded.
 
-  - `--out-link` / `-o` *outlink*\
+  - [`--out-link`]{#opt-out-link} / `-o` *outlink*\
     Change the name of the symlink to the output path created from
     `result` to *outlink*.
 

doc/manual/src/command-ref/nix-env.md

@@ -31,7 +31,7 @@ subcommand to be performed. These are documented below.
 Several commands, such as `nix-env -q` and `nix-env -i`, take a list of
 arguments that specify the packages on which to operate. These are
 extended regular expressions that must match the entire name of the
-package. (For details on regular expressions, see regex7.) The match is
+package. (For details on regular expressions, see **regex**(7).) The match is
 case-sensitive. The regular expression can optionally be followed by a
 dash and a version number; if omitted, any version of the package will
 match. Here are some examples:
@@ -198,7 +198,7 @@ a number of possible ways:
     another.
 
   - If `--from-expression` is given, *args* are Nix
-    [functions](../expressions/language-constructs.md#functions)
+    [functions](../language/constructs.md#functions)
     that are called with the active Nix expression as their single
     argument. The derivations returned by those function calls are
     installed. This allows derivations to be specified in an
@@ -412,7 +412,7 @@ The upgrade operation determines whether a derivation `y` is an upgrade
 of a derivation `x` by looking at their respective `name` attributes.
 The names (e.g., `gcc-3.3.1` are split into two parts: the package name
 (`gcc`), and the version (`3.3.1`). The version part starts after the
-first dash not followed by a letter. `x` is considered an upgrade of `y`
+first dash not followed by a letter. `y` is considered an upgrade of `x`
 if their package names match, and the version of `y` is higher than that
 of `x`.
 

doc/manual/src/command-ref/nix-instantiate.md

@@ -51,7 +51,7 @@ standard input.
   - `--strict`\
     When used with `--eval`, recursively evaluate list elements and
     attributes. Normally, such sub-expressions are left unevaluated
-    (since the Nix expression language is lazy).
+    (since the Nix language is lazy).
 
     > **Warning**
     >
@@ -66,7 +66,7 @@ standard input.
     When used with `--eval`, print the resulting value as an XML
     representation of the abstract syntax tree rather than as an ATerm.
     The schema is the same as that used by the [`toXML`
-    built-in](../expressions/builtins.md).
+    built-in](../language/builtins.md).
 
   - `--read-write-mode`\
     When used with `--eval`, perform evaluation in read/write mode so

doc/manual/src/command-ref/nix-shell.md

@@ -15,6 +15,12 @@
   [`--keep` *name*]
   {{`--packages` | `-p`} {*packages* | *expressions*} … | [*path*]}
 
+# Disambiguation
+
+This man page describes the command `nix-shell`, which is distinct from `nix
+shell`. For documentation on the latter, run `nix shell --help` or see `man
+nix3-shell`.
+
 # Description
 
 The command `nix-shell` will build the dependencies of the specified

doc/manual/src/command-ref/nix-store.md

@@ -22,7 +22,7 @@ This section lists the options that are common to all operations. These
 options are allowed for every subcommand, though they may not always
 have an effect.
 
-  - `--add-root` *path*\
+  - [`--add-root`]{#opt-add-root} *path*\
     Causes the result of a realisation (`--realise` and
     `--force-realise`) to be registered as a root of the garbage
     collector. *path* will be created as a symlink to the resulting
@@ -121,7 +121,7 @@ Special exit codes:
   - `102`\
     Hash mismatch, the build output was rejected because it does not
     match the [`outputHash` attribute of the
-    derivation](../expressions/advanced-attributes.md).
+    derivation](../language/advanced-attributes.md).
 
   - `104`\
     Not deterministic, the build succeeded in check mode but the

doc/manual/src/command-ref/opt-common.md

@@ -2,13 +2,13 @@
 
 Most Nix commands accept the following command-line options:
 
-  - `--help`\
+  - [`--help`]{#opt-help}\
     Prints out a summary of the command syntax and exits.
 
-  - `--version`\
+  - [`--version`]{#opt-version}\
     Prints out the Nix version number on standard output and exits.
 
-  - `--verbose` / `-v`\
+  - [`--verbose`]{#opt-verbose} / `-v`\
     Increases the level of verbosity of diagnostic messages printed on
     standard error. For each Nix operation, the information printed on
     standard output is well-defined; any diagnostic information is
@@ -37,14 +37,14 @@ Most Nix commands accept the following command-line options:
       - 5\
         “Vomit”: print vast amounts of debug information.
 
-  - `--quiet`\
+  - [`--quiet`]{#opt-quiet}\
     Decreases the level of verbosity of diagnostic messages printed on
     standard error. This is the inverse option to `-v` / `--verbose`.
 
     This option may be specified repeatedly. See the previous verbosity
     levels list.
 
-  - `--log-format` *format*\
+  - [`--log-format`]{#opt-log-format} *format*\
     This option can be used to change the output of the log format, with
     *format* being one of:
 
@@ -66,14 +66,14 @@ Most Nix commands accept the following command-line options:
       - bar-with-logs\
         Display the raw logs, with the progress bar at the bottom.
 
-  - `--no-build-output` / `-Q`\
+  - [`--no-build-output`]{#opt-no-build-output} / `-Q`\
     By default, output written by builders to standard output and
     standard error is echoed to the Nix command's standard error. This
     option suppresses this behaviour. Note that the builder's standard
     output and error are always written to a log file in
     `prefix/nix/var/log/nix`.
 
-  - `--max-jobs` / `-j` *number*\
+  - [`--max-jobs`]{#opt-max-jobs} / `-j` *number*\
     Sets the maximum number of build jobs that Nix will perform in
     parallel to the specified number. Specify `auto` to use the number
     of CPUs in the system. The default is specified by the `max-jobs`
@@ -83,7 +83,7 @@ Most Nix commands accept the following command-line options:
     Setting it to `0` disallows building on the local machine, which is
     useful when you want builds to happen only on remote builders.
 
-  - `--cores`\
+  - [`--cores`]{#opt-cores}\
     Sets the value of the `NIX_BUILD_CORES` environment variable in
     the invocation of builders. Builders can use this variable at
     their discretion to control the maximum amount of parallelism. For
@@ -94,18 +94,18 @@ Most Nix commands accept the following command-line options:
     means that the builder should use all available CPU cores in the
     system.
 
-  - `--max-silent-time`\
+  - [`--max-silent-time`]{#opt-max-silent-time}\
     Sets the maximum number of seconds that a builder can go without
     producing any data on standard output or standard error. The
     default is specified by the `max-silent-time` configuration
     setting. `0` means no time-out.
 
-  - `--timeout`\
+  - [`--timeout`]{#opt-timeout}\
     Sets the maximum number of seconds that a builder can run. The
     default is specified by the `timeout` configuration setting. `0`
     means no timeout.
 
-  - `--keep-going` / `-k`\
+  - [`--keep-going`]{#opt-keep-going} / `-k`\
     Keep going in case of failed builds, to the greatest extent
     possible. That is, if building an input of some derivation fails,
     Nix will still build the other inputs, but not the derivation
@@ -113,13 +113,13 @@ Most Nix commands accept the following command-line options:
     for builds of substitutes), possibly killing builds in progress (in
     case of parallel or distributed builds).
 
-  - `--keep-failed` / `-K`\
+  - [`--keep-failed`]{#opt-keep-failed} / `-K`\
     Specifies that in case of a build failure, the temporary directory
     (usually in `/tmp`) in which the build takes place should not be
     deleted. The path of the build directory is printed as an
     informational message.
 
-  - `--fallback`\
+  - [`--fallback`]{#opt-fallback}\
     Whenever Nix attempts to build a derivation for which substitutes
     are known for each output path, but realising the output paths
     through the substitutes fails, fall back on building the derivation.
@@ -134,18 +134,18 @@ Most Nix commands accept the following command-line options:
     failure in obtaining the substitutes to lead to a full build from
     source (with the related consumption of resources).
 
-  - `--readonly-mode`\
+  - [`--readonly-mode`]{#opt-readonly-mode}\
     When this option is used, no attempt is made to open the Nix
     database. Most Nix operations do need database access, so those
     operations will fail.
 
-  - `--arg` *name* *value*\
+  - [`--arg`]{#opt-arg} *name* *value*\
     This option is accepted by `nix-env`, `nix-instantiate`,
     `nix-shell` and `nix-build`. When evaluating Nix expressions, the
     expression evaluator will automatically try to call functions that
     it encounters. It can automatically call functions for which every
     argument has a [default
-    value](../expressions/language-constructs.md#functions) (e.g.,
+    value](../language/constructs.md#functions) (e.g.,
     `{ argName ?  defaultValue }: ...`). With `--arg`, you can also
     call functions that have arguments without a default value (or
     override a default value). That is, if the evaluator encounters a
@@ -164,19 +164,19 @@ Most Nix commands accept the following command-line options:
 
     So if you call this Nix expression (e.g., when you do `nix-env -iA
     pkgname`), the function will be called automatically using the
-    value [`builtins.currentSystem`](../expressions/builtins.md) for
+    value [`builtins.currentSystem`](../language/builtins.md) for
     the `system` argument. You can override this using `--arg`, e.g.,
     `nix-env -iA pkgname --arg system \"i686-freebsd\"`. (Note that
     since the argument is a Nix string literal, you have to escape the
     quotes.)
 
-  - `--argstr` *name* *value*\
+  - [`--argstr`]{#opt-argstr} *name* *value*\
     This option is like `--arg`, only the value is not a Nix
     expression but a string. So instead of `--arg system
     \"i686-linux\"` (the outer quotes are to keep the shell happy) you
     can say `--argstr system i686-linux`.
 
-  - `--attr` / `-A` *attrPath*\
+  - [`--attr`]{#opt-attr} / `-A` *attrPath*\
     Select an attribute from the top-level Nix expression being
     evaluated. (`nix-env`, `nix-instantiate`, `nix-build` and
     `nix-shell` only.) The *attribute path* *attrPath* is a sequence
@@ -191,7 +191,7 @@ Most Nix commands accept the following command-line options:
     attribute of the fourth element of the array in the `foo` attribute
     of the top-level expression.
 
-  - `--expr` / `-E`\
+  - [`--expr`]{#opt-expr} / `-E`\
     Interpret the command line arguments as a list of Nix expressions to
     be parsed and evaluated, rather than as a list of file names of Nix
     expressions. (`nix-instantiate`, `nix-build` and `nix-shell` only.)
@@ -202,17 +202,17 @@ Most Nix commands accept the following command-line options:
     use, give your expression to the `nix-shell -p` convenience flag
     instead.
 
-  - `-I` *path*\
+  - [`-I`]{#opt-I} *path*\
     Add a path to the Nix expression search path. This option may be
     given multiple times. See the `NIX_PATH` environment variable for
     information on the semantics of the Nix search path. Paths added
     through `-I` take precedence over `NIX_PATH`.
 
-  - `--option` *name* *value*\
+  - [`--option`]{#opt-option} *name* *value*\
     Set the Nix configuration option *name* to *value*. This overrides
     settings in the Nix configuration file (see nix.conf5).
 
-  - `--repair`\
+  - [`--repair`]{#opt-repair}\
     Fix corrupted or missing store paths by redownloading or rebuilding
     them. Note that this is slow because it requires computing a
     cryptographic hash of the contents of every path in the closure of

doc/manual/src/contributing/hacking.md

@@ -71,18 +71,6 @@ To install it in `$(pwd)/outputs` and test it:
 nix (Nix) 3.0
 ```
 
-To run a functional test:
-
-```console
-make tests/test-name-should-auto-complete.sh.test
-```
-
-To run the unit-tests for C++ code:
-
-```
-make check
-```
-
 If you have a flakes-enabled Nix you can replace:
 
 ```console
@@ -94,3 +82,29 @@ by:
 ```console
 $ nix develop
 ```
+
+## Testing
+
+Nix comes with three different flavors of tests: unit, functional and integration.
+
+### Unit-tests
+
+The unit-tests for each Nix library (`libexpr`, `libstore`, etc..) are defined
+under `src/{library_name}/tests` using the
+[googletest](https://google.github.io/googletest/) framework.
+
+You can run the whole testsuite with `make check`, or the tests for a specific component with `make libfoo-tests_RUN`. Finer-grained filtering is also possible using the [--gtest_filter](https://google.github.io/googletest/advanced.html#running-a-subset-of-the-tests) command-line option.
+
+### Functional tests
+
+The functional tests reside under the `tests` directory and are listed in `tests/local.mk`.
+The whole testsuite can be run with `make install && make installcheck`.
+Individual tests can be run with `make tests/{testName}.sh.test`.
+
+### Integration tests
+
+The integration tests are defined in the Nix flake under the `hydraJobs.tests` attribute.
+These tests include everything that needs to interact with external services or run Nix in a non-trivial distributed setup.
+Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on <https://hydra.nixos.org/jobset/nix/master>).
+
+You can run them manually with `nix build .#hydraJobs.tests.{testName}` or `nix-build -A hydraJobs.tests.{testName}`

doc/manual/src/expressions/arguments-variables.md

@@ -1,80 +0,0 @@
-# Arguments and Variables
-
-The [Nix expression for GNU Hello](expression-syntax.md) is a
-function; it is missing some arguments that have to be filled in
-somewhere. In the Nix Packages collection this is done in the file
-`pkgs/top-level/all-packages.nix`, where all Nix expressions for
-packages are imported and called with the appropriate arguments. Here
-are some fragments of `all-packages.nix`, with annotations of what
-they mean:
-
-```nix
-...
-
-rec { ①
-
-  hello = import ../applications/misc/hello/ex-1 ② { ③
-    inherit fetchurl stdenv perl;
-  };
-
-  perl = import ../development/interpreters/perl { ④
-    inherit fetchurl stdenv;
-  };
-
-  fetchurl = import ../build-support/fetchurl {
-    inherit stdenv; ...
-  };
-
-  stdenv = ...;
-
-}
-```
-
-1.  This file defines a set of attributes, all of which are concrete
-    derivations (i.e., not functions). In fact, we define a *mutually
-    recursive* set of attributes. That is, the attributes can refer to
-    each other. This is precisely what we want since we want to “plug”
-    the various packages into each other.
-
-2.  Here we *import* the Nix expression for GNU Hello. The import
-    operation just loads and returns the specified Nix expression. In
-    fact, we could just have put the contents of the Nix expression
-    for GNU Hello in `all-packages.nix` at this point. That would be
-    completely equivalent, but it would make `all-packages.nix` rather
-    bulky.
-    
-    Note that we refer to `../applications/misc/hello/ex-1`, not
-    `../applications/misc/hello/ex-1/default.nix`. When you try to
-    import a directory, Nix automatically appends `/default.nix` to the
-    file name.
-
-3.  This is where the actual composition takes place. Here we *call* the
-    function imported from `../applications/misc/hello/ex-1` with a set
-    containing the things that the function expects, namely `fetchurl`,
-    `stdenv`, and `perl`. We use inherit again to use the attributes
-    defined in the surrounding scope (we could also have written
-    `fetchurl = fetchurl;`, etc.).
-    
-    The result of this function call is an actual derivation that can be
-    built by Nix (since when we fill in the arguments of the function,
-    what we get is its body, which is the call to `stdenv.mkDerivation`
-    in the [Nix expression for GNU Hello](expression-syntax.md)).
-    
-    > **Note**
-    > 
-    > Nixpkgs has a convenience function `callPackage` that imports and
-    > calls a function, filling in any missing arguments by passing the
-    > corresponding attribute from the Nixpkgs set, like this:
-    > 
-    > ```nix
-    > hello = callPackage ../applications/misc/hello/ex-1 { };
-    > ```
-    > 
-    > If necessary, you can set or override arguments:
-    > 
-    > ```nix
-    > hello = callPackage ../applications/misc/hello/ex-1 { stdenv = myStdenv; };
-    > ```
-
-4.  Likewise, we have to instantiate Perl, `fetchurl`, and the standard
-    environment.

doc/manual/src/expressions/build-script.md

@@ -1,70 +0,0 @@
-# Build Script
-
-Here is the builder referenced from Hello's Nix expression (stored in
-`pkgs/applications/misc/hello/ex-1/builder.sh`):
-
-```bash
-source $stdenv/setup ①
-
-PATH=$perl/bin:$PATH ②
-
-tar xvfz $src ③
-cd hello-*
-./configure --prefix=$out ④
-make ⑤
-make install
-```
-
-The builder can actually be made a lot shorter by using the *generic
-builder* functions provided by `stdenv`, but here we write out the build
-steps to elucidate what a builder does. It performs the following steps:
-
-1.  When Nix runs a builder, it initially completely clears the
-    environment (except for the attributes declared in the derivation).
-    This is done to prevent undeclared inputs from being used in the
-    build process. If for example the `PATH` contained `/usr/bin`, then
-    you might accidentally use `/usr/bin/gcc`.
-    
-    So the first step is to set up the environment. This is done by
-    calling the `setup` script of the standard environment. The
-    environment variable `stdenv` points to the location of the
-    standard environment being used. (It wasn't specified explicitly
-    as an attribute in Hello's Nix expression, but `mkDerivation` adds
-    it automatically.)
-
-2.  Since Hello needs Perl, we have to make sure that Perl is in the
-    `PATH`. The `perl` environment variable points to the location of
-    the Perl package (since it was passed in as an attribute to the
-    derivation), so `$perl/bin` is the directory containing the Perl
-    interpreter.
-
-3.  Now we have to unpack the sources. The `src` attribute was bound to
-    the result of fetching the Hello source tarball from the network, so
-    the `src` environment variable points to the location in the Nix
-    store to which the tarball was downloaded. After unpacking, we `cd`
-    to the resulting source directory.
-    
-    The whole build is performed in a temporary directory created in
-    `/tmp`, by the way. This directory is removed after the builder
-    finishes, so there is no need to clean up the sources afterwards.
-    Also, the temporary directory is always newly created, so you don't
-    have to worry about files from previous builds interfering with the
-    current build.
-
-4.  GNU Hello is a typical Autoconf-based package, so we first have to
-    run its `configure` script. In Nix every package is stored in a
-    separate location in the Nix store, for instance
-    `/nix/store/9a54ba97fb71b65fda531012d0443ce2-hello-2.1.1`. Nix
-    computes this path by cryptographically hashing all attributes of
-    the derivation. The path is passed to the builder through the `out`
-    environment variable. So here we give `configure` the parameter
-    `--prefix=$out` to cause Hello to be installed in the expected
-    location.
-
-5.  Finally we build Hello (`make`) and install it into the location
-    specified by `out` (`make install`).
-
-If you are wondering about the absence of error checking on the result
-of various commands called in the builder: this is because the shell
-script is evaluated with Bash's `-e` option, which causes the script to
-be aborted if any command fails without an error check.

doc/manual/src/expressions/expression-language.md

@@ -1,12 +0,0 @@
-# Nix Expression Language
-
-The Nix expression language is a pure, lazy, functional language. Purity
-means that operations in the language don't have side-effects (for
-instance, there is no variable assignment). Laziness means that
-arguments to functions are evaluated only when they are needed.
-Functional means that functions are “normal” values that can be passed
-around and manipulated in interesting ways. The language is not a
-full-featured, general purpose language. Its main job is to describe
-packages, compositions of packages, and the variability within packages.
-
-This section presents the various features of the language.

doc/manual/src/expressions/expression-syntax.md

@@ -1,93 +0,0 @@
-# Expression Syntax
-
-Here is a Nix expression for GNU Hello:
-
-```nix
-{ stdenv, fetchurl, perl }: ①
-
-stdenv.mkDerivation { ②
-  name = "hello-2.1.1"; ③
-  builder = ./builder.sh; ④
-  src = fetchurl { ⑤
-    url = "ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz";
-    sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465";
-  };
-  inherit perl; ⑥
-}
-```
-
-This file is actually already in the Nix Packages collection in
-`pkgs/applications/misc/hello/ex-1/default.nix`. It is customary to
-place each package in a separate directory and call the single Nix
-expression in that directory `default.nix`. The file has the following
-elements (referenced from the figure by number):
-
-1.  This states that the expression is a *function* that expects to be
-    called with three arguments: `stdenv`, `fetchurl`, and `perl`. They
-    are needed to build Hello, but we don't know how to build them here;
-    that's why they are function arguments. `stdenv` is a package that
-    is used by almost all Nix Packages; it provides a
-    “standard” environment consisting of the things you would expect
-    in a basic Unix environment: a C/C++ compiler (GCC, to be precise),
-    the Bash shell, fundamental Unix tools such as `cp`, `grep`, `tar`,
-    etc. `fetchurl` is a function that downloads files. `perl` is the
-    Perl interpreter.
-    
-    Nix functions generally have the form `{ x, y, ..., z }: e` where
-    `x`, `y`, etc. are the names of the expected arguments, and where
-    *e* is the body of the function. So here, the entire remainder of
-    the file is the body of the function; when given the required
-    arguments, the body should describe how to build an instance of
-    the Hello package.
-
-2.  So we have to build a package. Building something from other stuff
-    is called a *derivation* in Nix (as opposed to sources, which are
-    built by humans instead of computers). We perform a derivation by
-    calling `stdenv.mkDerivation`. `mkDerivation` is a function
-    provided by `stdenv` that builds a package from a set of
-    *attributes*. A set is just a list of key/value pairs where each
-    key is a string and each value is an arbitrary Nix
-    expression. They take the general form `{ name1 = expr1; ...
-    nameN = exprN; }`.
-
-3.  The attribute `name` specifies the symbolic name and version of
-    the package. Nix doesn't really care about these things, but they
-    are used by for instance `nix-env -q` to show a “human-readable”
-    name for packages. This attribute is required by `mkDerivation`.
-
-4.  The attribute `builder` specifies the builder. This attribute can
-    sometimes be omitted, in which case `mkDerivation` will fill in a
-    default builder (which does a `configure; make; make install`, in
-    essence). Hello is sufficiently simple that the default builder
-    would suffice, but in this case, we will show an actual builder
-    for educational purposes. The value `./builder.sh` refers to the
-    shell script shown in the [next section](build-script.md),
-    discussed below.
-
-5.  The builder has to know what the sources of the package are. Here,
-    the attribute `src` is bound to the result of a call to the
-    `fetchurl` function. Given a URL and a SHA-256 hash of the expected
-    contents of the file at that URL, this function builds a derivation
-    that downloads the file and checks its hash. So the sources are a
-    dependency that like all other dependencies is built before Hello
-    itself is built.
-    
-    Instead of `src` any other name could have been used, and in fact
-    there can be any number of sources (bound to different attributes).
-    However, `src` is customary, and it's also expected by the default
-    builder (which we don't use in this example).
-
-6.  Since the derivation requires Perl, we have to pass the value of the
-    `perl` function argument to the builder. All attributes in the set
-    are actually passed as environment variables to the builder, so
-    declaring an attribute
-
-    ```nix
-    perl = perl;
-    ```
-    
-    will do the trick: it binds an attribute `perl` to the function
-    argument which also happens to be called `perl`. However, it looks a
-    bit silly, so there is a shorter syntax. The `inherit` keyword
-    causes the specified attributes to be bound to whatever variables
-    with the same name happen to be in scope.

doc/manual/src/expressions/generic-builder.md

@@ -1,66 +0,0 @@
-# Generic Builder Syntax
-
-Recall that the [build script for GNU Hello](build-script.md) looked
-something like this:
-
-```bash
-PATH=$perl/bin:$PATH
-tar xvfz $src
-cd hello-*
-./configure --prefix=$out
-make
-make install
-```
-
-The builders for almost all Unix packages look like this — set up some
-environment variables, unpack the sources, configure, build, and
-install. For this reason the standard environment provides some Bash
-functions that automate the build process. Here is what a builder using
-the generic build facilities looks like:
-
-```bash
-buildInputs="$perl" ①
-
-source $stdenv/setup ②
-
-genericBuild ③
-```
-
-Here is what each line means:
-
-1.  The `buildInputs` variable tells `setup` to use the indicated
-    packages as “inputs”. This means that if a package provides a `bin`
-    subdirectory, it's added to `PATH`; if it has a `include`
-    subdirectory, it's added to GCC's header search path; and so on.
-    (This is implemented in a modular way: `setup` tries to source the
-    file `pkg/nix-support/setup-hook` of all dependencies. These “setup
-    hooks” can then set up whatever environment variables they want; for
-    instance, the setup hook for Perl sets the `PERL5LIB` environment
-    variable to contain the `lib/site_perl` directories of all inputs.)
-
-2.  The function `genericBuild` is defined in the file `$stdenv/setup`.
-
-3.  The final step calls the shell function `genericBuild`, which
-    performs the steps that were done explicitly in the previous build
-    script. The generic builder is smart enough to figure out whether
-    to unpack the sources using `gzip`, `bzip2`, etc.  It can be
-    customised in many ways; see the Nixpkgs manual for details.
-
-Discerning readers will note that the `buildInputs` could just as well
-have been set in the Nix expression, like this:
-
-```nix
-  buildInputs = [ perl ];
-```
-
-The `perl` attribute can then be removed, and the builder becomes even
-shorter:
-
-```bash
-source $stdenv/setup
-genericBuild
-```
-
-In fact, `mkDerivation` provides a default builder that looks exactly
-like that, so it is actually possible to omit the builder for Hello
-entirely.

doc/manual/src/expressions/language-values.md

@@ -1,251 +0,0 @@
-# Values
-
-## Simple Values
-
-Nix has the following basic data types:
-
-  - *Strings* can be written in three ways.
-    
-    The most common way is to enclose the string between double quotes,
-    e.g., `"foo bar"`. Strings can span multiple lines. The special
-    characters `"` and `\` and the character sequence `${` must be
-    escaped by prefixing them with a backslash (`\`). Newlines, carriage
-    returns and tabs can be written as `\n`, `\r` and `\t`,
-    respectively.
-    
-    You can include the result of an expression into a string by
-    enclosing it in `${...}`, a feature known as *antiquotation*. The
-    enclosed expression must evaluate to something that can be coerced
-    into a string (meaning that it must be a string, a path, or a
-    derivation). For instance, rather than writing
-    
-    ```nix
-    "--with-freetype2-library=" + freetype + "/lib"
-    ```
-    
-    (where `freetype` is a derivation), you can instead write the more
-    natural
-    
-    ```nix
-    "--with-freetype2-library=${freetype}/lib"
-    ```
-    
-    The latter is automatically translated to the former. A more
-    complicated example (from the Nix expression for
-    [Qt](http://www.trolltech.com/products/qt)):
-    
-    ```nix
-    configureFlags = "
-      -system-zlib -system-libpng -system-libjpeg
-      ${if openglSupport then "-dlopen-opengl
-        -L${mesa}/lib -I${mesa}/include
-        -L${libXmu}/lib -I${libXmu}/include" else ""}
-      ${if threadSupport then "-thread" else "-no-thread"}
-    ";
-    ```
-    
-    Note that Nix expressions and strings can be arbitrarily nested; in
-    this case the outer string contains various antiquotations that
-    themselves contain strings (e.g., `"-thread"`), some of which in
-    turn contain expressions (e.g., `${mesa}`).
-    
-    The second way to write string literals is as an *indented string*,
-    which is enclosed between pairs of *double single-quotes*, like so:
-    
-    ```nix
-    ''
-      This is the first line.
-      This is the second line.
-        This is the third line.
-    ''
-    ```
-    
-    This kind of string literal intelligently strips indentation from
-    the start of each line. To be precise, it strips from each line a
-    number of spaces equal to the minimal indentation of the string as a
-    whole (disregarding the indentation of empty lines). For instance,
-    the first and second line are indented two spaces, while the third
-    line is indented four spaces. Thus, two spaces are stripped from
-    each line, so the resulting string is
-    
-    ```nix
-    "This is the first line.\nThis is the second line.\n  This is the third line.\n"
-    ```
-    
-    Note that the whitespace and newline following the opening `''` is
-    ignored if there is no non-whitespace text on the initial line.
-    
-    Antiquotation (`${expr}`) is supported in indented strings.
-    
-    Since `${` and `''` have special meaning in indented strings, you
-    need a way to quote them. `$` can be escaped by prefixing it with
-    `''` (that is, two single quotes), i.e., `''$`. `''` can be escaped
-    by prefixing it with `'`, i.e., `'''`. `$` removes any special
-    meaning from the following `$`. Linefeed, carriage-return and tab
-    characters can be written as `''\n`, `''\r`, `''\t`, and `''\`
-    escapes any other character.
-    
-    Indented strings are primarily useful in that they allow multi-line
-    string literals to follow the indentation of the enclosing Nix
-    expression, and that less escaping is typically necessary for
-    strings representing languages such as shell scripts and
-    configuration files because `''` is much less common than `"`.
-    Example:
-    
-    ```nix
-    stdenv.mkDerivation {
-      ...
-      postInstall =
-        ''
-          mkdir $out/bin $out/etc
-          cp foo $out/bin
-          echo "Hello World" > $out/etc/foo.conf
-          ${if enableBar then "cp bar $out/bin" else ""}
-        '';
-      ...
-    }
-    ```
-    
-    Finally, as a convenience, *URIs* as defined in appendix B of
-    [RFC 2396](http://www.ietf.org/rfc/rfc2396.txt) can be written *as
-    is*, without quotes. For instance, the string
-    `"http://example.org/foo.tar.bz2"` can also be written as
-    `http://example.org/foo.tar.bz2`.
-
-  - Numbers, which can be *integers* (like `123`) or *floating point*
-    (like `123.43` or `.27e13`).
-    
-    Numbers are type-compatible: pure integer operations will always
-    return integers, whereas any operation involving at least one
-    floating point number will have a floating point number as a result.
-
-  - *Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at
-    least one slash to be recognised as such. For instance, `builder.sh`
-    is not a path: it's parsed as an expression that selects the
-    attribute `sh` from the variable `builder`. If the file name is
-    relative, i.e., if it does not begin with a slash, it is made
-    absolute at parse time relative to the directory of the Nix
-    expression that contained it. For instance, if a Nix expression in
-    `/foo/bar/bla.nix` refers to `../xyzzy/fnord.nix`, the absolute path
-    is `/foo/xyzzy/fnord.nix`.
-    
-    If the first component of a path is a `~`, it is interpreted as if
-    the rest of the path were relative to the user's home directory.
-    e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
-    whose home directory is `/home/edolstra`.
-    
-    Paths can also be specified between angle brackets, e.g.
-    `<nixpkgs>`. This means that the directories listed in the
-    environment variable `NIX_PATH` will be searched for the given file
-    or directory name.
-
-    Antiquotation is supported in any paths except those in angle brackets.
-    `./${foo}-${bar}.nix` is a more convenient way of writing 
-    `./. + "/" + foo + "-" + bar + ".nix"` or `./. + "/${foo}-${bar}.nix"`. At
-    least one slash must appear *before* any antiquotations for this to be
-    recognized as a path. `a.${foo}/b.${bar}` is a syntactically valid division
-    operation. `./a.${foo}/b.${bar}` is a path.
-
-  - *Booleans* with values `true` and `false`.
-
-  - The null value, denoted as `null`.
-
-## Lists
-
-Lists are formed by enclosing a whitespace-separated list of values
-between square brackets. For example,
-
-```nix
-[ 123 ./foo.nix "abc" (f { x = y; }) ]
-```
-
-defines a list of four elements, the last being the result of a call to
-the function `f`. Note that function calls have to be enclosed in
-parentheses. If they had been omitted, e.g.,
-
-```nix
-[ 123 ./foo.nix "abc" f { x = y; } ]
-```
-
-the result would be a list of five elements, the fourth one being a
-function and the fifth being a set.
-
-Note that lists are only lazy in values, and they are strict in length.
-
-## Sets
-
-Sets are really the core of the language, since ultimately the Nix
-language is all about creating derivations, which are really just sets
-of attributes to be passed to build scripts.
-
-Sets are just a list of name/value pairs (called *attributes*) enclosed
-in curly brackets, where each value is an arbitrary expression
-terminated by a semicolon. For example:
-
-```nix
-{ x = 123;
-  text = "Hello";
-  y = f { bla = 456; };
-}
-```
-
-This defines a set with attributes named `x`, `text`, `y`. The order of
-the attributes is irrelevant. An attribute name may only occur once.
-
-Attributes can be selected from a set using the `.` operator. For
-instance,
-
-```nix
-{ a = "Foo"; b = "Bar"; }.a
-```
-
-evaluates to `"Foo"`. It is possible to provide a default value in an
-attribute selection using the `or` keyword. For example,
-
-```nix
-{ a = "Foo"; b = "Bar"; }.c or "Xyzzy"
-```
-
-will evaluate to `"Xyzzy"` because there is no `c` attribute in the set.
-
-You can use arbitrary double-quoted strings as attribute names:
-
-```nix
-{ "foo ${bar}" = 123; "nix-1.0" = 456; }."foo ${bar}"
-```
-
-This will evaluate to `123` (Assuming `bar` is antiquotable). In the
-case where an attribute name is just a single antiquotation, the quotes
-can be dropped:
-
-```nix
-{ foo = 123; }.${bar} or 456
-```
-
-This will evaluate to `123` if `bar` evaluates to `"foo"` when coerced
-to a string and `456` otherwise (again assuming `bar` is antiquotable).
-
-In the special case where an attribute name inside of a set declaration
-evaluates to `null` (which is normally an error, as `null` is not
-antiquotable), that attribute is simply not added to the set:
-
-```nix
-{ ${if foo then "bar" else null} = true; }
-```
-
-This will evaluate to `{}` if `foo` evaluates to `false`.
-
-A set that has a `__functor` attribute whose value is callable (i.e. is
-itself a function or a set with a `__functor` attribute whose value is
-callable) can be applied as if it were a function, with the set itself
-passed in first , e.g.,
-
-```nix
-let add = { __functor = self: x: x + self.x; };
-    inc = add // { x = 1; };
-in inc 1
-```
-
-evaluates to `2`. This can be used to attach metadata to a function
-without the caller needing to treat it specially, or to implement a form
-of object-oriented programming, for example.

doc/manual/src/expressions/simple-building-testing.md

@@ -1,61 +0,0 @@
-# Building and Testing
-
-You can now try to build Hello. Of course, you could do `nix-env -f . -iA
-hello`, but you may not want to install a possibly broken package just
-yet. The best way to test the package is by using the command
-`nix-build`, which builds a Nix expression and creates a symlink named
-`result` in the current directory:
-
-```console
-$ nix-build -A hello
-building path `/nix/store/632d2b22514d...-hello-2.1.1'
-hello-2.1.1/
-hello-2.1.1/intl/
-hello-2.1.1/intl/ChangeLog
-...
-
-$ ls -l result
-lrwxrwxrwx ... 2006-09-29 10:43 result -> /nix/store/632d2b22514d...-hello-2.1.1
-
-$ ./result/bin/hello
-Hello, world!
-```
-
-The `-A` option selects the `hello` attribute. This is faster than
-using the symbolic package name specified by the `name` attribute
-(which also happens to be `hello`) and is unambiguous (there can be
-multiple packages with the symbolic name `hello`, but there can be
-only one attribute in a set named `hello`).
-
-`nix-build` registers the `./result` symlink as a garbage collection
-root, so unless and until you delete the `./result` symlink, the output
-of the build will be safely kept on your system. You can use
-`nix-build`’s `-o` switch to give the symlink another name.
-
-Nix has transactional semantics. Once a build finishes successfully, Nix
-makes a note of this in its database: it registers that the path denoted
-by `out` is now “valid”. If you try to build the derivation again, Nix
-will see that the path is already valid and finish immediately. If a
-build fails, either because it returns a non-zero exit code, because Nix
-or the builder are killed, or because the machine crashes, then the
-output paths will not be registered as valid. If you try to build the
-derivation again, Nix will remove the output paths if they exist (e.g.,
-because the builder died half-way through `make
-install`) and try again. Note that there is no “negative caching”: Nix
-doesn't remember that a build failed, and so a failed build can always
-be repeated. This is because Nix cannot distinguish between permanent
-failures (e.g., a compiler error due to a syntax error in the source)
-and transient failures (e.g., a disk full condition).
-
-Nix also performs locking. If you run multiple Nix builds
-simultaneously, and they try to build the same derivation, the first Nix
-instance that gets there will perform the build, while the others block
-(or perform other derivations if available) until the build finishes:
-
-```console
-$ nix-build -A hello
-waiting for lock on `/nix/store/0h5b7hp8d4hqfrw8igvx97x1xawrjnac-hello-2.1.1x'
-```
-
-So it is always safe to run multiple instances of Nix in parallel (which
-isn’t the case with, say, `make`).

doc/manual/src/expressions/simple-expression.md

@@ -1,23 +0,0 @@
-# A Simple Nix Expression
-
-This section shows how to add and test the [GNU Hello
-package](http://www.gnu.org/software/hello/hello.html) to the Nix
-Packages collection. Hello is a program that prints out the text “Hello,
-world\!”.
-
-To add a package to the Nix Packages collection, you generally need to
-do three things:
-
-1.  Write a Nix expression for the package. This is a file that
-    describes all the inputs involved in building the package, such as
-    dependencies, sources, and so on.
-
-2.  Write a *builder*. This is a shell script that builds the package
-    from the inputs. (In fact, it can be written in any language, but
-    typically it's a `bash` shell script.)
-
-3.  Add the package to the file `pkgs/top-level/all-packages.nix`. The
-    Nix expression written in the first step is a *function*; it
-    requires other packages in order to build it. In this step you put
-    it all together, i.e., you call the function with the right
-    arguments to build the actual package.

doc/manual/src/expressions/writing-nix-expressions.md

@@ -1,12 +0,0 @@
-This chapter shows you how to write Nix expressions, which instruct Nix
-how to build packages. It starts with a simple example (a Nix expression
-for GNU Hello), and then moves on to a more in-depth look at the Nix
-expression language.
-
-> **Note**
-> 
-> This chapter is mostly about the Nix expression language. For more
-> extensive information on adding packages to the Nix Packages
-> collection (such as functions in the standard environment and coding
-> conventions), please consult [its
-> manual](http://nixos.org/nixpkgs/manual/).

doc/manual/src/glossary.md

@@ -1,48 +1,48 @@
 # Glossary
 
-  - derivation\
+  - [derivation]{#gloss-derivation}\
     A description of a build action. The result of a derivation is a
     store object. Derivations are typically specified in Nix expressions
-    using the [`derivation` primitive](expressions/derivations.md). These are
+    using the [`derivation` primitive](language/derivations.md). These are
     translated into low-level *store derivations* (implicitly by
     `nix-env` and `nix-build`, or explicitly by `nix-instantiate`).
 
-  - store\
+  - [store]{#gloss-store}\
     The location in the file system where store objects live. Typically
     `/nix/store`.
 
-  - store path\
+  - [store path]{#gloss-store-path}\
     The location in the file system of a store object, i.e., an
     immediate child of the Nix store directory.
 
-  - store object\
+  - [store object]{#gloss-store-object}\
     A file that is an immediate child of the Nix store directory. These
     can be regular files, but also entire directory trees. Store objects
     can be sources (objects copied from outside of the store),
     derivation outputs (objects produced by running a build action), or
     derivations (files describing a build action).
 
-  - substitute\
+  - [substitute]{#gloss-substitute}\
     A substitute is a command invocation stored in the Nix database that
     describes how to build a store object, bypassing the normal build
     mechanism (i.e., derivations). Typically, the substitute builds the
     store object by downloading a pre-built version of the store object
     from some server.
 
-  - purity\
+  - [purity]{#gloss-purity}\
     The assumption that equal Nix derivations when run always produce
     the same output. This cannot be guaranteed in general (e.g., a
     builder can rely on external inputs such as the network or the
     system time) but the Nix model assumes it.
 
-  - Nix expression\
+  - [Nix expression]{#gloss-nix-expression}\
     A high-level description of software packages and compositions
     thereof. Deploying software using Nix entails writing Nix
     expressions for your packages. Nix expressions are translated to
     derivations that are stored in the Nix store. These derivations can
     then be built.
 
-  - reference\
+  - [reference]{#gloss-reference}\
     A store path `P` is said to have a reference to a store path `Q` if
     the store object at `P` contains the path `Q` somewhere. The
     *references* of a store path are the set of store paths to which it
@@ -52,11 +52,11 @@
     output paths), whereas an output path only references other output
     paths.
 
-  - reachable\
+  - [reachable]{#gloss-reachable}\
     A store path `Q` is reachable from another store path `P` if `Q`
     is in the *closure* of the *references* relation.
 
-  - closure\
+  - [closure]{#gloss-closure}\
     The closure of a store path is the set of store paths that are
     directly or indirectly “reachable” from that store path; that is,
     it’s the closure of the path under the *references* relation. For
@@ -71,34 +71,34 @@
     to path `Q`, then `Q` is in the closure of `P`. Further, if `Q`
     references `R` then `R` is also in the closure of `P`.
 
-  - output path\
+  - [output path]{#gloss-output-path}\
     A store path produced by a derivation.
 
-  - deriver\
+  - [deriver]{#gloss-deriver}\
     The deriver of an *output path* is the store
     derivation that built it.
 
-  - validity\
+  - [validity]{#gloss-validity}\
     A store path is considered *valid* if it exists in the file system,
     is listed in the Nix database as being valid, and if all paths in
     its closure are also valid.
 
-  - user environment\
+  - [user environment]{#gloss-user-env}\
     An automatically generated store object that consists of a set of
     symlinks to “active” applications, i.e., other store paths. These
     are generated automatically by
     [`nix-env`](command-ref/nix-env.md). See *profiles*.
 
-  - profile\
+  - [profile]{#gloss-profile}\
     A symlink to the current *user environment* of a user, e.g.,
     `/nix/var/nix/profiles/default`.
 
-  - NAR\
+  - [NAR]{#gloss-nar}\
     A *N*ix *AR*chive. This is a serialisation of a path in the Nix
     store. It can contain regular files, directories and symbolic
     links.  NARs are generated and unpacked using `nix-store --dump`
     and `nix-store --restore`.
-  - `∅` \
+  - [`∅`]{#gloss-emtpy-set}\
     The empty set symbol. In the context of profile history, this denotes a package is not present in a particular version of the profile.
-  - `ε` \
+  - [`ε`]{#gloss-epsilon}\
     The epsilon symbol. In the context of a package, this means the version is empty. More precisely, the derivation does not have a version attribute.

doc/manual/src/installation/installing-binary.md

@@ -31,8 +31,8 @@ $ sh <(curl -L https://nixos.org/nix/install) --no-daemon
 ```
 
 This will perform a single-user installation of Nix, meaning that `/nix`
-is owned by the invoking user. You should run this under your usual user
+is owned by the invoking user. You can run this under your usual user
-account, *not* as root. The script will invoke `sudo` to create `/nix`
+account or root. The script will invoke `sudo` to create `/nix`
 if it doesn’t already exist. If you don’t have `sudo`, you should
 manually create `/nix` first as root, e.g.:
 
@@ -71,7 +71,7 @@ $ sh <(curl -L https://nixos.org/nix/install) --daemon
 
 The multi-user installation of Nix will create build users between the
 user IDs 30001 and 30032, and a group with the group ID 30000. You
-should run this under your usual user account, *not* as root. The script
+can run this under your usual user account or root. The script
 will invoke `sudo` as needed.
 
 > **Note**
@@ -148,7 +148,8 @@ and `/etc/zshrc` which you may remove.
    This will remove all the build users that no longer serve a purpose.
 
 4. Edit fstab using `sudo vifs` to remove the line mounting the Nix Store
-   volume on `/nix`, which looks like this,
+   volume on `/nix`, which looks like
+   `UUID=<uuid> /nix apfs rw,noauto,nobrowse,suid,owners` or
    `LABEL=Nix\040Store /nix apfs rw,nobrowse`. This will prevent automatic
    mounting of the Nix Store volume.
 
@@ -175,6 +176,18 @@ and `/etc/zshrc` which you may remove.
    This will remove the Nix Store volume and everything that was added to the
    store.
 
+   If the output indicates that the command couldn't remove the volume, you should
+   make sure you don't have an _unmounted_ Nix Store volume. Look for a
+   "Nix Store" volume in the output of the following command:
+
+   ```console
+   diskutil list
+   ```
+
+   If you _do_ see a "Nix Store" volume, delete it by re-running the diskutil
+   deleteVolume command, but replace `/nix` with the store volume's `diskXsY`
+   identifier.
+
 > **Note**
 >
 > After you complete the steps here, you will still have an empty `/nix`
@@ -186,12 +199,12 @@ and `/etc/zshrc` which you may remove.
 > read-only root will prevent you from manually deleting the empty `/nix`
 > mountpoint.
 
-# macOS Installation <a name="sect-macos-installation-change-store-prefix"></a><a name="sect-macos-installation-encrypted-volume"></a><a name="sect-macos-installation-symlink"></a><a name="sect-macos-installation-recommended-notes"></a>
+# macOS Installation
+[]{#sect-macos-installation-change-store-prefix}[]{#sect-macos-installation-encrypted-volume}[]{#sect-macos-installation-symlink}[]{#sect-macos-installation-recommended-notes}
 <!-- Note: anchors above to catch permalinks to old explanations -->
 
 We believe we have ironed out how to cleanly support the read-only root
-on modern macOS. New installs will do this automatically, and you can
+on modern macOS. New installs will do this automatically.
-also re-run a new installer to convert your existing setup.
 
 This section previously detailed the situation, options, and trade-offs,
 but it now only outlines what the installer does. You don't need to know

doc/manual/src/language/advanced-attributes.md

@@ -2,7 +2,7 @@
 
 Derivations can declare some infrequently used optional attributes.
 
-  - `allowedReferences`\
+  - [`allowedReferences`]{#adv-attr-allowedReferences}\
     The optional attribute `allowedReferences` specifies a list of legal
     references (dependencies) of the output of the builder. For example,
 
@@ -17,7 +17,7 @@ Derivations can declare some infrequently used optional attributes.
     booting Linux don’t have accidental dependencies on other paths in
     the Nix store.
 
-  - `allowedRequisites`\
+  - [`allowedRequisites`]{#adv-attr-allowedRequisites}\
     This attribute is similar to `allowedReferences`, but it specifies
     the legal requisites of the whole closure, so all the dependencies
     recursively. For example,
@@ -30,7 +30,7 @@ Derivations can declare some infrequently used optional attributes.
     runtime dependency than `foobar`, and in addition it enforces that
     `foobar` itself doesn't introduce any other dependency itself.
 
-  - `disallowedReferences`\
+  - [`disallowedReferences`]{#adv-attr-disallowedReferences}\
     The optional attribute `disallowedReferences` specifies a list of
     illegal references (dependencies) of the output of the builder. For
     example,
@@ -42,7 +42,7 @@ Derivations can declare some infrequently used optional attributes.
     enforces that the output of a derivation cannot have a direct
     runtime dependencies on the derivation `foo`.
 
-  - `disallowedRequisites`\
+  - [`disallowedRequisites`]{#adv-attr-disallowedRequisites}\
     This attribute is similar to `disallowedReferences`, but it
     specifies illegal requisites for the whole closure, so all the
     dependencies recursively. For example,
@@ -55,7 +55,7 @@ Derivations can declare some infrequently used optional attributes.
     dependency on `foobar` or any other derivation depending recursively
     on `foobar`.
 
-  - `exportReferencesGraph`\
+  - [`exportReferencesGraph`]{#adv-attr-exportReferencesGraph}\
     This attribute allows builders access to the references graph of
     their inputs. The attribute is a list of inputs in the Nix store
     whose references graph the builder needs to know. The value of
@@ -84,7 +84,7 @@ Derivations can declare some infrequently used optional attributes.
     with a Nix store containing the closure of a bootable NixOS
     configuration).
 
-  - `impureEnvVars`\
+  - [`impureEnvVars`]{#adv-attr-impureEnvVars}\
     This attribute allows you to specify a list of environment variables
     that should be passed from the environment of the calling user to
     the builder. Usually, the environment is cleared completely when the
@@ -112,7 +112,7 @@ Derivations can declare some infrequently used optional attributes.
     > environmental variables come from the environment of the
     > `nix-build`.
 
-  - `outputHash`; `outputHashAlgo`; `outputHashMode`\
+  - [`outputHash`]{#adv-attr-outputHash}; [`outputHashAlgo`]{#adv-attr-outputHashAlgo}; [`outputHashMode`]{#adv-attr-outputHashMode}\
     These attributes declare that the derivation is a so-called
     *fixed-output derivation*, which means that a cryptographic hash of
     the output is already known in advance. When the build of a
@@ -208,7 +208,7 @@ Derivations can declare some infrequently used optional attributes.
     [`nix-hash` command](../command-ref/nix-hash.md) for information
     about converting to and from base-32 notation.)
     
-  - `__contentAddressed`
+  - [`__contentAddressed`]{#adv-attr-__contentAddressed}
     If this **experimental** attribute is set to true, then the derivation
     outputs will be stored in a content-addressed location rather than the
     traditional input-addressed one.
@@ -216,7 +216,7 @@ Derivations can declare some infrequently used optional attributes.
     
     Setting this attribute also requires setting `outputHashMode` and `outputHashAlgo` like for *fixed-output derivations* (see above).
 
-  - `passAsFile`\
+  - [`passAsFile`]{#adv-attr-passAsFile}\
     A list of names of attributes that should be passed via files rather
     than environment variables. For example, if you have
 
@@ -234,7 +234,7 @@ Derivations can declare some infrequently used optional attributes.
     builder, since most operating systems impose a limit on the size
     of the environment (typically, a few hundred kilobyte).
 
-  - `preferLocalBuild`\
+  - [`preferLocalBuild`]{#adv-attr-preferLocalBuild}\
     If this attribute is set to `true` and [distributed building is
     enabled](../advanced-topics/distributed-builds.md), then, if
     possible, the derivation will be built locally instead of forwarded
@@ -242,7 +242,7 @@ Derivations can declare some infrequently used optional attributes.
     where the cost of doing a download or remote build would exceed
     the cost of building locally.
 
-  - `allowSubstitutes`\
+  - [`allowSubstitutes`]{#adv-attr-allowSubstitutes}\
     If this attribute is set to `false`, then Nix will always build this
     derivation; it will not try to substitute its outputs. This is
     useful for very trivial derivations (such as `writeText` in Nixpkgs)

doc/manual/src/language/builtin-constants.md

@@ -14,7 +14,7 @@ Here are the constants built into the Nix expression evaluator:
     This allows a Nix expression to fall back gracefully on older Nix
     installations that don’t have the desired built-in function.
 
-  - `builtins.currentSystem`\
+  - [`builtins.currentSystem`]{#builtins-currentSystem}\
     The built-in value `currentSystem` evaluates to the Nix platform
     identifier for the Nix installation on which the expression is being
     evaluated, such as `"i686-linux"` or `"x86_64-darwin"`.

doc/manual/src/language/derivations.md

@@ -4,7 +4,7 @@ The most important built-in function is `derivation`, which is used to
 describe a single derivation (a build action). It takes as input a set,
 the attributes of which specify the inputs of the build.
 
-  - There must be an attribute named `system` whose value must be a
+  - There must be an attribute named [`system`]{#attr-system} whose value must be a
     string specifying a Nix system type, such as `"i686-linux"` or
     `"x86_64-darwin"`. (To figure out your system type, run `nix -vv
     --version`.) The build can only be performed on a machine and

doc/manual/src/language/index.md

@@ -0,0 +1,33 @@
+# Nix Language
+
+The Nix language is
+
+- *domain-specific*
+
+  It only exists for the Nix package manager:
+  to describe packages and configurations as well as their variants and compositions.
+  It is not intended for general purpose use.
+
+- *declarative*
+
+  There is no notion of executing sequential steps.
+  Dependencies between operations are established only through data.
+
+- *pure*
+
+  Values cannot change during computation.
+  Functions always produce the same output if their input does not change.
+
+- *functional*
+
+  Functions are like any other value.
+  Functions can be assigned to names, taken as arguments, or returned by functions.
+
+- *lazy*
+
+  Expressions are only evaluated when their value is needed.
+
+- *dynamically typed*
+
+  Type errors are only detected when expressions are evaluated.
+

doc/manual/src/language/operators.md

@@ -1,6 +1,6 @@
 # Operators
 
-The table below lists the operators in the Nix expression language, in
+The table below lists the operators in the Nix language, in
 order of precedence (from strongest to weakest binding).
 
 | Name                     | Syntax                              | Associativity | Description                                                                                                                                                                                                                   | Precedence |

doc/manual/src/language/values.md

@@ -0,0 +1,261 @@
+# Data Types
+
+## Primitives
+
+- <a id="type-string" href="#type-string">String</a>
+
+  *Strings* can be written in three ways.
+
+  The most common way is to enclose the string between double quotes,
+  e.g., `"foo bar"`. Strings can span multiple lines. The special
+  characters `"` and `\` and the character sequence `${` must be
+  escaped by prefixing them with a backslash (`\`). Newlines, carriage
+  returns and tabs can be written as `\n`, `\r` and `\t`,
+  respectively.
+
+  You can include the result of an expression into a string by
+  enclosing it in `${...}`, a feature known as *antiquotation*. The
+  enclosed expression must evaluate to something that can be coerced
+  into a string (meaning that it must be a string, a path, or a
+  derivation). For instance, rather than writing
+
+  ```nix
+  "--with-freetype2-library=" + freetype + "/lib"
+  ```
+
+  (where `freetype` is a derivation), you can instead write the more
+  natural
+
+  ```nix
+  "--with-freetype2-library=${freetype}/lib"
+  ```
+
+  The latter is automatically translated to the former. A more
+  complicated example (from the Nix expression for
+  [Qt](http://www.trolltech.com/products/qt)):
+
+  ```nix
+  configureFlags = "
+    -system-zlib -system-libpng -system-libjpeg
+    ${if openglSupport then "-dlopen-opengl
+      -L${mesa}/lib -I${mesa}/include
+      -L${libXmu}/lib -I${libXmu}/include" else ""}
+    ${if threadSupport then "-thread" else "-no-thread"}
+  ";
+  ```
+
+  Note that Nix expressions and strings can be arbitrarily nested; in
+  this case the outer string contains various antiquotations that
+  themselves contain strings (e.g., `"-thread"`), some of which in
+  turn contain expressions (e.g., `${mesa}`).
+
+  The second way to write string literals is as an *indented string*,
+  which is enclosed between pairs of *double single-quotes*, like so:
+
+  ```nix
+  ''
+    This is the first line.
+    This is the second line.
+      This is the third line.
+  ''
+  ```
+
+  This kind of string literal intelligently strips indentation from
+  the start of each line. To be precise, it strips from each line a
+  number of spaces equal to the minimal indentation of the string as a
+  whole (disregarding the indentation of empty lines). For instance,
+  the first and second line are indented two spaces, while the third
+  line is indented four spaces. Thus, two spaces are stripped from
+  each line, so the resulting string is
+
+  ```nix
+  "This is the first line.\nThis is the second line.\n  This is the third line.\n"
+  ```
+
+  Note that the whitespace and newline following the opening `''` is
+  ignored if there is no non-whitespace text on the initial line.
+
+  Antiquotation (`${expr}`) is supported in indented strings.
+
+  Since `${` and `''` have special meaning in indented strings, you
+  need a way to quote them. `$` can be escaped by prefixing it with
+  `''` (that is, two single quotes), i.e., `''$`. `''` can be escaped
+  by prefixing it with `'`, i.e., `'''`. `$` removes any special
+  meaning from the following `$`. Linefeed, carriage-return and tab
+  characters can be written as `''\n`, `''\r`, `''\t`, and `''\`
+  escapes any other character.
+
+  Indented strings are primarily useful in that they allow multi-line
+  string literals to follow the indentation of the enclosing Nix
+  expression, and that less escaping is typically necessary for
+  strings representing languages such as shell scripts and
+  configuration files because `''` is much less common than `"`.
+  Example:
+
+  ```nix
+  stdenv.mkDerivation {
+    ...
+    postInstall =
+      ''
+        mkdir $out/bin $out/etc
+        cp foo $out/bin
+        echo "Hello World" > $out/etc/foo.conf
+        ${if enableBar then "cp bar $out/bin" else ""}
+      '';
+    ...
+  }
+  ```
+
+  Finally, as a convenience, *URIs* as defined in appendix B of
+  [RFC 2396](http://www.ietf.org/rfc/rfc2396.txt) can be written *as
+  is*, without quotes. For instance, the string
+  `"http://example.org/foo.tar.bz2"` can also be written as
+  `http://example.org/foo.tar.bz2`.
+
+- <a id="type-number" href="#type-number">Number</a>
+
+  Numbers, which can be *integers* (like `123`) or *floating point*
+  (like `123.43` or `.27e13`).
+
+  Numbers are type-compatible: pure integer operations will always
+  return integers, whereas any operation involving at least one
+  floating point number will have a floating point number as a result.
+
+- <a id="type-path" href="#type-path">Path</a>
+
+  *Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at
+  least one slash to be recognised as such. For instance, `builder.sh`
+  is not a path: it's parsed as an expression that selects the
+  attribute `sh` from the variable `builder`. If the file name is
+  relative, i.e., if it does not begin with a slash, it is made
+  absolute at parse time relative to the directory of the Nix
+  expression that contained it. For instance, if a Nix expression in
+  `/foo/bar/bla.nix` refers to `../xyzzy/fnord.nix`, the absolute path
+  is `/foo/xyzzy/fnord.nix`.
+
+  If the first component of a path is a `~`, it is interpreted as if
+  the rest of the path were relative to the user's home directory.
+  e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
+  whose home directory is `/home/edolstra`.
+
+  Paths can also be specified between angle brackets, e.g.
+  `<nixpkgs>`. This means that the directories listed in the
+  environment variable `NIX_PATH` will be searched for the given file
+  or directory name.
+
+  Antiquotation is supported in any paths except those in angle brackets.
+  `./${foo}-${bar}.nix` is a more convenient way of writing
+  `./. + "/" + foo + "-" + bar + ".nix"` or `./. + "/${foo}-${bar}.nix"`. At
+  least one slash must appear *before* any antiquotations for this to be
+  recognized as a path. `a.${foo}/b.${bar}` is a syntactically valid division
+  operation. `./a.${foo}/b.${bar}` is a path.
+
+- <a id="type-boolean" href="#type-boolean">Boolean</a>
+
+  *Booleans* with values `true` and `false`.
+
+- <a id="type-null" href="#type-null">Null</a>
+
+  The null value, denoted as `null`.
+
+## List
+
+Lists are formed by enclosing a whitespace-separated list of values
+between square brackets. For example,
+
+```nix
+[ 123 ./foo.nix "abc" (f { x = y; }) ]
+```
+
+defines a list of four elements, the last being the result of a call to
+the function `f`. Note that function calls have to be enclosed in
+parentheses. If they had been omitted, e.g.,
+
+```nix
+[ 123 ./foo.nix "abc" f { x = y; } ]
+```
+
+the result would be a list of five elements, the fourth one being a
+function and the fifth being a set.
+
+Note that lists are only lazy in values, and they are strict in length.
+
+## Attribute Set
+
+An attribute set is a collection of name-value-pairs (called *attributes*) enclosed in curly brackets (`{ }`).
+
+Names and values are separated by an equal sign (`=`).
+Each value is an arbitrary expression terminated by a semicolon (`;`).
+
+Attributes can appear in any order.
+An attribute name may only occur once.
+
+Example:
+
+```nix
+{
+  x = 123;
+  text = "Hello";
+  y = f { bla = 456; };
+}
+```
+
+This defines a set with attributes named `x`, `text`, `y`.
+
+Attributes can be selected from a set using the `.` operator. For
+instance,
+
+```nix
+{ a = "Foo"; b = "Bar"; }.a
+```
+
+evaluates to `"Foo"`. It is possible to provide a default value in an
+attribute selection using the `or` keyword. For example,
+
+```nix
+{ a = "Foo"; b = "Bar"; }.c or "Xyzzy"
+```
+
+will evaluate to `"Xyzzy"` because there is no `c` attribute in the set.
+
+You can use arbitrary double-quoted strings as attribute names:
+
+```nix
+{ "foo ${bar}" = 123; "nix-1.0" = 456; }."foo ${bar}"
+```
+
+This will evaluate to `123` (Assuming `bar` is antiquotable). In the
+case where an attribute name is just a single antiquotation, the quotes
+can be dropped:
+
+```nix
+{ foo = 123; }.${bar} or 456
+```
+
+This will evaluate to `123` if `bar` evaluates to `"foo"` when coerced
+to a string and `456` otherwise (again assuming `bar` is antiquotable).
+
+In the special case where an attribute name inside of a set declaration
+evaluates to `null` (which is normally an error, as `null` is not
+antiquotable), that attribute is simply not added to the set:
+
+```nix
+{ ${if foo then "bar" else null} = true; }
+```
+
+This will evaluate to `{}` if `foo` evaluates to `false`.
+
+A set that has a `__functor` attribute whose value is callable (i.e. is
+itself a function or a set with a `__functor` attribute whose value is
+callable) can be applied as if it were a function, with the set itself
+passed in first , e.g.,
+
+```nix
+let add = { __functor = self: x: x + self.x; };
+    inc = add // { x = 1; };
+in inc 1
+```
+
+evaluates to `2`. This can be used to attach metadata to a function
+without the caller needing to treat it specially, or to implement a form
+of object-oriented programming, for example.

doc/manual/src/package-management/package-management.md

@@ -1,5 +1,4 @@
 This chapter discusses how to do package management with Nix, i.e.,
 how to obtain, install, upgrade, and erase packages. This is the
 “user’s” perspective of the Nix system — people who want to *create*
-packages should consult the [chapter on writing Nix
+packages should consult the chapter on the [Nix language](../language/index.md).
-expressions](../expressions/writing-nix-expressions.md).

doc/manual/src/release-notes/rl-2.10.md

@@ -0,0 +1,31 @@
+# Release 2.10 (2022-07-11)
+
+* `nix repl` now takes installables on the command line, unifying the usage
+  with other commands that use `--file` and `--expr`. Primary breaking change
+  is for the common usage of `nix repl '<nixpkgs>'` which can be recovered with
+  `nix repl --file '<nixpkgs>'` or `nix repl --expr 'import <nixpkgs>{}'`.
+
+  This is currently guarded by the `repl-flake` experimental feature.
+
+* A new function `builtins.traceVerbose` is available. It is similar
+  to `builtins.trace` if the `trace-verbose` setting is set to true,
+  and it is a no-op otherwise.
+
+* `nix search` has a new flag `--exclude` to filter out packages.
+
+* On Linux, if `/nix` doesn't exist and cannot be created and you're
+  not running as root, Nix will automatically use
+  `~/.local/share/nix/root` as a chroot store. This enables non-root
+  users to download the statically linked Nix binary and have it work
+  out of the box, e.g.
+
+  ```
+  # ~/nix run nixpkgs#hello
+  warning: '/nix' does not exists, so Nix will use '/home/ubuntu/.local/share/nix/root' as a chroot store
+  Hello, world!
+  ```
+
+* `flake-registry.json` is now fetched from `channels.nixos.org`.
+
+* Nix can now be built with LTO by passing `--enable-lto` to `configure`.
+  LTO is currently only supported when building with GCC.

doc/manual/src/release-notes/rl-2.11.md

@@ -0,0 +1,5 @@
+# Release 2.11 (2022-08-24)
+
+* `nix copy` now copies the store paths in parallel as much as possible (again).
+  This doesn't apply for the `daemon` and `ssh-ng` stores which copy everything
+  in one batch to avoid latencies issues.

doc/manual/src/release-notes/rl-2.9.md

@@ -0,0 +1,47 @@
+# Release 2.9 (2022-05-30)
+
+* Running Nix with the new `--debugger` flag will cause it to start a
+  repl session if an exception is thrown during evaluation, or if
+  `builtins.break` is called.  From there you can inspect the values
+  of variables and evaluate Nix expressions.  In debug mode, the
+  following new repl commands are available:
+
+  ```
+  :env          Show env stack
+  :bt           Show trace stack
+  :st           Show current trace
+  :st <idx>     Change to another trace in the stack
+  :c            Go until end of program, exception, or builtins.break().
+  :s            Go one step
+  ```
+
+  Read more about the debugger
+  [here](https://www.zknotes.com/note/5970).
+
+* Nix now provides better integration with zsh's `run-help`
+  feature. It is now included in the Nix installation in the form of
+  an autoloadable shell function, `run-help-nix`. It picks up Nix
+  subcommands from the currently typed in command and directs the user
+  to the associated man pages.
+
+* `nix repl` has a new build-and-link (`:bl`) command that builds a
+  derivation while creating GC root symlinks.
+
+* The path produced by `builtins.toFile` is now allowed to be imported
+  or read even with restricted evaluation. Note that this will not
+  work with a read-only store.
+
+* `nix build` has a new `--print-out-paths` flag to print the
+  resulting output paths.  This matches the default behaviour of
+  `nix-build`.
+
+* You can now specify which outputs of a derivation `nix` should
+  operate on using the syntax `installable^outputs`,
+  e.g. `nixpkgs#glibc^dev,static` or `nixpkgs#glibc^*`. By default,
+  `nix` will use the outputs specified by the derivation's
+  `meta.outputsToInstall` attribute if it exists, or all outputs
+  otherwise.
+
+* `builtins.fetchTree` (and flake inputs) can now be used to fetch
+  plain files over the `http(s)` and `file` protocols in addition to
+  directory tarballs.

doc/manual/src/release-notes/rl-next.md

@@ -1,20 +1,5 @@
 # Release X.Y (202?-??-??)
 
-* Nix now provides better integration with zsh's run-help feature. It is now
-  included in the Nix installation in the form of an autoloadable shell
-  function, run-help-nix. It picks up Nix subcommands from the currently typed
-  in command and directs the user to the associated man pages.
-
-* `nix repl` has a new build-'n-link (`:bl`) command that builds a derivation
-  while creating GC root symlinks.
-
-* The path produced by `builtins.toFile` is now allowed to be imported or read
-  even with restricted evaluation. Note that this will not work with a
-  read-only store.
-
-* `nix build` has a new `--print-out-paths` flag to print the resulting output paths.
-  This matches the default behaviour of `nix-build`.
-
 * Error traces have been reworked to provide detailed explanations and more
   accurate error locations. A short excerpt of the trace is now shown by
   default when an error occurs.

docker.nix

@@ -2,8 +2,12 @@
 , lib ? pkgs.lib
 , name ? "nix"
 , tag ? "latest"
+, bundleNixpkgs ? true
 , channelName ? "nixpkgs"
 , channelURL ? "https://nixos.org/channels/nixpkgs-unstable"
+, extraPkgs ? []
+, maxLayers ? 100
+, nixConf ? {}
 }:
 let
   defaultPkgs = with pkgs; [
@@ -23,7 +27,7 @@ let
     iana-etc
     git
     openssh
-  ];
+  ] ++ extraPkgs;
 
   users = {
 
@@ -121,20 +125,27 @@ let
       (lib.attrValues (lib.mapAttrs groupToGroup groups))
   );
 
-  nixConf = {
+  defaultNixConf = {
     sandbox = "false";
     build-users-group = "nixbld";
-    trusted-public-keys = "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=";
+    trusted-public-keys = [ "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=" ];
   };
-  nixConfContents = (lib.concatStringsSep "\n" (lib.mapAttrsFlatten (n: v: "${n} = ${v}") nixConf)) + "\n";
+
+  nixConfContents = (lib.concatStringsSep "\n" (lib.mapAttrsFlatten (n: v:
+    let
+      vStr = if builtins.isList v then lib.concatStringsSep " " v else v;
+    in
+      "${n} = ${vStr}") (defaultNixConf // nixConf))) + "\n";
 
   baseSystem =
     let
       nixpkgs = pkgs.path;
-      channel = pkgs.runCommand "channel-nixos" { } ''
+      channel = pkgs.runCommand "channel-nixos" { inherit bundleNixpkgs; } ''
         mkdir $out
-        ln -s ${nixpkgs} $out/nixpkgs
+        if [ "$bundleNixpkgs" ]; then
-        echo "[]" > $out/manifest.nix
+          ln -s ${nixpkgs} $out/nixpkgs
+          echo "[]" > $out/manifest.nix
+        fi
       '';
       rootEnv = pkgs.buildPackages.buildEnv {
         name = "root-profile-env";
@@ -229,7 +240,7 @@ let
 in
 pkgs.dockerTools.buildLayeredImageWithNixDb {
 
-  inherit name tag;
+  inherit name tag maxLayers;
 
   contents = [ baseSystem ];
 

flake.lock

@@ -18,17 +18,18 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1645296114,
+        "lastModified": 1657693803,
-        "narHash": "sha256-y53N7TyIkXsjMpOG7RhvqJFGDacLs9HlyHeSTBioqYU=",
+        "narHash": "sha256-G++2CJ9u0E7NNTAi9n5G8TdDmGJXcIjkJ3NF8cetQB8=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "530a53dcbc9437363471167a5e4762c5fcfa34a1",
+        "rev": "365e1b3a859281cf11b94f87231adeabbdd878a2",
         "type": "github"
       },
       "original": {
-        "id": "nixpkgs",
+        "owner": "NixOS",
-        "ref": "nixos-21.05-small",
+        "ref": "nixos-22.05-small",
-        "type": "indirect"
+        "repo": "nixpkgs",
+        "type": "github"
       }
     },
     "nixpkgs-regression": {
@@ -41,9 +42,10 @@
         "type": "github"
       },
       "original": {
-        "id": "nixpkgs",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
         "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "indirect"
+        "type": "github"
       }
     },
     "root": {

flake.nix

@@ -1,8 +1,8 @@
 {
   description = "The purely functional package manager";
 
-  inputs.nixpkgs.url = "nixpkgs/nixos-21.05-small";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.05-small";
-  inputs.nixpkgs-regression.url = "nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
+  inputs.nixpkgs-regression.url = "github:NixOS/nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
   inputs.lowdown-src = { url = "github:kristapsdz/lowdown"; flake = false; };
 
   outputs = { self, nixpkgs, nixpkgs-regression, lowdown-src }:
@@ -23,7 +23,7 @@
 
       crossSystems = [ "armv6l-linux" "armv7l-linux" ];
 
-      stdenvs = [ "gccStdenv" "clangStdenv" "clang11Stdenv" "stdenv" ];
+      stdenvs = [ "gccStdenv" "clangStdenv" "clang11Stdenv" "stdenv" "libcxxStdenv" ];
 
       forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f system);
       forAllSystemsAndStdenvs = f: forAllSystems (system:
@@ -36,7 +36,7 @@
           )
       );
 
-      forAllStdenvs = stdenvs: f: nixpkgs.lib.genAttrs stdenvs (stdenv: f stdenv);
+      forAllStdenvs = f: nixpkgs.lib.genAttrs stdenvs (stdenv: f stdenv);
 
       # Memoize nixpkgs for different platforms for efficiency.
       nixpkgsFor =
@@ -54,7 +54,7 @@
         # we want most of the time and for backwards compatibility
         forAllSystems (system: stdenvsPackages.${system} // stdenvsPackages.${system}.stdenvPackages);
 
-      commonDeps = pkgs: with pkgs; rec {
+      commonDeps = { pkgs, isStatic ? false }: with pkgs; rec {
         # Use "busybox-sandbox-shell" if present,
         # if not (legacy) fallback and hope it's sufficient.
         sh = pkgs.busybox-sandbox-shell or (busybox.override {
@@ -85,10 +85,11 @@
           lib.optionals stdenv.isLinux [
             "--with-boost=${boost}/lib"
             "--with-sandbox-shell=${sh}/bin/busybox"
+          ]
+          ++ lib.optionals (stdenv.isLinux && !(isStatic && stdenv.system == "aarch64-linux")) [
             "LDFLAGS=-fuse-ld=gold"
           ];
 
-
         nativeBuildDeps =
           [
             buildPackages.bison
@@ -102,12 +103,12 @@
             # Tests
             buildPackages.git
             buildPackages.mercurial # FIXME: remove? only needed for tests
-            buildPackages.jq
+            buildPackages.jq # Also for custom mdBook preprocessor.
           ]
           ++ lib.optionals stdenv.hostPlatform.isLinux [(buildPackages.util-linuxMinimal or buildPackages.utillinuxMinimal)];
 
         buildDeps =
-          [ curl
+          [ (curl.override { patchNetrcRegression = true; })
             bzip2 xz brotli editline
             openssl sqlite
             libarchive
@@ -135,11 +136,6 @@
             }))
             nlohmann_json
           ];
-
-        perlDeps =
-          [ perl
-            perlPackages.DBDSQLite
-          ];
       };
 
       installScriptFor = systems:
@@ -176,7 +172,7 @@
             echo "file installer $out/install" >> $out/nix-support/hydra-build-products
           '';
 
-      testNixVersions = pkgs: client: daemon: with commonDeps pkgs; with pkgs.lib; pkgs.stdenv.mkDerivation {
+      testNixVersions = pkgs: client: daemon: with commonDeps { inherit pkgs; }; with pkgs.lib; pkgs.stdenv.mkDerivation {
         NIX_DAEMON_PACKAGE = daemon;
         NIX_CLIENT_PACKAGE = client;
         name =
@@ -264,6 +260,7 @@
             echo "file binary-dist $fn" >> $out/nix-support/hydra-build-products
             tar cvfJ $fn \
               --owner=0 --group=0 --mode=u+rw,uga+r \
+              --mtime='1970-01-01' \
               --absolute-names \
               --hard-dereference \
               --transform "s,$TMPDIR/install,$dir/install," \
@@ -287,7 +284,7 @@
           # Forward from the previous stage as we don’t want it to pick the lowdown override
           nixUnstable = prev.nixUnstable;
 
-          nix = with final; with commonDeps pkgs; currentStdenv.mkDerivation {
+          nix = with final; with commonDeps { inherit pkgs; }; currentStdenv.mkDerivation {
             name = "nix-${version}";
             inherit version;
 
@@ -319,6 +316,7 @@
                   for LIB in $out/lib/*.dylib; do
                     chmod u+w $LIB
                     install_name_tool -id $LIB $LIB
+                    install_name_tool -delete_rpath ${boost}/lib/ $LIB || true
                   done
                   install_name_tool -change ${boost}/lib/libboost_system.dylib $out/lib/libboost_system.dylib $out/lib/libboost_thread.dylib
                 ''}
@@ -353,7 +351,7 @@
 
             strictDeps = true;
 
-            passthru.perl-bindings = with final; currentStdenv.mkDerivation {
+            passthru.perl-bindings = with final; perl.pkgs.toPerlModule (currentStdenv.mkDerivation {
               name = "nix-perl-${version}";
 
               src = self;
@@ -366,7 +364,7 @@
 
               buildInputs =
                 [ nix
-                  curl
+                  (curl.override { patchNetrcRegression = true; })
                   bzip2
                   xz
                   pkgs.perl
@@ -375,16 +373,17 @@
                 ++ lib.optional (currentStdenv.isLinux || currentStdenv.isDarwin) libsodium
                 ++ lib.optional currentStdenv.isDarwin darwin.apple_sdk.frameworks.Security;
 
-              configureFlags = ''
+              configureFlags = [
-                --with-dbi=${perlPackages.DBI}/${pkgs.perl.libPrefix}
+                "--with-dbi=${perlPackages.DBI}/${pkgs.perl.libPrefix}"
-                --with-dbd-sqlite=${perlPackages.DBDSQLite}/${pkgs.perl.libPrefix}
+                "--with-dbd-sqlite=${perlPackages.DBDSQLite}/${pkgs.perl.libPrefix}"
-              '';
+              ];
 
               enableParallelBuilding = true;
 
               postUnpack = "sourceRoot=$sourceRoot/perl";
-            };
+            });
 
+            meta.platforms = systems;
           };
 
           lowdown-nix = with final; currentStdenv.mkDerivation rec {
@@ -409,7 +408,7 @@
 
       # A Nixpkgs overlay that overrides the 'nix' and
       # 'nix.perl-bindings' packages.
-      overlay = overlayFor (p: p.stdenv);
+      overlays.default = overlayFor (p: p.stdenv);
 
       hydraJobs = {
 
@@ -434,7 +433,7 @@
           value = let
             nixpkgsCross = import nixpkgs {
               inherit system crossSystem;
-              overlays = [ self.overlay ];
+              overlays = [ self.overlays.default ];
             };
           in binaryTarball nixpkgsFor.${system} self.packages.${system}."nix-${crossSystem}" nixpkgsCross;
         }) crossSystems));
@@ -452,7 +451,7 @@
         # Line coverage analysis.
         coverage =
           with nixpkgsFor.x86_64-linux;
-          with commonDeps pkgs;
+          with commonDeps { inherit pkgs; };
 
           releaseTools.coverageAnalysis {
             name = "nix-coverage-${version}";
@@ -480,31 +479,31 @@
         tests.remoteBuilds = import ./tests/remote-builds.nix {
           system = "x86_64-linux";
           inherit nixpkgs;
-          inherit (self) overlay;
+          overlay = self.overlays.default;
         };
 
         tests.nix-copy-closure = import ./tests/nix-copy-closure.nix {
           system = "x86_64-linux";
           inherit nixpkgs;
-          inherit (self) overlay;
+          overlay = self.overlays.default;
         };
 
         tests.nssPreload = (import ./tests/nss-preload.nix rec {
           system = "x86_64-linux";
           inherit nixpkgs;
-          inherit (self) overlay;
+          overlay = self.overlays.default;
         });
 
         tests.githubFlakes = (import ./tests/github-flakes.nix rec {
           system = "x86_64-linux";
           inherit nixpkgs;
-          inherit (self) overlay;
+          overlay = self.overlays.default;
         });
 
         tests.sourcehutFlakes = (import ./tests/sourcehut-flakes.nix rec {
           system = "x86_64-linux";
           inherit nixpkgs;
-          inherit (self) overlay;
+          overlay = self.overlays.default;
         });
 
         tests.setuid = nixpkgs.lib.genAttrs
@@ -512,7 +511,7 @@
           (system:
             import ./tests/setuid.nix rec {
               inherit nixpkgs system;
-              inherit (self) overlay;
+              overlay = self.overlays.default;
             });
 
         # Make sure that nix-env still produces the exact same result
@@ -557,12 +556,13 @@
         dockerImage = self.hydraJobs.dockerImage.${system};
       });
 
-      packages = forAllSystems (system: {
+      packages = forAllSystems (system: rec {
         inherit (nixpkgsFor.${system}) nix;
+        default = nix;
       } // (nixpkgs.lib.optionalAttrs (builtins.elem system linux64BitSystems) {
         nix-static = let
           nixpkgs = nixpkgsFor.${system}.pkgsStatic;
-        in with commonDeps nixpkgs; nixpkgs.stdenv.mkDerivation {
+        in with commonDeps { pkgs = nixpkgs; isStatic = true; }; nixpkgs.stdenv.mkDerivation {
           name = "nix-${version}";
 
           src = self;
@@ -574,14 +574,24 @@
           nativeBuildInputs = nativeBuildDeps;
           buildInputs = buildDeps ++ propagatedDeps;
 
-          configureFlags = [ "--sysconfdir=/etc" ];
+          # Work around pkgsStatic disabling all tests.
+          # Remove in NixOS 22.11, see https://github.com/NixOS/nixpkgs/pull/140271.
+          preHook =
+            ''
+              doCheck=1
+              doInstallCheck=1
+            '';
+
+          configureFlags =
+            configureFlags ++
+            [ "--sysconfdir=/etc"
+              "--enable-embedded-sandbox-shell"
+            ];
 
           enableParallelBuilding = true;
 
           makeFlags = "profiledir=$(out)/etc/profile.d";
 
-          doCheck = true;
-
           installFlags = "sysconfdir=$(out)/etc";
 
           postInstall = ''
@@ -591,7 +601,6 @@
             echo "file binary-dist $out/bin/nix" >> $out/nix-support/hydra-build-products
           '';
 
-          doInstallCheck = true;
           installCheckFlags = "sysconfdir=$(out)/etc";
 
           stripAllList = ["bin"];
@@ -600,6 +609,7 @@
 
           hardeningDisable = [ "pie" ];
         };
+
         dockerImage =
           let
             pkgs = nixpkgsFor.${system};
@@ -614,14 +624,16 @@
               ln -s ${image} $image
               echo "file binary-dist $image" >> $out/nix-support/hydra-build-products
             '';
-      } // builtins.listToAttrs (map (crossSystem: {
+      }
+
+      // builtins.listToAttrs (map (crossSystem: {
         name = "nix-${crossSystem}";
         value = let
           nixpkgsCross = import nixpkgs {
             inherit system crossSystem;
-            overlays = [ self.overlay ];
+            overlays = [ self.overlays.default ];
           };
-        in with commonDeps nixpkgsCross; nixpkgsCross.stdenv.mkDerivation {
+        in with commonDeps { pkgs = nixpkgsCross; }; nixpkgsCross.stdenv.mkDerivation {
           name = "nix-${version}";
 
           src = self;
@@ -653,44 +665,45 @@
           doInstallCheck = true;
           installCheckFlags = "sysconfdir=$(out)/etc";
         };
-      }) crossSystems)) // (builtins.listToAttrs (map (stdenvName:
+      }) (if system == "x86_64-linux" then crossSystems else [])))
+
+      // (builtins.listToAttrs (map (stdenvName:
         nixpkgsFor.${system}.lib.nameValuePair
           "nix-${stdenvName}"
           nixpkgsFor.${system}."${stdenvName}Packages".nix
       ) stdenvs)));
 
-      defaultPackage = forAllSystems (system: self.packages.${system}.nix);
+      devShells = forAllSystems (system:
+        forAllStdenvs (stdenv:
+          with nixpkgsFor.${system};
+          with commonDeps { inherit pkgs; };
+          nixpkgsFor.${system}.${stdenv}.mkDerivation {
+            name = "nix";
 
-      devShell = forAllSystems (system: self.devShells.${system}.stdenvPackages);
+            outputs = [ "out" "dev" "doc" ];
 
-      devShells = forAllSystemsAndStdenvs (system: stdenv:
+            nativeBuildInputs = nativeBuildDeps;
-        with nixpkgsFor.${system};
+            buildInputs = buildDeps ++ propagatedDeps ++ awsDeps;
-        with commonDeps pkgs;
 
-        nixpkgsFor.${system}.${stdenv}.mkDerivation {
+            inherit configureFlags;
-          name = "nix";
 
-          outputs = [ "out" "dev" "doc" ];
+            enableParallelBuilding = true;
 
-          nativeBuildInputs = nativeBuildDeps;
+            installFlags = "sysconfdir=$(out)/etc";
-          buildInputs = buildDeps ++ propagatedDeps ++ awsDeps ++ perlDeps;
 
-          inherit configureFlags;
+            shellHook =
+              ''
+                PATH=$prefix/bin:$PATH
+                unset PYTHONPATH
+                export MANPATH=$out/share/man:$MANPATH
 
-          enableParallelBuilding = true;
+                # Make bash completion work.
-
+                XDG_DATA_DIRS+=:$out/share
-          installFlags = "sysconfdir=$(out)/etc";
+              '';
-
+          }
-          shellHook =
+        )
-            ''
+        // { default = self.devShells.${system}.stdenv; }
-              PATH=$prefix/bin:$PATH
+      );
-              unset PYTHONPATH
-              export MANPATH=$out/share/man:$MANPATH
-
-              # Make bash completion work.
-              XDG_DATA_DIRS+=:$out/share
-            '';
-        });
 
   };
 }

misc/systemd/nix-daemon.service.in

@@ -9,6 +9,7 @@ ConditionPathIsReadWrite=@localstatedir@/nix/daemon-socket
 [Service]
 ExecStart=@@bindir@/nix-daemon nix-daemon --daemon
 KillMode=process
+LimitNOFILE=4096
 
 [Install]
 WantedBy=multi-user.target

misc/zsh/completion.zsh

@@ -10,14 +10,15 @@ function _nix() {
   local -a suggestions
   declare -a suggestions
   for suggestion in ${res:1}; do
-    # FIXME: This doesn't work properly if the suggestion word contains a `:`
+    suggestions+=("${suggestion%%	*}")
-    # itself
-    suggestions+="${suggestion/	/:}"
   done
+  local -a args
   if [[ "$tpe" == filenames ]]; then
-    compadd -f
+    args+=('-f')
+  elif [[ "$tpe" == attrs ]]; then
+    args+=('-S' '')
   fi
-  _describe 'nix' suggestions
+  compadd -J nix "${args[@]}" -a suggestions
 }
 
 _nix "$@"

mk/libraries.mk

@@ -91,7 +91,7 @@ define build-library
     $(1)_PATH := $$(_d)/$$($(1)_NAME).$(SO_EXT)
 
     $$($(1)_PATH): $$($(1)_OBJS) $$(_libs) | $$(_d)/
-	$$(trace-ld) $(CXX) -o $$(abspath $$@) -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE)) $$($(1)_LDFLAGS_UNINSTALLED)
+	+$$(trace-ld) $(CXX) -o $$(abspath $$@) -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE)) $$($(1)_LDFLAGS_UNINSTALLED)
 
     ifndef HOST_DARWIN
       $(1)_LDFLAGS_USE += -Wl,-rpath,$$(abspath $$(_d))
@@ -105,7 +105,7 @@ define build-library
     $$(eval $$(call create-dir, $$($(1)_INSTALL_DIR)))
 
     $$($(1)_INSTALL_PATH): $$($(1)_OBJS) $$(_libs_final) | $(DESTDIR)$$($(1)_INSTALL_DIR)/
-	$$(trace-ld) $(CXX) -o $$@ -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
+	+$$(trace-ld) $(CXX) -o $$@ -shared $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$($(1)_LDFLAGS_PROPAGATED) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
 
     $(1)_LDFLAGS_USE_INSTALLED += -L$$(DESTDIR)$$($(1)_INSTALL_DIR) -l$$(patsubst lib%,%,$$(strip $$($(1)_NAME)))
     ifndef HOST_DARWIN
@@ -125,7 +125,7 @@ define build-library
     $(1)_PATH := $$(_d)/$$($(1)_NAME).a
 
     $$($(1)_PATH): $$($(1)_OBJS) | $$(_d)/
-	$$(trace-ld) $(LD) -Ur -o $$(_d)/$$($(1)_NAME).o $$?
+	+$$(trace-ld) $(LD) -Ur -o $$(_d)/$$($(1)_NAME).o $$^
 	$$(trace-ar) $(AR) crs $$@ $$(_d)/$$($(1)_NAME).o
 
     $(1)_LDFLAGS_USE += $$($(1)_PATH) $$($(1)_LDFLAGS)

mk/programs.mk

@@ -32,7 +32,7 @@ define build-program
   $$(eval $$(call create-dir, $$(_d)))
 
   $$($(1)_PATH): $$($(1)_OBJS) $$(_libs) | $$(_d)/
-	$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE))
+	+$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE))
 
   $(1)_INSTALL_DIR ?= $$(bindir)
 
@@ -49,7 +49,7 @@ define build-program
       _libs_final := $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_INSTALL_PATH))
 
       $(DESTDIR)$$($(1)_INSTALL_PATH): $$($(1)_OBJS) $$(_libs_final) | $(DESTDIR)$$($(1)_INSTALL_DIR)/
-	$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
+	+$$(trace-ld) $(CXX) -o $$@ $$(LDFLAGS) $$(GLOBAL_LDFLAGS) $$($(1)_OBJS) $$($(1)_LDFLAGS) $$(foreach lib, $$($(1)_LIBS), $$($$(lib)_LDFLAGS_USE_INSTALLED))
 
     else
 

scripts/create-darwin-volume.sh

@@ -442,9 +442,14 @@ add_nix_vol_fstab_line() {
     local escaped_mountpoint="${NIX_ROOT/ /'\\\'040}"
     shift
 
-    # wrap `ex` to work around a problem with vim plugins breaking exit codes;
+    # wrap `ex` to work around problems w/ vim features breaking exit codes
-    # (see https://github.com/NixOS/nix/issues/5468)
+    # - plugins (see github.com/NixOS/nix/issues/5468): -u NONE
-    # we'd prefer EDITOR="/usr/bin/ex --noplugin" but vifs doesn't word-split
+    # - swap file: -n
+    #
+    # the first draft used `--noplugin`, but github.com/NixOS/nix/issues/6462
+    # suggests we need the less-semantic `-u NONE`
+    #
+    # we'd prefer EDITOR="/usr/bin/ex -u NONE" but vifs doesn't word-split
     # the EDITOR env.
     #
     # TODO: at some point we should switch to `--clean`, but it wasn't added
@@ -452,7 +457,7 @@ add_nix_vol_fstab_line() {
     # minver 10.12.6 seems to have released with vim 7.4
     cat > "$SCRATCH/ex_cleanroom_wrapper" <<EOF
 #!/bin/sh
-/usr/bin/ex --noplugin "\$@"
+/usr/bin/ex -u NONE -n "\$@"
 EOF
     chmod 755 "$SCRATCH/ex_cleanroom_wrapper"
 
@@ -646,8 +651,9 @@ EOF
         task "Configuring /etc/synthetic.conf to make a mount-point at $NIX_ROOT" >&2
         # technically /etc/synthetic.d/nix is supported in Big Sur+
         # but handling both takes even more code...
+        # See earlier note; `-u NONE` disables vim plugins/rc, `-n` skips swapfile
         _sudo "to add Nix to /etc/synthetic.conf" \
-            /usr/bin/ex --noplugin /etc/synthetic.conf <<EOF
+            /usr/bin/ex -u NONE -n /etc/synthetic.conf <<EOF
 :a
 ${NIX_ROOT:1}
 .
@@ -815,7 +821,8 @@ setup_volume_daemon() {
     local volume_uuid="$2"
     if ! test_voldaemon; then
         task "Configuring LaunchDaemon to mount '$NIX_VOLUME_LABEL'" >&2
-        _sudo "to install the Nix volume mounter" /usr/bin/ex --noplugin "$NIX_VOLUME_MOUNTD_DEST" <<EOF
+        # See earlier note; `-u NONE` disables vim plugins/rc, `-n` skips swapfile
+        _sudo "to install the Nix volume mounter" /usr/bin/ex -u NONE -n "$NIX_VOLUME_MOUNTD_DEST" <<EOF
 :a
 $(generate_mount_daemon "$cmd_type" "$volume_uuid")
 .

scripts/install-darwin-multi-user.sh

@@ -167,7 +167,7 @@ poly_user_shell_get() {
 }
 
 poly_user_shell_set() {
-    _sudo "in order to give $1 a safe home directory" \
+    _sudo "in order to give $1 a safe shell" \
           /usr/bin/dscl . -create "/Users/$1" "UserShell" "$2"
 }
 

scripts/install-multi-user.sh

@@ -59,6 +59,30 @@ headless() {
     fi
 }
 
+is_root() {
+    if [ "$EUID" -eq 0 ]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+is_os_linux() {
+    if [ "$(uname -s)" = "Linux" ]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+is_os_darwin() {
+    if [ "$(uname -s)" = "Darwin" ]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
 contact_us() {
     echo "You can open an issue at https://github.com/nixos/nix/issues"
     echo ""
@@ -313,14 +337,23 @@ __sudo() {
 _sudo() {
     local expl="$1"
     shift
-    if ! headless; then
+    if ! headless || is_root; then
         __sudo "$expl" "$*" >&2
     fi
-    sudo "$@"
+
+    if is_root; then
+        env "$@"
+    else
+        sudo "$@"
+    fi
 }
 
+# Ensure that $TMPDIR exists if defined.
+if [[ -n "${TMPDIR:-}" ]] && [[ ! -d "${TMPDIR:-}" ]]; then
+    mkdir -m 0700 -p "${TMPDIR:-}"
+fi
 
-readonly SCRATCH=$(mktemp -d "${TMPDIR:-/tmp/}tmp.XXXXXXXXXX")
+readonly SCRATCH=$(mktemp -d)
 finish_cleanup() {
     rm -rf "$SCRATCH"
 }
@@ -423,7 +456,7 @@ EOF
         fi
     done
 
-    if [ "$(uname -s)" = "Linux" ] && [ ! -e /run/systemd/system ]; then
+    if is_os_linux && [ ! -e /run/systemd/system ]; then
         warning <<EOF
 We did not detect systemd on your system. With a multi-user install
 without systemd you will have to manually configure your init system to
@@ -638,6 +671,17 @@ place_channel_configuration() {
     fi
 }
 
+check_selinux() {
+    if command -v getenforce > /dev/null 2>&1; then
+        if [ "$(getenforce)" = "Enforcing" ]; then
+            failure <<EOF
+Nix does not work with selinux enabled yet!
+see https://github.com/NixOS/nix/issues/2374
+EOF
+        fi
+    fi
+}
+
 welcome_to_nix() {
     ok "Welcome to the Multi-User Nix Installation"
 
@@ -766,7 +810,7 @@ EOF
         fi
 
         _sudo "to load data for the first time in to the Nix Database" \
-              "$NIX_INSTALLED_NIX/bin/nix-store" --load-db < ./.reginfo
+              HOME="$ROOT_HOME" "$NIX_INSTALLED_NIX/bin/nix-store" --load-db < ./.reginfo
 
         echo "      Just finished getting the nix database ready."
     )
@@ -854,22 +898,14 @@ EOF
           install -m 0664 "$SCRATCH/nix.conf" /etc/nix/nix.conf
 }
 
-main() {
-    # TODO: I've moved this out of validate_starting_assumptions so we
-    # can fail faster in this case. Sourcing install-darwin... now runs
-    # `touch /` to detect Read-only root, but it could update times on
-    # pre-Catalina macOS if run as root user.
-    if [ "$EUID" -eq 0 ]; then
-        failure <<EOF
-Please do not run this script with root privileges. I will call sudo
-when I need to.
-EOF
-    fi
 
-    if [ "$(uname -s)" = "Darwin" ]; then
+main() {
+    check_selinux
+
+    if is_os_darwin; then
         # shellcheck source=./install-darwin-multi-user.sh
         . "$EXTRACTED_NIX_PATH/install-darwin-multi-user.sh"
-    elif [ "$(uname -s)" = "Linux" ]; then
+    elif is_os_linux; then
         # shellcheck source=./install-systemd-multi-user.sh
         . "$EXTRACTED_NIX_PATH/install-systemd-multi-user.sh" # most of this works on non-systemd distros also
     else
@@ -877,7 +913,10 @@ EOF
     fi
 
     welcome_to_nix
-    chat_about_sudo
+
+    if ! is_root; then
+        chat_about_sudo
+    fi
 
     cure_artifacts
     # TODO: there's a tension between cure and validate. I moved the

scripts/install-nix-from-closure.sh

@@ -148,7 +148,9 @@ if ! [ -w "$dest" ]; then
     exit 1
 fi
 
-mkdir -p "$dest/store"
+# The auto-chroot code in openFromNonUri() checks for the
+# non-existence of /nix/var/nix, so we need to create it here.
+mkdir -p "$dest/store" "$dest/var/nix"
 
 printf "copying Nix to %s..." "${dest}/store" >&2
 # Insert a newline if no progress is shown.

src/libcmd/command.cc

@@ -86,6 +86,11 @@ ref<Store> CopyCommand::getDstStore()
 
 EvalCommand::EvalCommand()
 {
+    addFlag({
+        .longName = "debugger",
+        .description = "start an interactive environment if evaluation fails",
+        .handler = {&startReplOnEvalErrors, true},
+    });
 }
 
 EvalCommand::~EvalCommand()
@@ -103,7 +108,7 @@ ref<Store> EvalCommand::getEvalStore()
 
 ref<EvalState> EvalCommand::getEvalState()
 {
-    if (!evalState)
+    if (!evalState) {
         evalState =
             #if HAVE_BOEHMGC
             std::allocate_shared<EvalState>(traceable_allocator<EvalState>(),
@@ -113,6 +118,11 @@ ref<EvalState> EvalCommand::getEvalState()
                 searchPath, getEvalStore(), getStore())
             #endif
             ;
+
+        if (startReplOnEvalErrors) {
+            evalState->debugRepl = &runRepl;
+        };
+    }
     return ref<EvalState>(evalState);
 }
 

src/libcmd/command.hh

@@ -57,6 +57,9 @@ struct CopyCommand : virtual StoreCommand
 
 struct EvalCommand : virtual StoreCommand, MixEvalArgs
 {
+    bool startReplOnEvalErrors = false;
+    bool ignoreExceptionsDuringTry = false;
+
     EvalCommand();
 
     ~EvalCommand();
@@ -75,10 +78,16 @@ struct MixFlakeOptions : virtual Args, EvalCommand
 {
     flake::LockFlags lockFlags;
 
+    std::optional<std::string> needsFlakeInputCompletion = {};
+
     MixFlakeOptions();
 
-    virtual std::optional<FlakeRef> getFlakeRefForCompletion()
+    virtual std::vector<std::string> getFlakesForCompletion()
     { return {}; }
+
+    void completeFlakeInput(std::string_view prefix);
+
+    void completionHook() override;
 };
 
 struct SourceExprCommand : virtual Args, MixFlakeOptions
@@ -114,12 +123,13 @@ struct InstallablesCommand : virtual Args, SourceExprCommand
     InstallablesCommand();
 
     void prepare() override;
+    Installables load();
 
     virtual bool useDefaultInstallables() { return true; }
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override;
+    std::vector<std::string> getFlakesForCompletion() override;
 
-private:
+protected:
 
     std::vector<std::string> _installables;
 };
@@ -133,9 +143,9 @@ struct InstallableCommand : virtual Args, SourceExprCommand
 
     void prepare() override;
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override
+    std::vector<std::string> getFlakesForCompletion() override
     {
-        return parseFlakeRefWithFragment(_installable, absPath(".")).first;
+        return {_installable};
     }
 
 private:
@@ -270,4 +280,8 @@ void printClosureDiff(
     const StorePath & afterPath,
     std::string_view indent);
 
+
+void runRepl(
+    ref<EvalState> evalState,
+    const ValMap & extraEnv);
 }

src/libcmd/installables.cc

@@ -23,17 +23,6 @@
 
 namespace nix {
 
-void completeFlakeInputPath(
-    ref<EvalState> evalState,
-    const FlakeRef & flakeRef,
-    std::string_view prefix)
-{
-    auto flake = flake::getFlake(*evalState, flakeRef, true);
-    for (auto & input : flake.inputs)
-        if (hasPrefix(input.first, prefix))
-            completions->add(input.first);
-}
-
 MixFlakeOptions::MixFlakeOptions()
 {
     auto category = "Common flake-related options";
@@ -86,8 +75,7 @@ MixFlakeOptions::MixFlakeOptions()
             lockFlags.inputUpdates.insert(flake::parseInputPath(s));
         }},
         .completer = {[&](size_t, std::string_view prefix) {
-            if (auto flakeRef = getFlakeRefForCompletion())
+            needsFlakeInputCompletion = {std::string(prefix)};
-                completeFlakeInputPath(getEvalState(), *flakeRef, prefix);
         }}
     });
 
@@ -103,12 +91,10 @@ MixFlakeOptions::MixFlakeOptions()
                 parseFlakeRef(flakeRef, absPath("."), true));
         }},
         .completer = {[&](size_t n, std::string_view prefix) {
-            if (n == 0) {
+            if (n == 0)
-                if (auto flakeRef = getFlakeRefForCompletion())
+                needsFlakeInputCompletion = {std::string(prefix)};
-                    completeFlakeInputPath(getEvalState(), *flakeRef, prefix);
+            else if (n == 1)
-            } else if (n == 1) {
                 completeFlakeRef(getEvalState()->store, prefix);
-            }
         }}
     });
 
@@ -139,6 +125,24 @@ MixFlakeOptions::MixFlakeOptions()
     });
 }
 
+void MixFlakeOptions::completeFlakeInput(std::string_view prefix)
+{
+    auto evalState = getEvalState();
+    for (auto & flakeRefS : getFlakesForCompletion()) {
+        auto flakeRef = parseFlakeRefWithFragment(expandTilde(flakeRefS), absPath(".")).first;
+        auto flake = flake::getFlake(*evalState, flakeRef, true);
+        for (auto & input : flake.inputs)
+            if (hasPrefix(input.first, prefix))
+                completions->add(input.first);
+    }
+}
+
+void MixFlakeOptions::completionHook()
+{
+    if (auto & prefix = needsFlakeInputCompletion)
+        completeFlakeInput(*prefix);
+}
+
 SourceExprCommand::SourceExprCommand(bool supportReadOnlyMode)
 {
     addFlag({
@@ -146,7 +150,8 @@ SourceExprCommand::SourceExprCommand(bool supportReadOnlyMode)
         .shortName = 'f',
         .description =
             "Interpret installables as attribute paths relative to the Nix expression stored in *file*. "
-            "If *file* is the character -, then a Nix expression will be read from standard input.",
+            "If *file* is the character -, then a Nix expression will be read from standard input. "
+            "Implies `--impure`.",
         .category = installablesCategory,
         .labels = {"file"},
         .handler = {&file},
@@ -440,10 +445,8 @@ DerivedPaths InstallableValue::toDerivedPaths()
 
     // Group by derivation, helps with .all in particular
     for (auto & drv : toDerivations()) {
-        auto outputName = drv.outputName;
+        for (auto & outputName : drv.outputsToInstall)
-        if (outputName == "")
+            drvsToOutputs[drv.drvPath].insert(outputName);
-            throw Error("derivation '%s' lacks an 'outputName' attribute", state->store->printStorePath(drv.drvPath));
-        drvsToOutputs[drv.drvPath].insert(outputName);
         drvsToCopy.insert(drv.drvPath);
     }
 
@@ -466,9 +469,19 @@ struct InstallableAttrPath : InstallableValue
     SourceExprCommand & cmd;
     RootValue v;
     std::string attrPath;
+    OutputsSpec outputsSpec;
 
-    InstallableAttrPath(ref<EvalState> state, SourceExprCommand & cmd, Value * v, const std::string & attrPath)
+    InstallableAttrPath(
-        : InstallableValue(state), cmd(cmd), v(allocRootValue(v)), attrPath(attrPath)
+        ref<EvalState> state,
+        SourceExprCommand & cmd,
+        Value * v,
+        const std::string & attrPath,
+        OutputsSpec outputsSpec)
+        : InstallableValue(state)
+        , cmd(cmd)
+        , v(allocRootValue(v))
+        , attrPath(attrPath)
+        , outputsSpec(std::move(outputsSpec))
     { }
 
     std::string what() const override { return attrPath; }
@@ -497,7 +510,19 @@ std::vector<InstallableValue::DerivationInfo> InstallableAttrPath::toDerivations
         auto drvPath = drvInfo.queryDrvPath();
         if (!drvPath)
             throw Error("'%s' is not a derivation", what());
-        res.push_back({ *drvPath, drvInfo.queryOutputName() });
+
+        std::set<std::string> outputsToInstall;
+
+        if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
+            outputsToInstall = *outputNames;
+        else
+            for (auto & output : drvInfo.queryOutputs(false, std::get_if<DefaultOutputs>(&outputsSpec)))
+                outputsToInstall.insert(output.first);
+
+        res.push_back(DerivationInfo {
+            .drvPath = *drvPath,
+            .outputsToInstall = std::move(outputsToInstall)
+        });
     }
 
     return res;
@@ -574,6 +599,7 @@ InstallableFlake::InstallableFlake(
     ref<EvalState> state,
     FlakeRef && flakeRef,
     std::string_view fragment,
+    OutputsSpec outputsSpec,
     Strings attrPaths,
     Strings prefixes,
     const flake::LockFlags & lockFlags)
@@ -581,6 +607,7 @@ InstallableFlake::InstallableFlake(
       flakeRef(flakeRef),
       attrPaths(fragment == "" ? attrPaths : Strings{(std::string) fragment}),
       prefixes(fragment == "" ? Strings{} : prefixes),
+      outputsSpec(std::move(outputsSpec)),
       lockFlags(lockFlags)
 {
     if (cmd && cmd->getAutoArgs(*state)->size())
@@ -589,6 +616,8 @@ InstallableFlake::InstallableFlake(
 
 std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableFlake::toDerivation()
 {
+    Activity act(*logger, lvlTalkative, actUnknown, fmt("evaluating derivation '%s'", what()));
+
     auto attr = getCursor(*state);
 
     auto attrPath = attr->getAttrPathStr();
@@ -598,9 +627,41 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
 
     auto drvPath = attr->forceDerivation();
 
+    std::set<std::string> outputsToInstall;
+    std::optional<NixInt> priority;
+
+    if (auto aOutputSpecified = attr->maybeGetAttr(state->sOutputSpecified)) {
+        if (aOutputSpecified->getBool()) {
+            if (auto aOutputName = attr->maybeGetAttr("outputName"))
+                outputsToInstall = { aOutputName->getString() };
+        }
+    }
+
+    else if (auto aMeta = attr->maybeGetAttr(state->sMeta)) {
+        if (auto aOutputsToInstall = aMeta->maybeGetAttr("outputsToInstall"))
+            for (auto & s : aOutputsToInstall->getListOfStrings())
+                outputsToInstall.insert(s);
+        if (auto aPriority = aMeta->maybeGetAttr("priority"))
+            priority = aPriority->getInt();
+    }
+
+    if (outputsToInstall.empty() || std::get_if<AllOutputs>(&outputsSpec)) {
+        outputsToInstall.clear();
+        if (auto aOutputs = attr->maybeGetAttr(state->sOutputs))
+            for (auto & s : aOutputs->getListOfStrings())
+                outputsToInstall.insert(s);
+    }
+
+    if (outputsToInstall.empty())
+        outputsToInstall.insert("out");
+
+    if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
+        outputsToInstall = *outputNames;
+
     auto drvInfo = DerivationInfo {
-        std::move(drvPath),
+        .drvPath = std::move(drvPath),
-        attr->getAttr(state->sOutputName)->getString()
+        .outputsToInstall = std::move(outputsToInstall),
+        .priority = priority,
     };
 
     return {attrPath, getLockedFlake()->flake.lockedRef, std::move(drvInfo)};
@@ -723,8 +784,14 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
             state->eval(e, *vFile);
         }
 
-        for (auto & s : ss)
+        for (auto & s : ss) {
-            result.push_back(std::make_shared<InstallableAttrPath>(state, *this, vFile, s == "." ? "" : s));
+            auto [prefix, outputsSpec] = parseOutputsSpec(s);
+            result.push_back(
+                std::make_shared<InstallableAttrPath>(
+                    state, *this, vFile,
+                    prefix == "." ? "" : prefix,
+                    outputsSpec));
+        }
 
     } else {
 
@@ -743,12 +810,13 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
             }
 
             try {
-                auto [flakeRef, fragment] = parseFlakeRefWithFragment(s, absPath("."));
+                auto [flakeRef, fragment, outputsSpec] = parseFlakeRefWithFragmentAndOutputsSpec(s, absPath("."));
                 result.push_back(std::make_shared<InstallableFlake>(
                         this,
                         getEvalState(),
                         std::move(flakeRef),
                         fragment,
+                        outputsSpec,
                         getDefaultFlakeAttrPaths(),
                         getDefaultFlakeAttrPathPrefixes(),
                         lockFlags));
@@ -822,12 +890,13 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
                         auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
                         auto drvOutputs = drv.outputsAndOptPaths(*store);
                         for (auto & output : bfd.outputs) {
-                            if (!outputHashes.count(output))
+                            auto outputHash = get(outputHashes, output);
+                            if (!outputHash)
                                 throw Error(
                                     "the derivation '%s' doesn't have an output named '%s'",
                                     store->printStorePath(bfd.drvPath), output);
                             if (settings.isExperimentalFeatureEnabled(Xp::CaDerivations)) {
-                                DrvOutput outputId { outputHashes.at(output), output };
+                                DrvOutput outputId { *outputHash, output };
                                 auto realisation = store->queryRealisation(outputId);
                                 if (!realisation)
                                     throw Error(
@@ -838,10 +907,11 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
                             } else {
                                 // If ca-derivations isn't enabled, assume that
                                 // the output path is statically known.
-                                assert(drvOutputs.count(output));
+                                auto drvOutput = get(drvOutputs, output);
-                                assert(drvOutputs.at(output).second);
+                                assert(drvOutput);
+                                assert(drvOutput->second);
                                 outputs.insert_or_assign(
-                                    output, *drvOutputs.at(output).second);
+                                    output, *drvOutput->second);
                             }
                         }
                         res.push_back({installable, BuiltPath::Built { bfd.drvPath, outputs }});
@@ -856,6 +926,9 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPath>> Installable::bui
         break;
 
     case Realise::Outputs: {
+        if (settings.printMissing)
+          printMissing(store, pathsToBuild, lvlInfo);
+
         for (auto & buildResult : store->buildPathsWithResults(pathsToBuild, bMode, evalStore)) {
             if (!buildResult.success())
                 buildResult.rethrow();
@@ -969,21 +1042,26 @@ InstallablesCommand::InstallablesCommand()
 
 void InstallablesCommand::prepare()
 {
+    installables = load();
+}
+
+Installables InstallablesCommand::load() {
+    Installables installables;
     if (_installables.empty() && useDefaultInstallables())
         // FIXME: commands like "nix profile install" should not have a
         // default, probably.
         _installables.push_back(".");
-    installables = parseInstallables(getStore(), _installables);
+    return parseInstallables(getStore(), _installables);
 }
 
-std::optional<FlakeRef> InstallablesCommand::getFlakeRefForCompletion()
+std::vector<std::string> InstallablesCommand::getFlakesForCompletion()
 {
     if (_installables.empty()) {
         if (useDefaultInstallables())
-            return parseFlakeRefWithFragment(".", absPath(".")).first;
+            return {"."};
         return {};
     }
-    return parseFlakeRefWithFragment(_installables.front(), absPath(".")).first;
+    return _installables;
 }
 
 InstallableCommand::InstallableCommand(bool supportReadOnlyMode)

src/libcmd/installables.hh

@@ -132,6 +132,8 @@ struct Installable
         const std::vector<std::shared_ptr<Installable>> & installables);
 };
 
+typedef std::vector<std::shared_ptr<Installable>> Installables;
+
 struct InstallableValue : Installable
 {
     ref<EvalState> state;
@@ -141,7 +143,8 @@ struct InstallableValue : Installable
     struct DerivationInfo
     {
         StorePath drvPath;
-        std::string outputName;
+        std::set<std::string> outputsToInstall;
+        std::optional<NixInt> priority;
     };
 
     virtual std::vector<DerivationInfo> toDerivations() = 0;
@@ -156,6 +159,7 @@ struct InstallableFlake : InstallableValue
     FlakeRef flakeRef;
     Strings attrPaths;
     Strings prefixes;
+    OutputsSpec outputsSpec;
     const flake::LockFlags & lockFlags;
     mutable std::shared_ptr<flake::LockedFlake> _lockedFlake;
 
@@ -164,6 +168,7 @@ struct InstallableFlake : InstallableValue
         ref<EvalState> state,
         FlakeRef && flakeRef,
         std::string_view fragment,
+        OutputsSpec outputsSpec,
         Strings attrPaths,
         Strings prefixes,
         const flake::LockFlags & lockFlags);

src/libcmd/local.mk

@@ -6,9 +6,9 @@ libcmd_DIR := $(d)
 
 libcmd_SOURCES := $(wildcard $(d)/*.cc)
 
-libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers
+libcmd_CXXFLAGS += -I src/libutil -I src/libstore -I src/libexpr -I src/libmain -I src/libfetchers -I src/nix
 
-libcmd_LDFLAGS += $(LOWDOWN_LIBS) -pthread
+libcmd_LDFLAGS = $(EDITLINE_LIBS) -llowdown -pthread
 
 libcmd_LIBS = libstore libutil libexpr libmain libfetchers
 

src/libcmd/markdown.cc

@@ -9,14 +9,16 @@ namespace nix {
 
 std::string renderMarkdownToTerminal(std::string_view markdown)
 {
+    int windowWidth = getWindowSize().second;
+
     struct lowdown_opts opts {
         .type = LOWDOWN_TERM,
         .maxdepth = 20,
-        .cols = std::max(getWindowSize().second, (unsigned short) 80),
+        .cols = (size_t) std::max(windowWidth - 5, 60),
         .hmargin = 0,
         .vmargin = 0,
         .feat = LOWDOWN_COMMONMARK | LOWDOWN_FENCED | LOWDOWN_DEFLIST | LOWDOWN_TABLES,
-        .oflags = 0,
+        .oflags = LOWDOWN_TERM_NOLINK,
     };
 
     auto doc = lowdown_doc_new(&opts);

src/libcmd/repl.cc

@@ -22,6 +22,7 @@ extern "C" {
 #include "ansicolor.hh"
 #include "shared.hh"
 #include "eval.hh"
+#include "eval-cache.hh"
 #include "eval-inline.hh"
 #include "attr-path.hh"
 #include "store-api.hh"
@@ -34,6 +35,7 @@ extern "C" {
 #include "finally.hh"
 #include "markdown.hh"
 #include "local-fs-store.hh"
+#include "progress-bar.hh"
 
 #if HAVE_BOEHMGC
 #define GC_INCLUDE_NEW
@@ -48,38 +50,46 @@ struct NixRepl
     #endif
 {
     std::string curDir;
-    std::unique_ptr<EvalState> state;
+    ref<EvalState> state;
     Bindings * autoArgs;
 
+    size_t debugTraceIndex;
+
     Strings loadedFiles;
+    typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
+    std::function<AnnotatedValues()> getValues;
 
     const static int envSize = 32768;
-    StaticEnv staticEnv;
+    std::shared_ptr<StaticEnv> staticEnv;
     Env * env;
     int displ;
     StringSet varNames;
 
     const Path historyFile;
 
-    NixRepl(const Strings & searchPath, nix::ref<Store> store);
+    NixRepl(const Strings & searchPath, nix::ref<Store> store,ref<EvalState> state,
+            std::function<AnnotatedValues()> getValues);
     ~NixRepl();
-    void mainLoop(const std::vector<std::string> & files);
+    void mainLoop();
     StringSet completePrefix(const std::string & prefix);
-    bool getLine(std::string & input, const std::string &prompt);
+    bool getLine(std::string & input, const std::string & prompt);
     StorePath getDerivationPath(Value & v);
     bool processLine(std::string line);
+
     void loadFile(const Path & path);
     void loadFlake(const std::string & flakeRef);
     void initEnv();
+    void loadFiles();
     void reloadFiles();
     void addAttrsToScope(Value & attrs);
     void addVarToScope(const Symbol name, Value & v);
     Expr * parseString(std::string s);
     void evalString(std::string s, Value & v);
+    void loadDebugTraceEnv(DebugTrace & dt);
 
     typedef std::set<Value *> ValuesSeen;
-    std::ostream &  printValue(std::ostream & str, Value & v, unsigned int maxDepth);
+    std::ostream & printValue(std::ostream & str, Value & v, unsigned int maxDepth);
-    std::ostream &  printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen);
+    std::ostream & printValue(std::ostream & str, Value & v, unsigned int maxDepth, ValuesSeen & seen);
 };
 
 
@@ -92,9 +102,12 @@ std::string removeWhitespace(std::string s)
 }
 
 
-NixRepl::NixRepl(const Strings & searchPath, nix::ref<Store> store)
+NixRepl::NixRepl(const Strings & searchPath, nix::ref<Store> store, ref<EvalState> state,
-    : state(std::make_unique<EvalState>(searchPath, store))
+            std::function<NixRepl::AnnotatedValues()> getValues)
-    , staticEnv(false, &state->staticBaseEnv)
+    : state(state)
+    , debugTraceIndex(0)
+    , getValues(getValues)
+    , staticEnv(new StaticEnv(false, state->staticBaseEnv.get()))
     , historyFile(getDataDir() + "/nix/repl-history")
 {
     curDir = absPath(".");
@@ -106,23 +119,20 @@ NixRepl::~NixRepl()
     write_history(historyFile.c_str());
 }
 
-std::string runNix(Path program, const Strings & args,
+void runNix(Path program, const Strings & args,
     const std::optional<std::string> & input = {})
 {
     auto subprocessEnv = getEnv();
     subprocessEnv["NIX_CONFIG"] = globalConfig.toKeyValue();
 
-    auto res = runProgram(RunOptions {
+    runProgram2(RunOptions {
         .program = settings.nixBinDir+ "/" + program,
         .args = args,
         .environment = subprocessEnv,
         .input = input,
     });
 
-    if (!statusOk(res.first))
+    return;
-        throw ExecError(res.first, "program '%1%' %2%", program, statusToString(res.first));
-
-    return res.second;
 }
 
 static NixRepl * curRepl; // ugly
@@ -198,16 +208,37 @@ namespace {
     }
 }
 
-void NixRepl::mainLoop(const std::vector<std::string> & files)
+static std::ostream & showDebugTrace(std::ostream & out, const PosTable & positions, const DebugTrace & dt)
+{
+    if (dt.isError)
+        out << ANSI_RED "error: " << ANSI_NORMAL;
+    out << dt.hint.str() << "\n";
+
+    // prefer direct pos, but if noPos then try the expr.
+    auto pos = *dt.pos
+        ? *dt.pos
+        : positions[dt.expr.getPos() ? dt.expr.getPos() : noPos];
+
+    if (pos) {
+        printAtPos(pos, out);
+
+        auto loc = getCodeLines(pos);
+        if (loc.has_value()) {
+            out << "\n";
+            printCodeLines(out, "", pos, *loc);
+            out << "\n";
+        }
+    }
+
+    return out;
+}
+
+void NixRepl::mainLoop()
 {
     std::string error = ANSI_RED "error:" ANSI_NORMAL " ";
     notice("Welcome to Nix " + nixVersion + ". Type :? for help.\n");
 
-    for (auto & i : files)
+    loadFiles();
-        loadedFiles.push_back(i);
-
-    reloadFiles();
-    if (!loadedFiles.empty()) notice("");
 
     // Allow nix-repl specific settings in .inputrc
     rl_readline_name = "nix-repl";
@@ -222,14 +253,21 @@ void NixRepl::mainLoop(const std::vector<std::string> & files)
     rl_set_list_possib_func(listPossibleCallback);
 #endif
 
+    /* Stop the progress bar because it interferes with the display of
+       the repl. */
+    stopProgressBar();
+
     std::string input;
 
     while (true) {
         // When continuing input from previous lines, don't print a prompt, just align to the same
         // number of chars as the prompt.
-        if (!getLine(input, input.empty() ? "nix-repl> " : "          "))
+        if (!getLine(input, input.empty() ? "nix-repl> " : "          ")) {
+            // ctrl-D should exit the debugger.
+            state->debugStop = false;
+            state->debugQuit = true;
             break;
-
+        }
         try {
             if (!removeWhitespace(input).empty() && !processLine(input)) return;
         } catch (ParseError & e) {
@@ -240,6 +278,14 @@ void NixRepl::mainLoop(const std::vector<std::string> & files)
             } else {
               printMsg(lvlError, e.msg());
             }
+        } catch (EvalError & e) {
+            // in debugger mode, an EvalError should trigger another repl session.
+            // when that session returns the exception will land here.  No need to show it again;
+            // show the error for this repl session instead.
+            if (state->debugRepl && !state->debugTraces.empty())
+                showDebugTrace(std::cout, state->positions, state->debugTraces.front());
+            else
+                printMsg(lvlError, e.msg());
         } catch (Error & e) {
             printMsg(lvlError, e.msg());
         } catch (Interrupted & e) {
@@ -394,6 +440,19 @@ StorePath NixRepl::getDerivationPath(Value & v) {
     return *drvPath;
 }
 
+void NixRepl::loadDebugTraceEnv(DebugTrace & dt)
+{
+    initEnv();
+
+    auto se = state->getStaticEnv(dt.expr);
+    if (se) {
+        auto vm = mapStaticEnvBindings(state->symbols, *se.get(), dt.env);
+
+        // add staticenv vars.
+        for (auto & [name, value] : *(vm.get()))
+            addVarToScope(state->symbols.create(name), *value);
+    }
+}
 
 bool NixRepl::processLine(std::string line)
 {
@@ -429,12 +488,72 @@ bool NixRepl::processLine(std::string line)
              << "  :p <expr>     Evaluate and print expression recursively\n"
              << "  :q            Exit nix-repl\n"
              << "  :r            Reload all files\n"
-             << "  :s <expr>     Build dependencies of derivation, then start nix-shell\n"
+             << "  :sh <expr>    Build dependencies of derivation, then start nix-shell\n"
              << "  :t <expr>     Describe result of evaluation\n"
              << "  :u <expr>     Build derivation, then start nix-shell\n"
              << "  :doc <expr>   Show documentation of a builtin function\n"
              << "  :log <expr>   Show logs for a derivation\n"
-             << "  :st [bool]    Enable, disable or toggle showing traces for errors\n";
+             << "  :te [bool]    Enable, disable or toggle showing traces for errors\n"
+             ;
+        if (state->debugRepl) {
+             std::cout
+             << "\n"
+             << "        Debug mode commands\n"
+             << "  :env          Show env stack\n"
+             << "  :bt           Show trace stack\n"
+             << "  :st           Show current trace\n"
+             << "  :st <idx>     Change to another trace in the stack\n"
+             << "  :c            Go until end of program, exception, or builtins.break\n"
+             << "  :s            Go one step\n"
+             ;
+        }
+
+    }
+
+    else if (state->debugRepl && (command == ":bt" || command == ":backtrace")) {
+        for (const auto & [idx, i] : enumerate(state->debugTraces)) {
+            std::cout << "\n" << ANSI_BLUE << idx << ANSI_NORMAL << ": ";
+            showDebugTrace(std::cout, state->positions, i);
+        }
+    }
+
+    else if (state->debugRepl && (command == ":env")) {
+        for (const auto & [idx, i] : enumerate(state->debugTraces)) {
+            if (idx == debugTraceIndex) {
+                printEnvBindings(*state, i.expr, i.env);
+                break;
+            }
+        }
+    }
+
+    else if (state->debugRepl && (command == ":st")) {
+        try {
+            // change the DebugTrace index.
+            debugTraceIndex = stoi(arg);
+        } catch (...) { }
+
+        for (const auto & [idx, i] : enumerate(state->debugTraces)) {
+             if (idx == debugTraceIndex) {
+                 std::cout << "\n" << ANSI_BLUE << idx << ANSI_NORMAL << ": ";
+                 showDebugTrace(std::cout, state->positions, i);
+                 std::cout << std::endl;
+                 printEnvBindings(*state, i.expr, i.env);
+                 loadDebugTraceEnv(i);
+                 break;
+             }
+        }
+    }
+
+    else if (state->debugRepl && (command == ":s" || command == ":step")) {
+        // set flag to stop at next DebugTrace; exit repl.
+        state->debugStop = true;
+        return false;
+    }
+
+    else if (state->debugRepl && (command == ":c" || command == ":continue")) {
+        // set flag to run to next breakpoint or end of program; exit repl.
+        state->debugStop = false;
+        return false;
     }
 
     else if (command == ":a" || command == ":add") {
@@ -506,7 +625,7 @@ bool NixRepl::processLine(std::string line)
         runNix("nix-shell", {state->store->printStorePath(drvPath)});
     }
 
-    else if (command == ":b" || command == ":bl" || command == ":i" || command == ":s" || command == ":log") {
+    else if (command == ":b" || command == ":bl" || command == ":i" || command == ":sh" || command == ":log") {
         Value v;
         evalString(arg, v);
         StorePath drvPath = getDerivationPath(v);
@@ -567,8 +686,11 @@ bool NixRepl::processLine(std::string line)
         printValue(std::cout, v, 1000000000) << std::endl;
     }
 
-    else if (command == ":q" || command == ":quit")
+    else if (command == ":q" || command == ":quit") {
+        state->debugStop = false;
+        state->debugQuit = true;
         return false;
+    }
 
     else if (command == ":doc") {
         Value v;
@@ -593,7 +715,7 @@ bool NixRepl::processLine(std::string line)
             throw Error("value does not have documentation");
     }
 
-    else if (command == ":st" || command == ":show-trace") {
+    else if (command == ":te" || command == ":trace-enable") {
         if (arg == "false" || (arg == "" && loggerSettings.showTrace)) {
             std::cout << "not showing error traces\n";
             loggerSettings.showTrace = false;
@@ -630,7 +752,6 @@ bool NixRepl::processLine(std::string line)
     return true;
 }
 
-
 void NixRepl::loadFile(const Path & path)
 {
     loadedFiles.remove(path);
@@ -669,10 +790,10 @@ void NixRepl::initEnv()
     env = &state->allocEnv(envSize);
     env->up = &state->baseEnv;
     displ = 0;
-    staticEnv.vars.clear();
+    staticEnv->vars.clear();
 
     varNames.clear();
-    for (auto & i : state->staticBaseEnv.vars)
+    for (auto & i : state->staticBaseEnv->vars)
         varNames.emplace(state->symbols[i.first]);
 }
 
@@ -681,16 +802,24 @@ void NixRepl::reloadFiles()
 {
     initEnv();
 
+    loadFiles();
+}
+
+
+void NixRepl::loadFiles()
+{
     Strings old = loadedFiles;
     loadedFiles.clear();
 
-    bool first = true;
     for (auto & i : old) {
-        if (!first) notice("");
-        first = false;
         notice("Loading '%1%'...", i);
         loadFile(i);
     }
+
+    for (auto & [i, what] : getValues()) {
+        notice("Loading installable '%1%'...", what);
+        addAttrsToScope(*i);
+    }
 }
 
 
@@ -701,12 +830,12 @@ void NixRepl::addAttrsToScope(Value & attrs)
         throw Error("environment full; cannot add more variables");
 
     for (auto & i : *attrs.attrs) {
-        staticEnv.vars.emplace_back(i.name, displ);
+        staticEnv->vars.emplace_back(i.name, displ);
         env->values[displ++] = i.value;
         varNames.emplace(state->symbols[i.name]);
     }
-    staticEnv.sort();
+    staticEnv->sort();
-    staticEnv.deduplicate();
+    staticEnv->deduplicate();
     notice("Added %1% variables.", attrs.attrs->size());
 }
 
@@ -715,10 +844,10 @@ void NixRepl::addVarToScope(const Symbol name, Value & v)
 {
     if (displ >= envSize)
         throw Error("environment full; cannot add more variables");
-    if (auto oldVar = staticEnv.find(name); oldVar != staticEnv.vars.end())
+    if (auto oldVar = staticEnv->find(name); oldVar != staticEnv->vars.end())
-        staticEnv.vars.erase(oldVar);
+        staticEnv->vars.erase(oldVar);
-    staticEnv.vars.emplace_back(name, displ);
+    staticEnv->vars.emplace_back(name, displ);
-    staticEnv.sort();
+    staticEnv->sort();
     env->values[displ++] = &v;
     varNames.emplace(state->symbols[name]);
 }
@@ -886,17 +1015,66 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
     return str;
 }
 
-struct CmdRepl : StoreCommand, MixEvalArgs
+void runRepl(
+    ref<EvalState>evalState,
+    const ValMap & extraEnv)
 {
+    auto getValues = [&]()->NixRepl::AnnotatedValues{
+        NixRepl::AnnotatedValues values;
+        return values;
+    };
+    const Strings & searchPath = {};
+    auto repl = std::make_unique<NixRepl>(
+            searchPath,
+            openStore(),
+            evalState,
+            getValues
+        );
+
+    repl->initEnv();
+
+    // add 'extra' vars.
+    for (auto & [name, value] : extraEnv)
+        repl->addVarToScope(repl->state->symbols.create(name), *value);
+
+    repl->mainLoop();
+}
+
+struct CmdRepl : InstallablesCommand
+{
+    CmdRepl() {
+        evalSettings.pureEval = false;
+    }
+
+    void prepare()
+    {
+        if (!settings.isExperimentalFeatureEnabled(Xp::ReplFlake) && !(file) && this->_installables.size() >= 1) {
+            warn("future versions of Nix will require using `--file` to load a file");
+            if (this->_installables.size() > 1)
+                warn("more than one input file is not currently supported");
+            auto filePath = this->_installables[0].data();
+            file = std::optional(filePath);
+            _installables.front() = _installables.back();
+            _installables.pop_back();
+        }
+        installables = InstallablesCommand::load();
+    }
+
     std::vector<std::string> files;
 
-    CmdRepl()
+    Strings getDefaultFlakeAttrPaths() override
     {
-        expectArgs({
+        return {""};
-            .label = "files",
+    }
-            .handler = {&files},
+
-            .completer = completePath
+    bool useDefaultInstallables() override
-        });
+    {
+        return file.has_value() or expr.has_value();
+    }
+
+    bool forceImpureByDefault() override
+    {
+        return true;
     }
 
     std::string description() override
@@ -913,10 +1091,37 @@ struct CmdRepl : StoreCommand, MixEvalArgs
 
     void run(ref<Store> store) override
     {
-        evalSettings.pureEval = false;
+        auto state = getEvalState();
-        auto repl = std::make_unique<NixRepl>(searchPath, openStore());
+        auto getValues = [&]()->NixRepl::AnnotatedValues{
+            auto installables = load();
+            NixRepl::AnnotatedValues values;
+            for (auto & installable: installables){
+                auto what = installable->what();
+                if (file){
+                    auto [val, pos] = installable->toValue(*state);
+                    auto what = installable->what();
+                    state->forceValue(*val, pos);
+                    auto autoArgs = getAutoArgs(*state);
+                    auto valPost = state->allocValue();
+                    state->autoCallFunction(*autoArgs, *val, *valPost);
+                    state->forceValue(*valPost, pos);
+                    values.push_back( {valPost, what });
+                } else {
+                    auto [val, pos] = installable->toValue(*state);
+                    values.push_back( {val, what} );
+                }
+            }
+            return values;
+        };
+        auto repl = std::make_unique<NixRepl>(
+            searchPath,
+            openStore(),
+            state,
+            getValues
+        );
         repl->autoArgs = getAutoArgs(*repl->state);
-        repl->mainLoop(files);
+        repl->initEnv();
+        repl->mainLoop();
     }
 };
 

src/libexpr/eval-cache.cc

@@ -47,7 +47,7 @@ struct AttrDb
     {
         auto state(_state->lock());
 
-        Path cacheDir = getCacheDir() + "/nix/eval-cache-v2";
+        Path cacheDir = getCacheDir() + "/nix/eval-cache-v4";
         createDirs(cacheDir);
 
         Path dbPath = cacheDir + "/" + fingerprint.to_string(Base16, false) + ".sqlite";
@@ -175,6 +175,42 @@ struct AttrDb
         });
     }
 
+    AttrId setInt(
+        AttrKey key,
+        int n)
+    {
+        return doSQLite([&]()
+        {
+            auto state(_state->lock());
+
+            state->insertAttribute.use()
+                (key.first)
+                (symbols[key.second])
+                (AttrType::Int)
+                (n).exec();
+
+            return state->db.getLastInsertedRowId();
+        });
+    }
+
+    AttrId setListOfStrings(
+        AttrKey key,
+        const std::vector<std::string> & l)
+    {
+        return doSQLite([&]()
+        {
+            auto state(_state->lock());
+
+            state->insertAttribute.use()
+                (key.first)
+                (symbols[key.second])
+                (AttrType::ListOfStrings)
+                (concatStringsSep("\t", l)).exec();
+
+            return state->db.getLastInsertedRowId();
+        });
+    }
+
     AttrId setPlaceholder(AttrKey key)
     {
         return doSQLite([&]()
@@ -246,7 +282,7 @@ struct AttrDb
         auto queryAttribute(state->queryAttribute.use()(key.first)(symbols[key.second]));
         if (!queryAttribute.next()) return {};
 
-        auto rowId = (AttrType) queryAttribute.getInt(0);
+        auto rowId = (AttrId) queryAttribute.getInt(0);
         auto type = (AttrType) queryAttribute.getInt(1);
 
         switch (type) {
@@ -269,6 +305,10 @@ struct AttrDb
             }
             case AttrType::Bool:
                 return {{rowId, queryAttribute.getInt(2) != 0}};
+            case AttrType::Int:
+                return {{rowId, int_t{queryAttribute.getInt(2)}}};
+            case AttrType::ListOfStrings:
+                return {{rowId, tokenizeString<std::vector<std::string>>(queryAttribute.getStr(2), "\t")}};
             case AttrType::Missing:
                 return {{rowId, missing_t()}};
             case AttrType::Misc:
@@ -385,7 +425,7 @@ std::string AttrCursor::getAttrPathStr(Symbol name) const
 
 Value & AttrCursor::forceValue()
 {
-    debug("evaluating uncached attribute %s", getAttrPathStr());
+    debug("evaluating uncached attribute '%s'", getAttrPathStr());
 
     auto & v = getValue();
 
@@ -406,6 +446,8 @@ Value & AttrCursor::forceValue()
             cachedValue = {root->db->setString(getKey(), v.path), string_t{v.path, {}}};
         else if (v.type() == nBool)
             cachedValue = {root->db->setBool(getKey(), v.boolean), v.boolean};
+        else if (v.type() == nInt)
+            cachedValue = {root->db->setInt(getKey(), v.integer), int_t{v.integer}};
         else if (v.type() == nAttrs)
             ; // FIXME: do something?
         else
@@ -444,7 +486,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
                         return nullptr;
                     else if (std::get_if<failed_t>(&attr->second)) {
                         if (forceErrors)
-                            debug("reevaluating failed cached attribute '%s'");
+                            debug("reevaluating failed cached attribute '%s'", getAttrPathStr(name));
                         else
                             throw CachedEvalError("cached failure of attribute '%s'", getAttrPathStr(name));
                     } else
@@ -465,11 +507,6 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
         return nullptr;
         //throw TypeError("'%s' is not an attribute set", getAttrPathStr());
 
-    for (auto & attr : *v.attrs) {
-        if (root->db)
-            root->db->setPlaceholder({cachedValue->first, attr.name});
-    }
-
     auto attr = v.attrs->get(name);
 
     if (!attr) {
@@ -534,14 +571,14 @@ std::string AttrCursor::getString()
                 debug("using cached string attribute '%s'", getAttrPathStr());
                 return s->first;
             } else
-                throw TypeError("'%s' is not a string", getAttrPathStr());
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a string", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nString && v.type() != nPath)
-        throw TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type()));
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
 
     return v.type() == nString ? v.string.s : v.path;
 }
@@ -565,7 +602,7 @@ string_t AttrCursor::getStringWithContext()
                     return *s;
                 }
             } else
-                throw TypeError("'%s' is not a string", getAttrPathStr());
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a string", getAttrPathStr()));
         }
     }
 
@@ -576,7 +613,7 @@ string_t AttrCursor::getStringWithContext()
     else if (v.type() == nPath)
         return {v.path, {}};
     else
-        throw TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type()));
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
 }
 
 bool AttrCursor::getBool()
@@ -589,18 +626,73 @@ bool AttrCursor::getBool()
                 debug("using cached Boolean attribute '%s'", getAttrPathStr());
                 return *b;
             } else
-                throw TypeError("'%s' is not a Boolean", getAttrPathStr());
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a Boolean", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nBool)
-        throw TypeError("'%s' is not a Boolean", getAttrPathStr());
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a Boolean", getAttrPathStr()));
 
     return v.boolean;
 }
 
+NixInt AttrCursor::getInt()
+{
+    if (root->db) {
+        if (!cachedValue)
+            cachedValue = root->db->getAttr(getKey());
+        if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
+            if (auto i = std::get_if<int_t>(&cachedValue->second)) {
+                debug("using cached Integer attribute '%s'", getAttrPathStr());
+                return i->x;
+            } else
+                throw TypeError("'%s' is not an Integer", getAttrPathStr());
+        }
+    }
+
+    auto & v = forceValue();
+
+    if (v.type() != nInt)
+        throw TypeError("'%s' is not an Integer", getAttrPathStr());
+
+    return v.integer;
+}
+
+std::vector<std::string> AttrCursor::getListOfStrings()
+{
+    if (root->db) {
+        if (!cachedValue)
+            cachedValue = root->db->getAttr(getKey());
+        if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
+            if (auto l = std::get_if<std::vector<std::string>>(&cachedValue->second)) {
+                debug("using cached list of strings attribute '%s'", getAttrPathStr());
+                return *l;
+            } else
+                throw TypeError("'%s' is not a list of strings", getAttrPathStr());
+        }
+    }
+
+    debug("evaluating uncached attribute '%s'", getAttrPathStr());
+
+    auto & v = getValue();
+    root->state.forceValue(v, noPos);
+
+    if (v.type() != nList)
+        throw TypeError("'%s' is not a list", getAttrPathStr());
+
+    std::vector<std::string> res;
+
+    for (auto & elem : v.listItems())
+        res.push_back(std::string(root->state.forceStringNoCtx(*elem)));
+
+    if (root->db)
+        cachedValue = {root->db->setListOfStrings(getKey(), res), res};
+
+    return res;
+}
+
 std::vector<Symbol> AttrCursor::getAttrs()
 {
     if (root->db) {
@@ -611,14 +703,14 @@ std::vector<Symbol> AttrCursor::getAttrs()
                 debug("using cached attrset attribute '%s'", getAttrPathStr());
                 return *attrs;
             } else
-                throw TypeError("'%s' is not an attribute set", getAttrPathStr());
+                root->state.debugThrowLastTrace(TypeError("'%s' is not an attribute set", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nAttrs)
-        throw TypeError("'%s' is not an attribute set", getAttrPathStr());
+        root->state.debugThrowLastTrace(TypeError("'%s' is not an attribute set", getAttrPathStr()));
 
     std::vector<Symbol> attrs;
     for (auto & attr : *getValue().attrs)

src/libexpr/eval-cache.hh

@@ -44,12 +44,15 @@ enum AttrType {
     Misc = 4,
     Failed = 5,
     Bool = 6,
+    ListOfStrings = 7,
+    Int = 8,
 };
 
 struct placeholder_t {};
 struct missing_t {};
 struct misc_t {};
 struct failed_t {};
+struct int_t { NixInt x; };
 typedef uint64_t AttrId;
 typedef std::pair<AttrId, Symbol> AttrKey;
 typedef std::pair<std::string, NixStringContext> string_t;
@@ -61,7 +64,9 @@ typedef std::variant<
     missing_t,
     misc_t,
     failed_t,
-    bool
+    bool,
+    int_t,
+    std::vector<std::string>
     > AttrValue;
 
 class AttrCursor : public std::enable_shared_from_this<AttrCursor>
@@ -114,6 +119,10 @@ public:
 
     bool getBool();
 
+    NixInt getInt();
+
+    std::vector<std::string> getListOfStrings();
+
     std::vector<Symbol> getAttrs();
 
     bool isDerivation();

src/libexpr/eval-inline.hh

@@ -4,7 +4,6 @@
 
 namespace nix {
 
-
 /* Note: Various places expect the allocated memory to be zeroed. */
 [[gnu::always_inline]]
 inline void * allocBytes(size_t n)

src/libexpr/eval.cc

@@ -18,6 +18,7 @@
 #include <sys/resource.h>
 #include <iostream>
 #include <fstream>
+#include <functional>
 
 #include <sys/resource.h>
 
@@ -36,7 +37,6 @@
 
 namespace nix {
 
-
 static char * allocString(size_t size)
 {
     char * t;
@@ -147,7 +147,10 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
         else {
             str << "[ ";
             for (auto v2 : listItems()) {
-                v2->print(symbols, str, seen);
+                if (v2)
+                    v2->print(symbols, str, seen);
+                else
+                    str << "(nullptr)";
                 str << " ";
             }
             str << "]";
@@ -184,6 +187,11 @@ void Value::print(const SymbolTable & symbols, std::ostream & str, bool showRepe
     print(symbols, str, showRepeated ? nullptr : &seen);
 }
 
+// Pretty print types for assertion errors
+std::ostream & operator << (std::ostream & os, const ValueType t) {
+    os << showType(t);
+    return os;
+}
 
 std::string printValue(const EvalState & state, const Value & v)
 {
@@ -451,10 +459,15 @@ EvalState::EvalState(
     , sKey(symbols.create("key"))
     , sPath(symbols.create("path"))
     , sPrefix(symbols.create("prefix"))
+    , sOutputSpecified(symbols.create("outputSpecified"))
     , repair(NoRepair)
     , emptyBindings(0)
     , store(store)
     , buildStore(buildStore ? buildStore : store)
+    , debugRepl(nullptr)
+    , debugStop(false)
+    , debugQuit(false)
+    , trylevel(0)
     , regexCache(makeRegexCache())
 #if HAVE_BOEHMGC
     , valueAllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
@@ -464,7 +477,7 @@ EvalState::EvalState(
     , env1AllocCache(std::make_shared<void *>(nullptr))
 #endif
     , baseEnv(allocEnv(128))
-    , staticBaseEnv(false, 0)
+    , staticBaseEnv{std::make_shared<StaticEnv>(false, nullptr)}
 {
     countCalls = getEnv("NIX_COUNT_CALLS").value_or("0") != "0";
 
@@ -522,7 +535,7 @@ void EvalState::allowPath(const StorePath & storePath)
         allowedPaths->insert(store->toRealPath(storePath));
 }
 
-void EvalState::allowAndSetStorePathString(const StorePath &storePath, Value & v)
+void EvalState::allowAndSetStorePathString(const StorePath & storePath, Value & v)
 {
     allowPath(storePath);
 
@@ -630,7 +643,7 @@ Value * EvalState::addConstant(const std::string & name, Value & v)
 
 void EvalState::addConstant(const std::string & name, Value * v)
 {
-    staticBaseEnv.vars.emplace_back(symbols.create(name), baseEnvDispl);
+    staticBaseEnv->vars.emplace_back(symbols.create(name), baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
     auto name2 = name.substr(0, 2) == "__" ? name.substr(2) : name;
     baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v));
@@ -663,7 +676,7 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
 
     Value * v = allocValue();
     v->mkPrimOp(new PrimOp(primOp));
-    staticBaseEnv.vars.emplace_back(envName, baseEnvDispl);
+    staticBaseEnv->vars.emplace_back(envName, baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
     baseEnv.values[0]->attrs->push_back(Attr(symbols.create(primOp.name), v));
     return v;
@@ -693,11 +706,137 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
 }
 
 
+// just for the current level of StaticEnv, not the whole chain.
+void printStaticEnvBindings(const SymbolTable & st, const StaticEnv & se)
+{
+    std::cout << ANSI_MAGENTA;
+    for (auto & i : se.vars)
+        std::cout << st[i.first] << " ";
+    std::cout << ANSI_NORMAL;
+    std::cout << std::endl;
+}
+
+// just for the current level of Env, not the whole chain.
+void printWithBindings(const SymbolTable & st, const Env & env)
+{
+    if (env.type == Env::HasWithAttrs) {
+        std::cout << "with: ";
+        std::cout << ANSI_MAGENTA;
+        Bindings::iterator j = env.values[0]->attrs->begin();
+        while (j != env.values[0]->attrs->end()) {
+            std::cout << st[j->name] << " ";
+            ++j;
+        }
+        std::cout << ANSI_NORMAL;
+        std::cout << std::endl;
+    }
+}
+
+void printEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env, int lvl)
+{
+    std::cout << "Env level " << lvl << std::endl;
+
+    if (se.up && env.up) {
+        std::cout << "static: ";
+        printStaticEnvBindings(st, se);
+        printWithBindings(st, env);
+        std::cout << std::endl;
+        printEnvBindings(st, *se.up, *env.up, ++lvl);
+    } else {
+        std::cout << ANSI_MAGENTA;
+        // for the top level, don't print the double underscore ones;
+        // they are in builtins.
+        for (auto & i : se.vars)
+            if (!hasPrefix(st[i.first], "__"))
+                std::cout << st[i.first] << " ";
+        std::cout << ANSI_NORMAL;
+        std::cout << std::endl;
+        printWithBindings(st, env);  // probably nothing there for the top level.
+        std::cout << std::endl;
+
+    }
+}
+
+void printEnvBindings(const EvalState &es, const Expr & expr, const Env & env)
+{
+    // just print the names for now
+    auto se = es.getStaticEnv(expr);
+    if (se)
+        printEnvBindings(es.symbols, *se, env, 0);
+}
+
+void mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env, ValMap & vm)
+{
+    // add bindings for the next level up first, so that the bindings for this level
+    // override the higher levels.
+    // The top level bindings (builtins) are skipped since they are added for us by initEnv()
+    if (env.up && se.up) {
+        mapStaticEnvBindings(st, *se.up, *env.up, vm);
+
+        if (env.type == Env::HasWithAttrs) {
+            // add 'with' bindings.
+            Bindings::iterator j = env.values[0]->attrs->begin();
+            while (j != env.values[0]->attrs->end()) {
+                vm[st[j->name]] = j->value;
+                ++j;
+            }
+        } else {
+            // iterate through staticenv bindings and add them.
+            for (auto & i : se.vars)
+                vm[st[i.first]] = env.values[i.second];
+        }
+    }
+}
+
+std::unique_ptr<ValMap> mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env)
+{
+    auto vm = std::make_unique<ValMap>();
+    mapStaticEnvBindings(st, se, env, *vm);
+    return vm;
+}
+
+void EvalState::runDebugRepl(const Error * error, const Env & env, const Expr & expr)
+{
+    // double check we've got the debugRepl function pointer.
+    if (!debugRepl)
+        return;
+
+    auto dts =
+        error && expr.getPos()
+        ? std::make_unique<DebugTraceStacker>(
+            *this,
+            DebugTrace {
+                .pos = error->info().errPos ? *error->info().errPos : positions[expr.getPos()],
+                .expr = expr,
+                .env = env,
+                .hint = error->info().msg,
+                .isError = true
+            })
+        : nullptr;
+
+    if (error)
+    {
+        printError("%s\n\n", error->what());
+
+        if (trylevel > 0 && error->info().level != lvlInfo)
+            printError("This exception occurred in a 'tryEval' call. Use " ANSI_GREEN "--ignore-try" ANSI_NORMAL " to skip these.\n");
+
+        printError(ANSI_BOLD "Starting REPL to allow you to inspect the current state of the evaluator.\n" ANSI_NORMAL);
+    }
+
+    auto se = getStaticEnv(expr);
+    if (se) {
+        auto vm = mapStaticEnvBindings(symbols, *se.get(), env);
+        (debugRepl)(ref<EvalState>(shared_from_this()), *vm);
+    }
+}
+
 /* Every "format" object (even temporary) takes up a few hundred bytes
    of stack space, which is a real killer in the recursive
    evaluator.  So here are some helper functions for throwing
    exceptions. */
 
+// *WithTrace
 void EvalState::throwTypeErrorWithTrace(
             const PosIdx pos,
             const char * s,
@@ -759,6 +898,17 @@ void EvalState::throwEvalErrorWithTrace(const char * s, const std::string_view s
     throw e;
 }
 
+
+// *WithoutTrace coerce-strings
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
 void EvalState::throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s, const std::string_view s2) const
 {
     throw EvalError(ErrorInfo {
@@ -848,6 +998,167 @@ void EvalState::throwMissingArgumentError(const PosIdx pos, const char * s, cons
     });
 }
 
+
+// master
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const char * s, const std::string & s2)
+{
+    debugThrowLastTrace(EvalError(s, s2));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const std::string & s2, Env & env, Expr & expr)
+{
+    debugThrow(EvalError(ErrorInfo{
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos],
+        .suggestions = suggestions,
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const char * s, const std::string & s2,
+    const std::string & s3)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[noPos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+    const std::string & s3)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+    const std::string & s3, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2, Env & env, Expr & expr)
+{
+    // p1 is where the error occurred; p2 is a position mentioned in the message.
+    debugThrow(EvalError({
+        .msg = hintfmt(s, symbols[sym], positions[p2]),
+        .errPos = positions[p1]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const Value & v)
+{
+    debugThrowLastTrace(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const Value & v, Env & env, Expr & expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s)
+{
+    debugThrowLastTrace(TypeError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun,
+    const Symbol s2, Env & env, Expr &expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const ExprLambda & fun, const Symbol s2, Env & env, Expr &expr)
+{
+    debugThrow(TypeError(ErrorInfo {
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
+        .errPos = positions[pos],
+        .suggestions = suggestions,
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const char * s, const Value & v, Env & env, Expr &expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[expr.getPos()],
+    }), env, expr);
+}
+
+void EvalState::throwAssertionError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(AssertionError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(UndefinedVarError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(MissingArgumentError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
 void EvalState::addErrorTrace(Error & e, const char * s, const std::string & s2) const
 {
     e.addTrace(std::nullopt, s, s2);
@@ -858,6 +1169,32 @@ void EvalState::addErrorTrace(Error & e, const PosIdx pos, const char * s, const
     e.addTrace(positions[pos], s, s2);
 }
 
+static std::unique_ptr<DebugTraceStacker> makeDebugTraceStacker(
+    EvalState & state,
+    Expr & expr,
+    Env & env,
+    std::optional<ErrPos> pos,
+    const char * s,
+    const std::string & s2)
+{
+    return std::make_unique<DebugTraceStacker>(state,
+        DebugTrace {
+            .pos = pos,
+            .expr = expr,
+            .env = env,
+            .hint = hintfmt(s, s2),
+            .isError = false
+        });
+}
+
+DebugTraceStacker::DebugTraceStacker(EvalState & evalState, DebugTrace t)
+    : evalState(evalState)
+    , trace(std::move(t))
+{
+    evalState.debugTraces.push_front(trace);
+    if (evalState.debugStop && evalState.debugRepl)
+        evalState.runDebugRepl(nullptr, trace.env, trace.expr);
+}
 
 void Value::mkString(std::string_view s)
 {
@@ -916,12 +1253,11 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
             return j->value;
         }
         if (!env->prevWith)
-            throwUndefinedVarError(var.pos, "undefined variable '%1%'", symbols[var.name]);
+            throwUndefinedVarError(var.pos, "undefined variable '%1%'", symbols[var.name], *env, const_cast<ExprVar&>(var));
         for (size_t l = env->prevWith; l; --l, env = env->up) ;
     }
 }
 
-
 void EvalState::mkList(Value & v, size_t size)
 {
     v.mkList(size);
@@ -1054,8 +1390,19 @@ void EvalState::cacheFile(
     fileParseCache[resolvedPath] = e;
 
     try {
-        // Enforce that 'flake.nix' is a direct attrset, not a computation.
+        auto dts = debugRepl
-        if (mustBeTrivial && !(dynamic_cast<ExprAttrs *>(e)))
+            ? makeDebugTraceStacker(
+                *this,
+                *e,
+                this->baseEnv,
+                e->getPos() ? std::optional(ErrPos(positions[e->getPos()])) : std::nullopt,
+                "while evaluating the file '%1%':", resolvedPath)
+            : nullptr;
+
+        // Enforce that 'flake.nix' is a direct attrset, not a
+        // computation.
+        if (mustBeTrivial &&
+            !(dynamic_cast<ExprAttrs *>(e)))
             throwEvalError("file '%s' must be an attribute set", path);
         eval(e, v);
     } catch (Error & e) {
@@ -1094,7 +1441,7 @@ inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const PosIdx po
     try {
         e->eval(*this, env, v);
         if (v.type() != nAttrs)
-            throwTypeError("value is %1% while a set was expected", v);
+            throwTypeError("value is %1% while a set was expected", v, env, *e);
     } catch (Error & e) {
         e.addTrace(positions[pos], errorCtx);
         throw;
@@ -1203,7 +1550,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         auto nameSym = state.symbols.create(nameVal.string.s);
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
-            state.throwEvalError(i.pos, "dynamic attribute '%1%' already defined at %2%", nameSym, j->pos);
+            state.throwEvalError(i.pos, "dynamic attribute '%1%' already defined at %2%", nameSym, j->pos, env, *this);
 
         i.valueExpr->setName(nameSym);
         /* Keep sorted order so find can catch duplicates */
@@ -1277,6 +1624,15 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     e->eval(state, env, vTmp);
 
     try {
+        auto dts = state.debugRepl
+            ? makeDebugTraceStacker(
+                state,
+                *this,
+                env,
+                state.positions[pos2],
+                "while evaluating the attribute '%1%'",
+                showAttrPath(state, env, attrPath))
+            : nullptr;
 
         for (auto & i : attrPath) {
             state.nrLookups++;
@@ -1299,7 +1655,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                     state.throwEvalError(
                         pos,
                         Suggestions::bestMatches(allAttrNames, state.symbols[name]),
-                        "attribute '%1%' missing", state.symbols[name]);
+                        "attribute '%1%' missing", state.symbols[name], env, *this);
                 }
             }
             vAttrs = j->value;
@@ -1351,6 +1707,7 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
     v.mkLambda(&env, this);
 }
 
+
 void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
 {
     auto trace = evalSettings.traceFunctionCalls
@@ -1389,7 +1746,6 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
 
             if (!lambda.hasFormals())
                 env2.values[displ++] = args[0];
-
             else {
                 try {
                     forceAttrs(*args[0], lambda.pos, "while evaluating the value passed for the lambda argument");
@@ -1412,7 +1768,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                             throwTypeErrorWithTrace(lambda.pos,
                                     "function '%1%' called without required argument '%2%'",
                                     (lambda.name ? std::string(symbols[lambda.name]) : "anonymous lambda"),
-                                    i.name, pos, "from call site");
+                                    i.name, pos, "from call site", *fun.lambda.env, lambda);
                         }
                         env2.values[displ++] = i.def->maybeThunk(*this, env2);
                     } else {
@@ -1446,6 +1802,15 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
 
             /* Evaluate the body. */
             try {
+                auto dts = debugRepl
+                    ? makeDebugTraceStacker(
+                        *this, *lambda.body, env2, positions[lambda.pos],
+                        "while evaluating %s",
+                        lambda.name
+                        ? concatStrings("'", symbols[lambda.name], "'")
+                        : "anonymous lambda")
+                    : nullptr;
+
                 lambda.body->eval(*this, env2, vCur);
             } catch (Error & e) {
                 if (loggerSettings.showTrace.get()) {
@@ -1617,8 +1982,8 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
 Nix attempted to evaluate a function as a top level expression; in
 this case it must have its arguments supplied either by default
 values, or passed explicitly with '--arg' or '--argstr'. See
-https://nixos.org/manual/nix/stable/#ss-functions.)", symbols[i.name]);
+https://nixos.org/manual/nix/stable/expressions/language-constructs.html#functions.)", symbols[i.name],                 
-
+                *fun.lambda.env, *fun.lambda.fun);
             }
         }
     }
@@ -1641,7 +2006,7 @@ void ExprWith::eval(EvalState & state, Env & env, Value & v)
 
 void ExprIf::eval(EvalState & state, Env & env, Value & v)
 {
-    // We cheat in the parser, an pass the position of the condition as the position of the if itself.
+    // We cheat in the parser, and pass the position of the condition as the position of the if itself.
     (state.evalBool(env, cond, pos, "while evaluating a branch condition") ? then : else_)->eval(state, env, v);
 }
 
@@ -1651,7 +2016,7 @@ void ExprAssert::eval(EvalState & state, Env & env, Value & v)
     if (!state.evalBool(env, cond, pos, "in the condition of the assert statement")) {
         std::ostringstream out;
         cond->show(state.symbols, out);
-        state.throwAssertionError(pos, "assertion '%1%' failed", out.str());
+        state.throwAssertionError(pos, "assertion '%1%' failed", out.str(), env, *this);
     }
     body->eval(state, env, v);
 }
@@ -1828,14 +2193,14 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
                 nf = n;
                 nf += vTmp.fpoint;
             } else
-                state.throwEvalError(i_pos, "cannot add %1% to an integer", showType(vTmp));
+                state.throwEvalError(i_pos, "cannot add %1% to an integer", showType(vTmp), env, *this);
         } else if (firstType == nFloat) {
             if (vTmp.type() == nInt) {
                 nf += vTmp.integer;
             } else if (vTmp.type() == nFloat) {
                 nf += vTmp.fpoint;
             } else
-                state.throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp));
+                state.throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp), env, *this);
         } else {
             if (s.empty()) s.reserve(es->size());
             /* skip canonization of first path, which would only be not
@@ -1855,7 +2220,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         v.mkFloat(nf);
     else if (firstType == nPath) {
         if (!context.empty())
-            state.throwEvalError(pos, "a string that refers to a store path cannot be appended to a path");
+            state.throwEvalError(pos, "a string that refers to a store path cannot be appended to a path", env, *this);
         v.mkPath(canonPath(str()));
     } else
         v.mkStringMove(c_str(), context);
@@ -1882,6 +2247,12 @@ void EvalState::forceValueDeep(Value & v)
         if (v.type() == nAttrs) {
             for (auto & i : *v.attrs)
                 try {
+                    // If the value is a thunk, we're evaling. Otherwise no trace necessary.
+                    auto dts = debugRepl && i.value->isThunk()
+                        ? makeDebugTraceStacker(*this, *i.value->thunk.expr, *i.value->thunk.env, positions[i.pos],
+                            "while evaluating the attribute '%1%'", symbols[i.name])
+                        : nullptr;
+
                     recurse(*i.value);
                 } catch (Error & e) {
                     addErrorTrace(e, i.pos, "while evaluating the attribute '%1%'", symbols[i.name]);
@@ -2092,7 +2463,7 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
             return std::move(*maybeString);
         auto i = v.attrs->find(sOutPath);
         if (i == v.attrs->end())
-            throwTypeErrorWithTrace("cannot coerce %1% to a string", showType(v), pos, errorCtx);
+            throwTypeErrorWithTrace("cannot coerce a set to a string", pos, errorCtx);
         return coerceToString(pos, *i->value, context, coerceMore, copyToStore, canonicalizePath, errorCtx);
     }
 
@@ -2100,7 +2471,6 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore, errorCtx);
 
     if (coerceMore) {
-
         /* Note that `false' is represented as an empty string for
            shell scripting convenience, just like `null'. */
         if (v.type() == nBool && v.boolean) return "1";
@@ -2334,18 +2704,18 @@ void EvalState::printStats()
             }
             {
                 auto list = topObj.list("functions");
-                for (auto & i : functionCalls) {
+                for (auto & [fun, count] : functionCalls) {
                     auto obj = list.object();
-                    if (i.first->name)
+                    if (fun->name)
-                        obj.attr("name", (const std::string &) i.first->name);
+                        obj.attr("name", (std::string_view) symbols[fun->name]);
                     else
                         obj.attr("name", nullptr);
-                    if (auto pos = positions[i.first->pos]) {
+                    if (auto pos = positions[fun->pos]) {
-                        obj.attr("file", (const std::string &) pos.file);
+                        obj.attr("file", (std::string_view) pos.file);
                         obj.attr("line", pos.line);
                         obj.attr("column", pos.column);
                     }
-                    obj.attr("count", i.second);
+                    obj.attr("count", count);
                 }
             }
             {
@@ -2372,7 +2742,7 @@ void EvalState::printStats()
 
 std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, std::string_view errorCtx) const
 {
-    auto e = TypeError(ErrorInfo {
+    auto e = TypeError({
         .msg = hintfmt("cannot coerce %1% to a string", showType())
     });
     e.addTrace(pos, errorCtx);

src/libexpr/eval.hh

@@ -13,7 +13,6 @@
 #include <unordered_map>
 #include <mutex>
 
-
 namespace nix {
 
 
@@ -25,7 +24,6 @@ enum RepairFlag : bool;
 
 typedef void (* PrimOpFun) (EvalState & state, const PosIdx pos, Value * * args, Value & v);
 
-
 struct PrimOp
 {
     PrimOpFun fun;
@@ -35,6 +33,11 @@ struct PrimOp
     const char * doc = nullptr;
 };
 
+#if HAVE_BOEHMGC
+    typedef std::map<std::string, Value *, std::less<std::string>, traceable_allocator<std::pair<const std::string, Value *> > > ValMap;
+#else
+    typedef std::map<std::string, Value *> ValMap;
+#endif
 
 struct Env
 {
@@ -44,6 +47,10 @@ struct Env
     Value * values[0];
 };
 
+void printEnvBindings(const EvalState &es, const Expr & expr, const Env & env);
+void printEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env, int lvl = 0);
+
+std::unique_ptr<ValMap> mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env);
 
 void copyContext(const Value & v, PathSet & context);
 
@@ -55,6 +62,7 @@ typedef std::map<Path, StorePath> SrcToStore;
 
 std::ostream & printValue(const EvalState & state, std::ostream & str, const Value & v);
 std::string printValue(const EvalState & state, const Value & v);
+std::ostream & operator << (std::ostream & os, const ValueType t);
 
 
 typedef std::pair<std::string, std::string> SearchPathElem;
@@ -69,8 +77,17 @@ struct RegexCache;
 
 std::shared_ptr<RegexCache> makeRegexCache();
 
+struct DebugTrace {
+    std::optional<ErrPos> pos;
+    const Expr & expr;
+    const Env & env;
+    hintformat hint;
+    bool isError;
+};
 
-class EvalState
+void debugError(Error * e, Env & env, Expr & expr);
+
+class EvalState : public std::enable_shared_from_this<EvalState>
 {
 public:
     SymbolTable symbols;
@@ -86,7 +103,8 @@ public:
         sOutputHash, sOutputHashAlgo, sOutputHashMode,
         sRecurseForDerivations,
         sDescription, sSelf, sEpsilon, sStartSet, sOperator, sKey, sPath,
-        sPrefix;
+        sPrefix,
+        sOutputSpecified;
     Symbol sDerivationNix;
 
     /* If set, force copying files to the Nix store even if they
@@ -108,12 +126,56 @@ public:
     RootValue vCallFlake = nullptr;
     RootValue vImportedDrvToDerivation = nullptr;
 
+    /* Debugger */
+    void (* debugRepl)(ref<EvalState> es, const ValMap & extraEnv);
+    bool debugStop;
+    bool debugQuit;
+    int trylevel;
+    std::list<DebugTrace> debugTraces;
+    std::map<const Expr*, const std::shared_ptr<const StaticEnv>> exprEnvs;
+    const std::shared_ptr<const StaticEnv> getStaticEnv(const Expr & expr) const
+    {
+        auto i = exprEnvs.find(&expr);
+        if (i != exprEnvs.end())
+            return i->second;
+        else
+            return std::shared_ptr<const StaticEnv>();;
+    }
+
+    void runDebugRepl(const Error * error, const Env & env, const Expr & expr);
+
+    template<class E>
+    [[gnu::noinline, gnu::noreturn]]
+    void debugThrow(E && error, const Env & env, const Expr & expr)
+    {
+        if (debugRepl)
+            runDebugRepl(&error, env, expr);
+
+        throw std::move(error);
+    }
+
+    template<class E>
+    [[gnu::noinline, gnu::noreturn]]
+    void debugThrowLastTrace(E && e)
+    {
+        // Call this in the situation where Expr and Env are inaccessible.
+        // The debugger will start in the last context that's in the
+        // DebugTrace stack.
+        if (debugRepl && !debugTraces.empty()) {
+            const DebugTrace & last = debugTraces.front();
+            runDebugRepl(&e, last.env, last.expr);
+        }
+
+        throw std::move(e);
+    }
+
+
 private:
     SrcToStore srcToStore;
 
     /* A cache from path names to parse trees. */
 #if HAVE_BOEHMGC
-    typedef std::map<Path, Expr *, std::less<Path>, traceable_allocator<std::pair<const Path, Expr *> > > FileParseCache;
+    typedef std::map<Path, Expr *, std::less<Path>, traceable_allocator<std::pair<const Path, Expr *>>> FileParseCache;
 #else
     typedef std::map<Path, Expr *> FileParseCache;
 #endif
@@ -121,7 +183,7 @@ private:
 
     /* A cache from path names to values. */
 #if HAVE_BOEHMGC
-    typedef std::map<Path, Value, std::less<Path>, traceable_allocator<std::pair<const Path, Value> > > FileEvalCache;
+    typedef std::map<Path, Value, std::less<Path>, traceable_allocator<std::pair<const Path, Value>>> FileEvalCache;
 #else
     typedef std::map<Path, Value> FileEvalCache;
 #endif
@@ -184,10 +246,10 @@ public:
 
     /* Parse a Nix expression from the specified file. */
     Expr * parseExprFromFile(const Path & path);
-    Expr * parseExprFromFile(const Path & path, StaticEnv & staticEnv);
+    Expr * parseExprFromFile(const Path & path, std::shared_ptr<StaticEnv> & staticEnv);
 
     /* Parse a Nix expression from the specified string. */
-    Expr * parseExprFromString(std::string s, const Path & basePath, StaticEnv & staticEnv);
+    Expr * parseExprFromString(std::string s, const Path & basePath, std::shared_ptr<StaticEnv> & staticEnv);
     Expr * parseExprFromString(std::string s, const Path & basePath);
 
     Expr * parseStdin();
@@ -197,7 +259,7 @@ public:
        trivial (i.e. doesn't require arbitrary computation). */
     void evalFile(const Path & path, Value & v, bool mustBeTrivial = false);
 
-    /* Like `cacheFile`, but with an already parsed expression. */
+    /* Like `evalFile`, but with an already parsed expression. */
     void cacheFile(
         const Path & path,
         const Path & resolvedPath,
@@ -253,32 +315,123 @@ public:
     std::string_view forceString(Value & v, PathSet & context, const PosIdx pos, std::string_view errorCtx);
     std::string_view forceStringNoCtx(Value & v, const PosIdx pos, std::string_view errorCtx);
 
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx pos, const char * s) const;
+    // coerce-strings
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx pos, const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const char * s, const std::string_view s2) const;
+    void throwEvalError(const PosIdx pos, const char * s) const;
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s, const std::string_view s2) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx pos, const char * s, const std::string_view s2) const;
+    void throwEvalError(const PosIdx pos, const char * s, const Value & v) const;
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const char * s, const std::string_view s2, const std::string_view s3) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3) const;
+    void throwEvalError(const char * s, const std::string_view s2) const;
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwEvalError(const char * s, const Value & v) const;
+    void throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s, const std::string_view s2) const;
-    [[gnu::noinline, gnu::noreturn]] void throwTypeError(const PosIdx pos, const char * s) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwTypeError(const PosIdx pos, const char * s, const Value & v) const;
+    void throwEvalError(const PosIdx pos, const char * s, const std::string_view s2) const;
-    [[gnu::noinline, gnu::noreturn]] void throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun, const Symbol s2) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol s2) const;
+    void throwEvalError(const char * s, const std::string_view s2, const std::string_view s3) const;
-    [[gnu::noinline, gnu::noreturn]] void throwTypeError(const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwTypeErrorWithTrace(const PosIdx, const char*, std::string_view, const nix::Symbol&, const PosIdx, std::string_view) const;
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3) const;
-    [[gnu::noinline, gnu::noreturn]] void throwTypeErrorWithTrace(const PosIdx, const nix::Suggestions&, const char*, std::string_view, const nix::Symbol&, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwTypeErrorWithTrace(const char*, std::string_view, const Pos &, std::string_view) const;
+    void throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2) const;
-    [[gnu::noinline, gnu::noreturn]] void throwTypeErrorWithTrace(const char*, std::string_view, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwEvalErrorWithTrace(const char*, std::string_view, const PosIdx, std::string_view) const;
+    void throwEvalError(const char * s, const Value & v) const;
-    [[gnu::noinline, gnu::noreturn]] void throwEvalErrorWithTrace(const char*, std::string_view, std::string_view, nix::PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwAssertionError(const PosIdx pos, const char * s, const std::string & s1) const;
+    void throwTypeError(const PosIdx pos, const char * s) const;
-    [[gnu::noinline, gnu::noreturn]] void throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1) const;
+    [[gnu::noinline, gnu::noreturn]]
-    [[gnu::noinline, gnu::noreturn]] void throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1) const;
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun, const Symbol s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const char * s, const Value & v) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeErrorWithTrace(const PosIdx, const char*, std::string_view, const nix::Symbol&, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeErrorWithTrace(const PosIdx, const nix::Suggestions&, const char*, std::string_view, const nix::Symbol&, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeErrorWithTrace(const char*, std::string_view, const Pos &, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeErrorWithTrace(const char*, std::string_view, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalErrorWithTrace(const char*, std::string_view, const PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalErrorWithTrace(const char*, std::string_view, std::string_view, nix::PosIdx, std::string_view) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwAssertionError(const PosIdx pos, const char * s, const std::string & s1) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1) const;
 
-    [[gnu::noinline]] void addErrorTrace(Error & e, const char * s, const std::string & s2) const;
+    // origin/master
-    [[gnu::noinline]] void addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const;
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2, const std::string & s3,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2, const std::string & s3);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun, const Symbol s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const char * s, const Value & v,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwAssertionError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline]]
+    void addErrorTrace(Error & e, const char * s, const std::string & s2) const;
+    [[gnu::noinline]]
+    void addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const;
 
 public:
     /* Return true iff the value `v' denotes a derivation (i.e. a
@@ -314,7 +467,7 @@ public:
     Env & baseEnv;
 
     /* The same, but used during parsing to resolve variables. */
-    StaticEnv staticBaseEnv; // !!! should be private
+    std::shared_ptr<StaticEnv> staticBaseEnv; // !!! should be private
 
 private:
 
@@ -355,7 +508,7 @@ private:
     friend struct ExprLet;
 
     Expr * parse(char * text, size_t length, FileOrigin origin, const PathView path,
-        const PathView basePath, StaticEnv & staticEnv);
+        const PathView basePath, std::shared_ptr<StaticEnv> & staticEnv);
 
 public:
 
@@ -450,6 +603,16 @@ private:
     friend struct Value;
 };
 
+struct DebugTraceStacker {
+    DebugTraceStacker(EvalState & evalState, DebugTrace t);
+    ~DebugTraceStacker()
+    {
+        // assert(evalState.debugTraces.front() == trace);
+        evalState.debugTraces.pop_front();
+    }
+    EvalState & evalState;
+    DebugTrace trace;
+};
 
 /* Return a string representing the type of the value `v'. */
 std::string_view showType(ValueType type);
@@ -534,6 +697,15 @@ struct EvalSettings : Config
 
     Setting<bool> useEvalCache{this, true, "eval-cache",
         "Whether to use the flake evaluation cache."};
+
+    Setting<bool> ignoreExceptionsDuringTry{this, false, "ignore-try",
+        R"(
+          If set to true, ignore exceptions inside 'tryEval' calls when evaluating nix expressions in
+          debug mode (using the --debugger flag). By default the debugger will pause on all exceptions.
+        )"};
+
+    Setting<bool> traceVerbose{this, false, "trace-verbose",
+        "Whether `builtins.traceVerbose` should trace its first argument when evaluated."};
 };
 
 extern EvalSettings evalSettings;

src/libexpr/flake/config.cc

@@ -31,7 +31,7 @@ static void writeTrustedList(const TrustedList & trustedList)
 
 void ConfigFile::apply()
 {
-    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-suffix", "flake-registry"};
+    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-prefix", "bash-prompt-suffix", "flake-registry"};
 
     for (auto & [name, value] : settings) {
 
@@ -50,13 +50,11 @@ void ConfigFile::apply()
         else
             assert(false);
 
-        if (!whitelist.count(baseName)) {
+        if (!whitelist.count(baseName) && !nix::fetchSettings.acceptFlakeConfig) {
-            auto trustedList = readTrustedList();
-
             bool trusted = false;
-            if (nix::fetchSettings.acceptFlakeConfig){
+            auto trustedList = readTrustedList();
-                trusted = true;
+            auto tlname = get(trustedList, name);
-            } else if (auto saved = get(get(trustedList, name).value_or(std::map<std::string, bool>()), valueS)) {
+            if (auto saved = tlname ? get(*tlname, valueS) : nullptr) {
                 trusted = *saved;
                 warn("Using saved setting for '%s = %s' from ~/.local/share/nix/trusted-settings.json.", name,valueS);
             } else {
@@ -69,7 +67,6 @@ void ConfigFile::apply()
                     writeTrustedList(trustedList);
                 }
             }
-
             if (!trusted) {
                 warn("ignoring untrusted flake configuration setting '%s'", name);
                 continue;

src/libexpr/flake/flake.cc

@@ -341,7 +341,6 @@ LockedFlake lockFlake(
 
         debug("old lock file: %s", oldLockFile);
 
-        // FIXME: check whether all overrides are used.
         std::map<InputPath, FlakeInput> overrides;
         std::set<InputPath> overridesUsed, updatesUsed;
 
@@ -384,6 +383,18 @@ LockedFlake lockFlake(
                 }
             }
 
+            /* Check whether this input has overrides for a
+               non-existent input. */
+            for (auto [inputPath, inputOverride] : overrides) {
+                auto inputPath2(inputPath);
+                auto follow = inputPath2.back();
+                inputPath2.pop_back();
+                if (inputPath2 == inputPathPrefix && !flakeInputs.count(follow))
+                    warn(
+                        "input '%s' has an override for a non-existent input '%s'",
+                        printInputPath(inputPathPrefix), follow);
+            }
+
             /* Go over the flake inputs, resolve/fetch them if
                necessary (i.e. if they're new or the flakeref changed
                from what's in the lock file). */
@@ -513,6 +524,15 @@ LockedFlake lockFlake(
                         if (!lockFlags.allowMutable && !input.ref->input.isLocked())
                             throw Error("cannot update flake input '%s' in pure mode", inputPathS);
 
+                        /* Note: in case of an --override-input, we use
+                            the *original* ref (input2.ref) for the
+                            "original" field, rather than the
+                            override. This ensures that the override isn't
+                            nuked the next time we update the lock
+                            file. That is, overrides are sticky unless you
+                            use --no-write-lock-file. */
+                        auto ref = input2.ref ? *input2.ref : *input.ref;
+
                         if (input.isFlake) {
                             Path localPath = parentPath;
                             FlakeRef localRef = *input.ref;
@@ -524,15 +544,7 @@ LockedFlake lockFlake(
 
                             auto inputFlake = getFlake(state, localRef, useRegistries, flakeCache, inputPath);
 
-                            /* Note: in case of an --override-input, we use
+                            auto childNode = std::make_shared<LockedNode>(inputFlake.lockedRef, ref);
-                               the *original* ref (input2.ref) for the
-                               "original" field, rather than the
-                               override. This ensures that the override isn't
-                               nuked the next time we update the lock
-                               file. That is, overrides are sticky unless you
-                               use --no-write-lock-file. */
-                            auto childNode = std::make_shared<LockedNode>(
-                                inputFlake.lockedRef, input2.ref ? *input2.ref : *input.ref);
 
                             node->inputs.insert_or_assign(id, childNode);
 
@@ -560,7 +572,7 @@ LockedFlake lockFlake(
                             auto [sourceInfo, resolvedRef, lockedRef] = fetchOrSubstituteTree(
                                 state, *input.ref, useRegistries, flakeCache);
                             node->inputs.insert_or_assign(id,
-                                std::make_shared<LockedNode>(lockedRef, *input.ref, false));
+                                std::make_shared<LockedNode>(lockedRef, ref, false));
                         }
                     }
 
@@ -723,6 +735,7 @@ static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, V
         lockFlake(state, flakeRef,
             LockFlags {
                 .updateLockFile = false,
+                .writeLockFile = false,
                 .useRegistries = !evalSettings.pureEval && fetchSettings.useRegistries,
                 .allowMutable  = !evalSettings.pureEval,
             }),

src/libexpr/flake/flakeref.cc

@@ -176,7 +176,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                             parsedURL.query.insert_or_assign("shallow", "1");
 
                         return std::make_pair(
-                            FlakeRef(Input::fromURL(parsedURL), get(parsedURL.query, "dir").value_or("")),
+                            FlakeRef(Input::fromURL(parsedURL), getOr(parsedURL.query, "dir", "")),
                             fragment);
                     }
 
@@ -189,7 +189,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
             if (!hasPrefix(path, "/"))
                 throw BadURL("flake reference '%s' is not an absolute path", url);
             auto query = decodeQuery(match[2]);
-            path = canonPath(path + "/" + get(query, "dir").value_or(""));
+            path = canonPath(path + "/" + getOr(query, "dir", ""));
         }
 
         fetchers::Attrs attrs;
@@ -208,7 +208,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         input.parent = baseDir;
 
         return std::make_pair(
-            FlakeRef(std::move(input), get(parsedURL.query, "dir").value_or("")),
+            FlakeRef(std::move(input), getOr(parsedURL.query, "dir", "")),
             fragment);
     }
 }
@@ -238,4 +238,15 @@ std::pair<fetchers::Tree, FlakeRef> FlakeRef::fetchTree(ref<Store> store) const
     return {std::move(tree), FlakeRef(std::move(lockedInput), subdir)};
 }
 
+std::tuple<FlakeRef, std::string, OutputsSpec> parseFlakeRefWithFragmentAndOutputsSpec(
+    const std::string & url,
+    const std::optional<Path> & baseDir,
+    bool allowMissing,
+    bool isFlake)
+{
+    auto [prefix, outputsSpec] = parseOutputsSpec(url);
+    auto [flakeRef, fragment] = parseFlakeRefWithFragment(prefix, baseDir, allowMissing, isFlake);
+    return {std::move(flakeRef), fragment, outputsSpec};
+}
+
 }

src/libexpr/flake/flakeref.hh

@@ -3,6 +3,7 @@
 #include "types.hh"
 #include "hash.hh"
 #include "fetchers.hh"
+#include "path-with-outputs.hh"
 
 #include <variant>
 
@@ -27,7 +28,7 @@ typedef std::string FlakeId;
  * object that fetcher generates (usually via
  * FlakeRef::fromAttrs(attrs) or parseFlakeRef(url) calls).
  *
- * The actual fetch not have been performed yet (i.e. a FlakeRef may
+ * The actual fetch may not have been performed yet (i.e. a FlakeRef may
  * be lazy), but the fetcher can be invoked at any time via the
  * FlakeRef to ensure the store is populated with this input.
  */
@@ -79,4 +80,11 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
 std::optional<std::pair<FlakeRef, std::string>> maybeParseFlakeRefWithFragment(
     const std::string & url, const std::optional<Path> & baseDir = {});
 
+std::tuple<FlakeRef, std::string, OutputsSpec> parseFlakeRefWithFragmentAndOutputsSpec(
+    const std::string & url,
+    const std::optional<Path> & baseDir = {},
+    bool allowMissing = false,
+    bool isFlake = true);
+
+
 }

src/libexpr/get-drvs.cc

@@ -34,7 +34,7 @@ DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPat
 
     outputName =
         selectedOutputs.empty()
-        ? get(drv.env, "outputName").value_or("out")
+        ? getOr(drv.env, "outputName", "out")
         : *selectedOutputs.begin();
 
     auto i = drv.outputs.find(outputName);
@@ -132,23 +132,36 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         } else
             outputs.emplace("out", withPaths ? std::optional{queryOutPath()} : std::nullopt);
     }
+
     if (!onlyOutputsToInstall || !attrs)
         return outputs;
 
-    /* Check for `meta.outputsToInstall` and return `outputs` reduced to that. */
+    Bindings::iterator i;
-    const Value * outTI = queryMeta("outputsToInstall");
+    if (attrs && (i = attrs->find(state->sOutputSpecified)) != attrs->end() && state->forceBool(*i->value, i->pos)) {
-    if (!outTI) return outputs;
+        Outputs result;
-    const auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
+        auto out = outputs.find(queryOutputName());
-        /* ^ this shows during `nix-env -i` right under the bad derivation */
+        if (out == outputs.end())
-    if (!outTI->isList()) throw errMsg;
+            throw Error("derivation does not have output '%s'", queryOutputName());
-    Outputs result;
-    for (auto elem : outTI->listItems()) {
-        if (elem->type() != nString) throw errMsg;
-        auto out = outputs.find(elem->string.s);
-        if (out == outputs.end()) throw errMsg;
         result.insert(*out);
+        return result;
+    }
+
+    else {
+        /* Check for `meta.outputsToInstall` and return `outputs` reduced to that. */
+        const Value * outTI = queryMeta("outputsToInstall");
+        if (!outTI) return outputs;
+        const auto errMsg = Error("this derivation has bad 'meta.outputsToInstall'");
+            /* ^ this shows during `nix-env -i` right under the bad derivation */
+        if (!outTI->isList()) throw errMsg;
+        Outputs result;
+        for (auto elem : outTI->listItems()) {
+            if (elem->type() != nString) throw errMsg;
+            auto out = outputs.find(elem->string.s);
+            if (out == outputs.end()) throw errMsg;
+            result.insert(*out);
+        }
+        return result;
     }
-    return result;
 }
 
 

src/libexpr/get-drvs.hh

@@ -73,7 +73,7 @@ public:
 
 
 #if HAVE_BOEHMGC
-typedef std::list<DrvInfo, traceable_allocator<DrvInfo> > DrvInfos;
+typedef std::list<DrvInfo, traceable_allocator<DrvInfo>> DrvInfos;
 #else
 typedef std::list<DrvInfo> DrvInfos;
 #endif

src/libexpr/lexer.l

@@ -198,7 +198,7 @@ or          { return OR_KW; }
                    (...|\$[^\{\"\\]|\\.|\$\\.)+ would have triggered.
                    This is technically invalid, but we leave the problem to the
                    parser who fails with exact location. */
-                return STR;
+                return EOF;
               }
 
 \'\'(\ *\n)?     { PUSH_STATE(IND_STRING); return IND_STRING_OPEN; }

src/libexpr/nixexpr.cc

@@ -6,10 +6,8 @@
 
 #include <cstdlib>
 
-
 namespace nix {
 
-
 /* Displaying abstract syntax trees. */
 
 static void showString(std::ostream & str, std::string_view s)
@@ -294,35 +292,46 @@ std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath)
 
 /* Computing levels/displacements for variables. */
 
-void Expr::bindVars(const EvalState & es, const StaticEnv & env)
+void Expr::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
     abort();
 }
 
-void ExprInt::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprInt::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
 }
 
-void ExprFloat::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprFloat::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
 }
 
-void ExprString::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprString::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
 }
 
-void ExprPath::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprPath::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
 }
 
-void ExprVar::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprVar::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     /* Check whether the variable appears in the environment.  If so,
        set its level and displacement. */
     const StaticEnv * curEnv;
     Level level;
     int withLevel = -1;
-    for (curEnv = &env, level = 0; curEnv; curEnv = curEnv->up, level++) {
+    for (curEnv = env.get(), level = 0; curEnv; curEnv = curEnv->up, level++) {
         if (curEnv->isWith) {
             if (withLevel == -1) withLevel = level;
         } else {
@@ -348,8 +357,11 @@ void ExprVar::bindVars(const EvalState & es, const StaticEnv & env)
     this->level = withLevel;
 }
 
-void ExprSelect::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprSelect::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     e->bindVars(es, env);
     if (def) def->bindVars(es, env);
     for (auto & i : attrPath)
@@ -357,64 +369,78 @@ void ExprSelect::bindVars(const EvalState & es, const StaticEnv & env)
             i.expr->bindVars(es, env);
 }
 
-void ExprOpHasAttr::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprOpHasAttr::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     e->bindVars(es, env);
     for (auto & i : attrPath)
         if (!i.symbol)
             i.expr->bindVars(es, env);
 }
 
-void ExprAttrs::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprAttrs::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
-    const StaticEnv * dynamicEnv = &env;
+    if (es.debugRepl)
-    StaticEnv newEnv(false, &env, recursive ? attrs.size() : 0);
+        es.exprEnvs.insert(std::make_pair(this, env));
 
     if (recursive) {
-        dynamicEnv = &newEnv;
+        auto newEnv = std::make_shared<StaticEnv>(false, env.get(), recursive ? attrs.size() : 0);
 
         Displacement displ = 0;
         for (auto & i : attrs)
-            newEnv.vars.emplace_back(i.first, i.second.displ = displ++);
+            newEnv->vars.emplace_back(i.first, i.second.displ = displ++);
 
         // No need to sort newEnv since attrs is in sorted order.
 
         for (auto & i : attrs)
             i.second.e->bindVars(es, i.second.inherited ? env : newEnv);
-    }
 
-    else
+        for (auto & i : dynamicAttrs) {
+            i.nameExpr->bindVars(es, newEnv);
+            i.valueExpr->bindVars(es, newEnv);
+        }
+    }
+    else {
         for (auto & i : attrs)
             i.second.e->bindVars(es, env);
 
-    for (auto & i : dynamicAttrs) {
+        for (auto & i : dynamicAttrs) {
-        i.nameExpr->bindVars(es, *dynamicEnv);
+            i.nameExpr->bindVars(es, env);
-        i.valueExpr->bindVars(es, *dynamicEnv);
+            i.valueExpr->bindVars(es, env);
+        }
     }
 }
 
-void ExprList::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprList::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     for (auto & i : elems)
         i->bindVars(es, env);
 }
 
-void ExprLambda::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprLambda::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
-    StaticEnv newEnv(
+    if (es.debugRepl)
-        false, &env,
+        es.exprEnvs.insert(std::make_pair(this, env));
+
+    auto newEnv = std::make_shared<StaticEnv>(
+        false, env.get(),
         (hasFormals() ? formals->formals.size() : 0) +
         (!arg ? 0 : 1));
 
     Displacement displ = 0;
 
-    if (arg) newEnv.vars.emplace_back(arg, displ++);
+    if (arg) newEnv->vars.emplace_back(arg, displ++);
 
     if (hasFormals()) {
         for (auto & i : formals->formals)
-            newEnv.vars.emplace_back(i.name, displ++);
+            newEnv->vars.emplace_back(i.name, displ++);
 
-        newEnv.sort();
+        newEnv->sort();
 
         for (auto & i : formals->formals)
             if (i.def) i.def->bindVars(es, newEnv);
@@ -423,20 +449,26 @@ void ExprLambda::bindVars(const EvalState & es, const StaticEnv & env)
     body->bindVars(es, newEnv);
 }
 
-void ExprCall::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprCall::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     fun->bindVars(es, env);
     for (auto e : args)
         e->bindVars(es, env);
 }
 
-void ExprLet::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprLet::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
-    StaticEnv newEnv(false, &env, attrs->attrs.size());
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
+    auto newEnv = std::make_shared<StaticEnv>(false, env.get(), attrs->attrs.size());
 
     Displacement displ = 0;
     for (auto & i : attrs->attrs)
-        newEnv.vars.emplace_back(i.first, i.second.displ = displ++);
+        newEnv->vars.emplace_back(i.first, i.second.displ = displ++);
 
     // No need to sort newEnv since attrs->attrs is in sorted order.
 
@@ -446,51 +478,71 @@ void ExprLet::bindVars(const EvalState & es, const StaticEnv & env)
     body->bindVars(es, newEnv);
 }
 
-void ExprWith::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprWith::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     /* Does this `with' have an enclosing `with'?  If so, record its
        level so that `lookupVar' can look up variables in the previous
        `with' if this one doesn't contain the desired attribute. */
     const StaticEnv * curEnv;
     Level level;
     prevWith = 0;
-    for (curEnv = &env, level = 1; curEnv; curEnv = curEnv->up, level++)
+    for (curEnv = env.get(), level = 1; curEnv; curEnv = curEnv->up, level++)
         if (curEnv->isWith) {
             prevWith = level;
             break;
         }
 
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     attrs->bindVars(es, env);
-    StaticEnv newEnv(true, &env);
+    auto newEnv = std::make_shared<StaticEnv>(true, env.get());
     body->bindVars(es, newEnv);
 }
 
-void ExprIf::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprIf::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     cond->bindVars(es, env);
     then->bindVars(es, env);
     else_->bindVars(es, env);
 }
 
-void ExprAssert::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprAssert::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     cond->bindVars(es, env);
     body->bindVars(es, env);
 }
 
-void ExprOpNot::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprOpNot::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     e->bindVars(es, env);
 }
 
-void ExprConcatStrings::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprConcatStrings::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
+
     for (auto & i : *this->es)
         i.second->bindVars(es, env);
 }
 
-void ExprPos::bindVars(const EvalState & es, const StaticEnv & env)
+void ExprPos::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    if (es.debugRepl)
+        es.exprEnvs.insert(std::make_pair(this, env));
 }
 
 

src/libexpr/nixexpr.hh

@@ -21,7 +21,6 @@ MakeError(UndefinedVarError, Error);
 MakeError(MissingArgumentError, EvalError);
 MakeError(RestrictedPathError, Error);
 
-
 /* Position objects. */
 
 struct Pos
@@ -142,24 +141,25 @@ struct Expr
 {
     virtual ~Expr() { };
     virtual void show(const SymbolTable & symbols, std::ostream & str) const;
-    virtual void bindVars(const EvalState & es, const StaticEnv & env);
+    virtual void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env);
     virtual void eval(EvalState & state, Env & env, Value & v);
     virtual Value * maybeThunk(EvalState & state, Env & env);
     virtual void setName(Symbol name);
+    virtual PosIdx getPos() const { return noPos; }
 };
 
 #define COMMON_METHODS \
-    void show(const SymbolTable & symbols, std::ostream & str) const;    \
+    void show(const SymbolTable & symbols, std::ostream & str) const override; \
-    void eval(EvalState & state, Env & env, Value & v); \
+    void eval(EvalState & state, Env & env, Value & v) override; \
-    void bindVars(const EvalState & es, const StaticEnv & env);
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
 
 struct ExprInt : Expr
 {
     NixInt n;
     Value v;
     ExprInt(NixInt n) : n(n) { v.mkInt(n); };
+    Value * maybeThunk(EvalState & state, Env & env) override;
     COMMON_METHODS
-    Value * maybeThunk(EvalState & state, Env & env);
 };
 
 struct ExprFloat : Expr
@@ -167,8 +167,8 @@ struct ExprFloat : Expr
     NixFloat nf;
     Value v;
     ExprFloat(NixFloat nf) : nf(nf) { v.mkFloat(nf); };
+    Value * maybeThunk(EvalState & state, Env & env) override;
     COMMON_METHODS
-    Value * maybeThunk(EvalState & state, Env & env);
 };
 
 struct ExprString : Expr
@@ -176,8 +176,8 @@ struct ExprString : Expr
     std::string s;
     Value v;
     ExprString(std::string s) : s(std::move(s)) { v.mkString(this->s.data()); };
+    Value * maybeThunk(EvalState & state, Env & env) override;
     COMMON_METHODS
-    Value * maybeThunk(EvalState & state, Env & env);
 };
 
 struct ExprPath : Expr
@@ -185,8 +185,8 @@ struct ExprPath : Expr
     std::string s;
     Value v;
     ExprPath(std::string s) : s(std::move(s)) { v.mkPath(this->s.c_str()); };
+    Value * maybeThunk(EvalState & state, Env & env) override;
     COMMON_METHODS
-    Value * maybeThunk(EvalState & state, Env & env);
 };
 
 typedef uint32_t Level;
@@ -212,8 +212,9 @@ struct ExprVar : Expr
 
     ExprVar(Symbol name) : name(name) { };
     ExprVar(const PosIdx & pos, Symbol name) : pos(pos), name(name) { };
+    Value * maybeThunk(EvalState & state, Env & env) override;
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
-    Value * maybeThunk(EvalState & state, Env & env);
 };
 
 struct ExprSelect : Expr
@@ -223,6 +224,7 @@ struct ExprSelect : Expr
     AttrPath attrPath;
     ExprSelect(const PosIdx & pos, Expr * e, const AttrPath & attrPath, Expr * def) : pos(pos), e(e), def(def), attrPath(attrPath) { };
     ExprSelect(const PosIdx & pos, Expr * e, Symbol name) : pos(pos), e(e), def(0) { attrPath.push_back(AttrName(name)); };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -231,6 +233,7 @@ struct ExprOpHasAttr : Expr
     Expr * e;
     AttrPath attrPath;
     ExprOpHasAttr(Expr * e, const AttrPath & attrPath) : e(e), attrPath(attrPath) { };
+    PosIdx getPos() const override { return e->getPos(); }
     COMMON_METHODS
 };
 
@@ -259,6 +262,7 @@ struct ExprAttrs : Expr
     DynamicAttrDefs dynamicAttrs;
     ExprAttrs(const PosIdx &pos) : recursive(false), pos(pos) { };
     ExprAttrs() : recursive(false) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -267,6 +271,11 @@ struct ExprList : Expr
     std::vector<Expr *> elems;
     ExprList() { };
     COMMON_METHODS
+
+    PosIdx getPos() const override
+    {
+        return elems.empty() ? noPos : elems.front()->getPos();
+    }
 };
 
 struct Formal
@@ -316,9 +325,10 @@ struct ExprLambda : Expr
         : pos(pos), formals(formals), body(body)
     {
     }
-    void setName(Symbol name);
+    void setName(Symbol name) override;
     std::string showNamePos(const EvalState & state) const;
     inline bool hasFormals() const { return formals != nullptr; }
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -330,6 +340,7 @@ struct ExprCall : Expr
     ExprCall(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args)
         : fun(fun), args(args), pos(pos)
     { }
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -347,6 +358,7 @@ struct ExprWith : Expr
     Expr * attrs, * body;
     size_t prevWith;
     ExprWith(const PosIdx & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -355,6 +367,7 @@ struct ExprIf : Expr
     PosIdx pos;
     Expr * cond, * then, * else_;
     ExprIf(const PosIdx & pos, Expr * cond, Expr * then, Expr * else_) : pos(pos), cond(cond), then(then), else_(else_) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -363,6 +376,7 @@ struct ExprAssert : Expr
     PosIdx pos;
     Expr * cond, * body;
     ExprAssert(const PosIdx & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -380,15 +394,16 @@ struct ExprOpNot : Expr
         Expr * e1, * e2; \
         name(Expr * e1, Expr * e2) : e1(e1), e2(e2) { }; \
         name(const PosIdx & pos, Expr * e1, Expr * e2) : pos(pos), e1(e1), e2(e2) { }; \
-        void show(const SymbolTable & symbols, std::ostream & str) const \
+        void show(const SymbolTable & symbols, std::ostream & str) const override \
         { \
             str << "("; e1->show(symbols, str); str << " " s " "; e2->show(symbols, str); str << ")"; \
         } \
-        void bindVars(const EvalState & es, const StaticEnv & env)    \
+        void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override \
         { \
             e1->bindVars(es, env); e2->bindVars(es, env);    \
         } \
-        void eval(EvalState & state, Env & env, Value & v); \
+        void eval(EvalState & state, Env & env, Value & v) override; \
+        PosIdx getPos() const override { return pos; } \
     };
 
 MakeBinOp(ExprOpEq, "==")
@@ -403,9 +418,10 @@ struct ExprConcatStrings : Expr
 {
     PosIdx pos;
     bool forceString;
-    std::vector<std::pair<PosIdx, Expr *> > * es;
+    std::vector<std::pair<PosIdx, Expr *>> * es;
-    ExprConcatStrings(const PosIdx & pos, bool forceString, std::vector<std::pair<PosIdx, Expr *> > * es)
+    ExprConcatStrings(const PosIdx & pos, bool forceString, std::vector<std::pair<PosIdx, Expr *>> * es)
         : pos(pos), forceString(forceString), es(es) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 
@@ -413,6 +429,7 @@ struct ExprPos : Expr
 {
     PosIdx pos;
     ExprPos(const PosIdx & pos) : pos(pos) { };
+    PosIdx getPos() const override { return pos; }
     COMMON_METHODS
 };
 

src/libexpr/parser.y

@@ -193,7 +193,7 @@ static Formals * toFormals(ParseData & data, ParserFormals * formals,
 
 
 static Expr * stripIndentation(const PosIdx pos, SymbolTable & symbols,
-    std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken> > > & es)
+    std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>> & es)
 {
     if (es.empty()) return new ExprString("");
 
@@ -233,7 +233,7 @@ static Expr * stripIndentation(const PosIdx pos, SymbolTable & symbols,
     }
 
     /* Strip spaces from each line. */
-    auto * es2 = new std::vector<std::pair<PosIdx, Expr *> >;
+    auto * es2 = new std::vector<std::pair<PosIdx, Expr *>>;
     atStartOfLine = true;
     size_t curDropped = 0;
     size_t n = es.size();
@@ -320,8 +320,8 @@ void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * err
   StringToken uri;
   StringToken str;
   std::vector<nix::AttrName> * attrNames;
-  std::vector<std::pair<nix::PosIdx, nix::Expr *> > * string_parts;
+  std::vector<std::pair<nix::PosIdx, nix::Expr *>> * string_parts;
-  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, StringToken> > > * ind_string_parts;
+  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, StringToken>>> * ind_string_parts;
 }
 
 %type <e> start expr expr_function expr_if expr_op
@@ -503,9 +503,9 @@ string_parts_interpolated
   : string_parts_interpolated STR
   { $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(std::string($2))); }
   | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
-  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *> >; $$->emplace_back(makeCurPos(@1, data), $2); }
+  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *>>; $$->emplace_back(makeCurPos(@1, data), $2); }
   | STR DOLLAR_CURLY expr '}' {
-      $$ = new std::vector<std::pair<PosIdx, Expr *> >;
+      $$ = new std::vector<std::pair<PosIdx, Expr *>>;
       $$->emplace_back(makeCurPos(@1, data), new ExprString(std::string($1)));
       $$->emplace_back(makeCurPos(@2, data), $3);
     }
@@ -520,6 +520,12 @@ path_start
     $$ = new ExprPath(path);
   }
   | HPATH {
+    if (evalSettings.pureEval) {
+        throw Error(
+            "the path '%s' can not be resolved in pure mode",
+            std::string_view($1.p, $1.l)
+        );
+    }
     Path path(getHome() + std::string($1.p + 1, $1.l - 1));
     $$ = new ExprPath(path);
   }
@@ -528,7 +534,7 @@ path_start
 ind_string_parts
   : ind_string_parts IND_STR { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $2); }
   | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
-  | { $$ = new std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken> > >; }
+  | { $$ = new std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>>; }
   ;
 
 binds
@@ -643,7 +649,7 @@ namespace nix {
 
 
 Expr * EvalState::parse(char * text, size_t length, FileOrigin origin,
-    const PathView path, const PathView basePath, StaticEnv & staticEnv)
+    const PathView path, const PathView basePath, std::shared_ptr<StaticEnv> & staticEnv)
 {
     yyscan_t scanner;
     std::string file;
@@ -706,7 +712,7 @@ Expr * EvalState::parseExprFromFile(const Path & path)
 }
 
 
-Expr * EvalState::parseExprFromFile(const Path & path, StaticEnv & staticEnv)
+Expr * EvalState::parseExprFromFile(const Path & path, std::shared_ptr<StaticEnv> & staticEnv)
 {
     auto buffer = readFile(path);
     // readFile should have left some extra space for terminators
@@ -715,7 +721,7 @@ Expr * EvalState::parseExprFromFile(const Path & path, StaticEnv & staticEnv)
 }
 
 
-Expr * EvalState::parseExprFromString(std::string s, const Path & basePath, StaticEnv & staticEnv)
+Expr * EvalState::parseExprFromString(std::string s, const Path & basePath, std::shared_ptr<StaticEnv> & staticEnv)
 {
     s.append("\0\0", 2);
     return parse(s.data(), s.size(), foString, "", basePath, staticEnv);
@@ -782,13 +788,13 @@ Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, c
     if (hasPrefix(path, "nix/"))
         return concatStrings(corepkgsPrefix, path.substr(4));
 
-    throw ThrownError({
+    debugThrowLastTrace(ThrownError({
         .msg = hintfmt(evalSettings.pureEval
             ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
             : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
             path),
         .errPos = positions[pos]
-    });
+    }));
 }
 
 

src/libexpr/primops.cc

@@ -46,7 +46,7 @@ StringMap EvalState::realiseContext(const PathSet & context)
         auto [ctx, outputName] = decodeContext(*store, i);
         auto ctxS = store->printStorePath(ctx);
         if (!store->isValidPath(ctx))
-            throw InvalidPathError(store->printStorePath(ctx));
+            debugThrowLastTrace(InvalidPathError(store->printStorePath(ctx)));
         if (!outputName.empty() && ctx.isDerivation()) {
             drvs.push_back({ctx, {outputName}});
         } else {
@@ -57,9 +57,9 @@ StringMap EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return {};
 
     if (!evalSettings.enableImportFromDerivation)
-        throw Error(
+        debugThrowLastTrace(Error(
             "cannot build '%1%' during evaluation because the option 'allow-import-from-derivation' is disabled",
-            store->printStorePath(drvs.begin()->drvPath));
+            store->printStorePath(drvs.begin()->drvPath)));
 
     /* Build/substitute the context. */
     std::vector<DerivedPath> buildReqs;
@@ -68,14 +68,15 @@ StringMap EvalState::realiseContext(const PathSet & context)
 
     /* Get all the output paths corresponding to the placeholders we had */
     for (auto & [drvPath, outputs] : drvs) {
-        auto outputPaths = store->queryDerivationOutputMap(drvPath);
+        const auto outputPaths = store->queryDerivationOutputMap(drvPath);
         for (auto & outputName : outputs) {
-            if (outputPaths.count(outputName) == 0)
+            auto outputPath = get(outputPaths, outputName);
-                throw Error("derivation '%s' does not have an output named '%s'",
+            if (!outputPath)
-                        store->printStorePath(drvPath), outputName);
+                debugThrowLastTrace(Error("derivation '%s' does not have an output named '%s'",
+                    store->printStorePath(drvPath), outputName));
             res.insert_or_assign(
                 downstreamPlaceholder(*store, drvPath, outputName),
-                store->printStorePath(outputPaths.at(outputName))
+                store->printStorePath(*outputPath)
             );
         }
     }
@@ -207,11 +208,11 @@ static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * v
             Env * env = &state.allocEnv(vScope->attrs->size());
             env->up = &state.baseEnv;
 
-            StaticEnv staticEnv(false, &state.staticBaseEnv, vScope->attrs->size());
+            auto staticEnv = std::make_shared<StaticEnv>(false, state.staticBaseEnv.get(), vScope->attrs->size());
 
             unsigned int displ = 0;
             for (auto & attr : *vScope->attrs) {
-                staticEnv.vars.emplace_back(attr.name, displ);
+                staticEnv->vars.emplace_back(attr.name, displ);
                 env->values[displ++] = attr.value;
             }
 
@@ -310,17 +311,16 @@ void prim_importNative(EvalState & state, const PosIdx pos, Value * * args, Valu
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
     if (!handle)
-        throw EvalError("could not open '%1%': %2%", path, dlerror());
+        state.debugThrowLastTrace(EvalError("could not open '%1%': %2%", path, dlerror()));
 
     dlerror();
     ValueInitializer func = (ValueInitializer) dlsym(handle, sym.c_str());
     if(!func) {
         char *message = dlerror();
         if (message)
-            throw EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message);
+            state.debugThrowLastTrace(EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message));
         else
-            throw EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected",
+            state.debugThrowLastTrace(EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected", sym, path));
-                sym, path);
     }
 
     (func)(state, v);
@@ -335,12 +335,11 @@ void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v)
     state.forceList(*args[0], pos, "while evaluating the first argument passed to builtins.exec");
     auto elems = args[0]->listElems();
     auto count = args[0]->listSize();
-    if (count == 0) {
+    if (count == 0)
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("at least one argument to 'exec' required"),
             .errPos = state.positions[pos]
-        });
+        }));
-    }
     PathSet context;
     auto program = state.coerceToString(pos, *elems[0], context, false, false,
            "while evaluating the first element of the argument passed to builtins.exec").toOwned();
@@ -352,11 +351,11 @@ void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v)
     try {
         auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("cannot execute '%1%', since path '%2%' is not valid",
                 program, e.path),
             .errPos = state.positions[pos]
-        });
+        }));
     }
 
     auto output = runProgram(program, true, commandArgs);
@@ -561,10 +560,10 @@ struct CompareValues
             if (v1->type() == nInt && v2->type() == nFloat)
                 return v1->integer < v2->fpoint;
             if (v1->type() != v2->type())
-                throw EvalError({
+                state.debugThrowLastTrace(EvalError({
-                    .msg = hintfmt("%scannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
+                    ."cannot compare %1% with %2%", showType(*v1), showType(*v2)));
                     .errPos = std::nullopt,
-                });
+                }));
             switch (v1->type()) {
                 case nInt:
                     return v1->integer < v2->integer;
@@ -586,10 +585,10 @@ struct CompareValues
                         }
                     }
                 default:
-                    throw EvalError({
+                    state.debugThrowLastTrace(EvalError({
                         .msg = hintfmt("%scannot compare %s with %s", errorCtx, showType(*v1), showType(*v2)),
                         .errPos = std::nullopt,
-                    });
+                    }));
             }
         } catch (Error & e) {
             e.addTrace(std::nullopt, errorCtx);
@@ -600,7 +599,7 @@ struct CompareValues
 
 
 #if HAVE_BOEHMGC
-typedef std::list<Value *, gc_allocator<Value *> > ValueList;
+typedef std::list<Value *, gc_allocator<Value *>> ValueList;
 #else
 typedef std::list<Value *> ValueList;
 #endif
@@ -618,6 +617,12 @@ static Bindings::iterator getAttr(
             .msg = hintfmt("attribute '%s' missing %s", state.symbols[attrSym], errorCtx),
             .errPos = state.positions[attrSet->pos],
         });
+            // TODO XXX
+            // Adding another trace for the function name to make it clear
+            // which call received wrong arguments.
+            //e.addTrace(state.positions[pos], hintfmt("while invoking '%s'", funcName));
+            //state.debugThrowLastTrace(e);
+        }
     }
     return value;
 }
@@ -714,6 +719,41 @@ static RegisterPrimOp primop_genericClosure(RegisterPrimOp::Info {
     .fun = prim_genericClosure,
 });
 
+
+static RegisterPrimOp primop_break({
+    .name = "break",
+    .args = {"v"},
+    .doc = R"(
+      In debug mode (enabled using `--debugger`), pause Nix expression evaluation and enter the REPL.
+      Otherwise, return the argument `v`.
+    )",
+    .fun = [](EvalState & state, const PosIdx pos, Value * * args, Value & v)
+    {
+        if (state.debugRepl && !state.debugTraces.empty()) {
+            auto error = Error(ErrorInfo {
+                .level = lvlInfo,
+                .msg = hintfmt("breakpoint reached"),
+                .errPos = state.positions[pos],
+            });
+
+            auto & dt = state.debugTraces.front();
+            state.runDebugRepl(&error, dt.env, dt.expr);
+
+            if (state.debugQuit) {
+                // If the user elects to quit the repl, throw an exception.
+                throw Error(ErrorInfo{
+                    .level = lvlInfo,
+                    .msg = hintfmt("quit the debugger"),
+                    .errPos = state.positions[noPos],
+                });
+            }
+        }
+
+        // Return the value we were passed.
+        v = *args[0];
+    }
+});
+
 static RegisterPrimOp primop_abort({
     .name = "abort",
     .args = {"s"},
@@ -725,7 +765,7 @@ static RegisterPrimOp primop_abort({
         PathSet context;
         auto s = state.coerceToString(pos, *args[0], context,
                 "while evaluating the error message passed to builtins.abort").toOwned();
-        throw Abort("evaluation aborted with the following error message: '%1%'", s);
+        state.debugThrowLastTrace(Abort("evaluation aborted with the following error message: '%1%'", s));
     }
 });
 
@@ -744,7 +784,7 @@ static RegisterPrimOp primop_throw({
       PathSet context;
       auto s = state.coerceToString(pos, *args[0], context,
               "while evaluating the error message passed to builtin.throw").toOwned();
-      throw ThrownError(s);
+      state.debugThrowLastTrace(ThrownError(s));
     }
 });
 
@@ -811,6 +851,18 @@ static RegisterPrimOp primop_floor({
 static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     auto attrs = state.buildBindings(2);
+
+    /* increment state.trylevel, and decrement it when this function returns. */
+    MaintainCount trylevel(state.trylevel);
+
+    void (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
+    if (state.debugRepl && evalSettings.ignoreExceptionsDuringTry)
+    {
+        /* to prevent starting the repl from exceptions withing a tryEval, null it. */
+        savedDebugRepl = state.debugRepl;
+        state.debugRepl = nullptr;
+    }
+
     try {
         state.forceValue(*args[0], pos);
         attrs.insert(state.sValue, args[0]);
@@ -819,6 +871,11 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
         attrs.alloc(state.sValue).mkBool(false);
         attrs.alloc("success").mkBool(false);
     }
+
+    // restore the debugRepl pointer if we saved it earlier.
+    if (savedDebugRepl)
+        state.debugRepl = savedDebugRepl;
+
     v.mkAttrs(attrs);
 }
 
@@ -930,6 +987,15 @@ static RegisterPrimOp primop_trace({
 });
 
 
+/* Takes two arguments and evaluates to the second one. Used as the
+ * builtins.traceVerbose implementation when --trace-verbose is not enabled
+ */
+static void prim_second(EvalState & state, const PosIdx pos, Value * * args, Value & v)
+{
+    state.forceValue(*args[1], pos);
+    v = *args[1];
+}
+
 /*************************************************************
  * Derivations
  *************************************************************/
@@ -995,37 +1061,37 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
             else
-                throw EvalError({
+                state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
                     .errPos = state.positions[posDrvName]
-                });
+                }));
         };
 
         auto handleOutputs = [&](const Strings & ss) {
             outputs.clear();
             for (auto & j : ss) {
                 if (outputs.find(j) != outputs.end())
-                    throw EvalError({
+                    state.debugThrowLastTrace(EvalError({
                         .msg = hintfmt("duplicate derivation output '%1%'", j),
                         .errPos = state.positions[posDrvName]
-                    });
+                    }));
                 /* !!! Check whether j is a valid attribute
                    name. */
                 /* Derivations cannot be named ‘drv’, because
                    then we'd have an attribute ‘drvPath’ in
                    the resulting set. */
                 if (j == "drv")
-                    throw EvalError({
+                    state.debugThrowLastTrace(EvalError({
                         .msg = hintfmt("invalid derivation output name 'drv'" ),
                         .errPos = state.positions[posDrvName]
-                    });
+                    }));
                 outputs.insert(j);
             }
             if (outputs.empty())
-                throw EvalError({
+                state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("derivation cannot have an empty set of outputs"),
                     .errPos = state.positions[posDrvName]
-                });
+                }));
         };
 
         try {
@@ -1154,23 +1220,23 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
 
     /* Do we have all required attributes? */
     if (drv.builder == "")
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("required attribute 'builder' missing"),
             .errPos = state.positions[posDrvName]
-        });
+        }));
 
     if (drv.platform == "")
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("required attribute 'system' missing"),
             .errPos = state.positions[posDrvName]
-        });
+        }));
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName))
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("derivation names are not allowed to end in '%s'", drvExtension),
             .errPos = state.positions[posDrvName]
-        });
+        }));
 
     if (outputHash) {
         /* Handle fixed-output derivations.
@@ -1178,10 +1244,10 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
            Ignore `__contentAddressed` because fixed output derivations are
            already content addressed. */
         if (outputs.size() != 1 || *(outputs.begin()) != "out")
-            throw Error({
+            state.debugThrowLastTrace(Error({
                 .msg = hintfmt("multiple outputs are not supported in fixed-output derivations"),
                 .errPos = state.positions[posDrvName]
-            });
+            }));
 
         auto h = newHashAllowEmpty(*outputHash, parseHashTypeOpt(outputHashAlgo));
 
@@ -1241,8 +1307,13 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
         switch (hashModulo.kind) {
         case DrvHash::Kind::Regular:
             for (auto & i : outputs) {
-                auto h = hashModulo.hashes.at(i);
+                auto h = get(hashModulo.hashes, i);
-                auto outPath = state.store->makeOutputPath(i, h, drvName);
+                if (!h)
+                    throw AssertionError({
+                        .msg = hintfmt("derivation produced no hash for output '%s'", i),
+                        .errPos = state.positions[posDrvName],
+                    });
+                auto outPath = state.store->makeOutputPath(i, *h, drvName);
                 drv.env[i] = state.store->printStorePath(outPath);
                 drv.outputs.insert_or_assign(
                     i,
@@ -1344,10 +1415,10 @@ static RegisterPrimOp primop_toPath({
 static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     if (evalSettings.pureEval)
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("'%s' is not allowed in pure evaluation mode", "builtins.storePath"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     PathSet context;
     Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context, "while evaluating the first argument passed to builtins.storePath"));
@@ -1356,10 +1427,10 @@ static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args,
        e.g. nix-push does the right thing. */
     if (!state.store->isStorePath(path)) path = canonPath(path, true);
     if (!state.store->isInStore(path))
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("path '%1%' is not in the Nix store", path),
             .errPos = state.positions[pos]
-        });
+        }));
     auto path2 = state.store->toStorePath(path).first;
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
@@ -1462,7 +1533,7 @@ static void prim_readFile(EvalState & state, const PosIdx pos, Value * * args, V
     auto path = realisePath(state, pos, *args[0]);
     auto s = readFile(path);
     if (s.find((char) 0) != std::string::npos)
-        throw Error("the contents of the file '%1%' cannot be represented as a Nix string", path);
+        state.debugThrowLastTrace(Error("the contents of the file '%1%' cannot be represented as a Nix string", path));
     StorePathSet refs;
     if (state.store->isInStore(path)) {
         try {
@@ -1509,13 +1580,12 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value * * args, V
             auto rewrites = state.realiseContext(context);
             path = rewriteStrings(path, rewrites);
         } catch (InvalidPathError & e) {
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("cannot find '%1%', since path '%2%' is not valid", path, e.path),
                 .errPos = state.positions[pos]
-            });
+            }));
         }
 
-
         searchPath.emplace_back(prefix, path);
     }
 
@@ -1536,10 +1606,10 @@ static void prim_hashFile(EvalState & state, const PosIdx pos, Value * * args, V
     auto type = state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.hashFile");
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
-        throw Error({
+        state.debugThrowLastTrace(Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = state.positions[pos]
-        });
+        }));
 
     auto path = realisePath(state, pos, *args[1]);
 
@@ -1776,13 +1846,13 @@ static void prim_toFile(EvalState & state, const PosIdx pos, Value * * args, Val
 
     for (auto path : context) {
         if (path.at(0) != '/')
-            throw EvalError( {
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt(
                     "in 'toFile': the file named '%1%' must not contain a reference "
                     "to a derivation but contains (%2%)",
                     name, path),
                 .errPos = state.positions[pos]
-            });
+            }));
         refs.insert(state.store->parseStorePath(path));
     }
 
@@ -1940,7 +2010,7 @@ static void addPath(
                 ? state.store->computeStorePathForPath(name, path, method, htSHA256, filter).first
                 : state.store->addToStore(name, path, method, htSHA256, filter, state.repair, refs);
             if (expectedHash && expectedStorePath != dstPath)
-                throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
+                state.debugThrowLastTrace(Error("store path mismatch in (possibly filtered) path added from '%s'", path));
             state.allowAndSetStorePathString(dstPath, v);
         } else
             state.allowAndSetStorePathString(*expectedStorePath, v);
@@ -2037,16 +2107,16 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
         else if (n == "sha256")
             expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `sha256` attribute passed to builtins.path"), htSHA256);
         else
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("unsupported argument '%1%' to 'addPath'", state.symbols[attr.name]),
                 .errPos = state.positions[attr.pos]
-            });
+            }));
     }
     if (path.empty())
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("missing required 'path' attribute in the first argument to builtins.path"),
             .errPos = state.positions[pos]
-        });
+        }));
     if (name.empty())
         name = baseNameOf(path);
 
@@ -2405,10 +2475,10 @@ static void prim_functionArgs(EvalState & state, const PosIdx pos, Value * * arg
         return;
     }
     if (!args[0]->isLambda())
-        throw TypeError({
+        state.debugThrowLastTrace(TypeError({
             .msg = hintfmt("'functionArgs' requires a function"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     if (!args[0]->lambda.fun->hasFormals()) {
         v.mkAttrs(&state.emptyBindings);
@@ -2496,7 +2566,7 @@ static void prim_zipAttrsWith(EvalState & state, const PosIdx pos, Value * * arg
                 attrsSeen[attr.name].first++;
         } catch (TypeError & e) {
             e.addTrace(state.positions[pos], hintfmt("while invoking '%s'", "zipAttrsWith"));
-            throw;
+            state.debugThrowLastTrace(e);
         }
     }
 
@@ -2583,10 +2653,10 @@ static void elemAt(EvalState & state, const PosIdx pos, Value & list, int n, Val
 {
     state.forceList(list, pos, "while evaluating the first argument passed to builtins.elemAt");
     if (n < 0 || (unsigned int) n >= list.listSize())
-        throw Error({
+        state.debugThrowLastTrace(Error({
             .msg = hintfmt("list index %1% is out of bounds", n),
             .errPos = state.positions[pos]
-        });
+        }));
     state.forceValue(*list.listElems()[n], pos);
     v = *list.listElems()[n];
 }
@@ -2631,10 +2701,10 @@ static void prim_tail(EvalState & state, const PosIdx pos, Value * * args, Value
 {
     state.forceList(*args[0], pos, "while evaluating the first argument passed to builtins.tail");
     if (args[0]->listSize() == 0)
-        throw Error({
+        state.debugThrowLastTrace(Error({
             .msg = hintfmt("'tail' called on an empty list"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     state.mkList(v, args[0]->listSize() - 1);
     for (unsigned int n = 0; n < v.listSize(); ++n)
@@ -2881,10 +2951,10 @@ static void prim_genList(EvalState & state, const PosIdx pos, Value * * args, Va
     auto len = state.forceInt(*args[1], pos, "while evaluating the second argument passed to builtins.genList");
 
     if (len < 0)
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("cannot create list of size %1%", len),
             .errPos = state.positions[pos]
-        });
+        }));
 
     state.mkList(v, len);
 
@@ -3099,7 +3169,7 @@ static void prim_concatMap(EvalState & state, const PosIdx pos, Value * * args,
             state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)), "while evaluating the return value of the function passed to buitlins.concatMap");
         } catch (TypeError &e) {
             e.addTrace(state.positions[pos], hintfmt("while invoking '%s'", "concatMap"));
-            throw;
+            state.debugThrowLastTrace(e);
         }
         len += lists[n].listSize();
     }
@@ -3200,10 +3270,10 @@ static void prim_div(EvalState & state, const PosIdx pos, Value * * args, Value
 
     NixFloat f2 = state.forceFloat(*args[1], pos, "while evaluating the second operand of the division");
     if (f2 == 0)
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("division by zero"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     if (args[0]->type() == nFloat || args[1]->type() == nFloat) {
         v.mkFloat(state.forceFloat(*args[0], pos, "while evaluating the first operand of the division") / f2);
@@ -3212,10 +3282,10 @@ static void prim_div(EvalState & state, const PosIdx pos, Value * * args, Value
         NixInt i2 = state.forceInt(*args[1], pos, "while evaluating the second operand of the division");
         /* Avoid division overflow as it might raise SIGFPE. */
         if (i1 == std::numeric_limits<NixInt>::min() && i2 == -1)
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("overflow in integer division"),
                 .errPos = state.positions[pos]
-            });
+            }));
 
         v.mkInt(i1 / i2);
     }
@@ -3347,10 +3417,10 @@ static void prim_substring(EvalState & state, const PosIdx pos, Value * * args,
     auto s = state.coerceToString(pos, *args[2], context, "while evaluating the third argument (the string) passed to builtins.substring");
 
     if (start < 0)
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("negative start position in 'substring'"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     v.mkString((unsigned int) start >= s->size() ? "" : s->substr(start, len), context);
 }
@@ -3398,10 +3468,10 @@ static void prim_hashString(EvalState & state, const PosIdx pos, Value * * args,
     auto type = state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.hashString");
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
-        throw Error({
+        state.debugThrowLastTrace(Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = state.positions[pos]
-        });
+        }));
 
     PathSet context; // discarded
     auto s = state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.hashString");
@@ -3468,19 +3538,18 @@ void prim_match(EvalState & state, const PosIdx pos, Value * * args, Value & v)
                 (v.listElems()[i] = state.allocValue())->mkString(match[i + 1].str());
         }
 
-    } catch (std::regex_error &e) {
+    } catch (std::regex_error & e) {
         if (e.code() == std::regex_constants::error_space) {
             // limit is _GLIBCXX_REGEX_STATE_LIMIT for libstdc++
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = state.positions[pos]
-            });
+            }));
-        } else {
+        } else
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = state.positions[pos]
-            });
+            }));
-        }
     }
 }
 
@@ -3515,7 +3584,7 @@ static RegisterPrimOp primop_match({
       builtins.match "[[:space:]]+([[:upper:]]+)[[:space:]]+" "  FOO   "
       ```
 
-      Evaluates to `[ "foo" ]`.
+      Evaluates to `[ "FOO" ]`.
     )s",
     .fun = prim_match,
 });
@@ -3573,19 +3642,18 @@ void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 
         assert(idx == 2 * len + 1);
 
-    } catch (std::regex_error &e) {
+    } catch (std::regex_error & e) {
         if (e.code() == std::regex_constants::error_space) {
             // limit is _GLIBCXX_REGEX_STATE_LIMIT for libstdc++
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = state.positions[pos]
-            });
+            }));
-        } else {
+        } else
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = state.positions[pos]
-            });
+            }));
-        }
     }
 }
 
@@ -3618,7 +3686,7 @@ static RegisterPrimOp primop_split({
       Evaluates to `[ "" [ "a" null ] "b" [ null "c" ] "" ]`.
 
       ```nix
-      builtins.split "([[:upper:]]+)" "  FOO   "
+      builtins.split "([[:upper:]]+)" " FOO "
       ```
 
       Evaluates to `[ " " [ "FOO" ] " " ]`.
@@ -3661,10 +3729,10 @@ static void prim_replaceStrings(EvalState & state, const PosIdx pos, Value * * a
     state.forceList(*args[0], pos, "while evaluating the first argument passed to builtins.replaceStrings");
     state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.replaceStrings");
     if (args[0]->listSize() != args[1]->listSize())
-        throw EvalError({
+        state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("'from' and 'to' arguments to 'replaceStrings' have different lengths"),
             .errPos = state.positions[pos]
-        });
+        }));
 
     std::vector<std::string> from;
     from.reserve(args[0]->listSize());
@@ -3882,6 +3950,18 @@ void EvalState::createBaseEnv()
         addPrimOp("__exec", 1, prim_exec);
     }
 
+    addPrimOp({
+        .fun = evalSettings.traceVerbose ? prim_trace : prim_second,
+        .arity = 2,
+        .name = "__traceVerbose",
+        .args = { "e1", "e2" },
+        .doc = R"(
+          Evaluate *e1* and print its abstract syntax representation on standard
+          error if `--trace-verbose` is enabled. Then return *e2*. This function
+          is useful for debugging.
+        )",
+    });
+
     /* Add a value containing the current Nix expression search path. */
     mkList(v, searchPath.size());
     int n = 0;
@@ -3917,7 +3997,7 @@ void EvalState::createBaseEnv()
        because attribute lookups expect it to be sorted. */
     baseEnv.values[0]->attrs->sort();
 
-    staticBaseEnv.sort();
+    staticBaseEnv->sort();
 
     /* Note: we have to initialize the 'derivation' constant *after*
        building baseEnv/staticBaseEnv because it uses 'builtins'. */

src/libexpr/primops/fetchTree.cc

@@ -108,16 +108,16 @@ static void fetchTree(
 
         if (auto aType = args[0]->attrs->get(state.sType)) {
             if (type)
-                throw Error({
+                state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("unexpected attribute 'type'"),
                     .errPos = state.positions[pos]
-                });
+                }));
             type = state.forceStringNoCtx(*aType->value, aType->pos, "while evaluating the `type` attribute passed to builtins.fetchTree");
         } else if (!type)
-            throw Error({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
                 .errPos = state.positions[pos]
-            });
+            }));
 
         attrs.emplace("type", type.value());
 
@@ -138,16 +138,16 @@ static void fetchTree(
             else if (attr.value->type() == nInt)
                 attrs.emplace(state.symbols[attr.name], uint64_t(attr.value->integer));
             else
-                throw TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
+                state.debugThrowLastTrace(TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
-                    state.symbols[attr.name], showType(*attr.value));
+                    state.symbols[attr.name], showType(*attr.value)));
         }
 
         if (!params.allowNameArgument)
             if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
-                throw Error({
+                state.debugThrowLastTrace(EvalError({
-                    .msg = hintfmt("attribute 'name' isn't supported in call to 'fetchTree'"),
+                    .msg = hintfmt("attribute 'name' isn’t supported in call to 'fetchTree'"),
                     .errPos = state.positions[pos]
-                });
+                }));
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
@@ -167,7 +167,7 @@ static void fetchTree(
         input = lookupInRegistries(state.store, input).first;
 
     if (evalSettings.pureEval && !input.isLocked())
-        throw Error("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", state.positions[pos]);
+        state.debugThrowLastTrace(EvalError("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", state.positions[pos]));
 
     auto [tree, input2] = input.fetch(state.store);
 
@@ -204,17 +204,17 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
             else if (n == "name")
                 name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the name of the content we should fetch");
             else
-                throw EvalError({
+                state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("unsupported argument '%s' to '%s'", n, who),
                     .errPos = state.positions[attr.pos]
-                });
+                }));
-            }
+        }
 
         if (!url)
-            throw EvalError({
+            state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("'url' argument required"),
                 .errPos = state.positions[pos]
-            });
+            }));
     } else
         url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");
 
@@ -226,7 +226,7 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
         name = baseNameOf(*url);
 
     if (evalSettings.pureEval && !expectedHash)
-        throw Error("in pure evaluation mode, '%s' requires a 'sha256' argument", who);
+        state.debugThrowLastTrace(EvalError("in pure evaluation mode, '%s' requires a 'sha256' argument", who));
 
     // early exit if pinned and already in the store
     if (expectedHash && expectedHash->type == htSHA256) {
@@ -253,8 +253,8 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
             ? state.store->queryPathInfo(storePath)->narHash
             : hashFile(htSHA256, state.store->toRealPath(storePath));
         if (hash != *expectedHash)
-            throw Error((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
+            state.debugThrowLastTrace(EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
-                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true));
+                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true)));
     }
 
     state.allowAndSetStorePathString(storePath, v);
@@ -362,6 +362,10 @@ static RegisterPrimOp primop_fetchGit({
           A Boolean parameter that specifies whether submodules should be
           checked out. Defaults to `false`.
 
+        - shallow\
+          A Boolean parameter that specifies whether fetching a shallow clone
+          is allowed. Defaults to `false`.
+
         - allRefs\
           Whether to fetch all refs of the repository. With this argument being
           true, it's possible to load a `rev` from *any* `ref` (by default only

src/libexpr/tests/json.cc

@@ -0,0 +1,68 @@
+#include "libexprtests.hh"
+#include "value-to-json.hh"
+
+namespace nix {
+// Testing the conversion to JSON
+
+    class JSONValueTest : public LibExprTest {
+        protected:
+            std::string getJSONValue(Value& value) {
+                std::stringstream ss;
+                PathSet ps;
+                printValueAsJSON(state, true, value, noPos, ss, ps);
+                return ss.str();
+            }
+    };
+
+    TEST_F(JSONValueTest, null) {
+        Value v;
+        v.mkNull();
+        ASSERT_EQ(getJSONValue(v), "null");
+    }
+
+    TEST_F(JSONValueTest, BoolFalse) {
+        Value v;
+        v.mkBool(false);
+        ASSERT_EQ(getJSONValue(v),"false");
+    }
+
+    TEST_F(JSONValueTest, BoolTrue) {
+        Value v;
+        v.mkBool(true);
+        ASSERT_EQ(getJSONValue(v), "true");
+    }
+
+    TEST_F(JSONValueTest, IntPositive) {
+        Value v;
+        v.mkInt(100);
+        ASSERT_EQ(getJSONValue(v), "100");
+    }
+
+    TEST_F(JSONValueTest, IntNegative) {
+        Value v;
+        v.mkInt(-100);
+        ASSERT_EQ(getJSONValue(v), "-100");
+    }
+
+    TEST_F(JSONValueTest, String) {
+        Value v;
+        v.mkString("test");
+        ASSERT_EQ(getJSONValue(v), "\"test\"");
+    }
+
+    TEST_F(JSONValueTest, StringQuotes) {
+        Value v;
+
+        v.mkString("test\"");
+        ASSERT_EQ(getJSONValue(v), "\"test\\\"\"");
+    }
+
+    // The dummy store doesn't support writing files. Fails with this exception message:
+    // C++ exception with description "error: operation 'addToStoreFromDump' is
+    // not supported by store 'dummy'" thrown in the test body.
+    TEST_F(JSONValueTest, DISABLED_Path) {
+        Value v;
+        v.mkPath("test");
+        ASSERT_EQ(getJSONValue(v), "\"/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x\"");
+    }
+} /* namespace nix */

src/libexpr/tests/libexprtests.hh

@@ -0,0 +1,136 @@
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+
+#include "value.hh"
+#include "nixexpr.hh"
+#include "eval.hh"
+#include "eval-inline.hh"
+#include "store-api.hh"
+
+
+namespace nix {
+    class LibExprTest : public ::testing::Test {
+        public:
+            static void SetUpTestSuite() {
+                initGC();
+            }
+
+        protected:
+            LibExprTest()
+                : store(openStore("dummy://"))
+                , state({}, store)
+            {
+            }
+            Value eval(std::string input, bool forceValue = true) {
+                Value v;
+                Expr * e = state.parseExprFromString(input, "");
+                assert(e);
+                state.eval(e, v);
+                if (forceValue)
+                    state.forceValue(v, noPos);
+                return v;
+            }
+
+            Symbol createSymbol(const char * value) {
+                return state.symbols.create(value);
+            }
+
+            ref<Store> store;
+            EvalState state;
+    };
+
+    MATCHER(IsListType, "") {
+        return arg != nList;
+    }
+
+    MATCHER(IsList, "") {
+        return arg.type() == nList;
+    }
+
+    MATCHER(IsString, "") {
+        return arg.type() == nString;
+    }
+
+    MATCHER(IsNull, "") {
+        return arg.type() == nNull;
+    }
+
+    MATCHER(IsThunk, "") {
+        return arg.type() == nThunk;
+    }
+
+    MATCHER(IsAttrs, "") {
+        return arg.type() == nAttrs;
+    }
+
+    MATCHER_P(IsStringEq, s, fmt("The string is equal to \"%1%\"", s)) {
+        if (arg.type() != nString) {
+            return false;
+        }
+        return std::string_view(arg.string.s) == s;
+    }
+
+    MATCHER_P(IsIntEq, v, fmt("The string is equal to \"%1%\"", v)) {
+        if (arg.type() != nInt) {
+            return false;
+        }
+        return arg.integer == v;
+    }
+
+    MATCHER_P(IsFloatEq, v, fmt("The float is equal to \"%1%\"", v)) {
+        if (arg.type() != nFloat) {
+            return false;
+        }
+        return arg.fpoint == v;
+    }
+
+    MATCHER(IsTrue, "") {
+        if (arg.type() != nBool) {
+            return false;
+        }
+        return arg.boolean == true;
+    }
+
+    MATCHER(IsFalse, "") {
+        if (arg.type() != nBool) {
+            return false;
+        }
+        return arg.boolean == false;
+    }
+
+    MATCHER_P(IsPathEq, p, fmt("Is a path equal to \"%1%\"", p)) {
+            if (arg.type() != nPath) {
+                *result_listener << "Expected a path got " << arg.type();
+                return false;
+            } else if (std::string_view(arg.string.s) != p) {
+                *result_listener << "Expected a path that equals \"" << p << "\" but got: " << arg.string.s;
+                return false;
+            }
+            return true;
+    }
+
+
+    MATCHER_P(IsListOfSize, n, fmt("Is a list of size [%1%]", n)) {
+        if (arg.type() != nList) {
+            *result_listener << "Expected list got " << arg.type();
+            return false;
+        } else if (arg.listSize() != (size_t)n) {
+            *result_listener << "Expected as list of size " << n << " got " << arg.listSize();
+            return false;
+        }
+        return true;
+    }
+
+    MATCHER_P(IsAttrsOfSize, n, fmt("Is a set of size [%1%]", n)) {
+        if (arg.type() != nAttrs) {
+            *result_listener << "Expexted set got " << arg.type();
+            return false;
+        } else if (arg.attrs->size() != (size_t)n) {
+            *result_listener << "Expected a set with " << n << " attributes but got " << arg.attrs->size();
+            return false;
+        }
+        return true;
+    }
+
+
+} /* namespace nix */

src/libexpr/tests/local.mk

@@ -0,0 +1,15 @@
+check: libexpr-tests_RUN
+
+programs += libexpr-tests
+
+libexpr-tests_DIR := $(d)
+
+libexpr-tests_INSTALL_DIR :=
+
+libexpr-tests_SOURCES := $(wildcard $(d)/*.cc)
+
+libexpr-tests_CXXFLAGS += -I src/libexpr -I src/libutil -I src/libstore -I src/libexpr/tests
+
+libexpr-tests_LIBS = libexpr libutil libstore libfetchers
+
+libexpr-tests_LDFLAGS := $(GTEST_LIBS) -lgmock

src/libexpr/tests/primops.cc

@@ -0,0 +1,839 @@
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include "libexprtests.hh"
+
+namespace nix {
+    class CaptureLogger : public Logger
+    {
+        std::ostringstream oss;
+
+        public:
+            CaptureLogger() {}
+
+            std::string get() const {
+                return oss.str();
+            }
+
+            void log(Verbosity lvl, const FormatOrString & fs) override {
+                oss << fs.s << std::endl;
+            }
+
+            void logEI(const ErrorInfo & ei) override {
+                showErrorInfo(oss, ei, loggerSettings.showTrace.get());
+            }
+    };
+
+    class CaptureLogging {
+        Logger * oldLogger;
+        std::unique_ptr<CaptureLogger> tempLogger;
+        public:
+            CaptureLogging() : tempLogger(std::make_unique<CaptureLogger>()) {
+                oldLogger = logger;
+                logger = tempLogger.get();
+            }
+
+            ~CaptureLogging() {
+                logger = oldLogger;
+            }
+
+            std::string get() const {
+                return tempLogger->get();
+            }
+    };
+
+
+    // Testing eval of PrimOp's
+    class PrimOpTest : public LibExprTest {};
+
+
+    TEST_F(PrimOpTest, throw) {
+        ASSERT_THROW(eval("throw \"foo\""), ThrownError);
+    }
+
+    TEST_F(PrimOpTest, abort) {
+        ASSERT_THROW(eval("abort \"abort\""), Abort);
+    }
+
+    TEST_F(PrimOpTest, ceil) {
+        auto v = eval("builtins.ceil 1.9");
+        ASSERT_THAT(v, IsIntEq(2));
+    }
+
+    TEST_F(PrimOpTest, floor) {
+        auto v = eval("builtins.floor 1.9");
+        ASSERT_THAT(v, IsIntEq(1));
+    }
+
+    TEST_F(PrimOpTest, tryEvalFailure) {
+        auto v = eval("builtins.tryEval (throw \"\")");
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+        auto s = createSymbol("success");
+        auto p = v.attrs->get(s);
+        ASSERT_NE(p, nullptr);
+        ASSERT_THAT(*p->value, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, tryEvalSuccess) {
+        auto v = eval("builtins.tryEval 123");
+        ASSERT_THAT(v, IsAttrs());
+        auto s = createSymbol("success");
+        auto p = v.attrs->get(s);
+        ASSERT_NE(p, nullptr);
+        ASSERT_THAT(*p->value, IsTrue());
+        s = createSymbol("value");
+        p = v.attrs->get(s);
+        ASSERT_NE(p, nullptr);
+        ASSERT_THAT(*p->value, IsIntEq(123));
+    }
+
+    TEST_F(PrimOpTest, getEnv) {
+        setenv("_NIX_UNIT_TEST_ENV_VALUE", "test value", 1);
+        auto v = eval("builtins.getEnv \"_NIX_UNIT_TEST_ENV_VALUE\"");
+        ASSERT_THAT(v, IsStringEq("test value"));
+    }
+
+    TEST_F(PrimOpTest, seq) {
+        ASSERT_THROW(eval("let x = throw \"test\"; in builtins.seq x { }"), ThrownError);
+    }
+
+    TEST_F(PrimOpTest, seqNotDeep) {
+        auto v = eval("let x = { z =  throw \"test\"; }; in builtins.seq x { }");
+        ASSERT_THAT(v, IsAttrs());
+    }
+
+    TEST_F(PrimOpTest, deepSeq) {
+        ASSERT_THROW(eval("let x = { z =  throw \"test\"; }; in builtins.deepSeq x { }"), ThrownError);
+    }
+
+    TEST_F(PrimOpTest, trace) {
+        CaptureLogging l;
+        auto v = eval("builtins.trace \"test string 123\" 123");
+        ASSERT_THAT(v, IsIntEq(123));
+        auto text = l.get();
+        ASSERT_NE(text.find("test string 123"), std::string::npos);
+    }
+
+    TEST_F(PrimOpTest, placeholder) {
+        auto v = eval("builtins.placeholder \"out\"");
+        ASSERT_THAT(v, IsStringEq("/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9"));
+    }
+
+    TEST_F(PrimOpTest, baseNameOf) {
+        auto v = eval("builtins.baseNameOf /some/path");
+        ASSERT_THAT(v, IsStringEq("path"));
+    }
+
+    TEST_F(PrimOpTest, dirOf) {
+        auto v = eval("builtins.dirOf /some/path");
+        ASSERT_THAT(v, IsPathEq("/some"));
+    }
+
+    TEST_F(PrimOpTest, attrValues) {
+        auto v = eval("builtins.attrValues { x = \"foo\";  a = 1; }");
+        ASSERT_THAT(v, IsListOfSize(2));
+        ASSERT_THAT(*v.listElems()[0], IsIntEq(1));
+        ASSERT_THAT(*v.listElems()[1], IsStringEq("foo"));
+    }
+
+    TEST_F(PrimOpTest, getAttr) {
+        auto v = eval("builtins.getAttr \"x\" { x = \"foo\"; }");
+        ASSERT_THAT(v, IsStringEq("foo"));
+    }
+
+    TEST_F(PrimOpTest, getAttrNotFound) {
+        // FIXME: TypeError is really bad here, also the error wording is worse
+        // than on Nix <=2.3
+        ASSERT_THROW(eval("builtins.getAttr \"y\" { }"), TypeError);
+    }
+
+    TEST_F(PrimOpTest, unsafeGetAttrPos) {
+        // The `y` attribute is at position
+        const char* expr = "builtins.unsafeGetAttrPos \"y\" { y = \"x\"; }";
+        auto v = eval(expr);
+        ASSERT_THAT(v, IsAttrsOfSize(3));
+
+        auto file = v.attrs->find(createSymbol("file"));
+        ASSERT_NE(file, nullptr);
+        // FIXME: The file when running these tests is the input string?!?
+        ASSERT_THAT(*file->value, IsStringEq(expr));
+
+        auto line = v.attrs->find(createSymbol("line"));
+        ASSERT_NE(line, nullptr);
+        ASSERT_THAT(*line->value, IsIntEq(1));
+
+        auto column = v.attrs->find(createSymbol("column"));
+        ASSERT_NE(column, nullptr);
+        ASSERT_THAT(*column->value, IsIntEq(33));
+    }
+
+    TEST_F(PrimOpTest, hasAttr) {
+        auto v = eval("builtins.hasAttr \"x\" { x = 1; }");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, hasAttrNotFound) {
+        auto v = eval("builtins.hasAttr \"x\" { }");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, isAttrs) {
+        auto v = eval("builtins.isAttrs {}");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, isAttrsFalse) {
+        auto v = eval("builtins.isAttrs null");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, removeAttrs) {
+        auto v = eval("builtins.removeAttrs { x = 1; } [\"x\"]");
+        ASSERT_THAT(v, IsAttrsOfSize(0));
+    }
+
+    TEST_F(PrimOpTest, removeAttrsRetains) {
+        auto v = eval("builtins.removeAttrs { x = 1; y = 2; } [\"x\"]");
+        ASSERT_THAT(v, IsAttrsOfSize(1));
+        ASSERT_NE(v.attrs->find(createSymbol("y")), nullptr);
+    }
+
+    TEST_F(PrimOpTest, listToAttrsEmptyList) {
+        auto v = eval("builtins.listToAttrs []");
+        ASSERT_THAT(v, IsAttrsOfSize(0));
+        ASSERT_EQ(v.type(), nAttrs);
+        ASSERT_EQ(v.attrs->size(), 0);
+    }
+
+    TEST_F(PrimOpTest, listToAttrsNotFieldName) {
+        ASSERT_THROW(eval("builtins.listToAttrs [{}]"), Error);
+    }
+
+    TEST_F(PrimOpTest, listToAttrs) {
+        auto v = eval("builtins.listToAttrs [ { name = \"key\"; value = 123; } ]");
+        ASSERT_THAT(v, IsAttrsOfSize(1));
+        auto key = v.attrs->find(createSymbol("key"));
+        ASSERT_NE(key, nullptr);
+        ASSERT_THAT(*key->value, IsIntEq(123));
+    }
+
+    TEST_F(PrimOpTest, intersectAttrs) {
+        auto v = eval("builtins.intersectAttrs { a = 1; b = 2; } { b = 3; c = 4; }");
+        ASSERT_THAT(v, IsAttrsOfSize(1));
+        auto b = v.attrs->find(createSymbol("b"));
+        ASSERT_NE(b, nullptr);
+        ASSERT_THAT(*b->value, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, catAttrs) {
+        auto v = eval("builtins.catAttrs \"a\" [{a = 1;} {b = 0;} {a = 2;}]");
+        ASSERT_THAT(v, IsListOfSize(2));
+        ASSERT_THAT(*v.listElems()[0], IsIntEq(1));
+        ASSERT_THAT(*v.listElems()[1], IsIntEq(2));
+    }
+
+    TEST_F(PrimOpTest, functionArgs) {
+        auto v = eval("builtins.functionArgs ({ x, y ? 123}: 1)");
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+
+        auto x = v.attrs->find(createSymbol("x"));
+        ASSERT_NE(x, nullptr);
+        ASSERT_THAT(*x->value, IsFalse());
+
+        auto y = v.attrs->find(createSymbol("y"));
+        ASSERT_NE(y, nullptr);
+        ASSERT_THAT(*y->value, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, mapAttrs) {
+        auto v = eval("builtins.mapAttrs (name: value: value * 10) { a = 1; b = 2; }");
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+
+        auto a = v.attrs->find(createSymbol("a"));
+        ASSERT_NE(a, nullptr);
+        ASSERT_THAT(*a->value, IsThunk());
+        state.forceValue(*a->value, noPos);
+        ASSERT_THAT(*a->value, IsIntEq(10));
+
+        auto b = v.attrs->find(createSymbol("b"));
+        ASSERT_NE(b, nullptr);
+        ASSERT_THAT(*b->value, IsThunk());
+        state.forceValue(*b->value, noPos);
+        ASSERT_THAT(*b->value, IsIntEq(20));
+    }
+
+    TEST_F(PrimOpTest, isList) {
+        auto v = eval("builtins.isList []");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, isListFalse) {
+        auto v = eval("builtins.isList null");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, elemtAt) {
+        auto v = eval("builtins.elemAt [0 1 2 3] 3");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, elemtAtOutOfBounds) {
+        ASSERT_THROW(eval("builtins.elemAt [0 1 2 3] 5"), Error);
+    }
+
+    TEST_F(PrimOpTest, head) {
+        auto v = eval("builtins.head [ 3 2 1 0 ]");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, headEmpty) {
+        ASSERT_THROW(eval("builtins.head [ ]"), Error);
+    }
+
+    TEST_F(PrimOpTest, headWrongType) {
+        ASSERT_THROW(eval("builtins.head { }"), Error);
+    }
+
+    TEST_F(PrimOpTest, tail) {
+        auto v = eval("builtins.tail [ 3 2 1 0 ]");
+        ASSERT_THAT(v, IsListOfSize(3));
+        for (const auto [n, elem] : enumerate(v.listItems()))
+            ASSERT_THAT(*elem, IsIntEq(2 - static_cast<int>(n)));
+    }
+
+    TEST_F(PrimOpTest, tailEmpty) {
+        ASSERT_THROW(eval("builtins.tail []"), Error);
+    }
+
+    TEST_F(PrimOpTest, map) {
+        auto v = eval("map (x: \"foo\" + x) [ \"bar\" \"bla\" \"abc\" ]");
+        ASSERT_THAT(v, IsListOfSize(3));
+        auto elem = v.listElems()[0];
+        ASSERT_THAT(*elem, IsThunk());
+        state.forceValue(*elem, noPos);
+        ASSERT_THAT(*elem, IsStringEq("foobar"));
+
+        elem = v.listElems()[1];
+        ASSERT_THAT(*elem, IsThunk());
+        state.forceValue(*elem, noPos);
+        ASSERT_THAT(*elem, IsStringEq("foobla"));
+
+        elem = v.listElems()[2];
+        ASSERT_THAT(*elem, IsThunk());
+        state.forceValue(*elem, noPos);
+        ASSERT_THAT(*elem, IsStringEq("fooabc"));
+    }
+
+    TEST_F(PrimOpTest, filter) {
+        auto v = eval("builtins.filter (x: x == 2) [ 3 2 3 2 3 2 ]");
+        ASSERT_THAT(v, IsListOfSize(3));
+        for (const auto elem : v.listItems())
+            ASSERT_THAT(*elem, IsIntEq(2));
+    }
+
+    TEST_F(PrimOpTest, elemTrue) {
+        auto v = eval("builtins.elem 3 [ 1 2 3 4 5 ]");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, elemFalse) {
+        auto v = eval("builtins.elem 6 [ 1 2 3 4 5 ]");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, concatLists) {
+        auto v = eval("builtins.concatLists [[1 2] [3 4]]");
+        ASSERT_THAT(v, IsListOfSize(4));
+        for (const auto [i, elem] : enumerate(v.listItems()))
+            ASSERT_THAT(*elem, IsIntEq(static_cast<int>(i)+1));
+    }
+
+    TEST_F(PrimOpTest, length) {
+        auto v = eval("builtins.length [ 1 2 3 ]");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, foldStrict) {
+        auto v = eval("builtins.foldl' (a: b: a + b) 0 [1 2 3]");
+        ASSERT_THAT(v, IsIntEq(6));
+    }
+
+    TEST_F(PrimOpTest, anyTrue) {
+        auto v = eval("builtins.any (x: x == 2) [ 1 2 3 ]");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, anyFalse) {
+        auto v = eval("builtins.any (x: x == 5) [ 1 2 3 ]");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, allTrue) {
+        auto v = eval("builtins.all (x: x > 0) [ 1 2 3 ]");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, allFalse) {
+        auto v = eval("builtins.all (x: x <= 0) [ 1 2 3 ]");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, genList) {
+        auto v = eval("builtins.genList (x: x + 1) 3");
+        ASSERT_EQ(v.type(), nList);
+        ASSERT_EQ(v.listSize(), 3);
+        for (const auto [i, elem] : enumerate(v.listItems())) {
+            ASSERT_THAT(*elem, IsThunk());
+            state.forceValue(*elem, noPos);
+            ASSERT_THAT(*elem, IsIntEq(static_cast<int>(i)+1));
+        }
+    }
+
+    TEST_F(PrimOpTest, sortLessThan) {
+        auto v = eval("builtins.sort builtins.lessThan [ 483 249 526 147 42 77 ]");
+        ASSERT_EQ(v.type(), nList);
+        ASSERT_EQ(v.listSize(), 6);
+
+        const std::vector<int> numbers = { 42, 77, 147, 249, 483, 526 };
+        for (const auto [n, elem] : enumerate(v.listItems()))
+            ASSERT_THAT(*elem, IsIntEq(numbers[n]));
+    }
+
+    TEST_F(PrimOpTest, partition) {
+        auto v = eval("builtins.partition (x: x > 10) [1 23 9 3 42]");
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+
+        auto right = v.attrs->get(createSymbol("right"));
+        ASSERT_NE(right, nullptr);
+        ASSERT_THAT(*right->value, IsListOfSize(2));
+        ASSERT_THAT(*right->value->listElems()[0], IsIntEq(23));
+        ASSERT_THAT(*right->value->listElems()[1], IsIntEq(42));
+
+        auto wrong = v.attrs->get(createSymbol("wrong"));
+        ASSERT_NE(wrong, nullptr);
+        ASSERT_EQ(wrong->value->type(), nList);
+        ASSERT_EQ(wrong->value->listSize(), 3);
+        ASSERT_THAT(*wrong->value, IsListOfSize(3));
+        ASSERT_THAT(*wrong->value->listElems()[0], IsIntEq(1));
+        ASSERT_THAT(*wrong->value->listElems()[1], IsIntEq(9));
+        ASSERT_THAT(*wrong->value->listElems()[2], IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, concatMap) {
+        auto v = eval("builtins.concatMap (x: x ++ [0]) [ [1 2] [3 4] ]");
+        ASSERT_EQ(v.type(), nList);
+        ASSERT_EQ(v.listSize(), 6);
+
+        const std::vector<int> numbers = { 1, 2, 0, 3, 4, 0 };
+        for (const auto [n, elem] : enumerate(v.listItems()))
+            ASSERT_THAT(*elem, IsIntEq(numbers[n]));
+    }
+
+    TEST_F(PrimOpTest, addInt) {
+        auto v = eval("builtins.add 3 5");
+        ASSERT_THAT(v, IsIntEq(8));
+    }
+
+    TEST_F(PrimOpTest, addFloat) {
+        auto v = eval("builtins.add 3.0 5.0");
+        ASSERT_THAT(v, IsFloatEq(8.0));
+    }
+
+    TEST_F(PrimOpTest, addFloatToInt) {
+        auto v = eval("builtins.add 3.0 5");
+        ASSERT_THAT(v, IsFloatEq(8.0));
+
+        v = eval("builtins.add 3 5.0");
+        ASSERT_THAT(v, IsFloatEq(8.0));
+    }
+
+    TEST_F(PrimOpTest, subInt) {
+        auto v = eval("builtins.sub 5 2");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, subFloat) {
+        auto v = eval("builtins.sub 5.0 2.0");
+        ASSERT_THAT(v, IsFloatEq(3.0));
+    }
+
+    TEST_F(PrimOpTest, subFloatFromInt) {
+        auto v = eval("builtins.sub 5.0 2");
+        ASSERT_THAT(v, IsFloatEq(3.0));
+
+        v = eval("builtins.sub 4 2.0");
+        ASSERT_THAT(v, IsFloatEq(2.0));
+    }
+
+    TEST_F(PrimOpTest, mulInt) {
+        auto v = eval("builtins.mul 3 5");
+        ASSERT_THAT(v, IsIntEq(15));
+    }
+
+    TEST_F(PrimOpTest, mulFloat) {
+        auto v = eval("builtins.mul 3.0 5.0");
+        ASSERT_THAT(v, IsFloatEq(15.0));
+    }
+
+    TEST_F(PrimOpTest, mulFloatMixed) {
+        auto v = eval("builtins.mul 3 5.0");
+        ASSERT_THAT(v, IsFloatEq(15.0));
+
+        v = eval("builtins.mul 2.0 5");
+        ASSERT_THAT(v, IsFloatEq(10.0));
+    }
+
+    TEST_F(PrimOpTest, divInt) {
+        auto v = eval("builtins.div 5 (-1)");
+        ASSERT_THAT(v, IsIntEq(-5));
+    }
+
+    TEST_F(PrimOpTest, divIntZero) {
+        ASSERT_THROW(eval("builtins.div 5 0"), EvalError);
+    }
+
+    TEST_F(PrimOpTest, divFloat) {
+        auto v = eval("builtins.div 5.0 (-1)");
+        ASSERT_THAT(v, IsFloatEq(-5.0));
+    }
+
+    TEST_F(PrimOpTest, divFloatZero) {
+        ASSERT_THROW(eval("builtins.div 5.0 0.0"), EvalError);
+    }
+
+    TEST_F(PrimOpTest, bitOr) {
+        auto v = eval("builtins.bitOr 1 2");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(PrimOpTest, bitXor) {
+        auto v = eval("builtins.bitXor 3 2");
+        ASSERT_THAT(v, IsIntEq(1));
+    }
+
+    TEST_F(PrimOpTest, lessThanFalse) {
+        auto v = eval("builtins.lessThan 3 1");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(PrimOpTest, lessThanTrue) {
+        auto v = eval("builtins.lessThan 1 3");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(PrimOpTest, toStringAttrsThrows) {
+        ASSERT_THROW(eval("builtins.toString {}"), EvalError);
+    }
+
+    TEST_F(PrimOpTest, toStringLambdaThrows) {
+        ASSERT_THROW(eval("builtins.toString (x: x)"), EvalError);
+    }
+
+    class ToStringPrimOpTest :
+        public PrimOpTest,
+        public testing::WithParamInterface<std::tuple<std::string, std::string_view>>
+        {};
+
+    TEST_P(ToStringPrimOpTest, toString) {
+        const auto [input, output] = GetParam();
+        auto v = eval(input);
+        ASSERT_THAT(v, IsStringEq(output));
+    }
+
+#define CASE(input, output) (std::make_tuple(std::string_view("builtins.toString " input), std::string_view(output)))
+    INSTANTIATE_TEST_SUITE_P(
+            toString,
+            ToStringPrimOpTest,
+            testing::Values(
+                CASE(R"("foo")", "foo"),
+                CASE(R"(1)", "1"),
+                CASE(R"([1 2 3])", "1 2 3"),
+                CASE(R"(.123)", "0.123000"),
+                CASE(R"(true)", "1"),
+                CASE(R"(false)", ""),
+                CASE(R"(null)", ""),
+                CASE(R"({ v = "bar"; __toString = self: self.v; })", "bar"),
+                CASE(R"({ v = "bar"; __toString = self: self.v; outPath = "foo"; })", "bar"),
+                CASE(R"({ outPath = "foo"; })", "foo"),
+                CASE(R"(./test)", "/test")
+            )
+    );
+#undef CASE
+
+    TEST_F(PrimOpTest, substring){
+        auto v = eval("builtins.substring 0 3 \"nixos\"");
+        ASSERT_THAT(v, IsStringEq("nix"));
+    }
+
+    TEST_F(PrimOpTest, substringSmallerString){
+        auto v = eval("builtins.substring 0 3 \"n\"");
+        ASSERT_THAT(v, IsStringEq("n"));
+    }
+
+    TEST_F(PrimOpTest, substringEmptyString){
+        auto v = eval("builtins.substring 1 3 \"\"");
+        ASSERT_THAT(v, IsStringEq(""));
+    }
+
+    TEST_F(PrimOpTest, stringLength) {
+        auto v = eval("builtins.stringLength \"123\"");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+    TEST_F(PrimOpTest, hashStringMd5) {
+        auto v = eval("builtins.hashString \"md5\" \"asdf\"");
+        ASSERT_THAT(v, IsStringEq("912ec803b2ce49e4a541068d495ab570"));
+    }
+
+    TEST_F(PrimOpTest, hashStringSha1) {
+        auto v = eval("builtins.hashString \"sha1\" \"asdf\"");
+        ASSERT_THAT(v, IsStringEq("3da541559918a808c2402bba5012f6c60b27661c"));
+    }
+
+    TEST_F(PrimOpTest, hashStringSha256) {
+        auto v = eval("builtins.hashString \"sha256\" \"asdf\"");
+        ASSERT_THAT(v, IsStringEq("f0e4c2f76c58916ec258f246851bea091d14d4247a2fc3e18694461b1816e13b"));
+    }
+
+    TEST_F(PrimOpTest, hashStringSha512) {
+        auto v = eval("builtins.hashString \"sha512\" \"asdf\"");
+        ASSERT_THAT(v, IsStringEq("401b09eab3c013d4ca54922bb802bec8fd5318192b0a75f201d8b3727429080fb337591abd3e44453b954555b7a0812e1081c39b740293f765eae731f5a65ed1"));
+    }
+
+    TEST_F(PrimOpTest, hashStringInvalidHashType) {
+        ASSERT_THROW(eval("builtins.hashString \"foobar\" \"asdf\""), Error);
+    }
+
+    TEST_F(PrimOpTest, nixPath) {
+        auto v = eval("builtins.nixPath");
+        ASSERT_EQ(v.type(), nList);
+        // We can't test much more as currently the EvalSettings are a global
+        // that we can't easily swap / replace
+    }
+
+    TEST_F(PrimOpTest, langVersion) {
+        auto v = eval("builtins.langVersion");
+        ASSERT_EQ(v.type(), nInt);
+    }
+
+    TEST_F(PrimOpTest, storeDir) {
+        auto v = eval("builtins.storeDir");
+        ASSERT_THAT(v, IsStringEq("/nix/store"));
+    }
+
+    TEST_F(PrimOpTest, nixVersion) {
+        auto v = eval("builtins.nixVersion");
+        ASSERT_THAT(v, IsStringEq(nixVersion));
+    }
+
+    TEST_F(PrimOpTest, currentSystem) {
+        auto v = eval("builtins.currentSystem");
+        ASSERT_THAT(v, IsStringEq(settings.thisSystem.get()));
+    }
+
+    TEST_F(PrimOpTest, derivation) {
+        auto v = eval("derivation");
+        ASSERT_EQ(v.type(), nFunction);
+        ASSERT_TRUE(v.isLambda());
+        ASSERT_NE(v.lambda.fun, nullptr);
+        ASSERT_TRUE(v.lambda.fun->hasFormals());
+    }
+
+    TEST_F(PrimOpTest, currentTime) {
+        auto v = eval("builtins.currentTime");
+        ASSERT_EQ(v.type(), nInt);
+        ASSERT_TRUE(v.integer > 0);
+    }
+
+    TEST_F(PrimOpTest, splitVersion) {
+        auto v = eval("builtins.splitVersion \"1.2.3git\"");
+        ASSERT_THAT(v, IsListOfSize(4));
+
+        const std::vector<std::string_view> strings = { "1", "2", "3", "git" };
+        for (const auto [n, p] : enumerate(v.listItems()))
+            ASSERT_THAT(*p, IsStringEq(strings[n]));
+    }
+
+    class CompareVersionsPrimOpTest :
+        public PrimOpTest,
+        public testing::WithParamInterface<std::tuple<std::string, const int>>
+        {};
+
+    TEST_P(CompareVersionsPrimOpTest, compareVersions) {
+        auto [expression, expectation] = GetParam();
+        auto v = eval(expression);
+        ASSERT_THAT(v, IsIntEq(expectation));
+    }
+
+#define CASE(a, b, expected) (std::make_tuple("builtins.compareVersions \"" #a "\" \"" #b "\"", expected))
+    INSTANTIATE_TEST_SUITE_P(
+            compareVersions,
+            CompareVersionsPrimOpTest,
+            testing::Values(
+                // The first two are weird cases. Intuition tells they should
+                // be the same but they aren't.
+                CASE(1.0, 1.0.0, -1),
+                CASE(1.0.0, 1.0, 1),
+                // the following are from the nix-env manual:
+                CASE(1.0, 2.3, -1),
+                CASE(2.1, 2.3, -1),
+                CASE(2.3, 2.3, 0),
+                CASE(2.5, 2.3, 1),
+                CASE(3.1, 2.3, 1),
+                CASE(2.3.1, 2.3, 1),
+                CASE(2.3.1, 2.3a, 1),
+                CASE(2.3pre1, 2.3, -1),
+                CASE(2.3pre3, 2.3pre12, -1),
+                CASE(2.3a, 2.3c, -1),
+                CASE(2.3pre1, 2.3c, -1),
+                CASE(2.3pre1, 2.3q, -1)
+            )
+    );
+#undef CASE
+
+
+  class ParseDrvNamePrimOpTest :
+      public PrimOpTest,
+      public testing::WithParamInterface<std::tuple<std::string, std::string_view, std::string_view>>
+      {};
+
+    TEST_P(ParseDrvNamePrimOpTest, parseDrvName) {
+        auto [input, expectedName, expectedVersion] = GetParam();
+        const auto expr = fmt("builtins.parseDrvName \"%1%\"", input);
+        auto v = eval(expr);
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+
+        auto name = v.attrs->find(createSymbol("name"));
+        ASSERT_TRUE(name);
+        ASSERT_THAT(*name->value, IsStringEq(expectedName));
+
+        auto version = v.attrs->find(createSymbol("version"));
+        ASSERT_TRUE(version);
+        ASSERT_THAT(*version->value, IsStringEq(expectedVersion));
+    }
+
+    INSTANTIATE_TEST_SUITE_P(
+            parseDrvName,
+            ParseDrvNamePrimOpTest,
+            testing::Values(
+                std::make_tuple("nix-0.12pre12876", "nix", "0.12pre12876"),
+                std::make_tuple("a-b-c-1234pre5+git", "a-b-c", "1234pre5+git")
+            )
+    );
+
+    TEST_F(PrimOpTest, replaceStrings) {
+        // FIXME: add a test that verifies the string context is as expected
+        auto v = eval("builtins.replaceStrings [\"oo\" \"a\"] [\"a\" \"i\"] \"foobar\"");
+        ASSERT_EQ(v.type(), nString);
+        ASSERT_EQ(v.string.s, std::string_view("fabir"));
+    }
+
+    TEST_F(PrimOpTest, concatStringsSep) {
+        // FIXME: add a test that verifies the string context is as expected
+        auto v = eval("builtins.concatStringsSep \"%\" [\"foo\" \"bar\" \"baz\"]");
+        ASSERT_EQ(v.type(), nString);
+        ASSERT_EQ(std::string_view(v.string.s), "foo%bar%baz");
+    }
+
+    TEST_F(PrimOpTest, split1) {
+        // v = [ "" [ "a" ] "c" ]
+        auto v = eval("builtins.split \"(a)b\" \"abc\"");
+        ASSERT_THAT(v, IsListOfSize(3));
+
+        ASSERT_THAT(*v.listElems()[0], IsStringEq(""));
+
+        ASSERT_THAT(*v.listElems()[1], IsListOfSize(1));
+        ASSERT_THAT(*v.listElems()[1]->listElems()[0], IsStringEq("a"));
+
+        ASSERT_THAT(*v.listElems()[2], IsStringEq("c"));
+    }
+
+    TEST_F(PrimOpTest, split2) {
+        // v is expected to be a list [ "" [ "a" ] "b" [ "c"] "" ]
+        auto v = eval("builtins.split \"([ac])\" \"abc\"");
+        ASSERT_THAT(v, IsListOfSize(5));
+
+        ASSERT_THAT(*v.listElems()[0], IsStringEq(""));
+
+        ASSERT_THAT(*v.listElems()[1], IsListOfSize(1));
+        ASSERT_THAT(*v.listElems()[1]->listElems()[0], IsStringEq("a"));
+
+        ASSERT_THAT(*v.listElems()[2], IsStringEq("b"));
+
+        ASSERT_THAT(*v.listElems()[3], IsListOfSize(1));
+        ASSERT_THAT(*v.listElems()[3]->listElems()[0], IsStringEq("c"));
+
+        ASSERT_THAT(*v.listElems()[4], IsStringEq(""));
+    }
+
+    TEST_F(PrimOpTest, split3) {
+        auto v = eval("builtins.split \"(a)|(c)\" \"abc\"");
+        ASSERT_THAT(v, IsListOfSize(5));
+
+        // First list element
+        ASSERT_THAT(*v.listElems()[0], IsStringEq(""));
+
+        // 2nd list element is a list [ "" null ]
+        ASSERT_THAT(*v.listElems()[1], IsListOfSize(2));
+        ASSERT_THAT(*v.listElems()[1]->listElems()[0], IsStringEq("a"));
+        ASSERT_THAT(*v.listElems()[1]->listElems()[1], IsNull());
+
+        // 3rd element
+        ASSERT_THAT(*v.listElems()[2], IsStringEq("b"));
+
+        // 4th element is a list: [ null "c" ]
+        ASSERT_THAT(*v.listElems()[3], IsListOfSize(2));
+        ASSERT_THAT(*v.listElems()[3]->listElems()[0], IsNull());
+        ASSERT_THAT(*v.listElems()[3]->listElems()[1], IsStringEq("c"));
+
+        // 5th element is the empty string
+        ASSERT_THAT(*v.listElems()[4], IsStringEq(""));
+    }
+
+    TEST_F(PrimOpTest, split4) {
+        auto v = eval("builtins.split \"([[:upper:]]+)\" \" FOO \"");
+        ASSERT_THAT(v, IsListOfSize(3));
+        auto first = v.listElems()[0];
+        auto second = v.listElems()[1];
+        auto third = v.listElems()[2];
+
+        ASSERT_THAT(*first, IsStringEq(" "));
+
+        ASSERT_THAT(*second, IsListOfSize(1));
+        ASSERT_THAT(*second->listElems()[0], IsStringEq("FOO"));
+
+        ASSERT_THAT(*third, IsStringEq(" "));
+    }
+
+    TEST_F(PrimOpTest, match1) {
+        auto v = eval("builtins.match \"ab\" \"abc\"");
+        ASSERT_THAT(v, IsNull());
+    }
+
+    TEST_F(PrimOpTest, match2) {
+        auto v = eval("builtins.match \"abc\" \"abc\"");
+        ASSERT_THAT(v, IsListOfSize(0));
+    }
+
+    TEST_F(PrimOpTest, match3) {
+        auto v = eval("builtins.match \"a(b)(c)\" \"abc\"");
+        ASSERT_THAT(v, IsListOfSize(2));
+        ASSERT_THAT(*v.listElems()[0], IsStringEq("b"));
+        ASSERT_THAT(*v.listElems()[1], IsStringEq("c"));
+    }
+
+    TEST_F(PrimOpTest, match4) {
+        auto v = eval("builtins.match \"[[:space:]]+([[:upper:]]+)[[:space:]]+\" \"  FOO   \"");
+        ASSERT_THAT(v, IsListOfSize(1));
+        ASSERT_THAT(*v.listElems()[0], IsStringEq("FOO"));
+    }
+
+    TEST_F(PrimOpTest, attrNames) {
+        auto v = eval("builtins.attrNames { x = 1; y = 2; z = 3; a = 2; }");
+        ASSERT_THAT(v, IsListOfSize(4));
+
+        // ensure that the list is sorted
+        const std::vector<std::string_view> expected { "a", "x", "y", "z" };
+        for (const auto [n, elem] : enumerate(v.listItems()))
+            ASSERT_THAT(*elem, IsStringEq(expected[n]));
+    }
+} /* namespace nix */

src/libexpr/tests/trivial.cc

@@ -0,0 +1,196 @@
+#include "libexprtests.hh"
+
+namespace nix {
+    // Testing of trivial expressions
+    class TrivialExpressionTest : public LibExprTest {};
+
+    TEST_F(TrivialExpressionTest, true) {
+        auto v = eval("true");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(TrivialExpressionTest, false) {
+        auto v = eval("false");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(TrivialExpressionTest, null) {
+        auto v = eval("null");
+        ASSERT_THAT(v, IsNull());
+    }
+
+    TEST_F(TrivialExpressionTest, 1) {
+        auto v = eval("1");
+        ASSERT_THAT(v, IsIntEq(1));
+    }
+
+    TEST_F(TrivialExpressionTest, 1plus1) {
+        auto v = eval("1+1");
+        ASSERT_THAT(v, IsIntEq(2));
+    }
+
+    TEST_F(TrivialExpressionTest, minus1) {
+        auto v = eval("-1");
+        ASSERT_THAT(v, IsIntEq(-1));
+    }
+
+    TEST_F(TrivialExpressionTest, 1minus1) {
+        auto v = eval("1-1");
+        ASSERT_THAT(v, IsIntEq(0));
+    }
+
+    TEST_F(TrivialExpressionTest, lambdaAdd) {
+        auto v = eval("let add = a: b: a + b; in add 1 2");
+        ASSERT_THAT(v, IsIntEq(3));
+    }
+
+    TEST_F(TrivialExpressionTest, list) {
+        auto v = eval("[]");
+        ASSERT_THAT(v, IsListOfSize(0));
+    }
+
+    TEST_F(TrivialExpressionTest, attrs) {
+        auto v = eval("{}");
+        ASSERT_THAT(v, IsAttrsOfSize(0));
+    }
+
+    TEST_F(TrivialExpressionTest, float) {
+        auto v = eval("1.234");
+        ASSERT_THAT(v, IsFloatEq(1.234));
+    }
+
+    TEST_F(TrivialExpressionTest, updateAttrs) {
+        auto v = eval("{ a = 1; } // { b = 2; a = 3; }");
+        ASSERT_THAT(v, IsAttrsOfSize(2));
+        auto a = v.attrs->find(createSymbol("a"));
+        ASSERT_NE(a, nullptr);
+        ASSERT_THAT(*a->value, IsIntEq(3));
+
+        auto b = v.attrs->find(createSymbol("b"));
+        ASSERT_NE(b, nullptr);
+        ASSERT_THAT(*b->value, IsIntEq(2));
+    }
+
+    TEST_F(TrivialExpressionTest, hasAttrOpFalse) {
+        auto v = eval("{} ? a");
+        ASSERT_THAT(v, IsFalse());
+    }
+
+    TEST_F(TrivialExpressionTest, hasAttrOpTrue) {
+        auto v = eval("{ a = 123; } ? a");
+        ASSERT_THAT(v, IsTrue());
+    }
+
+    TEST_F(TrivialExpressionTest, withFound) {
+        auto v = eval("with { a = 23; }; a");
+        ASSERT_THAT(v, IsIntEq(23));
+    }
+
+    TEST_F(TrivialExpressionTest, withNotFound) {
+        ASSERT_THROW(eval("with {}; a"), Error);
+    }
+
+    TEST_F(TrivialExpressionTest, withOverride) {
+        auto v = eval("with { a = 23; }; with { a = 42; }; a");
+        ASSERT_THAT(v, IsIntEq(42));
+    }
+
+    TEST_F(TrivialExpressionTest, letOverWith) {
+        auto v = eval("let a = 23; in with { a = 1; }; a");
+        ASSERT_THAT(v, IsIntEq(23));
+    }
+
+    TEST_F(TrivialExpressionTest, multipleLet) {
+        auto v = eval("let a = 23; in let a = 42; in a");
+        ASSERT_THAT(v, IsIntEq(42));
+    }
+
+    TEST_F(TrivialExpressionTest, defaultFunctionArgs) {
+        auto v = eval("({ a ? 123 }: a) {}");
+        ASSERT_THAT(v, IsIntEq(123));
+    }
+
+    TEST_F(TrivialExpressionTest, defaultFunctionArgsOverride) {
+        auto v = eval("({ a ? 123 }: a) { a = 5; }");
+        ASSERT_THAT(v, IsIntEq(5));
+    }
+
+    TEST_F(TrivialExpressionTest, defaultFunctionArgsCaptureBack) {
+        auto v = eval("({ a ? 123 }@args: args) {}");
+        ASSERT_THAT(v, IsAttrsOfSize(0));
+    }
+
+    TEST_F(TrivialExpressionTest, defaultFunctionArgsCaptureFront) {
+        auto v = eval("(args@{ a ? 123 }: args) {}");
+        ASSERT_THAT(v, IsAttrsOfSize(0));
+    }
+
+    TEST_F(TrivialExpressionTest, assertThrows) {
+        ASSERT_THROW(eval("let x = arg: assert arg == 1; 123; in x 2"), Error);
+    }
+
+    TEST_F(TrivialExpressionTest, assertPassed) {
+        auto v = eval("let x = arg: assert arg == 1; 123; in x 1");
+        ASSERT_THAT(v, IsIntEq(123));
+    }
+
+    class AttrSetMergeTrvialExpressionTest :
+        public TrivialExpressionTest,
+        public testing::WithParamInterface<const char*>
+        {};
+
+    TEST_P(AttrSetMergeTrvialExpressionTest, attrsetMergeLazy) {
+        // Usually Nix rejects duplicate keys in an attrset but it does allow
+        // so if it is an attribute set that contains disjoint sets of keys.
+        // The below is equivalent to `{a.b = 1; a.c = 2; }`.
+        // The attribute set `a` will be a Thunk at first as the attribuets
+        // have to be merged (or otherwise computed) and that is done in a lazy
+        // manner.
+
+        auto expr = GetParam();
+        auto v = eval(expr);
+        ASSERT_THAT(v, IsAttrsOfSize(1));
+
+        auto a = v.attrs->find(createSymbol("a"));
+        ASSERT_NE(a, nullptr);
+
+        ASSERT_THAT(*a->value, IsThunk());
+        state.forceValue(*a->value, noPos);
+
+        ASSERT_THAT(*a->value, IsAttrsOfSize(2));
+
+        auto b = a->value->attrs->find(createSymbol("b"));
+        ASSERT_NE(b, nullptr);
+        ASSERT_THAT(*b->value, IsIntEq(1));
+
+        auto c = a->value->attrs->find(createSymbol("c"));
+        ASSERT_NE(c, nullptr);
+        ASSERT_THAT(*c->value, IsIntEq(2));
+    }
+
+    INSTANTIATE_TEST_SUITE_P(
+            attrsetMergeLazy,
+            AttrSetMergeTrvialExpressionTest,
+            testing::Values(
+                "{ a.b = 1; a.c = 2; }",
+                "{ a = { b = 1; }; a = { c = 2; }; }"
+            )
+    );
+
+    TEST_F(TrivialExpressionTest, functor) {
+        auto v = eval("{ __functor = self: arg: self.v + arg; v = 10; } 5");
+        ASSERT_THAT(v, IsIntEq(15));
+    }
+
+    TEST_F(TrivialExpressionTest, bindOr) {
+        auto v = eval("{ or = 1; }");
+        ASSERT_THAT(v, IsAttrsOfSize(1));
+        auto b = v.attrs->find(createSymbol("or"));
+        ASSERT_NE(b, nullptr);
+        ASSERT_THAT(*b->value, IsIntEq(1));
+    }
+
+    TEST_F(TrivialExpressionTest, orCantBeUsed) {
+        ASSERT_THROW(eval("let or = 1; in or"), Error);
+    }
+} /* namespace nix */

src/libexpr/value-to-json.cc

@@ -10,7 +10,7 @@
 namespace nix {
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context)
+    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context, bool copyToStore)
 {
     checkInterrupt();
 
@@ -32,7 +32,10 @@ void printValueAsJSON(EvalState & state, bool strict,
             break;
 
         case nPath:
-            out.write(state.copyPathToStore(context, v.path));
+            if (copyToStore)
+                out.write(state.copyPathToStore(context, v.path));
+            else
+                out.write(v.path);
             break;
 
         case nNull:
@@ -54,10 +57,10 @@ void printValueAsJSON(EvalState & state, bool strict,
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
                     auto placeholder(obj.placeholder(j));
-                    printValueAsJSON(state, strict, *a.value, a.pos, placeholder, context);
+                    printValueAsJSON(state, strict, *a.value, a.pos, placeholder, context, copyToStore);
                 }
             } else
-                printValueAsJSON(state, strict, *i->value, i->pos, out, context);
+                printValueAsJSON(state, strict, *i->value, i->pos, out, context, copyToStore);
             break;
         }
 
@@ -65,13 +68,13 @@ void printValueAsJSON(EvalState & state, bool strict,
             auto list(out.list());
             for (auto elem : v.listItems()) {
                 auto placeholder(list.placeholder());
-                printValueAsJSON(state, strict, *elem, pos, placeholder, context);
+                printValueAsJSON(state, strict, *elem, pos, placeholder, context, copyToStore);
             }
             break;
         }
 
         case nExternal:
-            v.external->printValueAsJSON(state, strict, out, context);
+            v.external->printValueAsJSON(state, strict, out, context, copyToStore);
             break;
 
         case nFloat:
@@ -85,21 +88,22 @@ void printValueAsJSON(EvalState & state, bool strict,
                 .errPos = state.positions[v.determinePos(pos)]
             });
             e.addTrace(state.positions[pos], hintfmt("message for the trace"));
+            state.debugThrowLastTrace(e);
             throw e;
     }
 }
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, std::ostream & str, PathSet & context)
+    Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore)
 {
     JSONPlaceholder out(str);
-    printValueAsJSON(state, strict, v, pos, out, context);
+    printValueAsJSON(state, strict, v, pos, out, context, copyToStore);
 }
 
 void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
-    JSONPlaceholder & out, PathSet & context) const
+    JSONPlaceholder & out, PathSet & context, bool copyToStore) const
 {
-    throw TypeError("cannot convert %1% to JSON", showType());
+    state.debugThrowLastTrace(TypeError("cannot convert %1% to JSON", showType()));
 }
 
 

src/libexpr/value-to-json.hh

@@ -11,9 +11,9 @@ namespace nix {
 class JSONPlaceholder;
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context);
+    Value & v, const PosIdx pos, JSONPlaceholder & out, PathSet & context, bool copyToStore = true);
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, std::ostream & str, PathSet & context);
+    Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore = true);
 
 }