Merge branch 'master' into referenceablePaths

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,28 @@
+# Motivation
+<!-- Briefly explain what the change is about and why it is desirable. -->
+
+# Context
+<!-- Provide context. Reference open issues if available. -->
+
+<!-- Non-trivial change: Briefly outline the implementation strategy. -->
+
+<!-- Invasive change: Discuss alternative designs or approaches you considered. -->
+
+<!-- Large change: Provide instructions to reviewers how to read the diff. -->
+
+# Checklist for maintainers
+
+<!-- Contributors: please leave this as is -->
+
+Maintainers: tick if completed or explain if not relevant
+
+ - [ ] agreed on idea
+ - [ ] agreed on implementation strategy
+ - [ ] tests, as appropriate
+   - functional tests - `tests/**.sh`
+   - unit tests - `src/*/tests`
+   - integration tests - `tests/nixos/*`
+ - [ ] documentation in the manual
+ - [ ] code and comments are self-explanatory
+ - [ ] commit message explains why the change was made
+ - [ ] new feature or bug fix: updated release notes

.github/workflows/backport.yml

@@ -21,7 +21,7 @@ jobs:
           fetch-depth: 0
       - name: Create backport PRs
         # should be kept in sync with `version`
-        uses: zeebe-io/backport-action@v1.0.1
+        uses: zeebe-io/backport-action@v1.1.0
         with:
           # Config README: https://github.com/zeebe-io/backport-action#backport-action
           github_token: ${{ secrets.GITHUB_TOKEN }}

.version

@@ -1 +1 @@
-2.13.0
+2.14.0

boehmgc-coroutine-sp-fallback.diff

@@ -0,0 +1,77 @@
+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 b5d71e62..aed7b0bf 100644
+--- a/pthread_stop_world.c
++++ b/pthread_stop_world.c
+@@ -768,6 +768,8 @@ STATIC void GC_restart_handler(int sig)
+ /* world is stopped.  Should not fail if it isn't.                      */
+ GC_INNER void GC_push_all_stacks(void)
+ {
++    size_t stack_limit;
++    pthread_attr_t pattr;
+     GC_bool found_me = FALSE;
+     size_t nthreads = 0;
+     int i;
+@@ -851,6 +853,31 @@ GC_INNER void GC_push_all_stacks(void)
+           hi = p->altstack + p->altstack_size;
+           /* FIXME: Need to scan the normal stack too, but how ? */
+           /* FIXME: Assume stack grows down */
++        } else {
++          if (pthread_getattr_np(p->id, &pattr)) {
++            ABORT("GC_push_all_stacks: pthread_getattr_np failed!");
++          }
++          if (pthread_attr_getstacksize(&pattr, &stack_limit)) {
++            ABORT("GC_push_all_stacks: pthread_attr_getstacksize failed!");
++          }
++          if (pthread_attr_destroy(&pattr)) {
++            ABORT("GC_push_all_stacks: pthread_attr_destroy failed!");
++          }
++          // 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.
++          #ifndef STACK_GROWS_UP
++            if (lo >= hi || lo < hi - stack_limit) { // sp outside stack
++              lo = hi - stack_limit;
++            }
++          #else
++          #error "STACK_GROWS_UP not supported in boost_coroutine2 (as of june 2021), so we don't support it in Nix."
++          #endif
+         }
+         GC_push_all_stack_sections(lo, hi, traced_stack_sect);
+ #       ifdef STACK_GROWS_UP

configure.ac

@@ -274,6 +274,12 @@ fi
 PKG_CHECK_MODULES([GTEST], [gtest_main])
 
 
+# Look for rapidcheck.
+# No pkg-config yet, https://github.com/emil-e/rapidcheck/issues/302
+AC_CHECK_HEADERS([rapidcheck/gtest.h], [], [], [#include <gtest/gtest.h>])
+AC_CHECK_LIB([rapidcheck], [])
+
+
 # Look for nlohmann/json.
 PKG_CHECK_MODULES([NLOHMANN_JSON], [nlohmann_json >= 3.9])
 

doc/manual/book.toml

@@ -10,3 +10,12 @@ git-repository-url = "https://github.com/NixOS/nix"
 [preprocessor.anchors]
 renderers = ["html"]
 command = "jq --from-file doc/manual/anchors.jq"
+
+[output.linkcheck]
+# no Internet during the build (in the sandbox)
+follow-web-links = false
+
+# mdbook-linkcheck does not understand [foo]{#bar} style links, resulting in
+# excessive "Potential incomplete link" warnings. No other kind of warning was
+# produced at the time of writing.
+warning-policy = "ignore"

doc/manual/local.mk

@@ -50,11 +50,16 @@ $(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 { toplevel = builtins.readFile $<; }'
+	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-manpage.nix { toplevel = builtins.readFile $<; }'
+	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	$(trace-gen) sed -i $@.tmp/*.md -e 's^@docroot@^../..^g'
+	@mv $@.tmp $@
 
 $(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
-	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-options.nix (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp
+	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-options.nix (builtins.fromJSON (builtins.readFile $<))' \
+	  | sed -e 's^@docroot@^..^g'>> $@.tmp
 	@mv $@.tmp $@
 
 $(d)/nix.json: $(bindir)/nix
@@ -67,7 +72,9 @@ $(d)/conf-file.json: $(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/language/builtins-prefix.md > $@.tmp
-	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' >> $@.tmp
+	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' \
+	  | sed -e 's^@docroot@^..^g' >> $@.tmp
 	@cat doc/manual/src/language/builtins-suffix.md >> $@.tmp
 	@mv $@.tmp $@
 
@@ -102,6 +109,12 @@ doc/manual/generated/man1/nix3-manpages: $(d)/src/command-ref/new-cli
 	@touch $@
 
 $(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
+	$(trace-gen) \
+	  set -euo pipefail; \
+	  RUST_LOG=warn mdbook build doc/manual -d $(DESTDIR)$(docdir)/manual.tmp 2>&1 \
+		  | { grep -Fv "because fragment resolution isn't implemented" || :; }
+	@rm -rf $(DESTDIR)$(docdir)/manual
+	@mv $(DESTDIR)$(docdir)/manual.tmp/html $(DESTDIR)$(docdir)/manual
+	@rm -rf $(DESTDIR)$(docdir)/manual.tmp
 
 endif

doc/manual/src/SUMMARY.md.in

@@ -67,6 +67,7 @@
   - [CLI guideline](contributing/cli-guideline.md)
 - [Release Notes](release-notes/release-notes.md)
   - [Release X.Y (202?-??-??)](release-notes/rl-next.md)
+  - [Release 2.13 (2023-01-17)](release-notes/rl-2.13.md)
   - [Release 2.12 (2022-12-06)](release-notes/rl-2.12.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)

doc/manual/src/architecture/architecture.md

@@ -68,7 +68,7 @@ It can also execute build plans to produce new data, which are made available to
 A build plan itself is a series of *build tasks*, together with their build inputs.
 
 > **Important**
-> A build task in Nix is called [derivation](../glossary#gloss-derivation).
+> A build task in Nix is called [derivation](../glossary.md#gloss-derivation).
 
 Each build task has a special build input executed as *build instructions* in order to perform the build.
 The result of a build task can be input to another build task.

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

@@ -11,7 +11,7 @@ Most Nix commands interpret the following environment variables:
     expressions using [paths](../language/values.md#type-path)
     enclosed in angle brackets (i.e., `<path>`),
     e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
-    [`-I` option](./opt-common#opt-I).
+    [`-I` option](./opt-common.md#opt-I).
 
   - [`NIX_IGNORE_SYMLINK_STORE`]{#env-NIX_IGNORE_SYMLINK_STORE}\
     Normally, the Nix store directory (typically `/nix/store`) is not

doc/manual/src/command-ref/nix-copy-closure.md

@@ -49,7 +49,7 @@ authentication, you can avoid typing the passphrase with `ssh-agent`.
   - `--include-outputs`\
     Also copy the outputs of [store derivation]s included in the closure.
 
-    [store derivation]: ../../glossary.md#gloss-store-derivation
+    [store derivation]: ../glossary.md#gloss-store-derivation
 
   - `--use-substitutes` / `-s`\
     Attempt to download missing paths on the target machine using Nix’s

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

@@ -66,11 +66,11 @@ The operation `--realise` essentially “builds” the specified store
 paths. Realisation is a somewhat overloaded term:
 
   - If the store path is a *derivation*, realisation ensures that the
-    output paths of the derivation are [valid](../glossary.md) (i.e.,
+    output paths of the derivation are [valid] (i.e.,
     the output path and its closure exist in the file system). This
     can be done in several ways. First, it is possible that the
     outputs are already valid, in which case we are done
-    immediately. Otherwise, there may be [substitutes](../glossary.md)
+    immediately. Otherwise, there may be [substitutes]
     that produce the outputs (e.g., by downloading them). Finally, the
     outputs can be produced by running the build task described
     by the derivation.
@@ -82,6 +82,9 @@ paths. Realisation is a somewhat overloaded term:
     produced through substitutes. If there are no (successful)
     substitutes, realisation fails.
 
+[valid]: ../glossary.md#gloss-validity
+[substitutes]: ../glossary.md#gloss-substitute
+
 The output path of each derivation is printed on standard output. (For
 non-derivations argument, the argument itself is printed.)
 
@@ -155,6 +158,12 @@ To test whether a previously-built derivation is deterministic:
 $ nix-build '<nixpkgs>' -A hello --check -K
 ```
 
+Use [`--read-log`](#operation---read-log) to show the stderr and stdout of a build:
+
+```console
+$ nix-store --read-log $(nix-instantiate ./test.nix)
+```
+
 # Operation `--serve`
 
 ## Synopsis
@@ -289,8 +298,8 @@ error: cannot delete path `/nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4'
 
 ## Description
 
-The operation `--query` displays various bits of information about the
+The operation `--query` displays information about [store path]s.
-store paths . The queries are described below. At most one query can be
+The queries are described below. At most one query can be
 specified. The default query is `--outputs`.
 
 The paths *paths* may also be symlinks from outside of the Nix store, to
@@ -310,12 +319,12 @@ symlink.
 ## Queries
 
   - `--outputs`\
-    Prints out the [output paths](../glossary.md) of the store
+    Prints out the [output path]s of the store
     derivations *paths*. These are the paths that will be produced when
     the derivation is built.
 
   - `--requisites`; `-R`\
-    Prints out the [closure](../glossary.md) of the store path *paths*.
+    Prints out the [closure] of the given *paths*.
 
     This query has one option:
 
@@ -332,10 +341,12 @@ symlink.
     derivation and specifying the option `--include-outputs`.
 
   - `--references`\
-    Prints the set of [references](../glossary.md) of the store paths
+    Prints the set of [references]s of the store paths
     *paths*, that is, their immediate dependencies. (For *all*
     dependencies, use `--requisites`.)
 
+    [reference]: ../glossary.md#gloss-reference
+
   - `--referrers`\
     Prints the set of *referrers* of the store paths *paths*, that is,
     the store paths currently existing in the Nix store that refer to
@@ -350,11 +361,13 @@ symlink.
     in the Nix store that are dependent on *paths*.
 
   - `--deriver`; `-d`\
-    Prints the [deriver](../glossary.md) of the store paths *paths*. If
+    Prints the [deriver] of the store paths *paths*. If
     the path has no deriver (e.g., if it is a source file), or if the
     deriver is not known (e.g., in the case of a binary-only
     deployment), the string `unknown-deriver` is printed.
 
+    [deriver]: ../glossary.md#gloss-deriver
+
   - `--graph`\
     Prints the references graph of the store paths *paths* in the format
     of the `dot` tool of AT\&T's [Graphviz

doc/manual/src/contributing/hacking.md

@@ -92,7 +92,8 @@ $ nix develop
 
 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.
+[googletest](https://google.github.io/googletest/) and
+[rapidcheck](https://github.com/emil-e/rapidcheck) frameworks.
 
 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.
 
@@ -249,3 +250,36 @@ search/replaced in it for each new build.
 The installer now supports a `--tarball-url-prefix` flag which _may_ have
 solved this need?
 -->
+
+### Checking links in the manual
+
+The build checks for broken internal links.
+This happens late in the process, so `nix build` is not suitable for iterating.
+To build the manual incrementally, run:
+
+```console
+make html -j $NIX_BUILD_CORES
+```
+
+In order to reflect changes to the [Makefile], clear all generated files before re-building:
+
+[Makefile]: https://github.com/NixOS/nix/blob/master/doc/manual/local.mk
+
+```console
+rm $(git ls-files doc/manual/ -o | grep -F '.md') && rmdir doc/manual/src/command-ref/new-cli && make html -j $NIX_BUILD_CORES
+```
+
+[`mdbook-linkcheck`] does not implement checking [URI fragments] yet.
+
+[`mdbook-linkcheck`]: https://github.com/Michael-F-Bryan/mdbook-linkcheck
+[URI fragments]: https://en.m.wikipedia.org/wiki/URI_fragment
+
+#### `@docroot@` variable
+
+`@docroot@` provides a base path for links that occur in reusable snippets or other documentation that doesn't have a base path of its own.
+
+If a broken link occurs in a snippet that was inserted into multiple generated files in different directories, use `@docroot@` to reference the `doc/manual/src` directory.
+
+If the `@docroot@` literal appears in an error message from the `mdbook-linkcheck` tool, the `@docroot@` replacement needs to be applied to the generated source file that mentions it.
+See existing `@docroot@` logic in the [Makefile].
+Regular markdown files used for the manual have a base path of their own and they can use relative paths instead of `@docroot@`.

doc/manual/src/glossary.md

@@ -19,6 +19,17 @@
 
     [store derivation]: #gloss-store-derivation
 
+  - [realise]{#gloss-realise}, realisation\
+    Ensure a [store path] is [valid][validity].
+
+    This means either running the `builder` executable as specified in the corresponding [derivation] or fetching a pre-built [store object] from a [substituter].
+
+    See [`nix-build`](./command-ref/nix-build.md) and [`nix-store --realise`](./command-ref/nix-store.md#operation---realise).
+
+    See [`nix build`](./command-ref/new-cli/nix3-build.md) (experimental).
+
+    [realise]: #gloss-realise
+
   - [content-addressed derivation]{#gloss-content-addressed-derivation}\
     A derivation which has the
     [`__contentAddressed`](./language/advanced-attributes.md#adv-attr-__contentAddressed)
@@ -101,6 +112,8 @@
     copy store objects it doesn't have.  For details, see the
     [`substituters` option](./command-ref/conf-file.md#conf-substituters).
 
+    [substituter]: #gloss-substituter
+
   - [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
@@ -143,19 +156,25 @@
     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`.
 
+    [closure]: #gloss-closure
+
   - [output path]{#gloss-output-path}\
     A [store path] produced by a [derivation].
 
     [output path]: #gloss-output-path
 
   - [deriver]{#gloss-deriver}\
-    The deriver of an *output path* is the store
+    The [store derivation] that produced an [output path].
-    derivation that built it.
 
   - [validity]{#gloss-validity}\
-    A store path is considered *valid* if it exists in the file system,
+    A store path is valid if all [store object]s in its [closure] can be read from the [store].
-    is listed in the Nix database as being valid, and if all paths in
+
-    its closure are also valid.
+    For a local store, this means:
+    - The store path leads to an existing [store object] in that [store].
+    - The store path is listed in the Nix database as being valid.
+    - All paths in the store path's [closure] are valid.
+
+    [validity]: #gloss-validity
 
   - [user environment]{#gloss-user-env}\
     An automatically generated store object that consists of a set of

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

@@ -120,10 +120,10 @@ sudo rm -rf /nix /etc/nix /etc/profile/nix.sh ~root/.nix-profile ~root/.nix-defe
 Remove build users and their group:
 
 ```console
-for i in $(seq 30001 30032); do
+for i in $(seq 1 32); do
-  sudo userdel $i
+  sudo userdel nixbld$i
 done
-sudo groupdel 30000
+sudo groupdel nixbld
 ```
 
 There may also be references to Nix in

doc/manual/src/language/index.md

@@ -191,12 +191,12 @@ This is an incomplete overview of language features, by example.
  <tr>
   <td>
 
-   <nixpkgs>
+   `<nixpkgs>`
 
   </td>
   <td>
 
-   Search path. Value determined by [`$NIX_PATH` environment variable](../command-ref/env-common.md#env-NIX_PATH).
+   Search path for Nix files. Value determined by [`$NIX_PATH` environment variable](../command-ref/env-common.md#env-NIX_PATH).
 
   </td>
  </tr>

doc/manual/src/language/operators.md

@@ -1,28 +1,167 @@
 # Operators
 
-The table below lists the operators in the Nix language, in
+| Name                                   | Syntax                                     | Associativity | Precedence |
-order of precedence (from strongest to weakest binding).
+|----------------------------------------|--------------------------------------------|---------------|------------|
+| [Attribute selection]                  | *attrset* `.` *attrpath* \[ `or` *expr* \] | none          | 1          |
+| Function application                   | *func* *expr*                              | left          | 2          |
+| [Arithmetic negation][arithmetic]      | `-` *number*                               | none          | 3          |
+| [Has attribute]                        | *attrset* `?` *attrpath*                   | none          | 4          |
+| List concatenation                     | *list* `++` *list*                         | right         | 5          |
+| [Multiplication][arithmetic]           | *number* `*` *number*                      | left          | 6          |
+| [Division][arithmetic]                 | *number* `/` *number*                      | left          | 6          |
+| [Subtraction][arithmetic]              | *number* `-` *number*                      | left          | 7          |
+| [Addition][arithmetic]                 | *number* `+` *number*                      | left          | 7          |
+| [String concatenation]                 | *string* `+` *string*                      | left          | 7          |
+| [Path concatenation]                   | *path* `+` *path*                          | left          | 7          |
+| [Path and string concatenation]        | *path* `+` *string*                        | left          | 7          |
+| [String and path concatenation]        | *string* `+` *path*                        | left          | 7          |
+| Logical negation (`NOT`)               | `!` *bool*                                 | none          | 8          |
+| [Update]                               | *attrset* `//` *attrset*                   | right         | 9          |
+| [Less than][Comparison]                | *expr* `<` *expr*                          | none          | 10         |
+| [Less than or equal to][Comparison]    | *expr* `<=` *expr*                         | none          | 10         |
+| [Greater than][Comparison]             | *expr* `>` *expr*                          | none          | 10         |
+| [Greater than or equal to][Comparison] | *expr* `>=` *expr*                         | none          | 10         |
+| [Equality]                             | *expr* `==` *expr*                         | none          | 11         |
+| Inequality                             | *expr* `!=` *expr*                         | none          | 11         |
+| Logical conjunction (`AND`)            | *bool* `&&` *bool*                         | left          | 12         |
+| Logical disjunction (`OR`)             | *bool* `\|\|` *bool*                       | left          | 13         |
+| [Logical implication]                  | *bool* `->` *bool*                         | none          | 14         |
+
+[string]: ./values.md#type-string
+[path]: ./values.md#type-path
+[number]: ./values.md#type-number
+[list]: ./values.md#list
+[attribute set]: ./values.md#attribute-set
+
+## Attribute selection
+
+Select the attribute denoted by attribute path *attrpath* from [attribute set] *attrset*.
+If the attribute doesn’t exist, return *value* if provided, otherwise abort evaluation.
+
+<!-- FIXME: the following should to into its own language syntax section, but that needs more work to fit in well -->
+
+An attribute path is a dot-separated list of attribute names.
+An attribute name can be an identifier or a string.
+
+> *attrpath* = *name* [ `.` *name* ]...
+> *name* = *identifier* | *string*
+> *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*`
+
+[Attribute selection]: #attribute-selection
+
+## Has attribute
+
+> *attrset* `?` *attrpath*
+
+Test whether [attribute set] *attrset* contains the attribute denoted by *attrpath*.
+The result is a [Boolean] value.
+
+[Boolean]: ./values.md#type-boolean
+
+[Has attribute]: #has-attribute
+
+## Arithmetic
+
+Numbers are type-compatible:
+Pure integer operations will always return integers, whereas any operation involving at least one floating point number return a floating point number.
+
+See also [Comparison] and [Equality].
+
+The `+` operator is overloaded to also work on strings and paths.
+
+[arithmetic]: #arithmetic
+
+## String concatenation
+
+> *string* `+` *string*
+
+Concatenate two [string]s and merge their string contexts.
+
+[String concatenation]: #string-concatenation
+
+## Path concatenation
+
+> *path* `+` *path*
+
+Concatenate two [path]s.
+The result is a path.
+
+[Path concatenation]: #path-concatenation
+
+## Path and string concatenation
+
+> *path* + *string*
+
+Concatenate *[path]* with *[string]*.
+The result is a path.
+
+> **Note**
+>
+> The string must not have a string context that refers to a [store path].
+
+[Path and string concatenation]: #path-and-string-concatenation
+
+## String and path concatenation
+
+> *string* + *path*
+
+Concatenate *[string]* with *[path]*.
+The result is a string.
+
+> **Important**
+>
+> The file or directory at *path* must exist and is copied to the [store].
+> The path appears in the result as the corresponding [store path].
+
+[store path]: ../glossary.md#gloss-store-path
+[store]: ../glossary.md#gloss-store
+
+[Path and string concatenation]: #path-and-string-concatenation
+
+## Update
+
+> *attrset1* // *attrset2*
+
+Update [attribute set] *attrset1* with names and values from *attrset2*.
+
+The returned attribute set will have of all the attributes in *attrset1* and *attrset2*.
+If an attribute name is present in both, the attribute value from the latter is taken.
+
+[Update]: #update
+
+## Comparison
+
+Comparison is
+
+- [arithmetic] for [number]s 
+- lexicographic for [string]s and [path]s
+- item-wise lexicographic for [list]s:
+  elements at the same index in both lists are compared according to their type and skipped if they are equal.
+
+All comparison operators are implemented in terms of `<`, and the following equivalencies hold:
+
+| comparison   | implementation        |
+|--------------|-----------------------|
+| *a* `<=` *b* | `! (` *b* `<` *a* `)` |
+| *a* `>`  *b* |       *b* `<` *a*     |
+| *a* `>=` *b* | `! (` *a* `<` *b* `)` |
+
+[Comparison]: #comparison-operators
+
+## Equality
+
+- [Attribute sets][attribute set] and [list]s are compared recursively, and therefore are fully evaluated.
+- Comparison of [function]s always returns `false`.
+- Numbers are type-compatible, see [arithmetic] operators.
+- Floating point numbers only differ up to a limited precision.
+
+[function]: ./constructs.md#functions
+
+[Equality]: #equality
+
+## Logical implication
+
+Equivalent to `!`*b1* `||` *b2*.
+
+[Logical implication]: #logical-implication
 
-| Name                     | Syntax                              | Associativity | Description                                                                                                                                                                                                                   | Precedence |
-| ------------------------ | ----------------------------------- | ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------- |
-| Select                   | *e* `.` *attrpath* \[ `or` *def* \] | none          | Select attribute denoted by the attribute path *attrpath* from set *e*. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return *def* if provided, otherwise abort evaluation. | 1          |
-| Application              | *e1* *e2*                           | left          | Call function *e1* with argument *e2*.                                                                                                                                                                                        | 2          |
-| Arithmetic Negation      | `-` *e*                             | none          | Arithmetic negation.                                                                                                                                                                                                          | 3          |
-| Has Attribute            | *e* `?` *attrpath*                  | none          | Test whether set *e* contains the attribute denoted by *attrpath*; return `true` or `false`.                                                                                                                                  | 4          |
-| List Concatenation       | *e1* `++` *e2*                      | right         | List concatenation.                                                                                                                                                                                                           | 5          |
-| Multiplication           | *e1* `*` *e2*,                      | left          | Arithmetic multiplication.                                                                                                                                                                                                    | 6          |
-| Division                 | *e1* `/` *e2*                       | left          | Arithmetic division.                                                                                                                                                                                                          | 6          |
-| Addition                 | *e1* `+` *e2*                       | left          | Arithmetic addition.                                                                                                                                                                                                          | 7          |
-| Subtraction              | *e1* `-` *e2*                       | left          | Arithmetic subtraction.                                                                                                                                                                                                       | 7          |
-| String Concatenation     | *string1* `+` *string2*             | left          | String concatenation.                                                                                                                                                                                                         | 7          |
-| Not                      | `!` *e*                             | none          | Boolean negation.                                                                                                                                                                                                             | 8          |
-| Update                   | *e1* `//` *e2*                      | right         | Return a set consisting of the attributes in *e1* and *e2* (with the latter taking precedence over the former in case of equally named attributes).                                                                           | 9          |
-| Less Than                | *e1* `<` *e2*,                      | none          | Arithmetic/lexicographic comparison.                                                                                                                                                                                                        | 10         |
-| Less Than or Equal To    | *e1* `<=` *e2*                      | none          | Arithmetic/lexicographic comparison.                                                                                                                                                                                                        | 10         |
-| Greater Than             | *e1* `>` *e2*                       | none          | Arithmetic/lexicographic comparison.                                                                                                                                                                                                        | 10         |
-| Greater Than or Equal To | *e1* `>=` *e2*                      | none          | Arithmetic/lexicographic comparison.                                                                                                                                                                                                        | 10         |
-| Equality                 | *e1* `==` *e2*                      | none          | Equality.                                                                                                                                                                                                                     | 11         |
-| Inequality               | *e1* `!=` *e2*                      | none          | Inequality.                                                                                                                                                                                                                   | 11         |
-| Logical AND              | *e1* `&&` *e2*                      | left          | Logical AND.                                                                                                                                                                                                                  | 12         |
-| Logical OR               | *e1* <code>&#124;&#124;</code> *e2* | left          | Logical OR.                                                                                                                                                                                                                   | 13         |
-| Logical Implication      | *e1* `->` *e2*                      | none          | Logical implication (equivalent to <code>!e1 &#124;&#124; e2</code>).                                                                                                                                                                            | 14         |

doc/manual/src/language/values.md

@@ -85,9 +85,10 @@
   Numbers, which can be *integers* (like `123`) or *floating point*
   (like `123.43` or `.27e13`).
 
-  Numbers are type-compatible: pure integer operations will always
+  See [arithmetic] and [comparison] operators for semantics.
-  return integers, whereas any operation involving at least one
+
-  floating point number will have a floating point number as a result.
+  [arithmetic]: ./operators.md#arithmetic
+  [comparison]: ./operators.md#comparison
 
 - <a id="type-path" href="#type-path">Path</a>
 

doc/manual/src/package-management/binary-cache-substituter.md

@@ -32,13 +32,13 @@ which should print something like:
     Priority: 30
 
 On the client side, you can tell Nix to use your binary cache using
-`--option extra-binary-caches`, e.g.:
+`--substituters`, e.g.:
 
 ```console
-$ nix-env -iA nixpkgs.firefox --option extra-binary-caches http://avalon:8080/
+$ nix-env -iA nixpkgs.firefox --substituters http://avalon:8080/
 ```
 
-The option `extra-binary-caches` tells Nix to use this binary cache in
+The option `substituters` tells Nix to use this binary cache in
 addition to your default caches, such as <https://cache.nixos.org>.
 Thus, for any path in the closure of Firefox, Nix will first check if
 the path is available on the server `avalon` or another binary caches.
@@ -47,4 +47,4 @@ If not, it will fall back to building from source.
 You can also tell Nix to always use your binary cache by adding a line
 to the `nix.conf` configuration file like this:
 
-    binary-caches = http://avalon:8080/ https://cache.nixos.org/
+    substituters = http://avalon:8080/ https://cache.nixos.org/

doc/manual/src/release-notes/rl-2.13.md

@@ -0,0 +1,44 @@
+# Release 2.13 (2023-01-17)
+
+* The `repeat` and `enforce-determinism` options have been removed
+  since they had been broken under many circumstances for a long time.
+
+* You can now use [flake references] in the [old command line interface], e.g.
+
+   [flake references]: ../command-ref/new-cli/nix3-flake.md#flake-references
+   [old command line interface]: ../command-ref/main-commands.md
+
+  ```shell-session
+  # nix-build flake:nixpkgs -A hello
+  # nix-build -I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05 \
+      '<nixpkgs>' -A hello
+  # NIX_PATH=nixpkgs=flake:nixpkgs nix-build '<nixpkgs>' -A hello
+  ```
+
+* Instead of "antiquotation", the more common term [string interpolation](../language/string-interpolation.md) is now used consistently.
+  Historical release notes were not changed.
+
+* 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.
+
+* Allow explicitly selecting outputs in a store derivation installable, just like we can do with other sorts of installables.
+  For example,
+  ```shell-session
+  # nix build /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^dev
+  ```
+  now works just as
+  ```shell-session
+  # nix build nixpkgs#glibc^dev
+  ```
+  does already.
+
+* On Linux, `nix develop` now sets the
+  [*personality*](https://man7.org/linux/man-pages/man2/personality.2.html)
+  for the development shell in the same way as the actual build of the
+  derivation. This makes shells for `i686-linux` derivations work
+  correctly on `x86_64-linux`.
+
+* You can now disable the global flake registry by setting the `flake-registry`
+  configuration option to an empty string. The same can be achieved at runtime with
+  `--flake-registry ""`.

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

@@ -1,27 +1,12 @@
-# Release X.Y (202?-??-??)
+* A new function `builtins.readFileType` is available. It is similar to
-
+  `builtins.readDir` but acts on a single file or directory.
-* The `repeat` and `enforce-determinism` options have been removed
-  since they had been broken under many circumstances for a long time.
-
-* You can now use [flake references] in the [old command line interface], e.g.
-
-   [flake references]: ../command-ref/new-cli/nix3-flake.md#flake-references
-   [old command line interface]: ../command-ref/main-commands.md
-
-  ```
-  # nix-build flake:nixpkgs -A hello
-  # nix-build -I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05 \
-      '<nixpkgs>' -A hello
-  # NIX_PATH=nixpkgs=flake:nixpkgs nix-build '<nixpkgs>' -A hello
-  ```
-
-* Instead of "antiquotation", the more common term [string interpolation](../language/string-interpolation.md) is now used consistently.
-  Historical release notes were not changed.
-
-* 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.
 
+* The `builtins.readDir` function has been optimized when encountering not-yet-known
+  file types from POSIX's `readdir`. In such cases the type of each file is/was
+  discovered by making multiple syscalls. This change makes these operations
+  lazy such that these lookups will only be performed if the attribute is used.
+  This optimization affects a minority of filesystems and operating systems.
+  
 * In derivations that use structured attributes, you can now use `unsafeDiscardReferences`
   to disable scanning a given output for runtime dependencies:
   ```nix
@@ -32,4 +17,4 @@
   their own embedded Nix store: hashes found inside such an image refer
   to the embedded store and not to the host's Nix store.
 
-  This requires the `discard-references` experimental feature.
+  This requires the `discard-references` experimental feature.

flake.nix

@@ -82,7 +82,9 @@
         });
 
         configureFlags =
-          lib.optionals stdenv.isLinux [
+          [
+            "CXXFLAGS=-I${lib.getDev rapidcheck}/extras/gtest/include"
+          ] ++ lib.optionals stdenv.isLinux [
             "--with-boost=${boost}/lib"
             "--with-sandbox-shell=${sh}/bin/busybox"
           ]
@@ -96,6 +98,7 @@
             buildPackages.flex
             (lib.getBin buildPackages.lowdown-nix)
             buildPackages.mdbook
+            buildPackages.mdbook-linkcheck
             buildPackages.autoconf-archive
             buildPackages.autoreconfHook
             buildPackages.pkg-config
@@ -115,6 +118,7 @@
             boost
             lowdown-nix
             gtest
+            rapidcheck
           ]
           ++ lib.optionals stdenv.isLinux [libseccomp]
           ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
@@ -127,9 +131,14 @@
           });
 
         propagatedDeps =
-          [ (boehmgc.override {
+          [ ((boehmgc.override {
               enableLargeConfig = true;
+            }).overrideAttrs(o: {
+              patches = (o.patches or []) ++ [
+                ./boehmgc-coroutine-sp-fallback.diff
+              ];
             })
+            )
             nlohmann_json
           ];
       };
@@ -400,6 +409,18 @@
           };
         };
 
+      nixos-lib = import (nixpkgs + "/nixos/lib") { };
+
+      # https://nixos.org/manual/nixos/unstable/index.html#sec-calling-nixos-tests
+      runNixOSTestFor = system: test: nixos-lib.runTest {
+        imports = [ test ];
+        hostPkgs = nixpkgsFor.${system};
+        defaults = {
+          nixpkgs.pkgs = nixpkgsFor.${system};
+        };
+        _module.args.nixpkgs = nixpkgs;
+      };
+
     in {
 
       # A Nixpkgs overlay that overrides the 'nix' and
@@ -456,6 +477,10 @@
 
             src = self;
 
+            configureFlags = [
+              "CXXFLAGS=-I${lib.getDev pkgs.rapidcheck}/extras/gtest/include"
+            ];
+
             enableParallelBuilding = true;
 
             nativeBuildInputs = nativeBuildDeps;
@@ -474,49 +499,22 @@
           };
 
         # System tests.
-        tests.remoteBuilds = import ./tests/remote-builds.nix {
+        tests.remoteBuilds = runNixOSTestFor "x86_64-linux" ./tests/nixos/remote-builds.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        };
 
-        tests.nix-copy-closure = import ./tests/nix-copy-closure.nix {
+        tests.nix-copy-closure = runNixOSTestFor "x86_64-linux" ./tests/nixos/nix-copy-closure.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        };
 
-        tests.nssPreload = (import ./tests/nss-preload.nix rec {
+        tests.nssPreload = runNixOSTestFor "x86_64-linux" ./tests/nixos/nss-preload.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        });
 
-        tests.githubFlakes = (import ./tests/github-flakes.nix rec {
+        tests.githubFlakes = runNixOSTestFor "x86_64-linux" ./tests/nixos/github-flakes.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        });
 
-        tests.sourcehutFlakes = (import ./tests/sourcehut-flakes.nix rec {
+        tests.sourcehutFlakes = runNixOSTestFor "x86_64-linux" ./tests/nixos/sourcehut-flakes.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        });
 
-        tests.containers = (import ./tests/containers.nix rec {
+        tests.containers = runNixOSTestFor "x86_64-linux" ./tests/nixos/containers/containers.nix;
-          system = "x86_64-linux";
-          inherit nixpkgs;
-          overlay = self.overlays.default;
-        });
 
         tests.setuid = nixpkgs.lib.genAttrs
           ["i686-linux" "x86_64-linux"]
-          (system:
+          (system: runNixOSTestFor system ./tests/nixos/setuid.nix);
-            import ./tests/setuid.nix rec {
+
-              inherit nixpkgs system;
-              overlay = self.overlays.default;
-            });
 
         # Make sure that nix-env still produces the exact same result
         # on a particular version of Nixpkgs.
@@ -531,6 +529,12 @@
               mkdir $out
             '';
 
+        tests.nixpkgsLibTests =
+          nixpkgs.lib.genAttrs systems (system:
+            import (nixpkgs + "/lib/tests/release.nix")
+              { pkgs = nixpkgsFor.${system}; }
+          );
+
         metrics.nixpkgs = import "${nixpkgs-regression}/pkgs/top-level/metrics.nix" {
           pkgs = nixpkgsFor.x86_64-linux;
           nixpkgs = nixpkgs-regression;
@@ -561,6 +565,7 @@
         binaryTarball = self.hydraJobs.binaryTarball.${system};
         perlBindings = self.hydraJobs.perlBindings.${system};
         installTests = self.hydraJobs.installTests.${system};
+        nixpkgsLibTests = self.hydraJobs.tests.nixpkgsLibTests.${system};
       } // (nixpkgs.lib.optionalAttrs (builtins.elem system linux64BitSystems)) {
         dockerImage = self.hydraJobs.dockerImage.${system};
       });
@@ -642,6 +647,7 @@
             inherit system crossSystem;
             overlays = [ self.overlays.default ];
           };
+          inherit (nixpkgsCross) lib;
         in with commonDeps { pkgs = nixpkgsCross; }; nixpkgsCross.stdenv.mkDerivation {
           name = "nix-${version}";
 
@@ -654,7 +660,11 @@
           nativeBuildInputs = nativeBuildDeps;
           buildInputs = buildDeps ++ propagatedDeps;
 
-          configureFlags = [ "--sysconfdir=/etc" "--disable-doc-gen" ];
+          configureFlags = [
+            "CXXFLAGS=-I${lib.getDev nixpkgsCross.rapidcheck}/extras/gtest/include"
+            "--sysconfdir=/etc"
+            "--disable-doc-gen"
+          ];
 
           enableParallelBuilding = true;
 

maintainers/README.md

@@ -36,17 +36,45 @@ Issues on the board progress through the following states:
 
 - No Status
 
-  Team members can add pull requests or issues to discuss or review together.
-
   During the discussion meeting, the team triages new items.
+  To be considered, issues and pull requests must have a high-level description to provide the whole team with the necessary context at a glance.
+
+  On every meeting, at least one item from each of the following categories is inspected:
+
+  1. [critical](https://github.com/NixOS/nix/labels/critical)
+  2. [security](https://github.com/NixOS/nix/labels/security)
+  3. [regression](https://github.com/NixOS/nix/labels/regression)
+  4. [bug](https://github.com/NixOS/nix/issues?q=is%3Aopen+label%3Abug+sort%3Areactions-%2B1-desc)
+
+  - [oldest pull requests](https://github.com/NixOS/nix/pulls?q=is%3Apr+is%3Aopen+sort%3Acreated-asc)
+  - [most popular pull requests](https://github.com/NixOS/nix/pulls?q=is%3Apr+is%3Aopen+sort%3Areactions-%2B1-desc)
+  - [oldest issues](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Acreated-asc)
+  - [most popular issues](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc)
+
+  Team members can also add pull requests or issues they would like the whole team to consider.
+
   If there is disagreement on the general idea behind an issue or pull request, it is moved to _To discuss_, otherwise to _In review_.
 
 - To discuss
 
-  Pull requests and issues that are important and controversial are discussed by the team during discussion meetings.
+  Pull requests and issues that are deemed important and controversial are discussed by the team during discussion meetings.
 
   This may be where the merit of the change itself or the implementation strategy is contested by a team member.
 
+  As a general guideline, the order of items is determined as follows:
+
+  - Prioritise pull requests over issues
+
+    Contributors who took the time to implement concrete change proposals should not wait indefinitely.
+
+  - Prioritise fixing bugs over documentation, improvements or new features
+
+    The team values stability and accessibility higher than raw functionality.
+
+  - Interleave issues and PRs
+
+    This way issues without attempts at a solution get a chance to get addressed.
+
 - In review
 
   Pull requests in this column are reviewed together during work meetings.

scripts/install-systemd-multi-user.sh

@@ -24,12 +24,17 @@ $1
 EOF
 }
 
+escape_systemd_env() {
+    temp_var="${1//\'/\\\'}"
+    echo "${temp_var//\%/%%}"
+}
+
 # Gather all non-empty proxy environment variables into a string
 create_systemd_proxy_env() {
     vars="http_proxy https_proxy ftp_proxy no_proxy HTTP_PROXY HTTPS_PROXY FTP_PROXY NO_PROXY"
     for v in $vars; do
         if [ "x${!v:-}" != "x" ]; then
-            echo "Environment=${v}=${!v}"
+            echo "Environment=${v}=$(escape_systemd_env ${!v})"
         fi
     done
 }

scripts/nix-profile-daemon.fish.in

@@ -1,3 +1,15 @@
+function add_path --argument-names new_path
+    if type -q fish_add_path
+        # fish 3.2.0 or newer
+	fish_add_path --prepend --global $new_path
+    else
+        # older versions of fish
+        if not contains $new_path $fish_user_paths
+            set --global fish_user_paths $new_path $fish_user_paths
+        end
+    end
+end
+
 # Only execute this file once per shell.
 if test -n "$__ETC_PROFILE_NIX_SOURCED"
   exit
@@ -31,5 +43,7 @@ else
   end
 end
 
-fish_add_path --prepend --global "@localstatedir@/nix/profiles/default/bin"
+add_path "@localstatedir@/nix/profiles/default/bin"
-fish_add_path --prepend --global "$HOME/.nix-profile/bin"
+add_path "$HOME/.nix-profile/bin"
+
+functions -e add_path

scripts/nix-profile.fish.in

@@ -1,3 +1,15 @@
+function add_path --argument-names new_path
+    if type -q fish_add_path
+        # fish 3.2.0 or newer
+	fish_add_path --prepend --global $new_path
+    else
+        # older versions of fish
+        if not contains $new_path $fish_user_paths
+            set --global fish_user_paths $new_path $fish_user_paths
+        end
+    end
+end
+
 if test -n "$HOME" && test -n "$USER"
 
     # Set up the per-user profile.
@@ -32,6 +44,8 @@ if test -n "$HOME" && test -n "$USER"
       set --export --prepend --path MANPATH "$NIX_LINK/share/man"
     end
 
-    fish_add_path --prepend --global "$NIX_LINK/bin"
+    add_path "$NIX_LINK/bin"
     set --erase NIX_LINK
 end
+
+functions -e add_path

src/libcmd/common-eval-args.cc

@@ -34,8 +34,8 @@ MixEvalArgs::MixEvalArgs()
         .shortName = 'I',
         .description = R"(
   Add *path* to the Nix search path. The Nix search path is
-  initialized from the colon-separated [`NIX_PATH`](./env-common.md#env-NIX_PATH) environment
+  initialized from the colon-separated [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH) environment
-  variable, and is used to look up the location of Nix expressions using [paths](../language/values.md#type-path) enclosed in angle
+  variable, and is used to look up the location of Nix expressions using [paths](@docroot@/language/values.md#type-path) enclosed in angle
   brackets (i.e., `<nixpkgs>`).
 
   For instance, passing

src/libcmd/installables.cc

@@ -1,5 +1,6 @@
 #include "globals.hh"
 #include "installables.hh"
+#include "outputs-spec.hh"
 #include "util.hh"
 #include "command.hh"
 #include "attr-path.hh"
@@ -358,7 +359,7 @@ void completeFlakeRef(ref<Store> store, std::string_view prefix)
     }
 }
 
-DerivedPath Installable::toDerivedPath()
+DerivedPathWithInfo Installable::toDerivedPath()
 {
     auto buildables = toDerivedPaths();
     if (buildables.size() != 1)
@@ -401,18 +402,6 @@ struct InstallableStorePath : Installable
     ref<Store> store;
     DerivedPath req;
 
-    InstallableStorePath(ref<Store> store, StorePath && storePath)
-        : store(store),
-          req(storePath.isDerivation()
-              ? (DerivedPath) DerivedPath::Built {
-                  .drvPath = std::move(storePath),
-                  .outputs = {},
-              }
-              : (DerivedPath) DerivedPath::Opaque {
-                  .path = std::move(storePath),
-              })
-    { }
-
     InstallableStorePath(ref<Store> store, DerivedPath && req)
         : store(store), req(std::move(req))
     { }
@@ -422,21 +411,9 @@ struct InstallableStorePath : Installable
         return req.to_string(*store);
     }
 
-    DerivedPaths toDerivedPaths() override
+    DerivedPathsWithInfo toDerivedPaths() override
     {
-        return { req };
+        return {{.path = req, .info = {} }};
-    }
-
-    StorePathSet toDrvPaths(ref<Store> store) override
-    {
-        return std::visit(overloaded {
-            [&](const DerivedPath::Built & bfd) -> StorePathSet {
-                return { bfd.drvPath };
-            },
-            [&](const DerivedPath::Opaque & bo) -> StorePathSet {
-                return { getDeriver(store, *this, bo.path) };
-            },
-        }, req.raw());
     }
 
     std::optional<StorePath> getStorePath() override
@@ -452,52 +429,24 @@ struct InstallableStorePath : Installable
     }
 };
 
-DerivedPaths InstallableValue::toDerivedPaths()
-{
-    DerivedPaths res;
-
-    std::map<StorePath, std::set<std::string>> drvsToOutputs;
-    RealisedPath::Set drvsToCopy;
-
-    // Group by derivation, helps with .all in particular
-    for (auto & drv : toDerivations()) {
-        for (auto & outputName : drv.outputsToInstall)
-            drvsToOutputs[drv.drvPath].insert(outputName);
-        drvsToCopy.insert(drv.drvPath);
-    }
-
-    for (auto & i : drvsToOutputs)
-        res.push_back(DerivedPath::Built { i.first, i.second });
-
-    return res;
-}
-
-StorePathSet InstallableValue::toDrvPaths(ref<Store> store)
-{
-    StorePathSet res;
-    for (auto & drv : toDerivations())
-        res.insert(drv.drvPath);
-    return res;
-}
-
 struct InstallableAttrPath : InstallableValue
 {
     SourceExprCommand & cmd;
     RootValue v;
     std::string attrPath;
-    OutputsSpec outputsSpec;
+    ExtendedOutputsSpec extendedOutputsSpec;
 
     InstallableAttrPath(
         ref<EvalState> state,
         SourceExprCommand & cmd,
         Value * v,
         const std::string & attrPath,
-        OutputsSpec outputsSpec)
+        ExtendedOutputsSpec extendedOutputsSpec)
         : InstallableValue(state)
         , cmd(cmd)
         , v(allocRootValue(v))
         , attrPath(attrPath)
-        , outputsSpec(std::move(outputsSpec))
+        , extendedOutputsSpec(std::move(extendedOutputsSpec))
     { }
 
     std::string what() const override { return attrPath; }
@@ -509,40 +458,54 @@ struct InstallableAttrPath : InstallableValue
         return {vRes, pos};
     }
 
-    virtual std::vector<InstallableValue::DerivationInfo> toDerivations() override;
+    DerivedPathsWithInfo toDerivedPaths() override
-};
+    {
+        auto v = toValue(*state).first;
 
-std::vector<InstallableValue::DerivationInfo> InstallableAttrPath::toDerivations()
+        Bindings & autoArgs = *cmd.getAutoArgs(*state);
-{
-    auto v = toValue(*state).first;
 
-    Bindings & autoArgs = *cmd.getAutoArgs(*state);
+        DrvInfos drvInfos;
+        getDerivations(*state, *v, "", autoArgs, drvInfos, false);
 
-    DrvInfos drvInfos;
+        // Backward compatibility hack: group results by drvPath. This
-    getDerivations(*state, *v, "", autoArgs, drvInfos, false);
+        // helps keep .all output together.
+        std::map<StorePath, OutputsSpec> byDrvPath;
 
-    std::vector<DerivationInfo> res;
+        for (auto & drvInfo : drvInfos) {
-    for (auto & drvInfo : drvInfos) {
+            auto drvPath = drvInfo.queryDrvPath();
-        auto drvPath = drvInfo.queryDrvPath();
+            if (!drvPath)
-        if (!drvPath)
+                throw Error("'%s' is not a derivation", what());
-            throw Error("'%s' is not a derivation", what());
 
-        std::set<std::string> outputsToInstall;
+            auto newOutputs = std::visit(overloaded {
+                [&](const ExtendedOutputsSpec::Default & d) -> OutputsSpec {
+                    std::set<std::string> outputsToInstall;
+                    for (auto & output : drvInfo.queryOutputs(false, true))
+                        outputsToInstall.insert(output.first);
+                    return OutputsSpec::Names { std::move(outputsToInstall) };
+                },
+                [&](const ExtendedOutputsSpec::Explicit & e) -> OutputsSpec {
+                    return e;
+                },
+            }, extendedOutputsSpec.raw());
 
-        if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
+            auto [iter, didInsert] = byDrvPath.emplace(*drvPath, newOutputs);
-            outputsToInstall = *outputNames;
-        else
-            for (auto & output : drvInfo.queryOutputs(false, std::get_if<DefaultOutputs>(&outputsSpec)))
-                outputsToInstall.insert(output.first);
 
-        res.push_back(DerivationInfo {
+            if (!didInsert)
-            .drvPath = *drvPath,
+                iter->second = iter->second.union_(newOutputs);
-            .outputsToInstall = std::move(outputsToInstall)
+        }
-        });
+
+        DerivedPathsWithInfo res;
+        for (auto & [drvPath, outputs] : byDrvPath)
+            res.push_back({
+                .path = DerivedPath::Built {
+                    .drvPath = drvPath,
+                    .outputs = outputs,
+                },
+            });
+
+        return res;
     }
-
+};
-    return res;
-}
 
 std::vector<std::string> InstallableFlake::getActualAttrPaths()
 {
@@ -615,7 +578,7 @@ InstallableFlake::InstallableFlake(
     ref<EvalState> state,
     FlakeRef && flakeRef,
     std::string_view fragment,
-    OutputsSpec outputsSpec,
+    ExtendedOutputsSpec extendedOutputsSpec,
     Strings attrPaths,
     Strings prefixes,
     const flake::LockFlags & lockFlags)
@@ -623,14 +586,14 @@ InstallableFlake::InstallableFlake(
       flakeRef(flakeRef),
       attrPaths(fragment == "" ? attrPaths : Strings{(std::string) fragment}),
       prefixes(fragment == "" ? Strings{} : prefixes),
-      outputsSpec(std::move(outputsSpec)),
+      extendedOutputsSpec(std::move(extendedOutputsSpec)),
       lockFlags(lockFlags)
 {
     if (cmd && cmd->getAutoArgs(*state)->size())
         throw UsageError("'--arg' and '--argstr' are incompatible with flakes");
 }
 
-std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableFlake::toDerivation()
+DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
 {
     Activity act(*logger, lvlTalkative, actUnknown, fmt("evaluating derivation '%s'", what()));
 
@@ -638,56 +601,84 @@ std::tuple<std::string, FlakeRef, InstallableValue::DerivationInfo> InstallableF
 
     auto attrPath = attr->getAttrPathStr();
 
-    if (!attr->isDerivation())
+    if (!attr->isDerivation()) {
-        throw Error("flake output attribute '%s' is not a derivation", attrPath);
+
+        // FIXME: use eval cache?
+        auto v = attr->forceValue();
+
+        if (v.type() == nPath) {
+            PathSet context;
+            auto storePath = state->copyPathToStore(context, Path(v.path));
+            return {{
+                .path = DerivedPath::Opaque {
+                    .path = std::move(storePath),
+                }
+            }};
+        }
+
+        else if (v.type() == nString) {
+            PathSet context;
+            auto s = state->forceString(v, context, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
+            auto storePath = state->store->maybeParseStorePath(s);
+            if (storePath && context.count(std::string(s))) {
+                return {{
+                    .path = DerivedPath::Opaque {
+                        .path = std::move(*storePath),
+                    }
+                }};
+            } else
+                throw Error("flake output attribute '%s' evaluates to the string '%s' which is not a store path", attrPath, s);
+        }
+
+        else
+            throw Error("flake output attribute '%s' is not a derivation or path", attrPath);
+    }
 
     auto drvPath = attr->forceDerivation();
 
-    std::set<std::string> outputsToInstall;
     std::optional<NixInt> priority;
 
-    if (auto aOutputSpecified = attr->maybeGetAttr(state->sOutputSpecified)) {
+    if (attr->maybeGetAttr(state->sOutputSpecified)) {
-        if (aOutputSpecified->getBool()) {
+    } else if (auto aMeta = attr->maybeGetAttr(state->sMeta)) {
-            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)) {
+    return {{
-        outputsToInstall.clear();
+        .path = DerivedPath::Built {
-        if (auto aOutputs = attr->maybeGetAttr(state->sOutputs))
+            .drvPath = std::move(drvPath),
-            for (auto & s : aOutputs->getListOfStrings())
+            .outputs = std::visit(overloaded {
-                outputsToInstall.insert(s);
+                [&](const ExtendedOutputsSpec::Default & d) -> OutputsSpec {
-    }
+                    std::set<std::string> outputsToInstall;
+                    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 (outputsToInstall.empty())
+                    if (outputsToInstall.empty())
-        outputsToInstall.insert("out");
+                        outputsToInstall.insert("out");
 
-    if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
+                    return OutputsSpec::Names { std::move(outputsToInstall) };
-        outputsToInstall = *outputNames;
+                },
-
+                [&](const ExtendedOutputsSpec::Explicit & e) -> OutputsSpec {
-    auto drvInfo = DerivationInfo {
+                    return e;
-        .drvPath = std::move(drvPath),
+                },
-        .outputsToInstall = std::move(outputsToInstall),
+            }, extendedOutputsSpec.raw()),
-        .priority = priority,
+        },
-    };
+        .info = {
-
+            .priority = priority,
-    return {attrPath, getLockedFlake()->flake.lockedRef, std::move(drvInfo)};
+            .originalRef = flakeRef,
-}
+            .resolvedRef = getLockedFlake()->flake.lockedRef,
-
+            .attrPath = attrPath,
-std::vector<InstallableValue::DerivationInfo> InstallableFlake::toDerivations()
+            .extendedOutputsSpec = extendedOutputsSpec,
-{
+        }
-    std::vector<DerivationInfo> res;
+    }};
-    res.push_back(std::get<2>(toDerivation()));
-    return res;
 }
 
 std::pair<Value *, PosIdx> InstallableFlake::toValue(EvalState & state)
@@ -802,12 +793,12 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         }
 
         for (auto & s : ss) {
-            auto [prefix, outputsSpec] = parseOutputsSpec(s);
+            auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(s);
             result.push_back(
                 std::make_shared<InstallableAttrPath>(
                     state, *this, vFile,
-                    prefix == "." ? "" : prefix,
+                    prefix == "." ? "" : std::string { prefix },
-                    outputsSpec));
+                    extendedOutputsSpec));
         }
 
     } else {
@@ -815,24 +806,46 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         for (auto & s : ss) {
             std::exception_ptr ex;
 
-            auto found = s.rfind('^');
+            auto [prefix_, extendedOutputsSpec_] = ExtendedOutputsSpec::parse(s);
-            if (found != std::string::npos) {
+            // To avoid clang's pedantry
-                try {
+            auto prefix = std::move(prefix_);
-                    result.push_back(std::make_shared<InstallableStorePath>(
+            auto extendedOutputsSpec = std::move(extendedOutputsSpec_);
-                        store,
-                        DerivedPath::Built::parse(*store, s.substr(0, found), s.substr(found + 1))));
-                    continue;
-                } catch (BadStorePath &) {
-                } catch (...) {
-                    if (!ex)
-                        ex = std::current_exception();
-                }
-            }
 
-            found = s.find('/');
+            auto found = prefix.find('/');
             if (found != std::string::npos) {
                 try {
-                    result.push_back(std::make_shared<InstallableStorePath>(store, store->followLinksToStorePath(s)));
+                    auto derivedPath = std::visit(overloaded {
+                        // If the user did not use ^, we treat the output more liberally.
+                        [&](const ExtendedOutputsSpec::Default &) -> DerivedPath {
+                            // First, we accept a symlink chain or an actual store path.
+                            auto storePath = store->followLinksToStorePath(prefix);
+                            // Second, we see if the store path ends in `.drv` to decide what sort
+                            // of derived path they want.
+                            //
+                            // This handling predates the `^` syntax. The `^*` in
+                            // `/nix/store/hash-foo.drv^*` unambiguously means "do the
+                            // `DerivedPath::Built` case", so plain `/nix/store/hash-foo.drv` could
+                            // also unambiguously mean "do the DerivedPath::Opaque` case".
+                            //
+                            // Issue #7261 tracks reconsidering this `.drv` dispatching.
+                            return storePath.isDerivation()
+                                ? (DerivedPath) DerivedPath::Built {
+                                    .drvPath = std::move(storePath),
+                                    .outputs = OutputsSpec::All {},
+                                }
+                                : (DerivedPath) DerivedPath::Opaque {
+                                    .path = std::move(storePath),
+                                };
+                        },
+                        // If the user did use ^, we just do exactly what is written.
+                        [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> DerivedPath {
+                            return DerivedPath::Built {
+                                .drvPath = store->parseStorePath(prefix),
+                                .outputs = outputSpec,
+                            };
+                        },
+                    }, extendedOutputsSpec.raw());
+                    result.push_back(std::make_shared<InstallableStorePath>(store, std::move(derivedPath)));
                     continue;
                 } catch (BadStorePath &) {
                 } catch (...) {
@@ -842,13 +855,13 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
             }
 
             try {
-                auto [flakeRef, fragment, outputsSpec] = parseFlakeRefWithFragmentAndOutputsSpec(s, absPath("."));
+                auto [flakeRef, fragment] = parseFlakeRefWithFragment(std::string { prefix }, absPath("."));
                 result.push_back(std::make_shared<InstallableFlake>(
                         this,
                         getEvalState(),
                         std::move(flakeRef),
                         fragment,
-                        outputsSpec,
+                        extendedOutputsSpec,
                         getDefaultFlakeAttrPaths(),
                         getDefaultFlakeAttrPathPrefixes(),
                         lockFlags));
@@ -895,13 +908,19 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
     if (mode == Realise::Nothing)
         settings.readOnlyMode = true;
 
+    struct Aux
+    {
+        ExtraPathInfo info;
+        std::shared_ptr<Installable> installable;
+    };
+
     std::vector<DerivedPath> pathsToBuild;
-    std::map<DerivedPath, std::vector<std::shared_ptr<Installable>>> backmap;
+    std::map<DerivedPath, std::vector<Aux>> backmap;
 
     for (auto & i : installables) {
         for (auto b : i->toDerivedPaths()) {
-            pathsToBuild.push_back(b);
+            pathsToBuild.push_back(b.path);
-            backmap[b].push_back(i);
+            backmap[b.path].push_back({.info = b.info, .installable = i});
         }
     }
 
@@ -914,42 +933,18 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
         printMissing(store, pathsToBuild, lvlError);
 
         for (auto & path : pathsToBuild) {
-            for (auto & installable : backmap[path]) {
+            for (auto & aux : backmap[path]) {
                 std::visit(overloaded {
                     [&](const DerivedPath::Built & bfd) {
-                        OutputPathMap outputs;
+                        auto outputs = resolveDerivedPath(*store, bfd, &*evalStore);
-                        auto drv = evalStore->readDerivation(bfd.drvPath);
+                        res.push_back({aux.installable, {
-                        auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
+                            .path = BuiltPath::Built { bfd.drvPath, outputs },
-                        auto drvOutputs = drv.outputsAndOptPaths(*store);
+                            .info = aux.info}});
-                        for (auto & output : bfd.outputs) {
-                            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 { *outputHash, output };
-                                auto realisation = store->queryRealisation(outputId);
-                                if (!realisation)
-                                    throw Error(
-                                        "cannot operate on an output of the "
-                                        "unbuilt derivation '%s'",
-                                        outputId.to_string());
-                                outputs.insert_or_assign(output, realisation->outPath);
-                            } else {
-                                // If ca-derivations isn't enabled, assume that
-                                // the output path is statically known.
-                                auto drvOutput = get(drvOutputs, output);
-                                assert(drvOutput);
-                                assert(drvOutput->second);
-                                outputs.insert_or_assign(
-                                    output, *drvOutput->second);
-                            }
-                        }
-                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Opaque { bo.path },
+                            .info = aux.info}});
                     },
                 }, path.raw());
             }
@@ -965,16 +960,22 @@ std::vector<std::pair<std::shared_ptr<Installable>, BuiltPathWithResult>> Instal
             if (!buildResult.success())
                 buildResult.rethrow();
 
-            for (auto & installable : backmap[buildResult.path]) {
+            for (auto & aux : backmap[buildResult.path]) {
                 std::visit(overloaded {
                     [&](const DerivedPath::Built & bfd) {
                         std::map<std::string, StorePath> outputs;
                         for (auto & path : buildResult.builtOutputs)
                             outputs.emplace(path.first.outputName, path.second.outPath);
-                        res.push_back({installable, {.path = BuiltPath::Built { bfd.drvPath, outputs }, .result = buildResult}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Built { bfd.drvPath, outputs },
+                            .info = aux.info,
+                            .result = buildResult}});
                     },
                     [&](const DerivedPath::Opaque & bo) {
-                        res.push_back({installable, {.path = BuiltPath::Opaque { bo.path }, .result = buildResult}});
+                        res.push_back({aux.installable, {
+                            .path = BuiltPath::Opaque { bo.path },
+                            .info = aux.info,
+                            .result = buildResult}});
                     },
                 }, buildResult.path.raw());
             }
@@ -1059,7 +1060,7 @@ StorePathSet Installable::toDerivations(
                 [&](const DerivedPath::Built & bfd) {
                     drvPaths.insert(bfd.drvPath);
                 },
-            }, b.raw());
+            }, b.path.raw());
 
     return drvPaths;
 }

src/libcmd/installables.hh

@@ -2,7 +2,7 @@
 
 #include "util.hh"
 #include "path.hh"
-#include "path-with-outputs.hh"
+#include "outputs-spec.hh"
 #include "derived-path.hh"
 #include "eval.hh"
 #include "store-api.hh"
@@ -20,7 +20,7 @@ namespace eval_cache { class EvalCache; class AttrCursor; }
 
 struct App
 {
-    std::vector<StorePathWithOutputs> context;
+    std::vector<DerivedPath> context;
     Path program;
     // FIXME: add args, sandbox settings, metadata, ...
 };
@@ -52,26 +52,42 @@ enum class OperateOn {
     Derivation
 };
 
+struct ExtraPathInfo
+{
+    std::optional<NixInt> priority;
+    std::optional<FlakeRef> originalRef;
+    std::optional<FlakeRef> resolvedRef;
+    std::optional<std::string> attrPath;
+    // FIXME: merge with DerivedPath's 'outputs' field?
+    std::optional<ExtendedOutputsSpec> extendedOutputsSpec;
+};
+
+/* A derived path with any additional info that commands might
+   need from the derivation. */
+struct DerivedPathWithInfo
+{
+    DerivedPath path;
+    ExtraPathInfo info;
+};
+
 struct BuiltPathWithResult
 {
     BuiltPath path;
+    ExtraPathInfo info;
     std::optional<BuildResult> result;
 };
 
+typedef std::vector<DerivedPathWithInfo> DerivedPathsWithInfo;
+
 struct Installable
 {
     virtual ~Installable() { }
 
     virtual std::string what() const = 0;
 
-    virtual DerivedPaths toDerivedPaths() = 0;
+    virtual DerivedPathsWithInfo toDerivedPaths() = 0;
 
-    virtual StorePathSet toDrvPaths(ref<Store> store)
+    DerivedPathWithInfo toDerivedPath();
-    {
-        throw Error("'%s' cannot be converted to a derivation path", what());
-    }
-
-    DerivedPath toDerivedPath();
 
     UnresolvedApp toApp(EvalState & state);
 
@@ -146,19 +162,6 @@ struct InstallableValue : Installable
     ref<EvalState> state;
 
     InstallableValue(ref<EvalState> state) : state(state) {}
-
-    struct DerivationInfo
-    {
-        StorePath drvPath;
-        std::set<std::string> outputsToInstall;
-        std::optional<NixInt> priority;
-    };
-
-    virtual std::vector<DerivationInfo> toDerivations() = 0;
-
-    DerivedPaths toDerivedPaths() override;
-
-    StorePathSet toDrvPaths(ref<Store> store) override;
 };
 
 struct InstallableFlake : InstallableValue
@@ -166,7 +169,7 @@ struct InstallableFlake : InstallableValue
     FlakeRef flakeRef;
     Strings attrPaths;
     Strings prefixes;
-    OutputsSpec outputsSpec;
+    ExtendedOutputsSpec extendedOutputsSpec;
     const flake::LockFlags & lockFlags;
     mutable std::shared_ptr<flake::LockedFlake> _lockedFlake;
 
@@ -175,7 +178,7 @@ struct InstallableFlake : InstallableValue
         ref<EvalState> state,
         FlakeRef && flakeRef,
         std::string_view fragment,
-        OutputsSpec outputsSpec,
+        ExtendedOutputsSpec extendedOutputsSpec,
         Strings attrPaths,
         Strings prefixes,
         const flake::LockFlags & lockFlags);
@@ -186,9 +189,7 @@ struct InstallableFlake : InstallableValue
 
     Value * getFlakeOutputs(EvalState & state, const flake::LockedFlake & lockedFlake);
 
-    std::tuple<std::string, FlakeRef, DerivationInfo> toDerivation();
+    DerivedPathsWithInfo toDerivedPaths() override;
-
-    std::vector<DerivationInfo> toDerivations() override;
 
     std::pair<Value *, PosIdx> toValue(EvalState & state) override;
 

src/libcmd/repl.cc

@@ -397,7 +397,7 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
             Expr * e = parseString(expr);
             Value v;
             e->eval(*state, *env, v);
-            state->forceAttrs(v, noPos, "nevermind, it is ignored anyway");
+            state->forceAttrs(v, noPos, "while evaluating an attrset for the purpose of completion (this error should not be displayed; file an issue?)");
 
             for (auto & i : *v.attrs) {
                 std::string_view name = state->symbols[i.name];
@@ -641,7 +641,12 @@ bool NixRepl::processLine(std::string line)
         Path drvPathRaw = state->store->printStorePath(drvPath);
 
         if (command == ":b" || command == ":bl") {
-            state->store->buildPaths({DerivedPath::Built{drvPath}});
+            state->store->buildPaths({
+                DerivedPath::Built {
+                    .drvPath = drvPath,
+                    .outputs = OutputsSpec::All { },
+                },
+            });
             auto drv = state->store->readDerivation(drvPath);
             logger->cout("\nThis derivation produced the following outputs:");
             for (auto & [outputName, outputPath] : state->store->queryDerivationOutputMap(drvPath)) {

src/libexpr/eval-cache.cc

@@ -300,7 +300,7 @@ struct AttrDb
                 NixStringContext context;
                 if (!queryAttribute.isNull(3))
                     for (auto & s : tokenizeString<std::vector<std::string>>(queryAttribute.getStr(3), ";"))
-                        context.push_back(decodeContext(cfg, s));
+                        context.push_back(NixStringContextElem::parse(cfg, s));
                 return {{rowId, string_t{queryAttribute.getStr(2), context}}};
             }
             case AttrType::Bool:
@@ -592,7 +592,18 @@ string_t AttrCursor::getStringWithContext()
             if (auto s = std::get_if<string_t>(&cachedValue->second)) {
                 bool valid = true;
                 for (auto & c : s->second) {
-                    if (!root->state.store->isValidPath(c.first)) {
+                    const StorePath & path = std::visit(overloaded {
+                        [&](const NixStringContextElem::DrvDeep & d) -> const StorePath & {
+                            return d.drvPath;
+                        },
+                        [&](const NixStringContextElem::Built & b) -> const StorePath & {
+                            return b.drvPath;
+                        },
+                        [&](const NixStringContextElem::Opaque & o) -> const StorePath & {
+                            return o.path;
+                        },
+                    }, c.raw());
+                    if (!root->state.store->isValidPath(path)) {
                         valid = false;
                         break;
                     }

src/libexpr/eval.cc

@@ -11,7 +11,9 @@
 
 #include <algorithm>
 #include <chrono>
+#include <iostream>
 #include <cstring>
+#include <optional>
 #include <unistd.h>
 #include <sys/time.h>
 #include <sys/resource.h>
@@ -517,6 +519,7 @@ EvalState::EvalState(
     static_assert(sizeof(Env) <= 16, "environment must be <= 16 bytes");
 
     /* Initialise the Nix expression search path. */
+    evalSettings.nixPath.setDefault(evalSettings.getDefaultNixPath());
     if (!evalSettings.pureEval) {
         for (auto & i : _searchPath) addToSearchPath(i);
         for (auto & i : evalSettings.nixPath.get()) addToSearchPath(i);
@@ -1927,7 +1930,9 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
             /* skip canonization of first path, which would only be not
             canonized in the first place if it's coming from a ./${foo} type
             path */
-            auto part = state.coerceToString(i_pos, vTmp, context, false, firstType == nString, !first, "while evaluating a path segment");
+            auto part = state.coerceToString(i_pos, vTmp, context,
+                                             "while evaluating a path segment",
+                                             false, firstType == nString, !first);
             sSize += part->size();
             s.emplace_back(std::move(part));
         }
@@ -2068,27 +2073,6 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
 }
 
 
-/* Decode a context string ‘!<name>!<path>’ into a pair <path,
-   name>. */
-NixStringContextElem decodeContext(const Store & store, std::string_view s)
-{
-    if (s.at(0) == '!') {
-        size_t index = s.find("!", 1);
-        return {
-            store.parseStorePath(s.substr(index + 1)),
-            std::string(s.substr(1, index - 1)),
-        };
-    } else
-        return {
-            store.parseStorePath(
-                s.at(0) == '/'
-                ? s
-                : s.substr(1)),
-            "",
-        };
-}
-
-
 void copyContext(const Value & v, PathSet & context)
 {
     if (v.string.context)
@@ -2103,7 +2087,7 @@ NixStringContext Value::getContext(const Store & store)
     assert(internalType == tString);
     if (string.context)
         for (const char * * p = string.context; *p; ++p)
-            res.push_back(decodeContext(store, *p));
+            res.push_back(NixStringContextElem::parse(store, *p));
     return res;
 }
 
@@ -2144,15 +2128,16 @@ std::optional<std::string> EvalState::tryAttrsToString(const PosIdx pos, Value &
     if (i != v.attrs->end()) {
         Value v1;
         callFunction(*i->value, v, v1, pos);
-        return coerceToString(pos, v1, context, coerceMore, copyToStore,
+        return coerceToString(pos, v1, context,
-                "while evaluating the result of the `toString` attribute").toOwned();
+                "while evaluating the result of the `__toString` attribute",
+                coerceMore, copyToStore).toOwned();
     }
 
     return {};
 }
 
-BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet & context,
+BackedStringView EvalState::coerceToString(const PosIdx pos, Value &v, PathSet &context,
-    bool coerceMore, bool copyToStore, bool canonicalizePath, std::string_view errorCtx)
+    std::string_view errorCtx, bool coerceMore, bool copyToStore, bool canonicalizePath)
 {
     forceValue(v, pos);
 
@@ -2166,7 +2151,7 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         if (canonicalizePath)
             path = canonPath(*path);
         if (copyToStore)
-            path = copyPathToStore(context, std::move(path).toOwned());
+            path = store->printStorePath(copyPathToStore(context, std::move(path).toOwned()));
         return path;
     }
 
@@ -2175,13 +2160,23 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         if (maybeString)
             return std::move(*maybeString);
         auto i = v.attrs->find(sOutPath);
-        if (i == v.attrs->end())
+        if (i == v.attrs->end()) {
-            error("cannot coerce a set to a string", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
+            error("cannot coerce %1% to a string", showType(v))
-        return coerceToString(pos, *i->value, context, coerceMore, copyToStore, canonicalizePath, errorCtx);
+                .withTrace(pos, errorCtx)
+                .debugThrow<TypeError>();
+        }
+        return coerceToString(pos, *i->value, context, errorCtx,
+                              coerceMore, copyToStore, canonicalizePath);
     }
 
-    if (v.type() == nExternal)
+    if (v.type() == nExternal) {
-        return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore, errorCtx);
+        try {
+            return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore);
+        } catch (Error & e) {
+            e.addTrace(nullptr, errorCtx);
+            throw;
+        }
+    }
 
     if (coerceMore) {
         /* Note that `false' is represented as an empty string for
@@ -2196,8 +2191,9 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
             std::string result;
             for (auto [n, v2] : enumerate(v.listItems())) {
                 try {
-                    result += *coerceToString(noPos, *v2, context, coerceMore, copyToStore, canonicalizePath,
+                    result += *coerceToString(noPos, *v2, context,
-                            "while evaluating one element of the list");
+                            "while evaluating one element of the list",
+                            coerceMore, copyToStore, canonicalizePath);
                 } catch (Error & e) {
                     e.addTrace(positions[pos], errorCtx);
                     throw;
@@ -2211,37 +2207,39 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         }
     }
 
-    error("cannot coerce %1% to a string", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
+    error("cannot coerce %1% to a string", showType(v))
+        .withTrace(pos, errorCtx)
+        .debugThrow<TypeError>();
 }
 
 
-std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
+StorePath EvalState::copyPathToStore(PathSet & context, const Path & path)
 {
     if (nix::isDerivation(path))
         error("file names are not allowed to end in '%1%'", drvExtension).debugThrow<EvalError>();
 
-    Path dstPath;
+    auto dstPath = [&]() -> StorePath
-    auto i = srcToStore.find(path);
+    {
-    if (i != srcToStore.end())
+        auto i = srcToStore.find(path);
-        dstPath = store->printStorePath(i->second);
+        if (i != srcToStore.end()) return i->second;
-    else {
+
-        auto p = settings.readOnlyMode
+        auto dstPath = settings.readOnlyMode
             ? store->computeStorePathForPath(std::string(baseNameOf(path)), checkSourcePath(path)).first
             : store->addToStore(std::string(baseNameOf(path)), checkSourcePath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
-        dstPath = store->printStorePath(p);
+        allowPath(dstPath);
-        allowPath(p);
+        srcToStore.insert_or_assign(path, dstPath);
-        srcToStore.insert_or_assign(path, std::move(p));
+        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, store->printStorePath(dstPath));
-        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
+        return dstPath;
-    }
+    }();
 
-    context.insert(dstPath);
+    context.insert(store->printStorePath(dstPath));
     return dstPath;
 }
 
 
 Path EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
 {
-    auto path = coerceToString(pos, v, context, false, false, true, errorCtx).toOwned();
+    auto path = coerceToString(pos, v, context, errorCtx, false, false, true).toOwned();
     if (path == "" || path[0] != '/')
         error("string '%1%' doesn't represent an absolute path", path).withTrace(pos, errorCtx).debugThrow<EvalError>();
     return path;
@@ -2250,7 +2248,7 @@ Path EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context, std
 
 StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
 {
-    auto path = coerceToString(pos, v, context, false, false, true, errorCtx).toOwned();
+    auto path = coerceToString(pos, v, context, errorCtx, false, false, true).toOwned();
     if (auto storePath = store->maybeParseStorePath(path))
         return *storePath;
     error("path '%1%' is not in the Nix store", path).withTrace(pos, errorCtx).debugThrow<EvalError>();
@@ -2454,13 +2452,11 @@ void EvalState::printStats()
 }
 
 
-std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, std::string_view errorCtx) const
+std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const
 {
-    auto e = TypeError({
+    throw TypeError({
         .msg = hintfmt("cannot coerce %1% to a string", showType())
     });
-    e.addTrace(pos, errorCtx);
-    throw e;
 }
 
 
@@ -2477,30 +2473,35 @@ std::ostream & operator << (std::ostream & str, const ExternalValueBase & v) {
 
 EvalSettings::EvalSettings()
 {
-    auto var = getEnv("NIX_PATH");
-    if (var) nixPath = parseNixPath(*var);
 }
 
+/* impure => NIX_PATH or a default path
+ * restrict-eval => NIX_PATH
+ * pure-eval => empty
+ */
 Strings EvalSettings::getDefaultNixPath()
 {
-    Strings res;
+    if (pureEval)
-    auto add = [&](const Path & p, const std::string & s = std::string()) {
+        return {};
-        if (pathExists(p)) {
+
-            if (s.empty()) {
+    auto var = getEnv("NIX_PATH");
-                res.push_back(p);
+    if (var) {
-            } else {
+        return parseNixPath(*var);
-                res.push_back(s + "=" + p);
+    } else if (restrictEval) {
-            }
+        return {};
-        }
+    } else {
-    };
+        Strings res;
+        auto add = [&](const Path & p, const std::optional<std::string> & s = std::nullopt) {
+            if (pathExists(p))
+                res.push_back(s ? *s + "=" + p : p);
+        };
 
-    if (!evalSettings.restrictEval && !evalSettings.pureEval) {
         add(getHome() + "/.nix-defexpr/channels");
         add(settings.nixStateDir + "/profiles/per-user/root/channels/nixpkgs", "nixpkgs");
         add(settings.nixStateDir + "/profiles/per-user/root/channels");
-    }
 
-    return res;
+        return res;
+    }
 }
 
 bool EvalSettings::isPseudoUrl(std::string_view s)

src/libexpr/eval.hh

@@ -203,6 +203,9 @@ public:
         throw std::move(error);
     }
 
+    // This is dangerous, but gets in line with the idea that error creation and
+    // throwing should not allocate on the stack of hot functions.
+    // as long as errors are immediately thrown, it works.
     ErrorBuilder * errorBuilder;
 
     template<typename... Args>
@@ -375,11 +378,11 @@ public:
        booleans and lists to a string.  If `copyToStore' is set,
        referenced paths are copied to the Nix store as a side effect. */
     BackedStringView coerceToString(const PosIdx pos, Value & v, PathSet & context,
+        std::string_view errorCtx,
         bool coerceMore = false, bool copyToStore = true,
-        bool canonicalizePath = true,
+        bool canonicalizePath = true);
-        std::string_view errorCtx = "");
 
-    std::string copyPathToStore(PathSet & context, const Path & path);
+    StorePath copyPathToStore(PathSet & context, const Path & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
@@ -551,10 +554,6 @@ struct DebugTraceStacker {
 std::string_view showType(ValueType type);
 std::string showType(const Value & v);
 
-/* Decode a context string ‘!<name>!<path>’ into a pair <path,
-   name>. */
-NixStringContextElem decodeContext(const Store & store, std::string_view s);
-
 /* If `path' refers to a directory, then append "/default.nix". */
 Path resolveExprPath(Path path);
 
@@ -571,7 +570,7 @@ struct EvalSettings : Config
 {
     EvalSettings();
 
-    static Strings getDefaultNixPath();
+    Strings getDefaultNixPath();
 
     static bool isPseudoUrl(std::string_view s);
 
@@ -581,8 +580,15 @@ struct EvalSettings : Config
         "Whether builtin functions that allow executing native code should be enabled."};
 
     Setting<Strings> nixPath{
-        this, getDefaultNixPath(), "nix-path",
+        this, {}, "nix-path",
-        "List of directories to be searched for `<...>` file references."};
+        R"(
+          List of directories to be searched for `<...>` file references.
+
+          If [pure evaluation](#conf-pure-eval) is disabled,
+          this is initialised using the [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH)
+          environment variable, or, if it is unset and [restricted evaluation](#conf-restrict-eval)
+          is disabled, a default search path including the user's and `root`'s channels.
+        )"};
 
     Setting<bool> restrictEval{
         this, false, "restrict-eval",

src/libexpr/flake/flake.cc

@@ -264,7 +264,7 @@ static Flake getFlake(
                 PathSet emptyContext = {};
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
-                    state.coerceToString(setting.pos, *setting.value, emptyContext, false, true, true, "") .toOwned());
+                    state.coerceToString(setting.pos, *setting.value, emptyContext, "", false, true, true) .toOwned());
             }
             else if (setting.value->type() == nInt)
                 flake.config.settings.emplace(

src/libexpr/flake/flakeref.cc

@@ -238,15 +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(
+std::tuple<FlakeRef, std::string, ExtendedOutputsSpec> parseFlakeRefWithFragmentAndExtendedOutputsSpec(
     const std::string & url,
     const std::optional<Path> & baseDir,
     bool allowMissing,
     bool isFlake)
 {
-    auto [prefix, outputsSpec] = parseOutputsSpec(url);
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(url);
-    auto [flakeRef, fragment] = parseFlakeRefWithFragment(prefix, baseDir, allowMissing, isFlake);
+    auto [flakeRef, fragment] = parseFlakeRefWithFragment(std::string { prefix }, baseDir, allowMissing, isFlake);
-    return {std::move(flakeRef), fragment, outputsSpec};
+    return {std::move(flakeRef), fragment, extendedOutputsSpec};
 }
 
 }

src/libexpr/flake/flakeref.hh

@@ -3,7 +3,7 @@
 #include "types.hh"
 #include "hash.hh"
 #include "fetchers.hh"
-#include "path-with-outputs.hh"
+#include "outputs-spec.hh"
 
 #include <variant>
 
@@ -80,7 +80,7 @@ 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(
+std::tuple<FlakeRef, std::string, ExtendedOutputsSpec> parseFlakeRefWithFragmentAndExtendedOutputsSpec(
     const std::string & url,
     const std::optional<Path> & baseDir = {},
     bool allowMissing = false,

src/libexpr/local.mk

@@ -6,6 +6,7 @@ libexpr_DIR := $(d)
 
 libexpr_SOURCES := \
   $(wildcard $(d)/*.cc) \
+  $(wildcard $(d)/value/*.cc) \
   $(wildcard $(d)/primops/*.cc) \
   $(wildcard $(d)/flake/*.cc) \
   $(d)/lexer-tab.cc \
@@ -37,6 +38,8 @@ clean-files += $(d)/parser-tab.cc $(d)/parser-tab.hh $(d)/lexer-tab.cc $(d)/lexe
 
 $(eval $(call install-file-in, $(d)/nix-expr.pc, $(libdir)/pkgconfig, 0644))
 
+$(foreach i, $(wildcard src/libexpr/value/*.hh), \
+  $(eval $(call install-file-in, $(i), $(includedir)/nix/value, 0644)))
 $(foreach i, $(wildcard src/libexpr/flake/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/flake, 0644)))
 

src/libexpr/primops.cc

@@ -43,16 +43,32 @@ StringMap EvalState::realiseContext(const PathSet & context)
     std::vector<DerivedPath::Built> drvs;
     StringMap res;
 
-    for (auto & i : context) {
+    for (auto & c_ : context) {
-        auto [ctx, outputName] = decodeContext(*store, i);
+        auto ensureValid = [&](const StorePath & p) {
-        auto ctxS = store->printStorePath(ctx);
+            if (!store->isValidPath(p))
-        if (!store->isValidPath(ctx))
+                debugThrowLastTrace(InvalidPathError(store->printStorePath(p)));
-            debugThrowLastTrace(InvalidPathError(store->printStorePath(ctx)));
+        };
-        if (!outputName.empty() && ctx.isDerivation()) {
+        auto c = NixStringContextElem::parse(*store, c_);
-            drvs.push_back({ctx, {outputName}});
+        std::visit(overloaded {
-        } else {
+            [&](const NixStringContextElem::Built & b) {
-            res.insert_or_assign(ctxS, ctxS);
+                drvs.push_back(DerivedPath::Built {
-        }
+                    .drvPath = b.drvPath,
+                    .outputs = OutputsSpec::Names { b.output },
+                });
+                ensureValid(b.drvPath);
+            },
+            [&](const NixStringContextElem::Opaque & o) {
+                auto ctxS = store->printStorePath(o.path);
+                res.insert_or_assign(ctxS, ctxS);
+                ensureValid(o.path);
+            },
+            [&](const NixStringContextElem::DrvDeep & d) {
+                /* Treat same as Opaque */
+                auto ctxS = store->printStorePath(d.drvPath);
+                res.insert_or_assign(ctxS, ctxS);
+                ensureValid(d.drvPath);
+            },
+        }, c.raw());
     }
 
     if (drvs.empty()) return {};
@@ -68,16 +84,12 @@ StringMap EvalState::realiseContext(const PathSet & context)
     store->buildPaths(buildReqs);
 
     /* Get all the output paths corresponding to the placeholders we had */
-    for (auto & [drvPath, outputs] : drvs) {
+    for (auto & drv : drvs) {
-        const auto outputPaths = store->queryDerivationOutputMap(drvPath);
+        auto outputs = resolveDerivedPath(*store, drv);
-        for (auto & outputName : outputs) {
+        for (auto & [outputName, outputPath] : outputs) {
-            auto outputPath = get(outputPaths, outputName);
-            if (!outputPath)
-                debugThrowLastTrace(Error("derivation '%s' does not have an output named '%s'",
-                    store->printStorePath(drvPath), outputName));
             res.insert_or_assign(
-                downstreamPlaceholder(*store, drvPath, outputName),
+                downstreamPlaceholder(*store, drv.drvPath, outputName),
-                store->printStorePath(*outputPath)
+                store->printStorePath(outputPath)
             );
         }
     }
@@ -240,6 +252,7 @@ static RegisterPrimOp primop_scopedImport(RegisterPrimOp::Info {
 static RegisterPrimOp primop_import({
     .name = "import",
     .args = {"path"},
+    // TODO turn "normal path values" into link below
     .doc = R"(
       Load, parse and return the Nix expression in the file *path*. If
       *path* is a directory, the file ` default.nix ` in that directory
@@ -253,7 +266,7 @@ static RegisterPrimOp primop_import({
       >
       > Unlike some languages, `import` is a regular function in Nix.
       > Paths using the angle bracket syntax (e.g., `import` *\<foo\>*)
-      > are [normal path values](language-values.md).
+      > are normal [path values](@docroot@/language/values.md#type-path).
 
       A Nix expression loaded by `import` must not contain any *free
       variables* (identifiers that are not defined in the Nix expression
@@ -337,26 +350,22 @@ void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v)
     auto elems = args[0]->listElems();
     auto count = args[0]->listSize();
     if (count == 0)
-        state.debugThrowLastTrace(EvalError({
+        state.error("at least one argument to 'exec' required").atPos(pos).debugThrow<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,
+    auto program = state.coerceToString(pos, *elems[0], context,
-           "while evaluating the first element of the argument passed to builtins.exec").toOwned();
+            "while evaluating the first element of the argument passed to builtins.exec",
+            false, false).toOwned();
     Strings commandArgs;
     for (unsigned int i = 1; i < args[0]->listSize(); ++i) {
-        commandArgs.push_back(state.coerceToString(pos, *elems[i], context, false, false,
+        commandArgs.push_back(
-                    "while evaluating an element of the argument passed to builtins.exec").toOwned());
+                state.coerceToString(pos, *elems[i], context,
+                        "while evaluating an element of the argument passed to builtins.exec",
+                        false, false).toOwned());
     }
     try {
         auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
-        state.debugThrowLastTrace(EvalError({
+        state.error("cannot execute '%1%', since path '%2%' is not valid", program, e.path).atPos(pos).debugThrow<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);
@@ -585,7 +594,8 @@ struct CompareValues
                     state.error("cannot compare %s with %s; values of that type are incomparable", showType(*v1), showType(*v2)).debugThrow<EvalError>();
             }
         } catch (Error & e) {
-            e.addTrace(nullptr, errorCtx);
+            if (!errorCtx.empty())
+                e.addTrace(nullptr, errorCtx);
             throw;
         }
     }
@@ -607,15 +617,7 @@ static Bindings::iterator getAttr(
 {
     Bindings::iterator value = attrSet->find(attrSym);
     if (value == attrSet->end()) {
-        throw TypeError({
+        state.error("attribute '%s' missing", state.symbols[attrSym]).withTrace(noPos, errorCtx).debugThrow<TypeError>();
-            .msg = hintfmt("attribute '%s' missing %s", state.symbols[attrSym], normaltxt(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;
 }
@@ -788,8 +790,10 @@ static void prim_addErrorContext(EvalState & state, const PosIdx pos, Value * *
         v = *args[1];
     } catch (Error & e) {
         PathSet context;
-        e.addTrace(nullptr, state.coerceToString(pos, *args[0], context,
+        auto message = state.coerceToString(pos, *args[0], context,
-                "while evaluating the error message passed to builtins.addErrorContext").toOwned());
+                "while evaluating the error message passed to builtins.addErrorContext",
+                false, false).toOwned();
+        e.addTrace(nullptr, message, true);
         throw;
     }
 }
@@ -993,6 +997,7 @@ static void prim_second(EvalState & state, const PosIdx pos, Value * * args, Val
  * Derivations
  *************************************************************/
 
+static void derivationStrictInternal(EvalState & state, const std::string & name, Bindings * attrs, Value & v);
 
 /* Construct (as a unobservable side effect) a Nix derivation
    expression that performs the derivation described by the argument
@@ -1003,32 +1008,68 @@ static void prim_second(EvalState & state, const PosIdx pos, Value * * args, Val
    derivation. */
 static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    using nlohmann::json;
     state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.derivationStrict");
 
+    Bindings * attrs = args[0]->attrs;
+
     /* Figure out the name first (for stack backtraces). */
-    Bindings::iterator attr = getAttr(state, state.sName, args[0]->attrs, "in the attrset passed as argument to builtins.derivationStrict");
+    Bindings::iterator nameAttr = getAttr(state, state.sName, attrs, "in the attrset passed as argument to builtins.derivationStrict");
 
     std::string drvName;
-    const auto posDrvName = attr->pos;
     try {
-        drvName = state.forceStringNoCtx(*attr->value, pos, "while evaluating the `name` attribute passed to builtins.derivationStrict");
+        drvName = state.forceStringNoCtx(*nameAttr->value, pos, "while evaluating the `name` attribute passed to builtins.derivationStrict");
     } catch (Error & e) {
-        e.addTrace(state.positions[posDrvName], "while evaluating the derivation attribute 'name'");
+        e.addTrace(state.positions[nameAttr->pos], "while evaluating the derivation attribute 'name'");
         throw;
     }
 
+    try {
+        derivationStrictInternal(state, drvName, attrs, v);
+    } catch (Error & e) {
+        Pos pos = state.positions[nameAttr->pos];
+        /*
+         * Here we make two abuses of the error system
+         *
+         * 1. We print the location as a string to avoid a code snippet being
+         * printed. While the location of the name attribute is a good hint, the
+         * exact code there is irrelevant.
+         *
+         * 2. We mark this trace as a frame trace, meaning that we stop printing
+         * less important traces from now on. In particular, this prevents the
+         * display of the automatic "while calling builtins.derivationStrict"
+         * trace, which is of little use for the public we target here.
+         *
+         * Please keep in mind that error reporting is done on a best-effort
+         * basis in nix. There is no accurate location for a derivation, as it
+         * often results from the composition of several functions
+         * (derivationStrict, derivation, mkDerivation, mkPythonModule, etc.)
+         */
+        e.addTrace(nullptr, hintfmt(
+                "while evaluating derivation '%s'\n"
+                "  whose name attribute is located at %s",
+                drvName, pos), true);
+        throw;
+    }
+}
+
+static void derivationStrictInternal(EvalState & state, const std::string &
+drvName, Bindings * attrs, Value & v)
+{
     /* Check whether attributes should be passed as a JSON file. */
+    using nlohmann::json;
     std::optional<json> jsonObject;
-    attr = args[0]->attrs->find(state.sStructuredAttrs);
+    auto attr = attrs->find(state.sStructuredAttrs);
-    if (attr != args[0]->attrs->end() && state.forceBool(*attr->value, pos, "while evaluating the `__structuredAttrs` attribute passed to builtins.derivationStrict"))
+    if (attr != attrs->end() &&
+        state.forceBool(*attr->value, noPos,
+                        "while evaluating the `__structuredAttrs` "
+                        "attribute passed to builtins.derivationStrict"))
         jsonObject = json::object();
 
     /* Check whether null attributes should be ignored. */
     bool ignoreNulls = false;
-    attr = args[0]->attrs->find(state.sIgnoreNulls);
+    attr = attrs->find(state.sIgnoreNulls);
-    if (attr != args[0]->attrs->end())
+    if (attr != attrs->end())
-        ignoreNulls = state.forceBool(*attr->value, pos, "while evaluating the `__ignoreNulls` attribute passed to builtins.derivationStrict");
+        ignoreNulls = state.forceBool(*attr->value, noPos, "while evaluating the `__ignoreNulls` attribute " "passed to builtins.derivationStrict");
 
     /* Build the derivation expression by processing the attributes. */
     Derivation drv;
@@ -1045,7 +1086,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
     StringSet outputs;
     outputs.insert("out");
 
-    for (auto & i : args[0]->attrs->lexicographicOrder(state.symbols)) {
+    for (auto & i : attrs->lexicographicOrder(state.symbols)) {
         if (i->name == state.sIgnoreNulls) continue;
         const std::string & key = state.symbols[i->name];
         vomit("processing attribute '%1%'", key);
@@ -1056,7 +1097,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
             else
                 state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
-                    .errPos = state.positions[posDrvName]
+                    .errPos = state.positions[noPos]
                 }));
         };
 
@@ -1066,7 +1107,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
                 if (outputs.find(j) != outputs.end())
                     state.debugThrowLastTrace(EvalError({
                         .msg = hintfmt("duplicate derivation output '%1%'", j),
-                        .errPos = state.positions[posDrvName]
+                        .errPos = state.positions[noPos]
                     }));
                 /* !!! Check whether j is a valid attribute
                    name. */
@@ -1076,34 +1117,35 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
                 if (j == "drv")
                     state.debugThrowLastTrace(EvalError({
                         .msg = hintfmt("invalid derivation output name 'drv'" ),
-                        .errPos = state.positions[posDrvName]
+                        .errPos = state.positions[noPos]
                     }));
                 outputs.insert(j);
             }
             if (outputs.empty())
                 state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("derivation cannot have an empty set of outputs"),
-                    .errPos = state.positions[posDrvName]
+                    .errPos = state.positions[noPos]
                 }));
         };
 
         try {
+            // This try-catch block adds context for most errors.
+            // Use this empty error context to signify that we defer to it.
+            const std::string_view context_below("");
 
             if (ignoreNulls) {
-                state.forceValue(*i->value, pos);
+                state.forceValue(*i->value, noPos);
                 if (i->value->type() == nNull) continue;
             }
 
             if (i->name == state.sContentAddressed) {
-                contentAddressed = state.forceBool(*i->value, pos,
+                contentAddressed = state.forceBool(*i->value, noPos, context_below);
-                        "while evaluating the `__contentAddressed` attribute passed to builtins.derivationStrict");
                 if (contentAddressed)
                     settings.requireExperimentalFeature(Xp::CaDerivations);
             }
 
             else if (i->name == state.sImpure) {
-                isImpure = state.forceBool(*i->value, pos,
+                isImpure = state.forceBool(*i->value, noPos, context_below);
-                        "while evaluating the 'impure' attribute passed to builtins.derivationStrict");
                 if (isImpure)
                     settings.requireExperimentalFeature(Xp::ImpureDerivations);
             }
@@ -1111,11 +1153,11 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
             /* The `args' attribute is special: it supplies the
                command-line arguments to the builder. */
             else if (i->name == state.sArgs) {
-                state.forceList(*i->value, pos,
+                state.forceList(*i->value, noPos, context_below);
-                        "while evaluating the `args` attribute passed to builtins.derivationStrict");
                 for (auto elem : i->value->listItems()) {
-                    auto s = state.coerceToString(posDrvName, *elem, context, true,
+                    auto s = state.coerceToString(noPos, *elem, context,
-                            "while evaluating an element of the `args` argument passed to builtins.derivationStrict").toOwned();
+                            "while evaluating an element of the argument list",
+                            true).toOwned();
                     drv.args.push_back(s);
                 }
             }
@@ -1128,29 +1170,29 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
 
                     if (i->name == state.sStructuredAttrs) continue;
 
-                    (*jsonObject)[key] = printValueAsJSON(state, true, *i->value, pos, context);
+                    (*jsonObject)[key] = printValueAsJSON(state, true, *i->value, noPos, context);
 
                     if (i->name == state.sBuilder)
-                        drv.builder = state.forceString(*i->value, context, posDrvName, "while evaluating the `builder` attribute passed to builtins.derivationStrict");
+                        drv.builder = state.forceString(*i->value, context, noPos, context_below);
                     else if (i->name == state.sSystem)
-                        drv.platform = state.forceStringNoCtx(*i->value, posDrvName, "while evaluating the `system` attribute passed to builtins.derivationStrict");
+                        drv.platform = state.forceStringNoCtx(*i->value, noPos, context_below);
                     else if (i->name == state.sOutputHash)
-                        outputHash = state.forceStringNoCtx(*i->value, posDrvName, "while evaluating the `outputHash` attribute passed to builtins.derivationStrict");
+                        outputHash = state.forceStringNoCtx(*i->value, noPos, context_below);
                     else if (i->name == state.sOutputHashAlgo)
-                        outputHashAlgo = state.forceStringNoCtx(*i->value, posDrvName, "while evaluating the `outputHashAlgo` attribute passed to builtins.derivationStrict");
+                        outputHashAlgo = state.forceStringNoCtx(*i->value, noPos, context_below);
                     else if (i->name == state.sOutputHashMode)
-                        handleHashMode(state.forceStringNoCtx(*i->value, posDrvName, "while evaluating the `outputHashMode` attribute passed to builtins.derivationStrict"));
+                        handleHashMode(state.forceStringNoCtx(*i->value, noPos, context_below));
                     else if (i->name == state.sOutputs) {
                         /* Require ‘outputs’ to be a list of strings. */
-                        state.forceList(*i->value, posDrvName, "while evaluating the `outputs` attribute passed to builtins.derivationStrict");
+                        state.forceList(*i->value, noPos, context_below);
                         Strings ss;
                         for (auto elem : i->value->listItems())
-                            ss.emplace_back(state.forceStringNoCtx(*elem, posDrvName, "while evaluating an element of the `outputs` attribute passed to builtins.derivationStrict"));
+                            ss.emplace_back(state.forceStringNoCtx(*elem, noPos, context_below));
                         handleOutputs(ss);
                     }
 
                 } else {
-                    auto s = state.coerceToString(i->pos, *i->value, context, true, "while evaluating an attribute passed to builtins.derivationStrict").toOwned();
+                    auto s = state.coerceToString(noPos, *i->value, context, context_below, true).toOwned();
                     drv.env.emplace(key, s);
                     if (i->name == state.sBuilder) drv.builder = std::move(s);
                     else if (i->name == state.sSystem) drv.platform = std::move(s);
@@ -1164,8 +1206,8 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
             }
 
         } catch (Error & e) {
-            e.addTrace(nullptr,
+            e.addTrace(state.positions[i->pos],
-                hintfmt("while evaluating the attribute '%1%' of the derivation '%2%'", key, drvName),
+                hintfmt("while evaluating attribute '%1%' of derivation '%2%'", key, drvName),
                 true);
             throw;
         }
@@ -1179,55 +1221,51 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
     /* Everything in the context of the strings in the derivation
        attributes should be added as dependencies of the resulting
        derivation. */
-    for (auto & path : context) {
+    for (auto & c_ : context) {
-
+        auto c = NixStringContextElem::parse(*state.store, c_);
-        /* Paths marked with `=' denote that the path of a derivation
+        std::visit(overloaded {
-           is explicitly passed to the builder.  Since that allows the
+            /* Since this allows the builder to gain access to every
-           builder to gain access to every path in the dependency
+               path in the dependency graph of the derivation (including
-           graph of the derivation (including all outputs), all paths
+               all outputs), all paths in the graph must be added to
-           in the graph must be added to this derivation's list of
+               this derivation's list of inputs to ensure that they are
-           inputs to ensure that they are available when the builder
+               available when the builder runs. */
-           runs. */
+            [&](const NixStringContextElem::DrvDeep & d) {
-        if (path.at(0) == '=') {
+                /* !!! This doesn't work if readOnlyMode is set. */
-            /* !!! This doesn't work if readOnlyMode is set. */
+                StorePathSet refs;
-            StorePathSet refs;
+                state.store->computeFSClosure(d.drvPath, refs);
-            state.store->computeFSClosure(state.store->parseStorePath(std::string_view(path).substr(1)), refs);
+                for (auto & j : refs) {
-            for (auto & j : refs) {
+                    drv.inputSrcs.insert(j);
-                drv.inputSrcs.insert(j);
+                    if (j.isDerivation())
-                if (j.isDerivation())
+                        drv.inputDrvs[j] = state.store->readDerivation(j).outputNames();
-                    drv.inputDrvs[j] = state.store->readDerivation(j).outputNames();
+                }
-            }
+            },
-        }
+            [&](const NixStringContextElem::Built & b) {
-
+                drv.inputDrvs[b.drvPath].insert(b.output);
-        /* Handle derivation outputs of the form ‘!<name>!<path>’. */
+            },
-        else if (path.at(0) == '!') {
+            [&](const NixStringContextElem::Opaque & o) {
-            auto ctx = decodeContext(*state.store, path);
+                drv.inputSrcs.insert(o.path);
-            drv.inputDrvs[ctx.first].insert(ctx.second);
+            },
-        }
+        }, c.raw());
-
-        /* Otherwise it's a source file. */
-        else
-            drv.inputSrcs.insert(state.store->parseStorePath(path));
     }
 
     /* Do we have all required attributes? */
     if (drv.builder == "")
         state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("required attribute 'builder' missing"),
-            .errPos = state.positions[posDrvName]
+            .errPos = state.positions[noPos]
         }));
 
     if (drv.platform == "")
         state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("required attribute 'system' missing"),
-            .errPos = state.positions[posDrvName]
+            .errPos = state.positions[noPos]
         }));
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName))
         state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("derivation names are not allowed to end in '%s'", drvExtension),
-            .errPos = state.positions[posDrvName]
+            .errPos = state.positions[noPos]
         }));
 
     if (outputHash) {
@@ -1238,7 +1276,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
         if (outputs.size() != 1 || *(outputs.begin()) != "out")
             state.debugThrowLastTrace(Error({
                 .msg = hintfmt("multiple outputs are not supported in fixed-output derivations"),
-                .errPos = state.positions[posDrvName]
+                .errPos = state.positions[noPos]
             }));
 
         auto h = newHashAllowEmpty(*outputHash, parseHashTypeOpt(outputHashAlgo));
@@ -1259,7 +1297,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
         if (contentAddressed && isImpure)
             throw EvalError({
                 .msg = hintfmt("derivation cannot be both content-addressed and impure"),
-                .errPos = state.positions[posDrvName]
+                .errPos = state.positions[noPos]
             });
 
         auto ht = parseHashTypeOpt(outputHashAlgo).value_or(htSHA256);
@@ -1303,7 +1341,7 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
                 if (!h)
                     throw AssertionError({
                         .msg = hintfmt("derivation produced no hash for output '%s'", i),
-                        .errPos = state.positions[posDrvName],
+                        .errPos = state.positions[noPos],
                     });
                 auto outPath = state.store->makeOutputPath(i, *h, drvName);
                 drv.env[i] = state.store->printStorePath(outPath);
@@ -1336,11 +1374,12 @@ static void prim_derivationStrict(EvalState & state, const PosIdx pos, Value * *
         drvHashes.lock()->insert_or_assign(drvPath, h);
     }
 
-    auto attrs = state.buildBindings(1 + drv.outputs.size());
+    auto result = state.buildBindings(1 + drv.outputs.size());
-    attrs.alloc(state.sDrvPath).mkString(drvPathS, {"=" + drvPathS});
+    result.alloc(state.sDrvPath).mkString(drvPathS, {"=" + drvPathS});
     for (auto & i : drv.outputs)
-        mkOutputString(state, attrs, drvPath, drv, i);
+        mkOutputString(state, result, drvPath, drv, i);
-    v.mkAttrs(attrs);
+
+    v.mkAttrs(result);
 }
 
 static RegisterPrimOp primop_derivationStrict(RegisterPrimOp::Info {
@@ -1483,7 +1522,9 @@ static RegisterPrimOp primop_pathExists({
 static void prim_baseNameOf(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to builtins.baseNameOf")), context);
+    v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context,
+            "while evaluating the first argument passed to builtins.baseNameOf",
+            false, false)), context);
 }
 
 static RegisterPrimOp primop_baseNameOf({
@@ -1503,7 +1544,9 @@ static RegisterPrimOp primop_baseNameOf({
 static void prim_dirOf(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto path = state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to builtins.dirOf");
+    auto path = state.coerceToString(pos, *args[0], context,
+            "while evaluating the first argument passed to builtins.dirOf",
+            false, false);
     auto dir = dirOf(*path);
     if (args[0]->type() == nPath) v.mkPath(dir); else v.mkString(dir, context);
 }
@@ -1569,8 +1612,9 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value * * args, V
         i = getAttr(state, state.sPath, v2->attrs, "in an element of the __nixPath");
 
         PathSet context;
-        auto path = state.coerceToString(pos, *i->value, context, false, false,
+        auto path = state.coerceToString(pos, *i->value, context,
-                "while evaluating the `path` attribute of an element of the list passed to builtins.findFile").toOwned();
+                "while evaluating the `path` attribute of an element of the list passed to builtins.findFile",
+                false, false).toOwned();
 
         try {
             auto rewrites = state.realiseContext(context);
@@ -1623,23 +1667,73 @@ static RegisterPrimOp primop_hashFile({
     .fun = prim_hashFile,
 });
 
+
+/* Stringize a directory entry enum. Used by `readFileType' and `readDir'. */
+static const char * dirEntTypeToString(unsigned char dtType)
+{
+    /* Enum DT_(DIR|LNK|REG|UNKNOWN) */
+    switch(dtType) {
+        case DT_REG: return "regular";   break;
+        case DT_DIR: return "directory"; break;
+        case DT_LNK: return "symlink";   break;
+        default:     return "unknown";   break;
+    }
+    return "unknown";  /* Unreachable */
+}
+
+
+static void prim_readFileType(EvalState & state, const PosIdx pos, Value * * args, Value & v)
+{
+    auto path = realisePath(state, pos, *args[0]);
+    /* Retrieve the directory entry type and stringize it. */
+    v.mkString(dirEntTypeToString(getFileType(path)));
+}
+
+static RegisterPrimOp primop_readFileType({
+    .name = "__readFileType",
+    .args = {"p"},
+    .doc = R"(
+      Determine the directory entry type of a filesystem node, being
+      one of "directory", "regular", "symlink", or "unknown".
+    )",
+    .fun = prim_readFileType,
+});
+
 /* Read a directory (without . or ..) */
 static void prim_readDir(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     auto path = realisePath(state, pos, *args[0]);
 
+    // Retrieve directory entries for all nodes in a directory.
+    // This is similar to `getFileType` but is optimized to reduce system calls
+    // on many systems.
     DirEntries entries = readDirectory(path);
 
     auto attrs = state.buildBindings(entries.size());
 
+    // If we hit unknown directory entry types we may need to fallback to
+    // using `getFileType` on some systems.
+    // In order to reduce system calls we make each lookup lazy by using
+    // `builtins.readFileType` application.
+    Value * readFileType = nullptr;
+
     for (auto & ent : entries) {
-        if (ent.type == DT_UNKNOWN)
+        auto & attr = attrs.alloc(ent.name);
-            ent.type = getFileType(path + "/" + ent.name);
+        if (ent.type == DT_UNKNOWN) {
-        attrs.alloc(ent.name).mkString(
+            // Some filesystems or operating systems may not be able to return
-            ent.type == DT_REG ? "regular" :
+            // detailed node info quickly in this case we produce a thunk to
-            ent.type == DT_DIR ? "directory" :
+            // query the file type lazily.
-            ent.type == DT_LNK ? "symlink" :
+            auto epath = state.allocValue();
-            "unknown");
+            Path path2 = path + "/" + ent.name;
+            epath->mkString(path2);
+            if (!readFileType)
+                readFileType = &state.getBuiltin("readFileType");
+            attr.mkApp(readFileType, epath);
+        } else {
+            // This branch of the conditional is much more likely.
+            // Here we just stringize the directory entry type.
+            attr.mkString(dirEntTypeToString(ent.type));
+        }
     }
 
     v.mkAttrs(attrs);
@@ -1872,8 +1966,7 @@ static RegisterPrimOp primop_toFile({
       path.  The file has suffix *name*. This file can be used as an
       input to derivations. One application is to write builders
       “inline”. For instance, the following Nix expression combines the
-      [Nix expression for GNU Hello](expression-syntax.md) and its
+      Nix expression for GNU Hello and its build script into one file:
-      [build script](build-script.md) into one file:
 
       ```nix
       { stdenv, fetchurl, perl }:
@@ -1917,7 +2010,7 @@ static RegisterPrimOp primop_toFile({
       ```
 
       Note that `${configFile}` is a
-      [string interpolation](language/values.md#type-string), so the result of the
+      [string interpolation](@docroot@/language/values.md#type-string), so the result of the
       expression `configFile`
       (i.e., a path like `/nix/store/m7p7jfny445k...-foo.conf`) will be
       spliced into the resulting string.
@@ -2614,14 +2707,9 @@ static void prim_zipAttrsWith(EvalState & state, const PosIdx pos, Value * * arg
 
     for (unsigned int n = 0; n < listSize; ++n) {
         Value * vElem = listElems[n];
-        try {
+        state.forceAttrs(*vElem, noPos, "while evaluating a value of the list passed as second argument to builtins.zipAttrsWith");
-            state.forceAttrs(*vElem, noPos, "while evaluating a value of the list passed as second argument to builtins.zipAttrsWith");
+        for (auto & attr : *vElem->attrs)
-            for (auto & attr : *vElem->attrs)
+            attrsSeen[attr.name].first++;
-                attrsSeen[attr.name].first++;
-        } catch (TypeError & e) {
-            e.addTrace(state.positions[pos], hintfmt("while invoking '%s'", "zipAttrsWith"));
-            state.debugThrowLastTrace(e);
-        }
     }
 
     auto attrs = state.buildBindings(attrsSeen.size());
@@ -2807,7 +2895,7 @@ static RegisterPrimOp primop_map({
       example,
 
       ```nix
-      map (x"foo" + x) [ "bar" "bla" "abc" ]
+      map (x: "foo" + x) [ "bar" "bla" "abc" ]
       ```
 
       evaluates to `[ "foobar" "foobla" "fooabc" ]`.
@@ -3005,13 +3093,13 @@ 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)
-        state.debugThrowLastTrace(EvalError({
+        state.error("cannot create list of size %1%", len).debugThrow<EvalError>();
-            .msg = hintfmt("cannot create list of size %1%", len),
+
-            .errPos = state.positions[pos]
+    // More strict than striclty (!) necessary, but acceptable
-        }));
+    // as evaluating map without accessing any values makes little sense.
+    state.forceFunction(*args[0], noPos, "while evaluating the first argument passed to builtins.genList");
 
     state.mkList(v, len);
-
     for (unsigned int n = 0; n < (unsigned int) len; ++n) {
         auto arg = state.allocValue();
         arg->mkInt(n);
@@ -3059,6 +3147,8 @@ static void prim_sort(EvalState & state, const PosIdx pos, Value * * args, Value
     auto comparator = [&](Value * a, Value * b) {
         /* Optimization: if the comparator is lessThan, bypass
            callFunction. */
+        /* TODO: (layus) this is absurd. An optimisation like this
+           should be outside the lambda creation */
         if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
             return CompareValues(state, noPos, "while evaluating the ordering function passed to builtins.sort")(a, b);
 
@@ -3219,12 +3309,7 @@ static void prim_concatMap(EvalState & state, const PosIdx pos, Value * * args,
     for (unsigned int n = 0; n < nrLists; ++n) {
         Value * vElem = args[1]->listElems()[n];
         state.callFunction(*args[0], *vElem, lists[n], pos);
-        try {
+        state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)), "while evaluating the return value of the function passed to buitlins.concatMap");
-            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"));
-            state.debugThrowLastTrace(e);
-        }
         len += lists[n].listSize();
     }
 
@@ -3404,7 +3489,7 @@ static void prim_lessThan(EvalState & state, const PosIdx pos, Value * * args, V
     state.forceValue(*args[0], pos);
     state.forceValue(*args[1], pos);
     // pos is exact here, no need for a message.
-    CompareValues comp(state, pos, "");
+    CompareValues comp(state, noPos, "");
     v.mkBool(comp(args[0], args[1]));
 }
 
@@ -3431,7 +3516,9 @@ static RegisterPrimOp primop_lessThan({
 static void prim_toString(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, true, false, "while evaluating the first argument passed to builtins.toString");
+    auto s = state.coerceToString(pos, *args[0], context,
+            "while evaluating the first argument passed to builtins.toString",
+            true, false);
     v.mkString(*s, context);
 }
 
@@ -3783,21 +3870,18 @@ 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())
-        state.debugThrowLastTrace(EvalError({
+        state.error("'from' and 'to' arguments passed to builtins.replaceStrings have different lengths").atPos(pos).debugThrow<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());
     for (auto elem : args[0]->listItems())
-        from.emplace_back(state.forceString(*elem, pos, "while evaluating one of the strings to replace in builtins.replaceStrings"));
+        from.emplace_back(state.forceString(*elem, pos, "while evaluating one of the strings to replace passed to builtins.replaceStrings"));
 
     std::vector<std::pair<std::string, PathSet>> to;
     to.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
         PathSet ctx;
-        auto s = state.forceString(*elem, ctx, pos, "while evaluating one of the replacement strings of builtins.replaceStrings");
+        auto s = state.forceString(*elem, ctx, pos, "while evaluating one of the replacement strings passed to builtins.replaceStrings");
         to.emplace_back(s, std::move(ctx));
     }
 

src/libexpr/primops/context.cc

@@ -37,8 +37,15 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx p
     auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardOutputDependency");
 
     PathSet context2;
-    for (auto & p : context)
+    for (auto && p : context) {
-        context2.insert(p.at(0) == '=' ? std::string(p, 1) : p);
+        auto c = NixStringContextElem::parse(*state.store, p);
+        if (auto * ptr = std::get_if<NixStringContextElem::DrvDeep>(&c)) {
+            context2.emplace(state.store->printStorePath(ptr->drvPath));
+        } else {
+            /* Can reuse original item */
+            context2.emplace(std::move(p));
+        }
+    }
 
     v.mkString(*s, context2);
 }
@@ -74,34 +81,20 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
     };
     PathSet context;
     state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.getContext");
-    auto contextInfos = std::map<Path, ContextInfo>();
+    auto contextInfos = std::map<StorePath, ContextInfo>();
     for (const auto & p : context) {
-        Path drv;
+        NixStringContextElem ctx = NixStringContextElem::parse(*state.store, p);
-        std::string output;
+        std::visit(overloaded {
-        const Path * path = &p;
+            [&](NixStringContextElem::DrvDeep & d) {
-        if (p.at(0) == '=') {
+                contextInfos[d.drvPath].allOutputs = true;
-            drv = std::string(p, 1);
+            },
-            path = &drv;
+            [&](NixStringContextElem::Built & b) {
-        } else if (p.at(0) == '!') {
+                contextInfos[b.drvPath].outputs.emplace_back(std::move(b.output));
-            NixStringContextElem ctx = decodeContext(*state.store, p);
+            },
-            drv = state.store->printStorePath(ctx.first);
+            [&](NixStringContextElem::Opaque & o) {
-            output = ctx.second;
+                contextInfos[o.path].path = true;
-            path = &drv;
+            },
-        }
+        }, ctx.raw());
-        auto isPath = drv.empty();
-        auto isAllOutputs = (!drv.empty()) && output.empty();
-
-        auto iter = contextInfos.find(*path);
-        if (iter == contextInfos.end()) {
-            contextInfos.emplace(*path, ContextInfo{isPath, isAllOutputs, output.empty() ? Strings{} : Strings{std::move(output)}});
-        } else {
-            if (isPath)
-                iter->second.path = true;
-            else if (isAllOutputs)
-                iter->second.allOutputs = true;
-            else
-                iter->second.outputs.emplace_back(std::move(output));
-        }
     }
 
     auto attrs = state.buildBindings(contextInfos.size());
@@ -120,7 +113,7 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
             for (const auto & [i, output] : enumerate(info.second.outputs))
                 (outputsVal.listElems()[i] = state.allocValue())->mkString(output);
         }
-        attrs.alloc(info.first).mkAttrs(infoAttrs);
+        attrs.alloc(state.store->printStorePath(info.first)).mkAttrs(infoAttrs);
     }
 
     v.mkAttrs(attrs);

src/libexpr/primops/fetchMercurial.cc

@@ -22,7 +22,9 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
         for (auto & attr : *args[0]->attrs) {
             std::string_view n(state.symbols[attr.name]);
             if (n == "url")
-                url = state.coerceToString(attr.pos, *attr.value, context, false, false, "while evaluating the `url` attribute passed to builtins.fetchMercurial").toOwned();
+                url = state.coerceToString(attr.pos, *attr.value, context,
+                        "while evaluating the `url` attribute passed to builtins.fetchMercurial",
+                        false, false).toOwned();
             else if (n == "rev") {
                 // Ugly: unlike fetchGit, here the "rev" attribute can
                 // be both a revision or a branch/tag name.
@@ -48,7 +50,9 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
             });
 
     } else
-        url = state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to builtins.fetchMercurial").toOwned();
+        url = state.coerceToString(pos, *args[0], context,
+                "while evaluating the first argument passed to builtins.fetchMercurial",
+                false, false).toOwned();
 
     // FIXME: git externals probably can be used to bypass the URI
     // whitelist. Ah well.

src/libexpr/primops/fetchTree.cc

@@ -125,7 +125,7 @@ static void fetchTree(
             if (attr.name == state.sType) continue;
             state.forceValue(*attr.value, attr.pos);
             if (attr.value->type() == nPath || attr.value->type() == nString) {
-                auto s = state.coerceToString(attr.pos, *attr.value, context, false, false, "").toOwned();
+                auto s = state.coerceToString(attr.pos, *attr.value, context, "", false, false).toOwned();
                 attrs.emplace(state.symbols[attr.name],
                     state.symbols[attr.name] == "url"
                     ? type == "git"
@@ -151,7 +151,9 @@ static void fetchTree(
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
-        auto url = state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to the fetcher").toOwned();
+        auto url = state.coerceToString(pos, *args[0], context,
+                "while evaluating the first argument passed to the fetcher",
+                false, false).toOwned();
 
         if (type == "git") {
             fetchers::Attrs attrs;
@@ -218,6 +220,9 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
     } else
         url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");
 
+    if (who == "fetchTarball")
+        url = evalSettings.resolvePseudoUrl(*url);
+
     state.checkURI(*url);
 
     if (name == "")

src/libexpr/tests/local.mk

@@ -6,7 +6,9 @@ libexpr-tests_DIR := $(d)
 
 libexpr-tests_INSTALL_DIR :=
 
-libexpr-tests_SOURCES := $(wildcard $(d)/*.cc)
+libexpr-tests_SOURCES := \
+    $(wildcard $(d)/*.cc) \
+    $(wildcard $(d)/value/*.cc)
 
 libexpr-tests_CXXFLAGS += -I src/libexpr -I src/libutil -I src/libstore -I src/libexpr/tests
 

src/libexpr/tests/value/context.cc

@@ -0,0 +1,72 @@
+#include "value/context.hh"
+
+#include "libexprtests.hh"
+
+namespace nix {
+
+// Testing of trivial expressions
+struct NixStringContextElemTest : public LibExprTest {
+   const Store & store() const {
+       return *LibExprTest::store;
+   }
+};
+
+TEST_F(NixStringContextElemTest, empty_invalid) {
+    EXPECT_THROW(
+        NixStringContextElem::parse(store(), ""),
+        BadNixStringContextElem);
+}
+
+TEST_F(NixStringContextElemTest, single_bang_invalid) {
+    EXPECT_THROW(
+        NixStringContextElem::parse(store(), "!"),
+        BadNixStringContextElem);
+}
+
+TEST_F(NixStringContextElemTest, double_bang_invalid) {
+    EXPECT_THROW(
+        NixStringContextElem::parse(store(), "!!/"),
+        BadStorePath);
+}
+
+TEST_F(NixStringContextElemTest, eq_slash_invalid) {
+    EXPECT_THROW(
+        NixStringContextElem::parse(store(), "=/"),
+        BadStorePath);
+}
+
+TEST_F(NixStringContextElemTest, slash_invalid) {
+    EXPECT_THROW(
+        NixStringContextElem::parse(store(), "/"),
+        BadStorePath);
+}
+
+TEST_F(NixStringContextElemTest, opaque) {
+    std::string_view opaque = "/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x";
+    auto elem = NixStringContextElem::parse(store(), opaque);
+    auto * p = std::get_if<NixStringContextElem::Opaque>(&elem);
+    ASSERT_TRUE(p);
+    ASSERT_EQ(p->path, store().parseStorePath(opaque));
+    ASSERT_EQ(elem.to_string(store()), opaque);
+}
+
+TEST_F(NixStringContextElemTest, drvDeep) {
+    std::string_view drvDeep = "=/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
+    auto elem = NixStringContextElem::parse(store(), drvDeep);
+    auto * p = std::get_if<NixStringContextElem::DrvDeep>(&elem);
+    ASSERT_TRUE(p);
+    ASSERT_EQ(p->drvPath, store().parseStorePath(drvDeep.substr(1)));
+    ASSERT_EQ(elem.to_string(store()), drvDeep);
+}
+
+TEST_F(NixStringContextElemTest, built) {
+    std::string_view built = "!foo!/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
+    auto elem = NixStringContextElem::parse(store(), built);
+    auto * p = std::get_if<NixStringContextElem::Built>(&elem);
+    ASSERT_TRUE(p);
+    ASSERT_EQ(p->output, "foo");
+    ASSERT_EQ(p->drvPath, store().parseStorePath(built.substr(5)));
+    ASSERT_EQ(elem.to_string(store()), built);
+}
+
+}

src/libexpr/value-to-json.cc

@@ -1,6 +1,7 @@
 #include "value-to-json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
+#include "store-api.hh"
 
 #include <cstdlib>
 #include <iomanip>
@@ -35,7 +36,7 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nPath:
             if (copyToStore)
-                out = state.copyPathToStore(context, v.path);
+                out = state.store->printStorePath(state.copyPathToStore(context, v.path));
             else
                 out = v.path;
             break;

src/libexpr/value.hh

@@ -3,6 +3,7 @@
 #include <cassert>
 
 #include "symbol-table.hh"
+#include "value/context.hh"
 
 #if HAVE_BOEHMGC
 #include <gc/gc_allocator.h>
@@ -67,8 +68,6 @@ class XMLWriter;
 
 typedef int64_t NixInt;
 typedef double NixFloat;
-typedef std::pair<StorePath, std::string> NixStringContextElem;
-typedef std::vector<NixStringContextElem> NixStringContext;
 
 /* External values must descend from ExternalValueBase, so that
  * type-agnostic nix functions (e.g. showType) can be implemented
@@ -90,7 +89,7 @@ class ExternalValueBase
     /* Coerce the value to a string. Defaults to uncoercable, i.e. throws an
      * error.
      */
-    virtual std::string coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, std::string_view errorCtx) const;
+    virtual std::string coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const;
 
     /* Compare to another value of the same type. Defaults to uncomparable,
      * i.e. always false.

src/libexpr/value/context.cc

@@ -0,0 +1,67 @@
+#include "value/context.hh"
+#include "store-api.hh"
+
+#include <optional>
+
+namespace nix {
+
+NixStringContextElem NixStringContextElem::parse(const Store & store, std::string_view s0)
+{
+    std::string_view s = s0;
+
+    if (s.size() == 0) {
+        throw BadNixStringContextElem(s0,
+            "String context element should never be an empty string");
+    }
+    switch (s.at(0)) {
+    case '!': {
+        s = s.substr(1); // advance string to parse after first !
+        size_t index = s.find("!");
+        // This makes index + 1 safe. Index can be the length (one after index
+        // of last character), so given any valid character index --- a
+        // successful find --- we can add one.
+        if (index == std::string_view::npos) {
+            throw BadNixStringContextElem(s0,
+                "String content element beginning with '!' should have a second '!'");
+        }
+        return NixStringContextElem::Built {
+            .drvPath = store.parseStorePath(s.substr(index + 1)),
+            .output = std::string(s.substr(0, index)),
+        };
+    }
+    case '=': {
+        return NixStringContextElem::DrvDeep {
+            .drvPath = store.parseStorePath(s.substr(1)),
+        };
+    }
+    default: {
+        return NixStringContextElem::Opaque {
+            .path = store.parseStorePath(s),
+        };
+    }
+    }
+}
+
+std::string NixStringContextElem::to_string(const Store & store) const {
+    return std::visit(overloaded {
+        [&](const NixStringContextElem::Built & b) {
+            std::string res;
+            res += '!';
+            res += b.output;
+            res += '!';
+            res += store.printStorePath(b.drvPath);
+            return res;
+        },
+        [&](const NixStringContextElem::DrvDeep & d) {
+            std::string res;
+            res += '=';
+            res += store.printStorePath(d.drvPath);
+            return res;
+        },
+        [&](const NixStringContextElem::Opaque & o) {
+            return store.printStorePath(o.path);
+        },
+    }, raw());
+}
+
+}

src/libexpr/value/context.hh

@@ -0,0 +1,90 @@
+#pragma once
+
+#include "util.hh"
+#include "path.hh"
+
+#include <optional>
+
+#include <nlohmann/json_fwd.hpp>
+
+namespace nix {
+
+class BadNixStringContextElem : public Error
+{
+public:
+    std::string_view raw;
+
+    template<typename... Args>
+    BadNixStringContextElem(std::string_view raw_, const Args & ... args)
+        : Error("")
+    {
+        raw = raw_;
+        auto hf = hintfmt(args...);
+        err.msg = hintfmt("Bad String Context element: %1%: %2%", normaltxt(hf.str()), raw);
+    }
+};
+
+class Store;
+
+/* Plain opaque path to some store object.
+
+   Encoded as just the path: ‘<path>’.
+*/
+struct NixStringContextElem_Opaque {
+   StorePath path;
+};
+
+/* Path to a derivation and its entire build closure.
+
+   The path doesn't just refer to derivation itself and its closure, but
+   also all outputs of all derivations in that closure (including the
+   root derivation).
+
+   Encoded in the form ‘=<drvPath>’.
+*/
+struct NixStringContextElem_DrvDeep {
+   StorePath drvPath;
+};
+
+/* Derivation output.
+
+   Encoded in the form ‘!<output>!<drvPath>’.
+*/
+struct NixStringContextElem_Built {
+   StorePath drvPath;
+   std::string output;
+};
+
+using _NixStringContextElem_Raw = std::variant<
+    NixStringContextElem_Opaque,
+    NixStringContextElem_DrvDeep,
+    NixStringContextElem_Built
+>;
+
+struct NixStringContextElem : _NixStringContextElem_Raw {
+    using Raw = _NixStringContextElem_Raw;
+    using Raw::Raw;
+
+    using Opaque = NixStringContextElem_Opaque;
+    using DrvDeep = NixStringContextElem_DrvDeep;
+    using Built = NixStringContextElem_Built;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
+    inline Raw & raw() {
+        return static_cast<Raw &>(*this);
+    }
+
+    /* Decode a context string, one of:
+       - ‘<path>’
+       - ‘=<path>’
+       - ‘!<name>!<path>’
+      */
+    static NixStringContextElem parse(const Store & store, std::string_view s);
+    std::string to_string(const Store & store) const;
+};
+
+typedef std::vector<NixStringContextElem> NixStringContext;
+
+}

src/libmain/shared.cc

@@ -363,6 +363,7 @@ void printVersion(const std::string & programName)
             << "\n";
         std::cout << "Store directory: " << settings.nixStore << "\n";
         std::cout << "State directory: " << settings.nixStateDir << "\n";
+        std::cout << "Data directory: " << settings.nixDataDir << "\n";
     }
     throw Exit();
 }

src/libmain/shared.hh

@@ -39,7 +39,6 @@ void printVersion(const std::string & programName);
 void printGCWarning();
 
 class Store;
-struct StorePathWithOutputs;
 
 void printMissing(
     ref<Store> store,

src/libstore/binary-cache-store.cc

@@ -502,22 +502,9 @@ void BinaryCacheStore::addSignatures(const StorePath & storePath, const StringSe
     writeNarInfo(narInfo);
 }
 
-std::optional<std::string> BinaryCacheStore::getBuildLog(const StorePath & path)
+std::optional<std::string> BinaryCacheStore::getBuildLogExact(const StorePath & path)
 {
-    auto drvPath = path;
+    auto logPath = "log/" + std::string(baseNameOf(printStorePath(path)));
-
-    if (!path.isDerivation()) {
-        try {
-            auto info = queryPathInfo(path);
-            // FIXME: add a "Log" field to .narinfo
-            if (!info->deriver) return std::nullopt;
-            drvPath = *info->deriver;
-        } catch (InvalidPath &) {
-            return std::nullopt;
-        }
-    }
-
-    auto logPath = "log/" + std::string(baseNameOf(printStorePath(drvPath)));
 
     debug("fetching build log from binary cache '%s/%s'", getUri(), logPath);
 

src/libstore/binary-cache-store.hh

@@ -129,7 +129,7 @@ public:
 
     void addSignatures(const StorePath & storePath, const StringSet & sigs) override;
 
-    std::optional<std::string> getBuildLog(const StorePath & path) override;
+    std::optional<std::string> getBuildLogExact(const StorePath & path) override;
 
     void addBuildLog(const StorePath & drvPath, std::string_view log) override;
 

src/libstore/build/derivation-goal.cc

@@ -63,7 +63,7 @@
 namespace nix {
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath,
-    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
+    const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
     : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
     , useDerivation(true)
     , drvPath(drvPath)
@@ -82,7 +82,7 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath,
 
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
-    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
+    const OutputsSpec & wantedOutputs, Worker & worker, BuildMode buildMode)
     : Goal(worker, DerivedPath::Built { .drvPath = drvPath, .outputs = wantedOutputs })
     , useDerivation(false)
     , drvPath(drvPath)
@@ -142,18 +142,12 @@ void DerivationGoal::work()
     (this->*state)();
 }
 
-void DerivationGoal::addWantedOutputs(const StringSet & outputs)
+void DerivationGoal::addWantedOutputs(const OutputsSpec & outputs)
 {
-    /* If we already want all outputs, there is nothing to do. */
+    auto newWanted = wantedOutputs.union_(outputs);
-    if (wantedOutputs.empty()) return;
+    if (!newWanted.isSubsetOf(wantedOutputs))
-
-    if (outputs.empty()) {
-        wantedOutputs.clear();
         needRestart = true;
-    } else
+    wantedOutputs = newWanted;
-        for (auto & i : outputs)
-            if (wantedOutputs.insert(i).second)
-                needRestart = true;
 }
 
 
@@ -390,7 +384,7 @@ void DerivationGoal::repairClosure()
     auto outputs = queryDerivationOutputMap();
     StorePathSet outputClosure;
     for (auto & i : outputs) {
-        if (!wantOutput(i.first, wantedOutputs)) continue;
+        if (!wantedOutputs.contains(i.first)) continue;
         worker.store.computeFSClosure(i.second, outputClosure);
     }
 
@@ -422,7 +416,7 @@ void DerivationGoal::repairClosure()
         if (drvPath2 == outputsToDrv.end())
             addWaitee(upcast_goal(worker.makePathSubstitutionGoal(i, Repair)));
         else
-            addWaitee(worker.makeDerivationGoal(drvPath2->second, StringSet(), bmRepair));
+            addWaitee(worker.makeDerivationGoal(drvPath2->second, OutputsSpec::All(), bmRepair));
     }
 
     if (waitees.empty()) {
@@ -544,7 +538,8 @@ void DerivationGoal::inputsRealised()
                    However, the impure derivations feature still relies on this
                    fragile way of doing things, because its builds do not have
                    a representation in the store, which is a usability problem
-                   in itself */
+                   in itself. When implementing this logic entirely with lookups
+                   make sure that they're cached. */
                 if (auto outPath = get(inputDrvOutputs, { depDrvPath, j })) {
                     worker.store.computeFSClosure(*outPath, inputPaths);
                 }
@@ -990,10 +985,15 @@ void DerivationGoal::resolvedFinished()
 
         StorePathSet outputPaths;
 
-        // `wantedOutputs` might be empty, which means “all the outputs”
+        // `wantedOutputs` might merely indicate “all the outputs”
-        auto realWantedOutputs = wantedOutputs;
+        auto realWantedOutputs = std::visit(overloaded {
-        if (realWantedOutputs.empty())
+            [&](const OutputsSpec::All &) {
-            realWantedOutputs = resolvedDrv.outputNames();
+                return resolvedDrv.outputNames();
+            },
+            [&](const OutputsSpec::Names & names) {
+                return static_cast<std::set<std::string>>(names);
+            },
+        }, wantedOutputs.raw());
 
         for (auto & wantedOutput : realWantedOutputs) {
             auto initialOutput = get(initialOutputs, wantedOutput);
@@ -1321,7 +1321,14 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
     if (!drv->type().isPure()) return { false, {} };
 
     bool checkHash = buildMode == bmRepair;
-    auto wantedOutputsLeft = wantedOutputs;
+    auto wantedOutputsLeft = std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            return StringSet {};
+        },
+        [&](const OutputsSpec::Names & names) {
+            return static_cast<StringSet>(names);
+        },
+    }, wantedOutputs.raw());
     DrvOutputs validOutputs;
 
     for (auto & i : queryPartialDerivationOutputMap()) {
@@ -1330,7 +1337,7 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
             // this is an invalid output, gets catched with (!wantedOutputsLeft.empty())
             continue;
         auto & info = *initialOutput;
-        info.wanted = wantOutput(i.first, wantedOutputs);
+        info.wanted = wantedOutputs.contains(i.first);
         if (info.wanted)
             wantedOutputsLeft.erase(i.first);
         if (i.second) {
@@ -1368,7 +1375,7 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
             validOutputs.emplace(drvOutput, Realisation { drvOutput, info.known->path });
     }
 
-    // If we requested all the outputs via the empty set, we are always fine.
+    // If we requested all the outputs, we are always fine.
     // If we requested specific elements, the loop above removes all the valid
     // ones, so any that are left must be invalid.
     if (!wantedOutputsLeft.empty())

src/libstore/build/derivation-goal.hh

@@ -2,6 +2,7 @@
 
 #include "parsed-derivations.hh"
 #include "lock.hh"
+#include "outputs-spec.hh"
 #include "store-api.hh"
 #include "pathlocks.hh"
 #include "goal.hh"
@@ -55,7 +56,7 @@ struct DerivationGoal : public Goal
 
     /* The specific outputs that we need to build.  Empty means all of
        them. */
-    StringSet wantedOutputs;
+    OutputsSpec wantedOutputs;
 
     /* Mapping from input derivations + output names to actual store
        paths. This is filled in by waiteeDone() as each dependency
@@ -128,10 +129,10 @@ struct DerivationGoal : public Goal
     std::string machineName;
 
     DerivationGoal(const StorePath & drvPath,
-        const StringSet & wantedOutputs, Worker & worker,
+        const OutputsSpec & wantedOutputs, Worker & worker,
         BuildMode buildMode = bmNormal);
     DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
-        const StringSet & wantedOutputs, Worker & worker,
+        const OutputsSpec & wantedOutputs, Worker & worker,
         BuildMode buildMode = bmNormal);
     virtual ~DerivationGoal();
 
@@ -142,7 +143,7 @@ struct DerivationGoal : public Goal
     void work() override;
 
     /* Add wanted outputs to an already existing derivation goal. */
-    void addWantedOutputs(const StringSet & outputs);
+    void addWantedOutputs(const OutputsSpec & outputs);
 
     /* The states. */
     void getDerivation();

src/libstore/build/entry-points.cc

@@ -80,7 +80,7 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
     BuildMode buildMode)
 {
     Worker worker(*this, *this);
-    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
+    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, OutputsSpec::All {}, buildMode);
 
     try {
         worker.run(Goals{goal});
@@ -89,7 +89,10 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
         return BuildResult {
             .status = BuildResult::MiscFailure,
             .errorMsg = e.msg(),
-            .path = DerivedPath::Built { .drvPath = drvPath },
+            .path = DerivedPath::Built {
+                .drvPath = drvPath,
+                .outputs = OutputsSpec::All { },
+            },
         };
     };
 }
@@ -130,7 +133,8 @@ void LocalStore::repairPath(const StorePath & path)
         auto info = queryPathInfo(path);
         if (info->deriver && isValidPath(*info->deriver)) {
             goals.clear();
-            goals.insert(worker.makeDerivationGoal(*info->deriver, StringSet(), bmRepair));
+            // FIXME: Should just build the specific output we need.
+            goals.insert(worker.makeDerivationGoal(*info->deriver, OutputsSpec::All { }, bmRepair));
             worker.run(goals);
         } else
             throw Error(worker.exitStatus(), "cannot repair path '%s'", printStorePath(path));

src/libstore/build/local-derivation-goal.cc

@@ -1459,7 +1459,7 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
             unknown, downloadSize, narSize);
     }
 
-    virtual std::optional<std::string> getBuildLog(const StorePath & path) override
+    virtual std::optional<std::string> getBuildLogExact(const StorePath & path) override
     { return std::nullopt; }
 
     virtual void addBuildLog(const StorePath & path, std::string_view log) override
@@ -2050,10 +2050,14 @@ void LocalDerivationGoal::runChild()
                     sandboxProfile += "(deny default (with no-log))\n";
                 }
 
-                sandboxProfile += "(import \"sandbox-defaults.sb\")\n";
+                sandboxProfile +=
+                    #include "sandbox-defaults.sb"
+                    ;
 
                 if (!derivationType.isSandboxed())
-                    sandboxProfile += "(import \"sandbox-network.sb\")\n";
+                    sandboxProfile +=
+                        #include "sandbox-network.sb"
+                        ;
 
                 /* Add the output paths we'll use at build-time to the chroot */
                 sandboxProfile += "(allow file-read* file-write* process-exec\n";
@@ -2096,7 +2100,9 @@ void LocalDerivationGoal::runChild()
 
                 sandboxProfile += additionalSandboxProfile;
             } else
-                sandboxProfile += "(import \"sandbox-minimal.sb\")\n";
+                sandboxProfile +=
+                    #include "sandbox-minimal.sb"
+                    ;
 
             debug("Generated sandbox profile:");
             debug(sandboxProfile);
@@ -2121,8 +2127,6 @@ void LocalDerivationGoal::runChild()
                 args.push_back(sandboxFile);
                 args.push_back("-D");
                 args.push_back("_GLOBAL_TMP_DIR=" + globalTmpDir);
-                args.push_back("-D");
-                args.push_back("IMPORT_DIR=" + settings.nixDataDir + "/nix/sandbox/");
                 if (allowLocalNetworking) {
                     args.push_back("-D");
                     args.push_back(std::string("_ALLOW_LOCAL_NETWORKING=1"));
@@ -2748,7 +2752,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             signRealisation(thisRealisation);
             worker.store.registerDrvOutput(thisRealisation);
         }
-        if (wantOutput(outputName, wantedOutputs))
+        if (wantedOutputs.contains(outputName))
             builtOutputs.emplace(thisRealisation.id, thisRealisation);
     }
 

src/libstore/build/sandbox-defaults.sb

@@ -1,3 +1,5 @@
+R""(
+
 (define TMPDIR (param "_GLOBAL_TMP_DIR"))
 
 (deny default)
@@ -104,3 +106,5 @@
        (subpath "/System/Library/Apple/usr/libexec/oah")
        (subpath "/System/Library/LaunchDaemons/com.apple.oahd.plist")
        (subpath "/Library/Apple/System/Library/LaunchDaemons/com.apple.oahd.plist"))
+
+)""

src/libstore/build/sandbox-minimal.sb

@@ -1,5 +1,9 @@
+R""(
+
 (allow default)
 
 ; Disallow creating setuid/setgid binaries, since that
 ; would allow breaking build user isolation.
 (deny file-write-setugid)
+
+)""

src/libstore/build/sandbox-network.sb

@@ -1,3 +1,5 @@
+R""(
+
 ; Allow local and remote network traffic.
 (allow network* (local ip) (remote ip))
 
@@ -18,3 +20,5 @@
 ; Allow access to trustd.
 (allow mach-lookup (global-name "com.apple.trustd"))
 (allow mach-lookup (global-name "com.apple.trustd.agent"))
+
+)""

src/libstore/build/worker.cc

@@ -42,7 +42,7 @@ Worker::~Worker()
 
 std::shared_ptr<DerivationGoal> Worker::makeDerivationGoalCommon(
     const StorePath & drvPath,
-    const StringSet & wantedOutputs,
+    const OutputsSpec & wantedOutputs,
     std::function<std::shared_ptr<DerivationGoal>()> mkDrvGoal)
 {
     std::weak_ptr<DerivationGoal> & goal_weak = derivationGoals[drvPath];
@@ -59,7 +59,7 @@ std::shared_ptr<DerivationGoal> Worker::makeDerivationGoalCommon(
 
 
 std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drvPath,
-    const StringSet & wantedOutputs, BuildMode buildMode)
+    const OutputsSpec & wantedOutputs, BuildMode buildMode)
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
         return !dynamic_cast<LocalStore *>(&store)
@@ -70,7 +70,7 @@ std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drv
 
 
 std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath & drvPath,
-    const BasicDerivation & drv, const StringSet & wantedOutputs, BuildMode buildMode)
+    const BasicDerivation & drv, const OutputsSpec & wantedOutputs, BuildMode buildMode)
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
         return !dynamic_cast<LocalStore *>(&store)

src/libstore/build/worker.hh

@@ -140,15 +140,15 @@ public:
     /* derivation goal */
 private:
     std::shared_ptr<DerivationGoal> makeDerivationGoalCommon(
-        const StorePath & drvPath, const StringSet & wantedOutputs,
+        const StorePath & drvPath, const OutputsSpec & wantedOutputs,
         std::function<std::shared_ptr<DerivationGoal>()> mkDrvGoal);
 public:
     std::shared_ptr<DerivationGoal> makeDerivationGoal(
         const StorePath & drvPath,
-        const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
+        const OutputsSpec & wantedOutputs, BuildMode buildMode = bmNormal);
     std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(
         const StorePath & drvPath, const BasicDerivation & drv,
-        const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
+        const OutputsSpec & wantedOutputs, BuildMode buildMode = bmNormal);
 
     /* substitution goal */
     std::shared_ptr<PathSubstitutionGoal> makePathSubstitutionGoal(const StorePath & storePath, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);

src/libstore/daemon.cc

@@ -222,7 +222,8 @@ struct ClientSettings
                     else if (!hasSuffix(s, "/") && trusted.count(s + "/"))
                         subs.push_back(s + "/");
                     else
-                        warn("ignoring untrusted substituter '%s'", s);
+                        warn("ignoring untrusted substituter '%s', you are not a trusted user.\n"
+                             "Run `man nix.conf` for more information on the `substituters` configuration option.", s);
                 res = subs;
                 return true;
             };

src/libstore/derivations.cc

@@ -688,12 +688,6 @@ std::map<std::string, Hash> staticOutputHashes(Store & store, const Derivation &
 }
 
 
-bool wantOutput(const std::string & output, const std::set<std::string> & wanted)
-{
-    return wanted.empty() || wanted.find(output) != wanted.end();
-}
-
-
 static DerivationOutput readDerivationOutput(Source & in, const Store & store)
 {
     const auto pathS = readString(in);

src/libstore/derivations.hh

@@ -13,6 +13,7 @@
 
 namespace nix {
 
+class Store;
 
 /* Abstract syntax of derivations. */
 
@@ -294,8 +295,6 @@ typedef std::map<StorePath, DrvHash> DrvHashes;
 // FIXME: global, though at least thread-safe.
 extern Sync<DrvHashes> drvHashes;
 
-bool wantOutput(const std::string & output, const std::set<std::string> & wanted);
-
 struct Source;
 struct Sink;
 

src/libstore/derived-path.cc

@@ -19,11 +19,11 @@ nlohmann::json DerivedPath::Built::toJSON(ref<Store> store) const {
     res["drvPath"] = store->printStorePath(drvPath);
     // Fallback for the input-addressed derivation case: We expect to always be
     // able to print the output paths, so let’s do it
-    const auto knownOutputs = store->queryPartialDerivationOutputMap(drvPath);
+    const auto outputMap = store->queryPartialDerivationOutputMap(drvPath);
-    for (const auto & output : outputs) {
+    for (const auto & [output, outputPathOpt] : outputMap) {
-        auto knownOutput = get(knownOutputs, output);
+        if (!outputs.contains(output)) continue;
-        if (knownOutput && *knownOutput)
+        if (outputPathOpt)
-            res["outputs"][output] = store->printStorePath(**knownOutput);
+            res["outputs"][output] = store->printStorePath(*outputPathOpt);
         else
             res["outputs"][output] = nullptr;
     }
@@ -63,7 +63,7 @@ std::string DerivedPath::Built::to_string(const Store & store) const
 {
     return store.printStorePath(drvPath)
         + "!"
-        + (outputs.empty() ? std::string { "*" } : concatStringsSep(",", outputs));
+        + outputs.to_string();
 }
 
 std::string DerivedPath::to_string(const Store & store) const
@@ -81,15 +81,10 @@ DerivedPath::Opaque DerivedPath::Opaque::parse(const Store & store, std::string_
 
 DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_view drvS, std::string_view outputsS)
 {
-    auto drvPath = store.parseStorePath(drvS);
+    return {
-    std::set<std::string> outputs;
+        .drvPath = store.parseStorePath(drvS),
-    if (outputsS != "*") {
+        .outputs = OutputsSpec::parse(outputsS),
-        outputs = tokenizeString<std::set<std::string>>(outputsS, ",");
+    };
-        if (outputs.empty())
-            throw Error(
-                 "Explicit list of wanted outputs '%s' must not be empty. Consider using '*' as a wildcard meaning all outputs if no output in particular is wanted.", outputsS);
-	}
-    return {drvPath, outputs};
 }
 
 DerivedPath DerivedPath::parse(const Store & store, std::string_view s)

src/libstore/derived-path.hh

@@ -3,6 +3,7 @@
 #include "util.hh"
 #include "path.hh"
 #include "realisation.hh"
+#include "outputs-spec.hh"
 
 #include <optional>
 
@@ -44,7 +45,7 @@ struct DerivedPathOpaque {
  */
 struct DerivedPathBuilt {
     StorePath drvPath;
-    std::set<std::string> outputs;
+    OutputsSpec outputs;
 
     std::string to_string(const Store & store) const;
     static DerivedPathBuilt parse(const Store & store, std::string_view, std::string_view);

src/libstore/gc.cc

@@ -77,60 +77,73 @@ Path LocalFSStore::addPermRoot(const StorePath & storePath, const Path & _gcRoot
 }
 
 
-void LocalStore::addTempRoot(const StorePath & path)
+void LocalStore::createTempRootsFile()
 {
-    auto state(_state.lock());
+    auto fdTempRoots(_fdTempRoots.lock());
 
     /* Create the temporary roots file for this process. */
-    if (!state->fdTempRoots) {
+    if (*fdTempRoots) return;
 
-        while (1) {
+    while (1) {
-            if (pathExists(fnTempRoots))
+        if (pathExists(fnTempRoots))
-                /* It *must* be stale, since there can be no two
+            /* It *must* be stale, since there can be no two
-                   processes with the same pid. */
+               processes with the same pid. */
-                unlink(fnTempRoots.c_str());
+            unlink(fnTempRoots.c_str());
 
-            state->fdTempRoots = openLockFile(fnTempRoots, true);
+        *fdTempRoots = openLockFile(fnTempRoots, true);
 
-            debug("acquiring write lock on '%s'", fnTempRoots);
+        debug("acquiring write lock on '%s'", fnTempRoots);
-            lockFile(state->fdTempRoots.get(), ltWrite, true);
+        lockFile(fdTempRoots->get(), ltWrite, true);
 
-            /* Check whether the garbage collector didn't get in our
+        /* Check whether the garbage collector didn't get in our
-               way. */
+           way. */
-            struct stat st;
+        struct stat st;
-            if (fstat(state->fdTempRoots.get(), &st) == -1)
+        if (fstat(fdTempRoots->get(), &st) == -1)
-                throw SysError("statting '%1%'", fnTempRoots);
+            throw SysError("statting '%1%'", fnTempRoots);
-            if (st.st_size == 0) break;
+        if (st.st_size == 0) break;
 
-            /* The garbage collector deleted this file before we could
+        /* The garbage collector deleted this file before we could get
-               get a lock.  (It won't delete the file after we get a
+           a lock.  (It won't delete the file after we get a lock.)
-               lock.)  Try again. */
+           Try again. */
-        }
+    }
+}
 
+
+void LocalStore::addTempRoot(const StorePath & path)
+{
+    createTempRootsFile();
+
+    /* Open/create the global GC lock file. */
+    {
+        auto fdGCLock(_fdGCLock.lock());
+        if (!*fdGCLock)
+            *fdGCLock = openGCLock();
     }
 
-    if (!state->fdGCLock)
-        state->fdGCLock = openGCLock();
-
  restart:
-    FdLock gcLock(state->fdGCLock.get(), ltRead, false, "");
+    /* Try to acquire a shared global GC lock (non-blocking). This
+       only succeeds if the garbage collector is not currently
+       running. */
+    FdLock gcLock(_fdGCLock.lock()->get(), ltRead, false, "");
 
     if (!gcLock.acquired) {
         /* We couldn't get a shared global GC lock, so the garbage
            collector is running. So we have to connect to the garbage
            collector and inform it about our root. */
-        if (!state->fdRootsSocket) {
+        auto fdRootsSocket(_fdRootsSocket.lock());
+
+        if (!*fdRootsSocket) {
             auto socketPath = stateDir.get() + gcSocketPath;
             debug("connecting to '%s'", socketPath);
-            state->fdRootsSocket = createUnixDomainSocket();
+            *fdRootsSocket = createUnixDomainSocket();
             try {
-                nix::connect(state->fdRootsSocket.get(), socketPath);
+                nix::connect(fdRootsSocket->get(), socketPath);
             } catch (SysError & e) {
                 /* The garbage collector may have exited, so we need to
                    restart. */
                 if (e.errNo == ECONNREFUSED) {
                     debug("GC socket connection refused");
-                    state->fdRootsSocket.close();
+                    fdRootsSocket->close();
                     goto restart;
                 }
                 throw;
@@ -139,9 +152,9 @@ void LocalStore::addTempRoot(const StorePath & path)
 
         try {
             debug("sending GC root '%s'", printStorePath(path));
-            writeFull(state->fdRootsSocket.get(), printStorePath(path) + "\n", false);
+            writeFull(fdRootsSocket->get(), printStorePath(path) + "\n", false);
             char c;
-            readFull(state->fdRootsSocket.get(), &c, 1);
+            readFull(fdRootsSocket->get(), &c, 1);
             assert(c == '1');
             debug("got ack for GC root '%s'", printStorePath(path));
         } catch (SysError & e) {
@@ -149,20 +162,21 @@ void LocalStore::addTempRoot(const StorePath & path)
                restart. */
             if (e.errNo == EPIPE || e.errNo == ECONNRESET) {
                 debug("GC socket disconnected");
-                state->fdRootsSocket.close();
+                fdRootsSocket->close();
                 goto restart;
             }
             throw;
         } catch (EndOfFile & e) {
             debug("GC socket disconnected");
-            state->fdRootsSocket.close();
+            fdRootsSocket->close();
             goto restart;
         }
     }
 
-    /* Append the store path to the temporary roots file. */
+    /* Record the store path in the temporary roots file so it will be
+       seen by a future run of the garbage collector. */
     auto s = printStorePath(path) + '\0';
-    writeFull(state->fdTempRoots.get(), s);
+    writeFull(_fdTempRoots.lock()->get(), s);
 }
 
 

src/libstore/globals.hh

@@ -570,11 +570,15 @@ public:
         {"cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="},
         "trusted-public-keys",
         R"(
-          A whitespace-separated list of public keys. When paths are copied
+          A whitespace-separated list of public keys.
-          from another Nix store (such as a binary cache), they must be
+
-          signed with one of these keys. For example:
+          At least one of the following condition must be met
-          `cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+          for Nix to accept copying a store object from another
-          hydra.nixos.org-1:CNHJZBh9K4tP3EKF6FkkgeVYsS3ohTl+oS0Qa8bezVs=`.
+          Nix store (such as a substituter):
+
+          - the store object has been signed using a key in the trusted keys list
+          - the [`require-sigs`](#conf-require-sigs) option has been set to `false`
+          - the store object is [output-addressed](@docroot@/glossary.md#gloss-output-addressed-store-object)
         )",
         {"binary-cache-public-keys"}};
 
@@ -670,13 +674,14 @@ public:
           independently. Lower value means higher priority.
           The default is `https://cache.nixos.org`, with a Priority of 40.
 
-          Nix will copy a store path from a remote store only if one
+          At least one of the following conditions must be met for Nix to use
-          of the following is true:
+          a substituter:
 
-          - the store object is signed by one of the [`trusted-public-keys`](#conf-trusted-public-keys)
           - the substituter is in the [`trusted-substituters`](#conf-trusted-substituters) list
-          - the [`require-sigs`](#conf-require-sigs) option has been set to `false`
+          - the user calling Nix is in the [`trusted-users`](#conf-trusted-users) list
-          - the store object is [output-addressed](glossary.md#gloss-output-addressed-store-object)
+
+          In addition, each store path should be trusted as described
+          in [`trusted-public-keys`](#conf-trusted-public-keys)
         )",
         {"binary-caches"}};
 

src/libstore/legacy-ssh-store.cc

@@ -279,7 +279,12 @@ public:
 
         conn->to.flush();
 
-        BuildResult status { .path = DerivedPath::Built { .drvPath = drvPath } };
+        BuildResult status {
+            .path = DerivedPath::Built {
+                .drvPath = drvPath,
+                .outputs = OutputsSpec::All { },
+            },
+        };
         status.status = (BuildResult::Status) readInt(conn->from);
         conn->from >> status.errorMsg;
 

src/libstore/local-fs-store.cc

@@ -87,20 +87,8 @@ void LocalFSStore::narFromPath(const StorePath & path, Sink & sink)
 
 const std::string LocalFSStore::drvsLogDir = "drvs";
 
-std::optional<std::string> LocalFSStore::getBuildLog(const StorePath & path_)
+std::optional<std::string> LocalFSStore::getBuildLogExact(const StorePath & path)
 {
-    auto path = path_;
-
-    if (!path.isDerivation()) {
-        try {
-            auto info = queryPathInfo(path);
-            if (!info->deriver) return std::nullopt;
-            path = *info->deriver;
-        } catch (InvalidPath &) {
-            return std::nullopt;
-        }
-    }
-
     auto baseName = path.to_string();
 
     for (int j = 0; j < 2; j++) {

src/libstore/local-fs-store.hh

@@ -50,7 +50,7 @@ public:
         return getRealStoreDir() + "/" + std::string(storePath, storeDir.size() + 1);
     }
 
-    std::optional<std::string> getBuildLog(const StorePath & path) override;
+    std::optional<std::string> getBuildLogExact(const StorePath & path) override;
 
 };
 

src/libstore/local-store.cc

@@ -441,9 +441,9 @@ LocalStore::~LocalStore()
     }
 
     try {
-        auto state(_state.lock());
+        auto fdTempRoots(_fdTempRoots.lock());
-        if (state->fdTempRoots) {
+        if (*fdTempRoots) {
-            state->fdTempRoots = -1;
+            *fdTempRoots = -1;
             unlink(fnTempRoots.c_str());
         }
     } catch (...) {

src/libstore/local-store.hh

@@ -59,15 +59,6 @@ private:
         struct Stmts;
         std::unique_ptr<Stmts> stmts;
 
-        /* The global GC lock  */
-        AutoCloseFD fdGCLock;
-
-        /* The file to which we write our temporary roots. */
-        AutoCloseFD fdTempRoots;
-
-        /* Connection to the garbage collector. */
-        AutoCloseFD fdRootsSocket;
-
         /* The last time we checked whether to do an auto-GC, or an
            auto-GC finished. */
         std::chrono::time_point<std::chrono::steady_clock> lastGCCheck;
@@ -156,6 +147,21 @@ public:
 
     void addTempRoot(const StorePath & path) override;
 
+private:
+
+    void createTempRootsFile();
+
+    /* The file to which we write our temporary roots. */
+    Sync<AutoCloseFD> _fdTempRoots;
+
+    /* The global GC lock. */
+    Sync<AutoCloseFD> _fdGCLock;
+
+    /* Connection to the garbage collector. */
+    Sync<AutoCloseFD> _fdRootsSocket;
+
+public:
+
     void addIndirectRoot(const Path & path) override;
 
 private:

src/libstore/local.mk

@@ -13,10 +13,6 @@ ifdef HOST_LINUX
  libstore_LDFLAGS += -ldl
 endif
 
-ifdef HOST_DARWIN
-libstore_FILES = sandbox-defaults.sb sandbox-minimal.sb sandbox-network.sb
-endif
-
 $(foreach file,$(libstore_FILES),$(eval $(call install-data-in,$(d)/$(file),$(datadir)/nix/sandbox)))
 
 ifeq ($(ENABLE_S3), 1)

src/libstore/lock.cc

@@ -123,8 +123,12 @@ struct AutoUserLock : UserLock
 
     std::vector<gid_t> getSupplementaryGIDs() override { return {}; }
 
-    static std::unique_ptr<UserLock> acquire(uid_t nrIds, bool useChroot)
+    static std::unique_ptr<UserLock> acquire(uid_t nrIds, bool useUserNamespace)
     {
+        #if !defined(__linux__)
+        useUserNamespace = false;
+        #endif
+
         settings.requireExperimentalFeature(Xp::AutoAllocateUids);
         assert(settings.startId > 0);
         assert(settings.uidCount % maxIdsPerBuild == 0);
@@ -157,7 +161,7 @@ struct AutoUserLock : UserLock
                 auto lock = std::make_unique<AutoUserLock>();
                 lock->fdUserLock = std::move(fd);
                 lock->firstUid = firstUid;
-                if (useChroot)
+                if (useUserNamespace)
                     lock->firstGid = firstUid;
                 else {
                     struct group * gr = getgrnam(settings.buildUsersGroup.get().c_str());
@@ -174,10 +178,10 @@ struct AutoUserLock : UserLock
     }
 };
 
-std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useChroot)
+std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useUserNamespace)
 {
     if (settings.autoAllocateUids)
-        return AutoUserLock::acquire(nrIds, useChroot);
+        return AutoUserLock::acquire(nrIds, useUserNamespace);
     else
         return SimpleUserLock::acquire();
 }

src/libstore/lock.hh

@@ -31,7 +31,7 @@ struct UserLock
 
 /* Acquire a user lock for a UID range of size `nrIds`. Note that this
    may return nullptr if no user is available. */
-std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useChroot);
+std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds, bool useUserNamespace);
 
 bool useBuildUsers();
 

src/libstore/log-store.cc

@@ -0,0 +1,12 @@
+#include "log-store.hh"
+
+namespace nix {
+
+std::optional<std::string> LogStore::getBuildLog(const StorePath & path) {
+    auto maybePath = getBuildDerivationPath(path);
+    if (!maybePath)
+        return std::nullopt;
+    return getBuildLogExact(maybePath.value());
+}
+
+}

src/libstore/log-store.hh

@@ -11,7 +11,9 @@ struct LogStore : public virtual Store
 
     /* Return the build log of the specified store path, if available,
        or null otherwise. */
-    virtual std::optional<std::string> getBuildLog(const StorePath & path) = 0;
+    std::optional<std::string> getBuildLog(const StorePath & path);
+
+    virtual std::optional<std::string> getBuildLogExact(const StorePath & path) = 0;
 
     virtual void addBuildLog(const StorePath & path, std::string_view log) = 0;
 

src/libstore/misc.cc

@@ -185,7 +185,7 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
                     knownOutputPaths = false;
                     break;
                 }
-                if (wantOutput(outputName, bfd.outputs) && !isValidPath(*pathOpt))
+                if (bfd.outputs.contains(outputName) && !isValidPath(*pathOpt))
                     invalid.insert(*pathOpt);
             }
             if (knownOutputPaths && invalid.empty()) return;
@@ -301,4 +301,47 @@ std::map<DrvOutput, StorePath> drvOutputReferences(
     return drvOutputReferences(Realisation::closure(store, inputRealisations), info->references);
 }
 
+OutputPathMap resolveDerivedPath(Store & store, const DerivedPath::Built & bfd, Store * evalStore_)
+{
+    auto & evalStore = evalStore_ ? *evalStore_ : store;
+
+    OutputPathMap outputs;
+    auto drv = evalStore.readDerivation(bfd.drvPath);
+    auto outputHashes = staticOutputHashes(store, drv);
+    auto drvOutputs = drv.outputsAndOptPaths(store);
+    auto outputNames = std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            StringSet names;
+            for (auto & [outputName, _] : drv.outputs)
+                names.insert(outputName);
+            return names;
+        },
+        [&](const OutputsSpec::Names & names) {
+            return static_cast<std::set<std::string>>(names);
+        },
+    }, bfd.outputs.raw());
+    for (auto & output : outputNames) {
+        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 { *outputHash, output };
+            auto realisation = store.queryRealisation(outputId);
+            if (!realisation)
+                throw MissingRealisation(outputId);
+            outputs.insert_or_assign(output, realisation->outPath);
+        } else {
+            // If ca-derivations isn't enabled, assume that
+            // the output path is statically known.
+            auto drvOutput = get(drvOutputs, output);
+            assert(drvOutput);
+            assert(drvOutput->second);
+            outputs.insert_or_assign(output, *drvOutput->second);
+        }
+    }
+    return outputs;
+}
+
 }

src/libstore/outputs-spec.cc

@@ -0,0 +1,195 @@
+#include <regex>
+#include <nlohmann/json.hpp>
+
+#include "util.hh"
+#include "regex-combinators.hh"
+#include "outputs-spec.hh"
+#include "path-regex.hh"
+
+namespace nix {
+
+bool OutputsSpec::contains(const std::string & outputName) const
+{
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            return true;
+        },
+        [&](const OutputsSpec::Names & outputNames) {
+            return outputNames.count(outputName) > 0;
+        },
+    }, raw());
+}
+
+static std::string outputSpecRegexStr =
+    regex::either(
+        regex::group(R"(\*)"),
+        regex::group(regex::list(nameRegexStr)));
+
+std::optional<OutputsSpec> OutputsSpec::parseOpt(std::string_view s)
+{
+    static std::regex regex(std::string { outputSpecRegexStr });
+
+    std::smatch match;
+    std::string s2 { s }; // until some improves std::regex
+    if (!std::regex_match(s2, match, regex))
+        return std::nullopt;
+
+    if (match[1].matched)
+        return { OutputsSpec::All {} };
+
+    if (match[2].matched)
+        return OutputsSpec::Names { tokenizeString<StringSet>(match[2].str(), ",") };
+
+    assert(false);
+}
+
+
+OutputsSpec OutputsSpec::parse(std::string_view s)
+{
+    std::optional spec = parseOpt(s);
+    if (!spec)
+        throw Error("invalid outputs specifier '%s'", s);
+    return *spec;
+}
+
+
+std::optional<std::pair<std::string_view, ExtendedOutputsSpec>> ExtendedOutputsSpec::parseOpt(std::string_view s)
+{
+    auto found = s.rfind('^');
+
+    if (found == std::string::npos)
+        return std::pair { s, ExtendedOutputsSpec::Default {} };
+
+    auto specOpt = OutputsSpec::parseOpt(s.substr(found + 1));
+    if (!specOpt)
+        return std::nullopt;
+    return std::pair { s.substr(0, found), ExtendedOutputsSpec::Explicit { *std::move(specOpt) } };
+}
+
+
+std::pair<std::string_view, ExtendedOutputsSpec> ExtendedOutputsSpec::parse(std::string_view s)
+{
+    std::optional spec = parseOpt(s);
+    if (!spec)
+        throw Error("invalid extended outputs specifier '%s'", s);
+    return *spec;
+}
+
+
+std::string OutputsSpec::to_string() const
+{
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) -> std::string {
+            return "*";
+        },
+        [&](const OutputsSpec::Names & outputNames) -> std::string {
+            return concatStringsSep(",", outputNames);
+        },
+    }, raw());
+}
+
+
+std::string ExtendedOutputsSpec::to_string() const
+{
+    return std::visit(overloaded {
+        [&](const ExtendedOutputsSpec::Default &) -> std::string {
+            return "";
+        },
+        [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> std::string {
+            return "^" + outputSpec.to_string();
+        },
+    }, raw());
+}
+
+
+OutputsSpec OutputsSpec::union_(const OutputsSpec & that) const
+{
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) -> OutputsSpec {
+            return OutputsSpec::All { };
+        },
+        [&](const OutputsSpec::Names & theseNames) -> OutputsSpec {
+            return std::visit(overloaded {
+                [&](const OutputsSpec::All &) -> OutputsSpec {
+                    return OutputsSpec::All {};
+                },
+                [&](const OutputsSpec::Names & thoseNames) -> OutputsSpec {
+                    OutputsSpec::Names ret = theseNames;
+                    ret.insert(thoseNames.begin(), thoseNames.end());
+                    return ret;
+                },
+            }, that.raw());
+        },
+    }, raw());
+}
+
+
+bool OutputsSpec::isSubsetOf(const OutputsSpec & that) const
+{
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            return true;
+        },
+        [&](const OutputsSpec::Names & thoseNames) {
+            return std::visit(overloaded {
+                [&](const OutputsSpec::All &) {
+                    return false;
+                },
+                [&](const OutputsSpec::Names & theseNames) {
+                    bool ret = true;
+                    for (auto & o : theseNames)
+                        if (thoseNames.count(o) == 0)
+                            ret = false;
+                    return ret;
+                },
+            }, raw());
+        },
+    }, that.raw());
+}
+
+}
+
+namespace nlohmann {
+
+using namespace nix;
+
+OutputsSpec adl_serializer<OutputsSpec>::from_json(const json & json) {
+    auto names = json.get<StringSet>();
+    if (names == StringSet({"*"}))
+        return OutputsSpec::All {};
+    else
+        return OutputsSpec::Names { std::move(names) };
+}
+
+void adl_serializer<OutputsSpec>::to_json(json & json, OutputsSpec t) {
+    std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            json = std::vector<std::string>({"*"});
+        },
+        [&](const OutputsSpec::Names & names) {
+            json = names;
+        },
+    }, t.raw());
+}
+
+
+ExtendedOutputsSpec adl_serializer<ExtendedOutputsSpec>::from_json(const json & json) {
+    if (json.is_null())
+        return ExtendedOutputsSpec::Default {};
+    else {
+        return ExtendedOutputsSpec::Explicit { json.get<OutputsSpec>() };
+    }
+}
+
+void adl_serializer<ExtendedOutputsSpec>::to_json(json & json, ExtendedOutputsSpec t) {
+    std::visit(overloaded {
+        [&](const ExtendedOutputsSpec::Default &) {
+            json = nullptr;
+        },
+        [&](const ExtendedOutputsSpec::Explicit & e) {
+            adl_serializer<OutputsSpec>::to_json(json, e);
+        },
+    }, t.raw());
+}
+
+}

src/libstore/outputs-spec.hh

@@ -0,0 +1,95 @@
+#pragma once
+
+#include <cassert>
+#include <optional>
+#include <set>
+#include <variant>
+
+#include "json-impls.hh"
+
+namespace nix {
+
+struct OutputNames : std::set<std::string> {
+    using std::set<std::string>::set;
+
+    /* These need to be "inherited manually" */
+
+    OutputNames(const std::set<std::string> & s)
+        : std::set<std::string>(s)
+    { assert(!empty()); }
+
+    OutputNames(std::set<std::string> && s)
+        : std::set<std::string>(s)
+    { assert(!empty()); }
+
+    /* This set should always be non-empty, so we delete this
+       constructor in order make creating empty ones by mistake harder.
+       */
+    OutputNames() = delete;
+};
+
+struct AllOutputs : std::monostate { };
+
+typedef std::variant<AllOutputs, OutputNames> _OutputsSpecRaw;
+
+struct OutputsSpec : _OutputsSpecRaw {
+    using Raw = _OutputsSpecRaw;
+    using Raw::Raw;
+
+    /* Force choosing a variant */
+    OutputsSpec() = delete;
+
+    using Names = OutputNames;
+    using All = AllOutputs;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
+
+    inline Raw & raw() {
+        return static_cast<Raw &>(*this);
+    }
+
+    bool contains(const std::string & output) const;
+
+    /* Create a new OutputsSpec which is the union of this and that. */
+    OutputsSpec union_(const OutputsSpec & that) const;
+
+    /* Whether this OutputsSpec is a subset of that. */
+    bool isSubsetOf(const OutputsSpec & outputs) const;
+
+    /* Parse a string of the form 'output1,...outputN' or
+       '*', returning the outputs spec. */
+    static OutputsSpec parse(std::string_view s);
+    static std::optional<OutputsSpec> parseOpt(std::string_view s);
+
+    std::string to_string() const;
+};
+
+struct DefaultOutputs : std::monostate { };
+
+typedef std::variant<DefaultOutputs, OutputsSpec> _ExtendedOutputsSpecRaw;
+
+struct ExtendedOutputsSpec : _ExtendedOutputsSpecRaw {
+    using Raw = _ExtendedOutputsSpecRaw;
+    using Raw::Raw;
+
+    using Default = DefaultOutputs;
+    using Explicit = OutputsSpec;
+
+    inline const Raw & raw() const {
+        return static_cast<const Raw &>(*this);
+    }
+
+    /* Parse a string of the form 'prefix^output1,...outputN' or
+       'prefix^*', returning the prefix and the extended outputs spec. */
+    static std::pair<std::string_view, ExtendedOutputsSpec> parse(std::string_view s);
+    static std::optional<std::pair<std::string_view, ExtendedOutputsSpec>> parseOpt(std::string_view s);
+
+    std::string to_string() const;
+};
+
+}
+
+JSON_IMPL(OutputsSpec)
+JSON_IMPL(ExtendedOutputsSpec)

src/libstore/path-info.cc

@@ -3,6 +3,80 @@
 
 namespace nix {
 
+std::string ValidPathInfo::fingerprint(const Store & store) const
+{
+    if (narSize == 0)
+        throw Error("cannot calculate fingerprint of path '%s' because its size is not known",
+            store.printStorePath(path));
+    return
+        "1;" + store.printStorePath(path) + ";"
+        + narHash.to_string(Base32, true) + ";"
+        + std::to_string(narSize) + ";"
+        + concatStringsSep(",", store.printStorePathSet(references));
+}
+
+
+void ValidPathInfo::sign(const Store & store, const SecretKey & secretKey)
+{
+    sigs.insert(secretKey.signDetached(fingerprint(store)));
+}
+
+
+bool ValidPathInfo::isContentAddressed(const Store & store) const
+{
+    if (! ca) return false;
+
+    auto caPath = std::visit(overloaded {
+        [&](const TextHash & th) {
+            return store.makeTextPath(path.name(), th.hash, references);
+        },
+        [&](const FixedOutputHash & fsh) {
+            auto refs = references;
+            bool hasSelfReference = false;
+            if (refs.count(path)) {
+                hasSelfReference = true;
+                refs.erase(path);
+            }
+            return store.makeFixedOutputPath(fsh.method, fsh.hash, path.name(), refs, hasSelfReference);
+        }
+    }, *ca);
+
+    bool res = caPath == path;
+
+    if (!res)
+        printError("warning: path '%s' claims to be content-addressed but isn't", store.printStorePath(path));
+
+    return res;
+}
+
+
+size_t ValidPathInfo::checkSignatures(const Store & store, const PublicKeys & publicKeys) const
+{
+    if (isContentAddressed(store)) return maxSigs;
+
+    size_t good = 0;
+    for (auto & sig : sigs)
+        if (checkSignature(store, publicKeys, sig))
+            good++;
+    return good;
+}
+
+
+bool ValidPathInfo::checkSignature(const Store & store, const PublicKeys & publicKeys, const std::string & sig) const
+{
+    return verifyDetached(fingerprint(store), sig, publicKeys);
+}
+
+
+Strings ValidPathInfo::shortRefs() const
+{
+    Strings refs;
+    for (auto & r : references)
+        refs.push_back(std::string(r.to_string()));
+    return refs;
+}
+
+
 ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format)
 {
     return read(source, store, format, store.parseStorePath(readString(source)));
@@ -24,6 +98,7 @@ ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned
     return info;
 }
 
+
 void ValidPathInfo::write(
     Sink & sink,
     const Store & store,

src/libstore/path-regex.hh

@@ -0,0 +1,7 @@
+#pragma once
+
+namespace nix {
+
+static constexpr std::string_view nameRegexStr = R"([0-9a-zA-Z\+\-\._\?=]+)";
+
+}

src/libstore/path-with-outputs.cc

@@ -1,6 +1,5 @@
 #include "path-with-outputs.hh"
 #include "store-api.hh"
-#include "nlohmann/json.hpp"
 
 #include <regex>
 
@@ -16,10 +15,14 @@ std::string StorePathWithOutputs::to_string(const Store & store) const
 
 DerivedPath StorePathWithOutputs::toDerivedPath() const
 {
-    if (!outputs.empty() || path.isDerivation())
+    if (!outputs.empty()) {
-        return DerivedPath::Built { path, outputs };
+        return DerivedPath::Built { path, OutputsSpec::Names { outputs } };
-    else
+    } else if (path.isDerivation()) {
+        assert(outputs.empty());
+        return DerivedPath::Built { path, OutputsSpec::All { } };
+    } else {
         return DerivedPath::Opaque { path };
+    }
 }
 
 
@@ -42,7 +45,18 @@ std::variant<StorePathWithOutputs, StorePath> StorePathWithOutputs::tryFromDeriv
             return StorePathWithOutputs { bo.path };
         },
         [&](const DerivedPath::Built & bfd) -> std::variant<StorePathWithOutputs, StorePath> {
-            return StorePathWithOutputs { bfd.drvPath, bfd.outputs };
+            return StorePathWithOutputs {
+                .path = bfd.drvPath,
+                // Use legacy encoding of wildcard as empty set
+                .outputs = std::visit(overloaded {
+                    [&](const OutputsSpec::All &) -> StringSet {
+                        return {};
+                    },
+                    [&](const OutputsSpec::Names & outputs) {
+                        return static_cast<StringSet>(outputs);
+                    },
+                }, bfd.outputs.raw()),
+            };
         },
     }, p.raw());
 }
@@ -53,8 +67,8 @@ std::pair<std::string_view, StringSet> parsePathWithOutputs(std::string_view s)
     size_t n = s.find("!");
     return n == s.npos
         ? std::make_pair(s, std::set<std::string>())
-        : std::make_pair(((std::string_view) s).substr(0, n),
+        : std::make_pair(s.substr(0, n),
-            tokenizeString<std::set<std::string>>(((std::string_view) s).substr(n + 1), ","));
+            tokenizeString<std::set<std::string>>(s.substr(n + 1), ","));
 }
 
 
@@ -71,57 +85,4 @@ StorePathWithOutputs followLinksToStorePathWithOutputs(const Store & store, std:
     return StorePathWithOutputs { store.followLinksToStorePath(path), std::move(outputs) };
 }
 
-std::pair<std::string, OutputsSpec> parseOutputsSpec(const std::string & s)
-{
-    static std::regex regex(R"((.*)\^((\*)|([a-z]+(,[a-z]+)*)))");
-
-    std::smatch match;
-    if (!std::regex_match(s, match, regex))
-        return {s, DefaultOutputs()};
-
-    if (match[3].matched)
-        return {match[1], AllOutputs()};
-
-    return {match[1], tokenizeString<OutputNames>(match[4].str(), ",")};
-}
-
-std::string printOutputsSpec(const OutputsSpec & outputsSpec)
-{
-    if (std::get_if<DefaultOutputs>(&outputsSpec))
-        return "";
-
-    if (std::get_if<AllOutputs>(&outputsSpec))
-        return "^*";
-
-    if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
-        return "^" + concatStringsSep(",", *outputNames);
-
-    assert(false);
-}
-
-void to_json(nlohmann::json & json, const OutputsSpec & outputsSpec)
-{
-    if (std::get_if<DefaultOutputs>(&outputsSpec))
-        json = nullptr;
-
-    else if (std::get_if<AllOutputs>(&outputsSpec))
-        json = std::vector<std::string>({"*"});
-
-    else if (auto outputNames = std::get_if<OutputNames>(&outputsSpec))
-        json = *outputNames;
-}
-
-void from_json(const nlohmann::json & json, OutputsSpec & outputsSpec)
-{
-    if (json.is_null())
-        outputsSpec = DefaultOutputs();
-    else {
-        auto names = json.get<OutputNames>();
-        if (names == OutputNames({"*"}))
-            outputsSpec = AllOutputs();
-        else
-            outputsSpec = names;
-    }
-}
-
 }

src/libstore/path-with-outputs.hh

@@ -1,13 +1,17 @@
 #pragma once
 
-#include <variant>
-
 #include "path.hh"
 #include "derived-path.hh"
-#include "nlohmann/json_fwd.hpp"
 
 namespace nix {
 
+/* This is a deprecated old type just for use by the old CLI, and older
+   versions of the RPC protocols. In new code don't use it; you want
+   `DerivedPath` instead.
+
+   `DerivedPath` is better because it handles more cases, and does so more
+   explicitly without devious punning tricks.
+*/
 struct StorePathWithOutputs
 {
     StorePath path;
@@ -33,25 +37,4 @@ StorePathWithOutputs parsePathWithOutputs(const Store & store, std::string_view
 
 StorePathWithOutputs followLinksToStorePathWithOutputs(const Store & store, std::string_view pathWithOutputs);
 
-typedef std::set<std::string> OutputNames;
-
-struct AllOutputs {
-    bool operator < (const AllOutputs & _) const { return false; }
-};
-
-struct DefaultOutputs {
-    bool operator < (const DefaultOutputs & _) const { return false; }
-};
-
-typedef std::variant<DefaultOutputs, AllOutputs, OutputNames> OutputsSpec;
-
-/* Parse a string of the form 'prefix^output1,...outputN' or
-   'prefix^*', returning the prefix and the outputs spec. */
-std::pair<std::string, OutputsSpec> parseOutputsSpec(const std::string & s);
-
-std::string printOutputsSpec(const OutputsSpec & outputsSpec);
-
-void to_json(nlohmann::json &, const OutputsSpec &);
-void from_json(const nlohmann::json &, OutputsSpec &);
-
 }

src/libstore/path.cc

@@ -8,8 +8,10 @@ static void checkName(std::string_view path, std::string_view name)
 {
     if (name.empty())
         throw BadStorePath("store path '%s' has an empty name", path);
-    if (name.size() > 211)
+    if (name.size() > StorePath::MaxPathLen)
-        throw BadStorePath("store path '%s' has a name longer than 211 characters", path);
+        throw BadStorePath("store path '%s' has a name longer than '%d characters",
+            StorePath::MaxPathLen, path);
+    // See nameRegexStr for the definition
     for (auto c : name)
         if (!((c >= '0' && c <= '9')
                 || (c >= 'a' && c <= 'z')

src/libstore/path.hh

@@ -5,7 +5,6 @@
 
 namespace nix {
 
-class Store;
 struct Hash;
 
 class StorePath
@@ -17,6 +16,8 @@ public:
     /* Size of the hash part of store paths, in base-32 characters. */
     constexpr static size_t HashLen = 32; // i.e. 160 bits
 
+    constexpr static size_t MaxPathLen = 211;
+
     StorePath() = delete;
 
     StorePath(std::string_view baseName);
@@ -64,7 +65,6 @@ public:
 
 typedef std::set<StorePath> StorePathSet;
 typedef std::vector<StorePath> StorePaths;
-typedef std::map<std::string, StorePath> OutputPathMap;
 
 typedef std::map<StorePath, std::optional<ContentAddress>> StorePathCAMap;
 

src/libstore/realisation.hh

@@ -7,6 +7,8 @@
 
 namespace nix {
 
+class Store;
+
 struct DrvOutput {
     // The hash modulo of the derivation
     Hash drvHash;
@@ -93,4 +95,14 @@ struct RealisedPath {
     GENERATE_CMP(RealisedPath, me->raw);
 };
 
+class MissingRealisation : public Error
+{
+public:
+    MissingRealisation(DrvOutput & outputId)
+        : Error( "cannot operate on an output of the "
+                "unbuilt derivation '%s'",
+                outputId.to_string())
+    {}
+};
+
 }

src/libstore/remote-store.cc

@@ -867,8 +867,8 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
                         OutputPathMap outputs;
                         auto drv = evalStore->readDerivation(bfd.drvPath);
                         const auto outputHashes = staticOutputHashes(*evalStore, drv); // FIXME: expensive
-                        const auto drvOutputs = drv.outputsAndOptPaths(*this);
+                        auto built = resolveDerivedPath(*this, bfd, &*evalStore);
-                        for (auto & output : bfd.outputs) {
+                        for (auto & [output, outputPath] : built) {
                             auto outputHash = get(outputHashes, output);
                             if (!outputHash)
                                 throw Error(
@@ -879,22 +879,14 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
                                 auto realisation =
                                     queryRealisation(outputId);
                                 if (!realisation)
-                                    throw Error(
+                                    throw MissingRealisation(outputId);
-                                        "cannot operate on an output of unbuilt "
-                                        "content-addressed derivation '%s'",
-                                        outputId.to_string());
                                 res.builtOutputs.emplace(realisation->id, *realisation);
                             } else {
-                                // If ca-derivations isn't enabled, assume that
-                                // the output path is statically known.
-                                const auto drvOutput = get(drvOutputs, output);
-                                assert(drvOutput);
-                                assert(drvOutput->second);
                                 res.builtOutputs.emplace(
                                     outputId,
                                     Realisation {
                                         .id = outputId,
-                                        .outPath = *drvOutput->second,
+                                        .outPath = outputPath,
                                     });
                             }
                         }
@@ -918,7 +910,12 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
     writeDerivation(conn->to, *this, drv);
     conn->to << buildMode;
     conn.processStderr();
-    BuildResult res { .path = DerivedPath::Built { .drvPath = drvPath } };
+    BuildResult res {
+        .path = DerivedPath::Built {
+            .drvPath = drvPath,
+            .outputs = OutputsSpec::All { },
+        },
+    };
     res.status = (BuildResult::Status) readInt(conn->from);
     conn->from >> res.errorMsg;
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {

src/libstore/ssh-store.cc

@@ -53,8 +53,8 @@ public:
     { return false; }
 
     // FIXME extend daemon protocol, move implementation to RemoteStore
-    std::optional<std::string> getBuildLog(const StorePath & path) override
+    std::optional<std::string> getBuildLogExact(const StorePath & path) override
-    { unsupported("getBuildLog"); }
+    { unsupported("getBuildLogExact"); }
 
 private:
 

src/libstore/store-api.cc

@@ -1210,79 +1210,6 @@ std::string showPaths(const PathSet & paths)
 }
 
 
-std::string ValidPathInfo::fingerprint(const Store & store) const
-{
-    if (narSize == 0)
-        throw Error("cannot calculate fingerprint of path '%s' because its size is not known",
-            store.printStorePath(path));
-    return
-        "1;" + store.printStorePath(path) + ";"
-        + narHash.to_string(Base32, true) + ";"
-        + std::to_string(narSize) + ";"
-        + concatStringsSep(",", store.printStorePathSet(references));
-}
-
-
-void ValidPathInfo::sign(const Store & store, const SecretKey & secretKey)
-{
-    sigs.insert(secretKey.signDetached(fingerprint(store)));
-}
-
-bool ValidPathInfo::isContentAddressed(const Store & store) const
-{
-    if (! ca) return false;
-
-    auto caPath = std::visit(overloaded {
-        [&](const TextHash & th) {
-            return store.makeTextPath(path.name(), th.hash, references);
-        },
-        [&](const FixedOutputHash & fsh) {
-            auto refs = references;
-            bool hasSelfReference = false;
-            if (refs.count(path)) {
-                hasSelfReference = true;
-                refs.erase(path);
-            }
-            return store.makeFixedOutputPath(fsh.method, fsh.hash, path.name(), refs, hasSelfReference);
-        }
-    }, *ca);
-
-    bool res = caPath == path;
-
-    if (!res)
-        printError("warning: path '%s' claims to be content-addressed but isn't", store.printStorePath(path));
-
-    return res;
-}
-
-
-size_t ValidPathInfo::checkSignatures(const Store & store, const PublicKeys & publicKeys) const
-{
-    if (isContentAddressed(store)) return maxSigs;
-
-    size_t good = 0;
-    for (auto & sig : sigs)
-        if (checkSignature(store, publicKeys, sig))
-            good++;
-    return good;
-}
-
-
-bool ValidPathInfo::checkSignature(const Store & store, const PublicKeys & publicKeys, const std::string & sig) const
-{
-    return verifyDetached(fingerprint(store), sig, publicKeys);
-}
-
-
-Strings ValidPathInfo::shortRefs() const
-{
-    Strings refs;
-    for (auto & r : references)
-        refs.push_back(std::string(r.to_string()));
-    return refs;
-}
-
-
 Derivation Store::derivationFromPath(const StorePath & drvPath)
 {
     ensurePath(drvPath);
@@ -1301,6 +1228,34 @@ Derivation readDerivationCommon(Store& store, const StorePath& drvPath, bool req
     }
 }
 
+std::optional<StorePath> Store::getBuildDerivationPath(const StorePath & path)
+{
+
+    if (!path.isDerivation()) {
+        try {
+            auto info = queryPathInfo(path);
+            if (!info->deriver) return std::nullopt;
+            return *info->deriver;
+        } catch (InvalidPath &) {
+            return std::nullopt;
+        }
+    }
+
+    if (!settings.isExperimentalFeatureEnabled(Xp::CaDerivations) || !isValidPath(path))
+        return path;
+
+    auto drv = readDerivation(path);
+    if (!drv.type().hasKnownOutputPaths()) {
+        // The build log is actually attached to the corresponding
+        // resolved derivation, so we need to get it first
+        auto resolvedDrv = drv.tryResolve(*this);
+        if (resolvedDrv)
+            return writeDerivation(*this, *resolvedDrv, NoRepair, true);
+    }
+
+    return path;
+}
+
 Derivation Store::readDerivation(const StorePath & drvPath)
 { return readDerivationCommon(*this, drvPath, true); }
 

src/libstore/store-api.hh

@@ -71,6 +71,9 @@ class NarInfoDiskCache;
 class Store;
 
 
+typedef std::map<std::string, StorePath> OutputPathMap;
+
+
 enum CheckSigsFlag : bool { NoCheckSigs = false, CheckSigs = true };
 enum SubstituteFlag : bool { NoSubstitute = false, Substitute = true };
 enum AllowInvalidFlag : bool { DisallowInvalid = false, AllowInvalid = true };
@@ -120,6 +123,8 @@ public:
 
     typedef std::map<std::string, std::string> Params;
 
+
+
 protected:
 
     struct PathInfoCacheValue {
@@ -618,6 +623,13 @@ public:
      */
     StorePathSet exportReferences(const StorePathSet & storePaths, const StorePathSet & inputPaths);
 
+    /**
+     * Given a store path, return the realisation actually used in the realisation of this path:
+     * - If the path is a content-addressed derivation, try to resolve it
+     * - Otherwise, find one of its derivers
+     */
+    std::optional<StorePath> getBuildDerivationPath(const StorePath &);
+
     /* Hack to allow long-running processes like hydra-queue-runner to
        occasionally flush their path info cache. */
     void clearPathInfoCache()
@@ -719,6 +731,11 @@ void copyClosure(
 void removeTempRoots();
 
 
+/* Resolve the derived path completely, failing if any derivation output
+   is unknown. */
+OutputPathMap resolveDerivedPath(Store &, const DerivedPath::Built &, Store * evalStore = nullptr);
+
+
 /* Return a Store object to access the Nix store denoted by
    ‘uri’ (slight misnomer...). Supported values are:
 

src/libstore/tests/libstoretests.hh

@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+
+#include "store-api.hh"
+
+namespace nix {
+
+class LibStoreTest : public ::testing::Test {
+    public:
+        static void SetUpTestSuite() {
+            initLibStore();
+        }
+
+    protected:
+        LibStoreTest()
+            : store(openStore("dummy://"))
+        { }
+
+        ref<Store> store;
+};
+
+
+} /* namespace nix */

src/libstore/tests/local.mk

@@ -12,4 +12,4 @@ libstore-tests_CXXFLAGS += -I src/libstore -I src/libutil
 
 libstore-tests_LIBS = libstore libutil
 
-libstore-tests_LDFLAGS := $(GTEST_LIBS)
+libstore-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)

src/libstore/tests/outputs-spec.cc

@@ -0,0 +1,201 @@
+#include "outputs-spec.hh"
+
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+
+namespace nix {
+
+#ifndef NDEBUG
+TEST(OutputsSpec, no_empty_names) {
+    ASSERT_DEATH(OutputsSpec::Names { std::set<std::string> { } }, "");
+}
+#endif
+
+#define TEST_DONT_PARSE(NAME, STR)           \
+    TEST(OutputsSpec, bad_ ## NAME) {        \
+        std::optional OutputsSpecOpt =       \
+            OutputsSpec::parseOpt(STR);      \
+        ASSERT_FALSE(OutputsSpecOpt);        \
+    }
+
+TEST_DONT_PARSE(empty, "")
+TEST_DONT_PARSE(garbage, "&*()")
+TEST_DONT_PARSE(double_star, "**")
+TEST_DONT_PARSE(star_first, "*,foo")
+TEST_DONT_PARSE(star_second, "foo,*")
+
+#undef TEST_DONT_PARSE
+
+TEST(OutputsSpec, all) {
+    std::string_view str = "*";
+    OutputsSpec expected = OutputsSpec::All { };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
+TEST(OutputsSpec, names_out) {
+    std::string_view str = "out";
+    OutputsSpec expected = OutputsSpec::Names { "out" };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
+TEST(OutputsSpec, names_underscore) {
+    std::string_view str = "a_b";
+    OutputsSpec expected = OutputsSpec::Names { "a_b" };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
+TEST(OutputsSpec, names_numberic) {
+    std::string_view str = "01";
+    OutputsSpec expected = OutputsSpec::Names { "01" };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
+TEST(OutputsSpec, names_out_bin) {
+    OutputsSpec expected = OutputsSpec::Names { "out", "bin" };
+    ASSERT_EQ(OutputsSpec::parse("out,bin"), expected);
+    // N.B. This normalization is OK.
+    ASSERT_EQ(expected.to_string(), "bin,out");
+}
+
+#define TEST_SUBSET(X, THIS, THAT) \
+    X((OutputsSpec { THIS }).isSubsetOf(THAT));
+
+TEST(OutputsSpec, subsets_all_all) {
+    TEST_SUBSET(ASSERT_TRUE, OutputsSpec::All { }, OutputsSpec::All { });
+}
+
+TEST(OutputsSpec, subsets_names_all) {
+    TEST_SUBSET(ASSERT_TRUE, OutputsSpec::Names { "a" }, OutputsSpec::All { });
+}
+
+TEST(OutputsSpec, subsets_names_names_eq) {
+    TEST_SUBSET(ASSERT_TRUE, OutputsSpec::Names { "a" }, OutputsSpec::Names { "a" });
+}
+
+TEST(OutputsSpec, subsets_names_names_noneq) {
+    TEST_SUBSET(ASSERT_TRUE, OutputsSpec::Names { "a" }, (OutputsSpec::Names { "a", "b" }));
+}
+
+TEST(OutputsSpec, not_subsets_all_names) {
+    TEST_SUBSET(ASSERT_FALSE, OutputsSpec::All { }, OutputsSpec::Names { "a" });
+}
+
+TEST(OutputsSpec, not_subsets_names_names) {
+    TEST_SUBSET(ASSERT_FALSE, (OutputsSpec::Names { "a", "b" }), (OutputsSpec::Names { "a" }));
+}
+
+#undef TEST_SUBSET
+
+#define TEST_UNION(RES, THIS, THAT) \
+    ASSERT_EQ(OutputsSpec { RES }, (OutputsSpec { THIS }).union_(THAT));
+
+TEST(OutputsSpec, union_all_all) {
+    TEST_UNION(OutputsSpec::All { }, OutputsSpec::All { }, OutputsSpec::All { });
+}
+
+TEST(OutputsSpec, union_all_names) {
+    TEST_UNION(OutputsSpec::All { }, OutputsSpec::All { }, OutputsSpec::Names { "a" });
+}
+
+TEST(OutputsSpec, union_names_all) {
+    TEST_UNION(OutputsSpec::All { }, OutputsSpec::Names { "a" }, OutputsSpec::All { });
+}
+
+TEST(OutputsSpec, union_names_names) {
+    TEST_UNION((OutputsSpec::Names { "a", "b" }), OutputsSpec::Names { "a" }, OutputsSpec::Names { "b" });
+}
+
+#undef TEST_UNION
+
+#define TEST_DONT_PARSE(NAME, STR)                   \
+    TEST(ExtendedOutputsSpec, bad_ ## NAME) {        \
+        std::optional extendedOutputsSpecOpt =       \
+            ExtendedOutputsSpec::parseOpt(STR);      \
+        ASSERT_FALSE(extendedOutputsSpecOpt);        \
+    }
+
+TEST_DONT_PARSE(carot_empty, "^")
+TEST_DONT_PARSE(prefix_carot_empty, "foo^")
+TEST_DONT_PARSE(garbage, "^&*()")
+TEST_DONT_PARSE(double_star, "^**")
+TEST_DONT_PARSE(star_first, "^*,foo")
+TEST_DONT_PARSE(star_second, "^foo,*")
+
+#undef TEST_DONT_PARSE
+
+TEST(ExtendedOutputsSpec, defeault) {
+    std::string_view str = "foo";
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(str);
+    ASSERT_EQ(prefix, "foo");
+    ExtendedOutputsSpec expected = ExtendedOutputsSpec::Default { };
+    ASSERT_EQ(extendedOutputsSpec, expected);
+    ASSERT_EQ(std::string { prefix } + expected.to_string(), str);
+}
+
+TEST(ExtendedOutputsSpec, all) {
+    std::string_view str = "foo^*";
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(str);
+    ASSERT_EQ(prefix, "foo");
+    ExtendedOutputsSpec expected = OutputsSpec::All { };
+    ASSERT_EQ(extendedOutputsSpec, expected);
+    ASSERT_EQ(std::string { prefix } + expected.to_string(), str);
+}
+
+TEST(ExtendedOutputsSpec, out) {
+    std::string_view str = "foo^out";
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(str);
+    ASSERT_EQ(prefix, "foo");
+    ExtendedOutputsSpec expected = OutputsSpec::Names { "out" };
+    ASSERT_EQ(extendedOutputsSpec, expected);
+    ASSERT_EQ(std::string { prefix } + expected.to_string(), str);
+}
+
+TEST(ExtendedOutputsSpec, out_bin) {
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse("foo^out,bin");
+    ASSERT_EQ(prefix, "foo");
+    ExtendedOutputsSpec expected = OutputsSpec::Names { "out", "bin" };
+    ASSERT_EQ(extendedOutputsSpec, expected);
+    ASSERT_EQ(std::string { prefix } + expected.to_string(), "foo^bin,out");
+}
+
+TEST(ExtendedOutputsSpec, many_carrot) {
+    auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse("foo^bar^out,bin");
+    ASSERT_EQ(prefix, "foo^bar");
+    ExtendedOutputsSpec expected = OutputsSpec::Names { "out", "bin" };
+    ASSERT_EQ(extendedOutputsSpec, expected);
+    ASSERT_EQ(std::string { prefix } + expected.to_string(), "foo^bar^bin,out");
+}
+
+
+#define TEST_JSON(TYPE, NAME, STR, VAL)                    \
+                                                           \
+    TEST(TYPE, NAME ## _to_json) {                         \
+        using nlohmann::literals::operator "" _json;       \
+        ASSERT_EQ(                                         \
+            STR ## _json,                                  \
+            ((nlohmann::json) TYPE { VAL }));              \
+    }                                                      \
+                                                           \
+    TEST(TYPE, NAME ## _from_json) {                       \
+        using nlohmann::literals::operator "" _json;       \
+        ASSERT_EQ(                                         \
+            TYPE { VAL },                                  \
+            (STR ## _json).get<TYPE>());                   \
+    }
+
+TEST_JSON(OutputsSpec, all, R"(["*"])", OutputsSpec::All { })
+TEST_JSON(OutputsSpec, name, R"(["a"])", OutputsSpec::Names { "a" })
+TEST_JSON(OutputsSpec, names, R"(["a","b"])", (OutputsSpec::Names { "a", "b" }))
+
+TEST_JSON(ExtendedOutputsSpec, def, R"(null)", ExtendedOutputsSpec::Default { })
+TEST_JSON(ExtendedOutputsSpec, all, R"(["*"])", ExtendedOutputsSpec::Explicit { OutputsSpec::All { } })
+TEST_JSON(ExtendedOutputsSpec, name, R"(["a"])", ExtendedOutputsSpec::Explicit { OutputsSpec::Names { "a" } })
+TEST_JSON(ExtendedOutputsSpec, names, R"(["a","b"])", (ExtendedOutputsSpec::Explicit { OutputsSpec::Names { "a", "b" } }))
+
+#undef TEST_JSON
+
+}

src/libstore/tests/path-with-outputs.cc

@@ -1,46 +0,0 @@
-#include "path-with-outputs.hh"
-
-#include <gtest/gtest.h>
-
-namespace nix {
-
-TEST(parseOutputsSpec, basic)
-{
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo");
-        ASSERT_EQ(prefix, "foo");
-        ASSERT_TRUE(std::get_if<DefaultOutputs>(&outputsSpec));
-    }
-
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo^*");
-        ASSERT_EQ(prefix, "foo");
-        ASSERT_TRUE(std::get_if<AllOutputs>(&outputsSpec));
-    }
-
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo^out");
-        ASSERT_EQ(prefix, "foo");
-        ASSERT_TRUE(std::get<OutputNames>(outputsSpec) == OutputNames({"out"}));
-    }
-
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo^out,bin");
-        ASSERT_EQ(prefix, "foo");
-        ASSERT_TRUE(std::get<OutputNames>(outputsSpec) == OutputNames({"out", "bin"}));
-    }
-
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo^bar^out,bin");
-        ASSERT_EQ(prefix, "foo^bar");
-        ASSERT_TRUE(std::get<OutputNames>(outputsSpec) == OutputNames({"out", "bin"}));
-    }
-
-    {
-        auto [prefix, outputsSpec] = parseOutputsSpec("foo^&*()");
-        ASSERT_EQ(prefix, "foo^&*()");
-        ASSERT_TRUE(std::get_if<DefaultOutputs>(&outputsSpec));
-    }
-}
-
-}

src/libstore/tests/path.cc

@@ -0,0 +1,144 @@
+#include <regex>
+
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+#include <rapidcheck/gtest.h>
+
+#include "path-regex.hh"
+#include "store-api.hh"
+
+#include "libstoretests.hh"
+
+namespace nix {
+
+#define STORE_DIR "/nix/store/"
+#define HASH_PART "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q"
+
+class StorePathTest : public LibStoreTest
+{
+};
+
+static std::regex nameRegex { std::string { nameRegexStr } };
+
+#define TEST_DONT_PARSE(NAME, STR)                           \
+    TEST_F(StorePathTest, bad_ ## NAME) {                    \
+        std::string_view str =                               \
+            STORE_DIR HASH_PART "-" STR;                     \
+        ASSERT_THROW(                                        \
+            store->parseStorePath(str),                      \
+            BadStorePath);                                   \
+        std::string name { STR };                            \
+        EXPECT_FALSE(std::regex_match(name, nameRegex));     \
+    }
+
+TEST_DONT_PARSE(empty, "")
+TEST_DONT_PARSE(garbage, "&*()")
+TEST_DONT_PARSE(double_star, "**")
+TEST_DONT_PARSE(star_first, "*,foo")
+TEST_DONT_PARSE(star_second, "foo,*")
+TEST_DONT_PARSE(bang, "foo!o")
+
+#undef TEST_DONT_PARSE
+
+#define TEST_DO_PARSE(NAME, STR)                             \
+    TEST_F(StorePathTest, good_ ## NAME) {                   \
+        std::string_view str =                               \
+            STORE_DIR HASH_PART "-" STR;                     \
+        auto p = store->parseStorePath(str);                 \
+        std::string name { p.name() };                       \
+        EXPECT_TRUE(std::regex_match(name, nameRegex));      \
+    }
+
+// 0-9 a-z A-Z + - . _ ? =
+
+TEST_DO_PARSE(numbers, "02345")
+TEST_DO_PARSE(lower_case, "foo")
+TEST_DO_PARSE(upper_case, "FOO")
+TEST_DO_PARSE(plus, "foo+bar")
+TEST_DO_PARSE(dash, "foo-dev")
+TEST_DO_PARSE(underscore, "foo_bar")
+TEST_DO_PARSE(period, "foo.txt")
+TEST_DO_PARSE(question_mark, "foo?why")
+TEST_DO_PARSE(equals_sign, "foo=foo")
+
+#undef TEST_DO_PARSE
+
+// For rapidcheck
+void showValue(const StorePath & p, std::ostream & os) {
+    os << p.to_string();
+}
+
+}
+
+namespace rc {
+using namespace nix;
+
+template<>
+struct Arbitrary<StorePath> {
+    static Gen<StorePath> arbitrary();
+};
+
+Gen<StorePath> Arbitrary<StorePath>::arbitrary()
+{
+    auto len = *gen::inRange<size_t>(1, StorePath::MaxPathLen);
+
+    std::string pre { HASH_PART "-" };
+    pre.reserve(pre.size() + len);
+
+    for (size_t c = 0; c < len; ++c) {
+        switch (auto i = *gen::inRange<uint8_t>(0, 10 + 2 * 26 + 6)) {
+            case 0 ... 9:
+                pre += '0' + i;
+            case 10 ... 35:
+                pre += 'A' + (i - 10);
+                break;
+            case 36 ... 61:
+                pre += 'a' + (i - 36);
+                break;
+            case 62:
+                pre += '+';
+                break;
+            case 63:
+                pre += '-';
+                break;
+            case 64:
+                pre += '.';
+                break;
+            case 65:
+                pre += '_';
+                break;
+            case 66:
+                pre += '?';
+                break;
+            case 67:
+                pre += '=';
+                break;
+            default:
+                assert(false);
+        }
+    }
+
+    return gen::just(StorePath { pre });
+}
+
+} // namespace rc
+
+namespace nix {
+
+RC_GTEST_FIXTURE_PROP(
+    StorePathTest,
+    prop_regex_accept,
+    (const StorePath & p))
+{
+    RC_ASSERT(std::regex_match(std::string { p.name() }, nameRegex));
+}
+
+RC_GTEST_FIXTURE_PROP(
+    StorePathTest,
+    prop_round_rip,
+    (const StorePath & p))
+{
+    RC_ASSERT(p == store->parseStorePath(store->printStorePath(p)));
+}
+
+}

src/libutil/error.hh

@@ -74,6 +74,8 @@ struct AbstractPos
     virtual void print(std::ostream & out) const = 0;
 
     std::optional<LinesOfCode> getCodeLines() const;
+
+    virtual ~AbstractPos() = default;
 };
 
 std::ostream & operator << (std::ostream & str, const AbstractPos & pos);

src/libutil/json-impls.hh

@@ -0,0 +1,14 @@
+#pragma once
+
+#include "nlohmann/json_fwd.hpp"
+
+// Following https://github.com/nlohmann/json#how-can-i-use-get-for-non-default-constructiblenon-copyable-types
+#define JSON_IMPL(TYPE)                                                \
+    namespace nlohmann {                                               \
+        using namespace nix;                                           \
+        template <>                                                    \
+        struct adl_serializer<TYPE> {                                  \
+            static TYPE from_json(const json & json);                  \
+            static void to_json(json & json, TYPE t);                  \
+        };                                                             \
+    }

src/libutil/monitor-fd.hh

@@ -22,27 +22,38 @@ public:
     {
         thread = std::thread([fd]() {
             while (true) {
-              /* Wait indefinitely until a POLLHUP occurs. */
+                /* Wait indefinitely until a POLLHUP occurs. */
-              struct pollfd fds[1];
+                struct pollfd fds[1];
-              fds[0].fd = fd;
+                fds[0].fd = fd;
-              /* This shouldn't be necessary, but macOS doesn't seem to
+                /* Polling for no specific events (i.e. just waiting
-                 like a zeroed out events field.
+                   for an error/hangup) doesn't work on macOS
-                 See rdar://37537852.
+                   anymore. So wait for read events and ignore
-              */
+                   them. */
-              fds[0].events = POLLHUP;
+                fds[0].events =
-              auto count = poll(fds, 1, -1);
+                    #ifdef __APPLE__
-              if (count == -1) abort(); // can't happen
+                    POLLRDNORM
-              /* This shouldn't happen, but can on macOS due to a bug.
+                    #else
-                 See rdar://37550628.
+                    0
+                    #endif
+                    ;
+                auto count = poll(fds, 1, -1);
+                if (count == -1) abort(); // can't happen
+                /* This shouldn't happen, but can on macOS due to a bug.
+                   See rdar://37550628.
 
-                 This may eventually need a delay or further
+                   This may eventually need a delay or further
-                 coordination with the main thread if spinning proves
+                   coordination with the main thread if spinning proves
-                 too harmful.
+                   too harmful.
-               */
+                */
-              if (count == 0) continue;
+                if (count == 0) continue;
-              assert(fds[0].revents & POLLHUP);
+                if (fds[0].revents & POLLHUP) {
-              triggerInterrupt();
+                    triggerInterrupt();
-              break;
+                    break;
+                }
+                /* This will only happen on macOS. We sleep a bit to
+                   avoid waking up too often if the client is sending
+                   input. */
+                sleep(1);
             }
         });
     };