add VM test for nix upgrade-nix

This commit adds a new NixOS VM test, which tests that `nix upgrade-nix`
works on both kinds of profiles (manifest.nix and manifest.json).

Done as a separate commit from 831d18a13, since it relies on the
--store-path argument from 026c90e5f as well.

Change-Id: I5fc94b751d252862cb6cffb541a4c072faad9f3b

doc/manual/rl-next/upgrade-nix-override.md

@@ -0,0 +1,6 @@
+---
+synopsis: add --store-path argument to `nix upgrade-nix`, to manually specify the Nix to upgrade to
+cls: 953
+---
+
+`nix upgrade-nix` by default downloads a manifest to find the new Nix version to upgrade to, but now you can specify `--store-path` to upgrade Nix to an arbitrary version from the Nix store.

doc/manual/rl-next/upgrade-nix-profile-compat.md

@@ -0,0 +1,8 @@
+---
+synopsis: using `nix profile` on `/nix/var/nix/profiles/default` no longer breaks `nix upgrade-nix`
+cls: 952
+---
+
+On non-NixOS, Nix is conventionally installed into a `nix-env` style profile at /nix/var/nix/profiles/default.
+Like any `nix-env` profile, using `nix profile` on it automatically migrates it to a `nix profile` style profile, which is incompatible with `nix-env`.
+`nix upgrade-nix` previously relied solely on `nix-env` to do the upgrade, but now will work fine with either kind of profile.

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

@@ -25,17 +25,17 @@ individual users can switch between different environments.
 `nix-env` takes exactly one *operation* flag which indicates the
 subcommand to be performed. The following operations are available:
 
-- [`--install`](./nix-env/install.md)
-- [`--upgrade`](./nix-env/upgrade.md)
-- [`--uninstall`](./nix-env/uninstall.md)
-- [`--set`](./nix-env/set.md)
-- [`--set-flag`](./nix-env/set-flag.md)
-- [`--query`](./nix-env/query.md)
-- [`--switch-profile`](./nix-env/switch-profile.md)
-- [`--list-generations`](./nix-env/list-generations.md)
-- [`--delete-generations`](./nix-env/delete-generations.md)
-- [`--switch-generation`](./nix-env/switch-generation.md)
-- [`--rollback`](./nix-env/rollback.md)
+- [`--install`](./nix-env/install.md) - add packages to user environment
+- [`--upgrade`](./nix-env/upgrade.md) - upgrade packages in user environment
+- [`--uninstall`](./nix-env/uninstall.md) - remove packages from user environment
+- [`--set`](./nix-env/set.md) - set profile to contain a specified derivation
+- [`--set-flag`](./nix-env/set-flag.md) - modify meta attributes of installed packages
+- [`--query`](./nix-env/query.md) - display information about packages
+- [`--switch-profile`](./nix-env/switch-profile.md) - set user environment to a given profile
+- [`--list-generations`](./nix-env/list-generations.md) - list profile generations
+- [`--delete-generations`](./nix-env/delete-generations.md) - delete profile generations
+- [`--switch-generation`](./nix-env/switch-generation.md) - set user environment to a given profile generation
+- [`--rollback`](./nix-env/rollback.md) - set user environment to previous generation
 
 These pages can be viewed offline:
 

doc/manual/src/contributing/hacking.md

@@ -1,61 +1,125 @@
 # Hacking
 
-This section provides some notes on how to hack on Nix. To get the
-latest version of Nix from GitHub:
+This section provides some notes on how to hack on Nix. To get the latest version of Lix from Forgejo:
 
 ```console
-$ git clone https://github.com/NixOS/nix.git
-$ cd nix
+$ git clone https://git.lix.systems/lix-project/lix
+$ cd lix
 ```
 
-The following instructions assume you already have some version of Nix installed locally, so that you can use it to set up the development environment. If you don't have it installed, follow the [installation instructions].
+The following instructions assume you already have some version of Nix or Lix installed locally, so that you can use it to set up the development environment. If you don't have it installed, follow the [installation instructions].
 
 [installation instructions]: ../installation/installation.md
 
-## Building Nix with flakes
+## Building Lix in a development shell
 
-This section assumes you are using Nix with the [`flakes`] and [`nix-command`] experimental features enabled.
-See the [Building Nix](#building-nix) section for equivalent instructions using stable Nix interfaces.
+### Setting up the development shell
+
+If you are using Lix or Nix with the [`flakes`] and [`nix-command`] experimental features enabled, the following command will build all dependencies and start a shell in which all environment variables are setup for those dependencies to be found:
+
+```bash
+$ nix develop
+```
+
+That will use the default stdenv for your system. To get a shell with one of the other [supported compilation environments](#compilation-environments), specify its attribute name after a hash (which you may need to quote, depending on your shell):
+
+```bash
+$ nix develop ".#native-clangStdenvPackages"
+```
+
+For classic Nix, use:
+
+```bash
+$ nix-shell -A native-clangStdenvPackages
+```
 
 [`flakes`]: @docroot@/contributing/experimental-features.md#xp-feature-flakes
 [`nix-command`]: @docroot@/contributing/experimental-features.md#xp-nix-command
 
-To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
 
-```console
-$ nix develop
+### Building from the development shell
+
+As always you may run [stdenv's phases by name](https://nixos.org/manual/nixpkgs/unstable/#sec-building-stdenv-package-in-nix-shell), e.g.:
+
+```bash
+$ configurePhase
+$ buildPhase
+$ checkPhase
+$ installPhase
+$ installCheckPhase
 ```
 
-This shell also adds `./outputs/bin/nix` to your `$PATH` so you can run `nix` immediately after building it.
+To build manually, however, use the following:
 
-To get a shell with one of the other [supported compilation environments](#compilation-environments):
-
-```console
-$ nix develop .#native-clangStdenvPackages
+```bash
+$ meson setup ./build "--prefix=$out" $mesonFlags
 ```
 
-> **Note**
->
-> Use `ccacheStdenv` to drastically improve rebuild time.
-> By default, [ccache](https://ccache.dev) keeps artifacts in `~/.cache/ccache/`.
+(A simple `meson setup ./build` will also build, but will do a different thing, not having the settings from package.nix applied).
 
-To build Nix itself in this shell:
-
-```console
-[nix-shell]$ autoreconfPhase
-[nix-shell]$ configurePhase
-[nix-shell]$ make -j $NIX_BUILD_CORES
+```bash
+$ meson compile -C build
+$ meson test -C build --suite=check
+$ meson install -C build
+$ meson test -C build --suite=installcheck
 ```
 
-To install it in `$(pwd)/outputs` and test it:
+(Check and installcheck may both be done after install, allowing you to omit the --suite argument entirely, but this is the order package.nix runs them in.)
 
-```console
-[nix-shell]$ make install
-[nix-shell]$ make installcheck -j $NIX_BUILD_CORES
-[nix-shell]$ nix --version
-nix (Nix) 2.12
+This will install Lix to `$PWD/outputs`, the `/bin` of which is prepended to PATH in the development shells.
+
+If the tests fail and Meson helpfully has no output for why, use the `--print-error-logs` option to `meson test`.
+
+If you change a setting in the buildsystem (i.e., any of the `meson.build` files), most cases will automatically regenerate the Meson configuration just before compiling.
+Some cases, however, like trying to build a specific target whose name is new to the buildsystem (e.g. `meson compile -C build src/libmelt/libmelt.dylib`, when `libmelt.dylib` did not exist as a target the last time the buildsystem was generated), then you can reconfigure using new settings but existing options, and only recompiling stuff affected by the changes:
+
+```bash
+$ meson setup --reconfigure build
 ```
 
+Note that changes to the default values in `meson.options` or in the `default_options :` argument to `project()` are **not** propagated with `--reconfigure`.
+
+If you want a totally clean build, you can use:
+
+```bash
+$ meson setup --wipe build
+```
+
+That will work regardless of if `./build` exists or not.
+
+Specific, named targets may be addressed in `meson build -C build <target>`, with the "target ID", if there is one, which is the first string argument passed to target functions that have one, and unrelated to the variable name, e.g.:
+
+```meson
+libexpr_dylib = library('nixexpr', …)
+```
+
+can be addressed with:
+
+```bash
+$ meson compile -C build nixexpr
+```
+
+All targets may be addressed as their output, relative to the build directory, e.g.:
+
+```bash
+$ meson compile -C build src/libexpr/libnixexpr.so
+```
+
+But Meson does not consider intermediate files like object files targets.
+To build a specific object file, use Ninja directly and specify the output file relative to the build directory:
+
+```bash
+$ ninja -C build src/libexpr/libnixexpr.so.p/nixexpr.cc.o
+```
+
+To inspect the canonical source of truth on what the state of the buildsystem configuration is, use:
+
+```bash
+$ meson introspect
+```
+
+## Building Lix outside of development shells
+
 To build a release version of Nix for the current operating system and CPU architecture:
 
 ```console
@@ -64,50 +128,11 @@ $ nix build
 
 You can also build Nix for one of the [supported platforms](#platforms).
 
-## Building Nix
-
-To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
-
-```console
-$ nix-shell
-```
-
-To get a shell with one of the other [supported compilation environments](#compilation-environments):
-
-```console
-$ nix-shell --attr devShells.x86_64-linux.native-clangStdenvPackages
-```
-
 > **Note**
 >
 > You can use `native-ccacheStdenvPackages` to drastically improve rebuild time.
 > By default, [ccache](https://ccache.dev) keeps artifacts in `~/.cache/ccache/`.
 
-To build Nix itself in this shell:
-
-```console
-[nix-shell]$ autoreconfPhase
-[nix-shell]$ ./configure $configureFlags --prefix=$(pwd)/outputs/out
-[nix-shell]$ make -j $NIX_BUILD_CORES
-```
-
-To install it in `$(pwd)/outputs` and test it:
-
-```console
-[nix-shell]$ make install
-[nix-shell]$ make installcheck -j $NIX_BUILD_CORES
-[nix-shell]$ ./outputs/out/bin/nix --version
-nix (Nix) 2.12
-```
-
-To build a release version of Nix for the current operating system and CPU architecture:
-
-```console
-$ nix-build
-```
-
-You can also build Nix for one of the [supported platforms](#platforms).
-
 ## Platforms
 
 Nix can be built for various platforms, as specified in [`flake.nix`]:
@@ -148,55 +173,38 @@ Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootst
 
 ### Building for multiple platforms at once
 
-It is useful to perform multiple cross and native builds on the same source tree,
-for example to ensure that better support for one platform doesn't break the build for another.
-In order to facilitate this, Nix has some support for being built out of tree – that is, placing build artefacts in a different directory than the source code:
+It is useful to perform multiple cross and native builds on the same source tree, for example to ensure that better support for one platform doesn't break the build for another.
+As Lix now uses Meson, out-of-tree builds are supported first class. In the invocation
 
-1. Create a directory for the build, e.g.
+```bash
+$ meson setup build
+```
 
-   ```bash
-   mkdir build
-   ```
+the argument after `setup` specifies the directory for this build, conventionally simply called "build", but it may be called anything, and you may run `meson setup <somedir>` for as many different directories as you want.
+To compile the configuration for a given build directory, pass that build directory to the `-C` argument of `meson compile`:
 
-2. Run the configure script from that directory, e.g.
-
-   ```bash
-   cd build
-   ../configure <configure flags>
-   ```
-
-3. Run make from the source directory, but with the build directory specified, e.g.
-
-   ```bash
-   make builddir=build <make flags>
-   ```
+```bash
+$ meson setup some-custom-build
+$ meson compile -C some-custom-build
+```
 
 ## System type
 
-Nix uses a string with he following format to identify the *system type* or *platform* it runs on:
+Lix uses a string with the following format to identify the *system type* or *platform* it runs on:
 
 ```
 <cpu>-<os>[-<abi>]
 ```
 
-It is set when Nix is compiled for the given system, and based on the output of [`config.guess`](https://github.com/nixos/nix/blob/master/config/config.guess) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess)):
+It is set when Nix is compiled for the given system, and determined by [Meson's `host_machine.cpu_family()` and `host_machine.system()` values](https://mesonbuild.com/Reference-manual_builtin_host_machine.html).
 
-```
-<cpu>-<vendor>-<os>[<version>][-<abi>]
-```
+For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`meson.build`](https://git.lix.systems/lix-project/lix/blob/main/meson.build) as follows:
 
-When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://github.com/nixos/nix/blob/master/config/config.sub) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub)):
-
-```
-<cpu>-<vendor>[-<kernel>]-<os>
-```
-
-For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`configure.ac`](https://github.com/nixos/nix/blob/master/configure.ac) as follows:
-
-| `config.guess`             | Nix                 |
+| `host_machine.cpu_family()`             | Nix                 |
 |----------------------------|---------------------|
-| `amd64`                    | `x86_64`            |
-| `i*86`                     | `i686`              |
+| `x86`                      | `i686`              |
+| `i686`                     | `i686`              |
+| `i686`                     | `i686`              |
 | `arm6`                     | `arm6l`             |
 | `arm7`                     | `arm7l`             |
 | `linux-gnu*`               | `linux`             |
@@ -229,13 +237,14 @@ You can use any of the other supported environments in place of `nix-ccacheStden
 
 ## Editor integration
 
-The `clangd` LSP server is installed by default on the `clang`-based `devShell`s.
+The `clangd` LSP server is installed by default in each development shell.
 See [supported compilation environments](#compilation-environments) and instructions how to set up a shell [with flakes](#nix-with-flakes) or in [classic Nix](#classic-nix).
 
-To use the LSP with your editor, you first need to [set up `clangd`](https://clangd.llvm.org/installation#project-setup) by running:
+Clangd requires a compilation database, which Meson generates by default. After running `meson setup`, there will already be a `compile_commands.json` file in the build directory.
+Some editor configurations may prefer that file to be in the root directory, which you can accomplish with a simple:
 
-```console
-make clean && bear -- make -j$NIX_BUILD_CORES install
+```bash
+$ ln -sf ./build/compile_commands.json ./compile_commands.json
 ```
 
 Configure your editor to use the `clangd` from the shell, either by running it inside the development shell, or by using [nix-direnv](https://github.com/nix-community/nix-direnv) and [the appropriate editor plugin](https://github.com/direnv/direnv/wiki#editor-integration).
@@ -253,15 +262,7 @@ 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
+meson compile -C build manual
 ```
 
 [`mdbook-linkcheck`] does not implement checking [URI fragments] yet.
@@ -292,9 +293,9 @@ can also build and view it yourself:
 
 or inside a `nix develop` shell by running:
 
-```
-# make internal-api-html
-# xdg-open ./outputs/doc/share/doc/nix/internal-api/html/index.html
+```bash
+$ meson compile -C build internal-api-docs
+$ xdg-open ./outputs/doc/share/doc/nix/internal-api/html/index.html
 ```
 
 ## Coverage analysis

flake.nix

@@ -196,24 +196,6 @@
           }
         );
 
-        # FIXME(Qyriad): remove this when the migration to Meson has been completed.
-        # NOTE: mesonBuildClang depends on mesonBuild depends on build to avoid OOMs
-        # on aarch64 builders caused by too many parallel compiler/linker processes.
-        mesonBuild = forAllSystems (
-          system:
-          (self.packages.${system}.nix.override { buildWithMeson = true; }).overrideAttrs (prev: {
-            buildInputs = prev.buildInputs ++ [ self.packages.${system}.nix ];
-          })
-        );
-        mesonBuildClang = forAllSystems (
-          system:
-          (nixpkgsFor.${system}.stdenvs.clangStdenvPackages.nix.override { buildWithMeson = true; })
-          .overrideAttrs
-            (prev: {
-              buildInputs = prev.buildInputs ++ [ self.hydraJobs.mesonBuild.${system} ];
-            })
-        );
-
         # Perl bindings for various platforms.
         perlBindings = forAllSystems (system: nixpkgsFor.${system}.native.nix.perl-bindings);
 
@@ -237,7 +219,6 @@
               inherit (pkgs) build-release-notes;
               internalApiDocs = true;
               busybox-sandbox-shell = pkgs.busybox-sandbox-shell;
-              buildWithMeson = true;
             };
           in
           nix.overrideAttrs (prev: {
@@ -367,9 +348,6 @@
       checks = forAllSystems (
         system:
         {
-          # FIXME(Qyriad): remove this when the migration to Meson has been completed.
-          mesonBuild = self.hydraJobs.mesonBuild.${system};
-          mesonBuildClang = self.hydraJobs.mesonBuildClang.${system};
           binaryTarball = self.hydraJobs.binaryTarball.${system};
           perlBindings = self.hydraJobs.perlBindings.${system};
           nixpkgsLibTests = self.hydraJobs.tests.nixpkgsLibTests.${system};

justfile

@@ -6,13 +6,13 @@ clean:
 setup:
     meson setup build --prefix="$PWD/outputs/out"
 
-build:
-    meson compile -C build
+build *OPTIONS:
+    meson compile -C build {{ OPTIONS }}
 
 compile:
     just build
 
-install:
+install *OPTIONS: (build OPTIONS)
     meson install -C build
 
 test *OPTIONS:

meson.build

@@ -85,8 +85,8 @@ endif
 enable_docs = get_option('enable-docs')
 enable_internal_api_docs = get_option('internal-api-docs')
 
-doxygen = find_program('doxygen', required : enable_internal_api_docs)
-bash = find_program('bash')
+doxygen = find_program('doxygen', required : enable_internal_api_docs, native : true)
+bash = find_program('bash', native : true)
 
 rapidcheck_meson = dependency('rapidcheck', required : enable_internal_api_docs)
 
@@ -114,6 +114,25 @@ endif
 
 cxx = meson.get_compiler('cpp')
 
+# Translate some historical and Mesony CPU names to Lixy CPU names.
+# FIXME(Qyriad): the 32-bit x86 code is not tested right now, because cross compilation for Lix
+# to those architectures is currently broken for other reasons, namely:
+# - nixos-23.11's x86_64-linux -> i686-linux glibc does not build (also applies to cppnix)
+# - nixpkgs-unstable (as of 2024/04)'s boehmgc is not compatible with our patches
+# It's also broken in cppnix, though.
+host_cpu = host_machine.cpu_family()
+if host_cpu in ['x86', 'i686', 'i386']
+  # Meson considers 32-bit x86 CPUs to be "x86", and does not consider 64-bit
+  # x86 CPUs to be "x86" (instead using "x86_64", which needs no translation).
+  host_cpu = 'i686'
+elif host_cpu == 'amd64'
+  # This should not be needed under normal circumstances, but someone could pass a --cross-file
+  # that sets the cpu_family to this.
+  host_cpu = 'x86_64'
+elif host_cpu in ['armv6', 'armv7']
+  host_cpu += 'l'
+endif
+
 host_system = host_machine.cpu_family() + '-' + host_machine.system()
 message('canonical Nix system name:', host_system)
 
@@ -181,6 +200,7 @@ openssl = dependency('libcrypto', 'openssl', required : true)
 deps += openssl
 
 aws_sdk = dependency('aws-cpp-sdk-core', required : false)
+aws_sdk_transfer = dependency('aws-cpp-sdk-transfer', required : aws_sdk.found())
 if aws_sdk.found()
   # The AWS pkg-config adds -std=c++11.
   # https://github.com/aws/aws-sdk-cpp/issues/2673
@@ -198,7 +218,7 @@ if aws_sdk.found()
     'AWS_VERSION_MINOR': s[1].to_int(),
     'AWS_VERSION_PATCH': s[2].to_int(),
   }
-  aws_sdk_transfer = dependency('aws-cpp-sdk-transfer', required : true).partial_dependency(
+  aws_sdk_transfer = aws_sdk_transfer.partial_dependency(
     compile_args : false,
     includes : true,
     link_args : true,
@@ -255,7 +275,7 @@ gtest = [
 ]
 deps += gtest
 
-toml11 = dependency('toml11', version : '>=3.7.0', required : true)
+toml11 = dependency('toml11', version : '>=3.7.0', required : true, method : 'cmake')
 deps += toml11
 
 nlohmann_json = dependency('nlohmann_json', required : true)
@@ -272,17 +292,17 @@ deps += lix_doc
 #
 # Build-time tools
 #
-coreutils = find_program('coreutils')
-dot = find_program('dot', required : false)
+coreutils = find_program('coreutils', native : true)
+dot = find_program('dot', required : false, native : true)
 pymod = import('python')
 python = pymod.find_installation('python3')
 
 if enable_docs
-  mdbook = find_program('mdbook')
+  mdbook = find_program('mdbook', native : true)
 endif
 
 # Used to workaround https://github.com/mesonbuild/meson/issues/2320 in src/nix/meson.build.
-installcmd = find_program('install')
+installcmd = find_program('install', native : true)
 
 enable_embedded_sandbox_shell = get_option('enable-embedded-sandbox-shell')
 if enable_embedded_sandbox_shell
@@ -307,9 +327,9 @@ endif
 # FIXME(Qyriad): the autoconf system checks that busybox has the "standalone" feature, indicating
 # that busybox sh won't run busybox applets as builtins (which would break our sandbox).
 
-lsof = find_program('lsof')
-bison = find_program('bison')
-flex = find_program('flex')
+lsof = find_program('lsof', native : true)
+bison = find_program('bison', native : true)
+flex = find_program('flex', native : true)
 
 # This is how Nix does generated headers...
 # other instances of header generation use a very similar command.

package.nix

@@ -62,7 +62,7 @@
 
   # FIXME(Qyriad): build Lix using Meson instead of autoconf and make.
   # This flag will be removed when the migration to Meson is complete.
-  buildWithMeson ? false,
+  buildWithMeson ? true,
 
   # Not a real argument, just the only way to approximate let-binding some
   # stuff for argument defaults.
@@ -100,6 +100,34 @@ let
 
   testConfigureFlags = [ "RAPIDCHECK_HEADERS=${lib.getDev rapidcheck}/extras/gtest/include" ];
 
+  # Reimplementation of Nixpkgs' Meson cross file, with some additions to make
+  # it actually work.
+  mesonCrossFile =
+    let
+      cpuFamily =
+        platform:
+        with platform;
+        if isAarch32 then
+          "arm"
+        else if isx86_32 then
+          "x86"
+        else
+          platform.uname.processor;
+    in
+    builtins.toFile "lix-cross-file.conf" ''
+      [properties]
+      # Meson is convinced that if !buildPlatform.canExecute hostPlatform then we cannot
+      # build anything at all, which is not at all correct. If we can't execute the host
+      # platform, we'll just disable tests and doc gen.
+      needs_exe_wrapper = false
+
+      [binaries]
+      # Meson refuses to consider any CMake binary during cross compilation if it's
+      # not explicitly specified here, in the cross file.
+      # https://github.com/mesonbuild/meson/blob/0ed78cf6fa6d87c0738f67ae43525e661b50a8a2/mesonbuild/cmake/executor.py#L72
+      cmake = 'cmake'
+    '';
+
   # The internal API docs need these for the build, but if we're not building
   # Nix itself, then these don't need to be propagated.
   maybePropagatedInputs = [
@@ -184,10 +212,15 @@ stdenv.mkDerivation (finalAttrs: {
     ]
     ++ lib.optional stdenv.hostPlatform.isStatic "-Denable-embedded-sandbox-shell=true"
     ++ lib.optional (finalAttrs.dontBuild) "-Denable-build=false"
+    ++ [
       # mesonConfigurePhase automatically passes -Dauto_features=enabled,
       # so we must explicitly enable or disable features that we are not passing
       # dependencies for.
-    ++ lib.singleton (lib.mesonEnable "internal-api-docs" internalApiDocs);
+      (lib.mesonEnable "internal-api-docs" internalApiDocs)
+      (lib.mesonBool "enable-tests" finalAttrs.doCheck)
+      (lib.mesonBool "enable-docs" canRunInstalled)
+    ]
+    ++ lib.optional (stdenv.hostPlatform != stdenv.buildPlatform) "--cross-file=${mesonCrossFile}";
 
   # We only include CMake so that Meson can locate toml11, which only ships CMake dependency metadata.
   dontUseCmakeConfigure = true;
@@ -315,7 +348,7 @@ stdenv.mkDerivation (finalAttrs: {
 
   makeFlags = "profiledir=$(out)/etc/profile.d PRECOMPILE_HEADERS=1";
 
-  doCheck = true;
+  doCheck = canRunInstalled;
 
   mesonCheckFlags = lib.optionals (buildWithMeson || forDevShell) [ "--suite=check" ];
 

src/libcmd/cmd-profiles.cc

@@ -0,0 +1,274 @@
+#include "cmd-profiles.hh"
+#include "built-path.hh"
+#include "builtins/buildenv.hh"
+#include "names.hh"
+#include "store-api.hh"
+
+namespace nix
+{
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
+{
+    DrvInfos elems;
+    if (pathExists(userEnv + "/manifest.json"))
+        throw Error("profile '%s' is incompatible with 'nix-env'; please use 'nix profile' instead", userEnv);
+    auto manifestFile = userEnv + "/manifest.nix";
+    if (pathExists(manifestFile)) {
+        Value v;
+        state.evalFile(state.rootPath(CanonPath(manifestFile)), v);
+        Bindings & bindings(*state.allocBindings(0));
+        getDerivations(state, v, "", bindings, elems, false);
+    }
+    return elems;
+}
+
+std::string showVersions(const std::set<std::string> & versions)
+{
+    if (versions.empty()) return "∅";
+    std::set<std::string> versions2;
+    for (auto & version : versions)
+        versions2.insert(version.empty() ? "ε" : version);
+    return concatStringsSep(", ", versions2);
+}
+
+bool ProfileElementSource::operator<(const ProfileElementSource & other) const
+{
+    return std::tuple(originalRef.to_string(), attrPath, outputs)
+        < std::tuple(other.originalRef.to_string(), other.attrPath, other.outputs);
+}
+
+std::string ProfileElementSource::to_string() const
+{
+    return fmt("%s#%s%s", originalRef, attrPath, outputs.to_string());
+}
+
+std::string ProfileElement::identifier() const
+{
+    if (source) {
+        return source->to_string();
+    }
+    StringSet names;
+    for (auto & path : storePaths) {
+        names.insert(DrvName(path.name()).name);
+    }
+    return concatStringsSep(", ", names);
+}
+
+std::set<std::string> ProfileElement::toInstallables(Store & store)
+{
+    if (source) {
+        return {source->to_string()};
+    }
+    StringSet rawPaths;
+    for (auto & path : storePaths) {
+        rawPaths.insert(store.printStorePath(path));
+    }
+    return rawPaths;
+}
+
+std::string ProfileElement::versions() const
+{
+    StringSet versions;
+    for (auto & path : storePaths) {
+        versions.insert(DrvName(path.name()).version);
+    }
+    return showVersions(versions);
+}
+
+bool ProfileElement::operator<(const ProfileElement & other) const
+{
+    return std::tuple(identifier(), storePaths) < std::tuple(other.identifier(), other.storePaths);
+}
+
+void ProfileElement::updateStorePaths(
+    ref<Store> evalStore, ref<Store> store, const BuiltPaths & builtPaths
+)
+{
+    storePaths.clear();
+    for (auto & buildable : builtPaths) {
+        std::visit(
+            overloaded{
+                [&](const BuiltPath::Opaque & bo) { storePaths.insert(bo.path); },
+                [&](const BuiltPath::Built & bfd) {
+                    for (auto & output : bfd.outputs) {
+                        storePaths.insert(output.second);
+                    }
+                },
+            },
+            buildable.raw()
+        );
+    }
+}
+
+ProfileManifest::ProfileManifest(EvalState & state, const Path & profile)
+{
+    auto manifestPath = profile + "/manifest.json";
+
+    if (pathExists(manifestPath)) {
+        auto json = nlohmann::json::parse(readFile(manifestPath));
+
+        auto version = json.value("version", 0);
+        std::string sUrl;
+        std::string sOriginalUrl;
+        switch (version) {
+        case 1:
+            sUrl = "uri";
+            sOriginalUrl = "originalUri";
+            break;
+        case 2:
+            sUrl = "url";
+            sOriginalUrl = "originalUrl";
+            break;
+        default:
+            throw Error("profile manifest '%s' has unsupported version %d", manifestPath, version);
+        }
+
+        for (auto & e : json["elements"]) {
+            ProfileElement element;
+            for (auto & p : e["storePaths"]) {
+                element.storePaths.insert(state.store->parseStorePath((std::string) p));
+            }
+            element.active = e["active"];
+            if (e.contains("priority")) {
+                element.priority = e["priority"];
+            }
+            if (e.value(sUrl, "") != "") {
+                element.source = ProfileElementSource{
+                    parseFlakeRef(e[sOriginalUrl]),
+                    parseFlakeRef(e[sUrl]),
+                    e["attrPath"],
+                    e["outputs"].get<ExtendedOutputsSpec>()};
+            }
+            elements.emplace_back(std::move(element));
+        }
+    } else if (pathExists(profile + "/manifest.nix")) {
+        // FIXME: needed because of pure mode; ugly.
+        state.allowPath(state.store->followLinksToStore(profile));
+        state.allowPath(state.store->followLinksToStore(profile + "/manifest.nix"));
+
+        auto drvInfos = queryInstalled(state, state.store->followLinksToStore(profile));
+
+        for (auto & drvInfo : drvInfos) {
+            ProfileElement element;
+            element.storePaths = {drvInfo.queryOutPath()};
+            elements.emplace_back(std::move(element));
+        }
+    }
+}
+
+nlohmann::json ProfileManifest::toJSON(Store & store) const
+{
+    auto array = nlohmann::json::array();
+    for (auto & element : elements) {
+        auto paths = nlohmann::json::array();
+        for (auto & path : element.storePaths) {
+            paths.push_back(store.printStorePath(path));
+        }
+        nlohmann::json obj;
+        obj["storePaths"] = paths;
+        obj["active"] = element.active;
+        obj["priority"] = element.priority;
+        if (element.source) {
+            obj["originalUrl"] = element.source->originalRef.to_string();
+            obj["url"] = element.source->lockedRef.to_string();
+            obj["attrPath"] = element.source->attrPath;
+            obj["outputs"] = element.source->outputs;
+        }
+        array.push_back(obj);
+    }
+    nlohmann::json json;
+    json["version"] = 2;
+    json["elements"] = array;
+    return json;
+}
+
+StorePath ProfileManifest::build(ref<Store> store)
+{
+    auto tempDir = createTempDir();
+
+    StorePathSet references;
+
+    Packages pkgs;
+    for (auto & element : elements) {
+        for (auto & path : element.storePaths) {
+            if (element.active) {
+                pkgs.emplace_back(store->printStorePath(path), true, element.priority);
+            }
+            references.insert(path);
+        }
+    }
+
+    buildProfile(tempDir, std::move(pkgs));
+
+    writeFile(tempDir + "/manifest.json", toJSON(*store).dump());
+
+    /* Add the symlink tree to the store. */
+    StringSink sink;
+    dumpPath(tempDir, sink);
+
+    auto narHash = hashString(htSHA256, sink.s);
+
+    ValidPathInfo info{
+        *store,
+        "profile",
+        FixedOutputInfo{
+            .method = FileIngestionMethod::Recursive,
+            .hash = narHash,
+            .references =
+                {
+                    .others = std::move(references),
+                    // profiles never refer to themselves
+                    .self = false,
+                },
+        },
+        narHash,
+    };
+    info.narSize = sink.s.size();
+
+    StringSource source(sink.s);
+    store->addToStore(info, source);
+
+    return std::move(info.path);
+}
+
+void ProfileManifest::printDiff(
+    const ProfileManifest & prev, const ProfileManifest & cur, std::string_view indent
+)
+{
+    auto prevElems = prev.elements;
+    std::sort(prevElems.begin(), prevElems.end());
+
+    auto curElems = cur.elements;
+    std::sort(curElems.begin(), curElems.end());
+
+    auto i = prevElems.begin();
+    auto j = curElems.begin();
+
+    bool changes = false;
+
+    while (i != prevElems.end() || j != curElems.end()) {
+        if (j != curElems.end() && (i == prevElems.end() || i->identifier() > j->identifier())) {
+            logger->cout("%s%s: ∅ -> %s", indent, j->identifier(), j->versions());
+            changes = true;
+            ++j;
+        } else if (i != prevElems.end() && (j == curElems.end() || i->identifier() < j->identifier())) {
+            logger->cout("%s%s: %s -> ∅", indent, i->identifier(), i->versions());
+            changes = true;
+            ++i;
+        } else {
+            auto v1 = i->versions();
+            auto v2 = j->versions();
+            if (v1 != v2) {
+                logger->cout("%s%s: %s -> %s", indent, i->identifier(), v1, v2);
+                changes = true;
+            }
+            ++i;
+            ++j;
+        }
+    }
+
+    if (!changes) {
+        logger->cout("%sNo changes.", indent);
+    }
+}
+}

src/libcmd/cmd-profiles.hh

@@ -0,0 +1,73 @@
+#pragma once
+///@file
+
+#include "built-path.hh"
+#include "eval.hh"
+#include "flake/flakeref.hh"
+#include "get-drvs.hh"
+#include "types.hh"
+
+#include <string>
+#include <set>
+
+#include <nlohmann/json.hpp>
+
+namespace nix
+{
+
+struct ProfileElementSource
+{
+    FlakeRef originalRef;
+    // FIXME: record original attrpath.
+    FlakeRef lockedRef;
+    std::string attrPath;
+    ExtendedOutputsSpec outputs;
+
+    bool operator<(const ProfileElementSource & other) const;
+
+    std::string to_string() const;
+};
+
+constexpr int DEFAULT_PRIORITY = 5;
+
+struct ProfileElement
+{
+    StorePathSet storePaths;
+    std::optional<ProfileElementSource> source;
+    bool active = true;
+    int priority = DEFAULT_PRIORITY;
+
+    std::string identifier() const;
+
+    /**
+     * Return a string representing an installable corresponding to the current
+     * element, either a flakeref or a plain store path
+     */
+    std::set<std::string> toInstallables(Store & store);
+
+    std::string versions() const;
+
+    bool operator<(const ProfileElement & other) const;
+
+    void updateStorePaths(ref<Store> evalStore, ref<Store> store, const BuiltPaths & builtPaths);
+};
+
+struct ProfileManifest
+{
+    std::vector<ProfileElement> elements;
+
+    ProfileManifest() { }
+
+    ProfileManifest(EvalState & state, const Path & profile);
+
+    nlohmann::json toJSON(Store & store) const;
+
+    StorePath build(ref<Store> store);
+
+    static void printDiff(const ProfileManifest & prev, const ProfileManifest & cur, std::string_view indent);
+};
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv);
+std::string showVersions(const std::set<std::string> & versions);
+
+}

src/libcmd/command.hh

@@ -342,8 +342,6 @@ void completeFlakeRefWithFragment(
     const Strings & defaultFlakeAttrPaths,
     std::string_view prefix);
 
-std::string showVersions(const std::set<std::string> & versions);
-
 void printClosureDiff(
     ref<Store> store,
     const StorePath & beforePath,

src/libcmd/meson.build

@@ -1,6 +1,7 @@
 libcmd_sources = files(
   'built-path.cc',
   'command-installable-value.cc',
+  'cmd-profiles.cc',
   'command.cc',
   'common-eval-args.cc',
   'editor-for.cc',
@@ -18,6 +19,7 @@ libcmd_sources = files(
 libcmd_headers = files(
   'built-path.hh',
   'command-installable-value.hh',
+  'cmd-profiles.hh',
   'command.hh',
   'common-eval-args.hh',
   'editor-for.hh',

src/libfetchers/github.cc

@@ -195,32 +195,12 @@ struct GitArchiveInputScheme : InputScheme
         input.attrs.erase("ref");
         input.attrs.insert_or_assign("rev", rev->gitRev());
 
-        Attrs lockedAttrs({
-            {"type", "git-tarball"},
-            {"rev", rev->gitRev()},
-        });
-
-        if (auto res = getCache()->lookup(store, lockedAttrs)) {
-            input.attrs.insert_or_assign("lastModified", getIntAttr(res->first, "lastModified"));
-            return {std::move(res->second), input};
-        }
-
         auto url = getDownloadUrl(input);
 
         auto result = downloadTarball(store, url.url, input.getName(), true, url.headers);
 
         input.attrs.insert_or_assign("lastModified", uint64_t(result.lastModified));
 
-        getCache()->add(
-            store,
-            lockedAttrs,
-            {
-                {"rev", rev->gitRev()},
-                {"lastModified", uint64_t(result.lastModified)}
-            },
-            result.tree.storePath,
-            true);
-
         return {result.tree.storePath, input};
     }
 };

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

@@ -52,6 +52,9 @@
 #if __APPLE__
 #include <spawn.h>
 #include <sys/sysctl.h>
+
+/* This definition is undocumented but depended upon by all major browsers. */
+extern "C" int sandbox_init_with_parameters(const char *profile, uint64_t flags, const char *const parameters[], char **errorbuf);
 #endif
 
 #include <pwd.h>
@@ -1711,7 +1714,7 @@ void LocalDerivationGoal::runChild()
            (which may run under a different uid and/or in a sandbox). */
         std::string netrcData;
         try {
-            if (drv->isBuiltin() && drv->builder == "builtin:fetchurl")
+            if (drv->isBuiltin() && drv->builder == "builtin:fetchurl" && !derivationType->isSandboxed())
                 netrcData = readFile(settings.netrcFile);
         } catch (SysError &) { }
 
@@ -2005,11 +2008,7 @@ void LocalDerivationGoal::runChild()
 
         std::string builder = "invalid";
 
-        if (drv->isBuiltin()) {
-            ;
-        }
 #if __APPLE__
-        else {
         /* This has to appear before import statements. */
         std::string sandboxProfile = "(version 1)\n";
 
@@ -2078,13 +2077,13 @@ void LocalDerivationGoal::runChild()
                         i.first, i.second.source);
 
                 std::string path = i.first;
-                    auto optSt = maybeLstat(path.c_str());
-                    if (!optSt) {
-                        if (i.second.optional)
+                struct stat st;
+                if (lstat(path.c_str(), &st)) {
+                    if (i.second.optional && errno == ENOENT)
                         continue;
-                        throw SysError("getting attributes of required path '%s", path);
+                    throw SysError("getting attributes of path '%s", path);
                 }
-                    if (S_ISDIR(optSt->st_mode))
+                if (S_ISDIR(st.st_mode))
                     sandboxProfile += fmt("\t(subpath \"%s\")\n", path);
                 else
                     sandboxProfile += fmt("\t(literal \"%s\")\n", path);
@@ -2107,10 +2106,6 @@ void LocalDerivationGoal::runChild()
         debug("Generated sandbox profile:");
         debug(sandboxProfile);
 
-            Path sandboxFile = tmpDir + "/.sandbox.sb";
-
-            writeFile(sandboxFile, sandboxProfile);
-
         bool allowLocalNetworking = parsedDrv->getBoolAttr("__darwinAllowLocalNetworking");
 
         /* The tmpDir in scope points at the temporary build directory for our derivation. Some packages try different mechanisms
@@ -2121,24 +2116,23 @@ void LocalDerivationGoal::runChild()
         if (globalTmpDir.back() == '/') globalTmpDir.pop_back();
 
         if (getEnv("_NIX_TEST_NO_SANDBOX") != "1") {
-                builder = "/usr/bin/sandbox-exec";
-                args.push_back("sandbox-exec");
-                args.push_back("-f");
-                args.push_back(sandboxFile);
-                args.push_back("-D");
-                args.push_back("_GLOBAL_TMP_DIR=" + globalTmpDir);
+            Strings sandboxArgs;
+            sandboxArgs.push_back("_GLOBAL_TMP_DIR");
+            sandboxArgs.push_back(globalTmpDir);
             if (allowLocalNetworking) {
-                    args.push_back("-D");
-                    args.push_back(std::string("_ALLOW_LOCAL_NETWORKING=1"));
+                sandboxArgs.push_back("_ALLOW_LOCAL_NETWORKING");
+                sandboxArgs.push_back("1");
             }
-                args.push_back(drv->builder);
-            } else {
+            if (sandbox_init_with_parameters(sandboxProfile.c_str(), 0, stringsToCharPtrs(sandboxArgs).data(), NULL)) {
+                writeFull(STDERR_FILENO, "failed to configure sandbox\n");
+                _exit(1);
+            }
+        }
+
         builder = drv->builder;
         args.push_back(std::string(baseNameOf(drv->builder)));
-            }
-        }
 #else
-        else {
+        if (!drv->isBuiltin()) {
             builder = drv->builder;
             args.push_back(std::string(baseNameOf(drv->builder)));
         }

src/libstore/builtins/fetchurl.cc

@@ -38,7 +38,6 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
                the result anyway. */
             FileTransferRequest request(url);
             request.verifyTLS = false;
-            request.decompress = false;
 
             auto decompressor = makeDecompressionSink(
                 unpack && mainUrl.ends_with(".xz") ? "xz" : "none", sink);

src/libstore/filetransfer.cc

@@ -49,8 +49,10 @@ struct curlFileTransfer : public FileTransfer
         Activity act;
         bool done = false; // whether either the success or failure function has been called
         Callback<FileTransferResult> callback;
+        std::function<void(TransferItem &, std::string_view data)> dataCallback;
         CURL * req = 0;
         bool active = false; // whether the handle has been added to the multi object
+        bool headersProcessed = false;
         std::string statusMsg;
 
         unsigned int attempt = 0;
@@ -81,30 +83,15 @@ struct curlFileTransfer : public FileTransfer
 
         TransferItem(curlFileTransfer & fileTransfer,
             const FileTransferRequest & request,
-            Callback<FileTransferResult> && callback)
+            Callback<FileTransferResult> && callback,
+            std::function<void(TransferItem &, std::string_view data)> dataCallback)
             : fileTransfer(fileTransfer)
             , request(request)
             , act(*logger, lvlTalkative, actFileTransfer,
                 fmt(request.data ? "uploading '%s'" : "downloading '%s'", request.uri),
                 {request.uri}, request.parentAct)
             , callback(std::move(callback))
-            , finalSink([this](std::string_view data) {
-                if (errorSink) {
-                    (*errorSink)(data);
-                }
-
-                if (this->request.dataCallback) {
-                    auto httpStatus = getHTTPStatus();
-
-                    /* Only write data to the sink if this is a
-                       successful response. */
-                    if (successfulStatuses.count(httpStatus)) {
-                        writtenToSink += data.size();
-                        this->request.dataCallback(data);
-                    }
-                } else
-                    this->result.data.append(data);
-              })
+            , dataCallback(std::move(dataCallback))
         {
             requestHeaders = curl_slist_append(requestHeaders, "Accept-Encoding: zstd, br, gzip, deflate, bzip2, xz");
             if (!request.expectedETag.empty())
@@ -145,30 +132,44 @@ struct curlFileTransfer : public FileTransfer
             failEx(std::make_exception_ptr(std::forward<T>(e)));
         }
 
-        LambdaSink finalSink;
-        std::shared_ptr<FinishSink> decompressionSink;
-        std::optional<StringSink> errorSink;
-
         std::exception_ptr writeException;
 
+        std::optional<std::string> getHeader(const char * name)
+        {
+            curl_header * result;
+            auto e = curl_easy_header(req, name, 0, CURLH_HEADER, -1, &result);
+            if (e == CURLHE_OK) {
+                return result->value;
+            } else if (e == CURLHE_MISSING || e == CURLHE_NOHEADERS) {
+                return std::nullopt;
+            } else {
+                throw nix::Error("unexpected error from curl_easy_header(): %i", e);
+            }
+        }
+
         size_t writeCallback(void * contents, size_t size, size_t nmemb)
         {
             try {
+                if (!headersProcessed) {
+                    if (auto h = getHeader("content-encoding")) {
+                        encoding = std::move(*h);
+                    }
+                    if (auto h = getHeader("accept-ranges"); h && *h == "bytes") {
+                        acceptRanges = true;
+                    }
+
+                    headersProcessed = true;
+                }
+
                 size_t realSize = size * nmemb;
                 result.bodySize += realSize;
 
-                if (!decompressionSink) {
-                    decompressionSink = makeDecompressionSink(encoding, finalSink);
-                    if (! successfulStatuses.count(getHTTPStatus())) {
-                        // In this case we want to construct a TeeSink, to keep
-                        // the response around (which we figure won't be big
-                        // like an actual download should be) to improve error
-                        // messages.
-                        errorSink = StringSink { };
+                if (successfulStatuses.count(getHTTPStatus()) && this->dataCallback) {
+                    writtenToSink += realSize;
+                    dataCallback(*this, {(const char *) contents, realSize});
+                } else {
+                    this->result.data.append((const char *) contents, realSize);
                 }
-                }
-
-                (*decompressionSink)({(char *) contents, realSize});
 
                 return realSize;
             } catch (...) {
@@ -196,42 +197,7 @@ struct curlFileTransfer : public FileTransfer
                 statusMsg = trim(match.str(1));
                 acceptRanges = false;
                 encoding = "";
-            } else {
-
-                auto i = line.find(':');
-                if (i != std::string::npos) {
-                    std::string name = toLower(trim(line.substr(0, i)));
-
-                    if (name == "etag") {
-                        result.etag = trim(line.substr(i + 1));
-                        /* Hack to work around a GitHub bug: it sends
-                           ETags, but ignores If-None-Match. So if we get
-                           the expected ETag on a 200 response, then shut
-                           down the connection because we already have the
-                           data. */
-                        long httpStatus = 0;
-                        curl_easy_getinfo(req, CURLINFO_RESPONSE_CODE, &httpStatus);
-                        if (result.etag == request.expectedETag && httpStatus == 200) {
-                            debug("shutting down on 200 HTTP response with expected ETag");
-                            return 0;
-                        }
-                    }
-
-                    else if (name == "content-encoding")
-                        encoding = trim(line.substr(i + 1));
-
-                    else if (name == "accept-ranges" && toLower(trim(line.substr(i + 1))) == "bytes")
-                        acceptRanges = true;
-
-                    else if (name == "link" || name == "x-amz-meta-link") {
-                        auto value = trim(line.substr(i + 1));
-                        static std::regex linkRegex("<([^>]*)>; rel=\"immutable\"", std::regex::extended | std::regex::icase);
-                        if (std::smatch match; std::regex_match(value, match, linkRegex))
-                            result.immutableUrl = match.str(1);
-                        else
-                            debug("got invalid link header '%s'", value);
-                    }
-                }
+                headersProcessed = false;
             }
             return realSize;
         }
@@ -301,15 +267,11 @@ struct curlFileTransfer : public FileTransfer
             curl_easy_setopt(req, CURLOPT_USERAGENT,
                 ("curl/" LIBCURL_VERSION " Lix/" + nixVersion +
                     (fileTransferSettings.userAgentSuffix != "" ? " " + fileTransferSettings.userAgentSuffix.get() : "")).c_str());
-            #if LIBCURL_VERSION_NUM >= 0x072b00
             curl_easy_setopt(req, CURLOPT_PIPEWAIT, 1);
-            #endif
-            #if LIBCURL_VERSION_NUM >= 0x072f00
             if (fileTransferSettings.enableHttp2)
                 curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
             else
                 curl_easy_setopt(req, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
-            #endif
             curl_easy_setopt(req, CURLOPT_WRITEFUNCTION, TransferItem::writeCallbackWrapper);
             curl_easy_setopt(req, CURLOPT_WRITEDATA, this);
             curl_easy_setopt(req, CURLOPT_HEADERFUNCTION, TransferItem::headerCallbackWrapper);
@@ -371,17 +333,31 @@ struct curlFileTransfer : public FileTransfer
             debug("finished %s of '%s'; curl status = %d, HTTP status = %d, body = %d bytes",
                 request.verb(), request.uri, code, httpStatus, result.bodySize);
 
-            if (decompressionSink) {
-                try {
-                    decompressionSink->finish();
-                } catch (...) {
-                    writeException = std::current_exception();
+            auto link = getHeader("link");
+            if (!link) {
+                link = getHeader("x-amz-meta-link");
+            }
+            if (link) {
+                static std::regex linkRegex(
+                    "<([^>]*)>; rel=\"immutable\"", std::regex::extended | std::regex::icase
+                );
+                if (std::smatch match; std::regex_match(*link, match, linkRegex)) {
+                    result.immutableUrl = match.str(1);
+                } else {
+                    debug("got invalid link header '%s'", *link);
                 }
             }
 
-            if (code == CURLE_WRITE_ERROR && result.etag == request.expectedETag) {
-                code = CURLE_OK;
-                httpStatus = 304;
+            if (auto etag = getHeader("etag")) {
+                result.etag = std::move(*etag);
+            }
+
+            // this has to happen here until we can return an actual future.
+            // wrapping user `callback`s instead is not possible because the
+            // Callback api expects std::functions, and copying Callbacks is
+            // not possible due the promises they hold.
+            if (code == CURLE_OK && !dataCallback) {
+                result.data = decompress(encoding, result.data);
             }
 
             if (writeException)
@@ -390,13 +366,6 @@ struct curlFileTransfer : public FileTransfer
             else if (code == CURLE_OK && successfulStatuses.count(httpStatus))
             {
                 result.cached = httpStatus == 304;
-
-                // In 2021, GitHub responds to If-None-Match with 304,
-                // but omits ETag. We just use the If-None-Match etag
-                // since 304 implies they are the same.
-                if (httpStatus == 304 && result.etag == "")
-                    result.etag = request.expectedETag;
-
                 act.progress(result.bodySize, result.bodySize);
                 done = true;
                 callback(std::move(result));
@@ -455,16 +424,16 @@ struct curlFileTransfer : public FileTransfer
                 attempt++;
 
                 std::optional<std::string> response;
-                if (errorSink)
-                    response = std::move(errorSink->s);
+                if (!successfulStatuses.count(httpStatus))
+                    response = std::move(result.data);
                 auto exc =
                     code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
                     ? FileTransferError(Interrupted, std::move(response), "%s of '%s' was interrupted", request.verb(), request.uri)
                     : httpStatus != 0
                     ? FileTransferError(err,
                         std::move(response),
-                        "unable to %s '%s': HTTP error %d%s",
-                        request.verb(), request.uri, httpStatus,
+                        "unable to %s '%s': HTTP error %d (%s)%s",
+                        request.verb(), request.uri, httpStatus, statusMsg,
                         code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
                     : FileTransferError(err,
                         std::move(response),
@@ -477,7 +446,7 @@ struct curlFileTransfer : public FileTransfer
                    ranged requests. */
                 if (err == Transient
                     && attempt < request.tries
-                    && (!this->request.dataCallback
+                    && (!this->dataCallback
                         || writtenToSink == 0
                         || (acceptRanges && encoding.empty())))
                 {
@@ -508,11 +477,6 @@ struct curlFileTransfer : public FileTransfer
 
     Sync<State> state_;
 
-    /* We can't use a std::condition_variable to wake up the curl
-       thread, because it only monitors file descriptors. So use a
-       pipe instead. */
-    Pipe wakeupPipe;
-
     std::thread workerThread;
 
     curlFileTransfer()
@@ -523,16 +487,9 @@ struct curlFileTransfer : public FileTransfer
 
         curlm = curl_multi_init();
 
-        #if LIBCURL_VERSION_NUM >= 0x072b00 // Multiplex requires >= 7.43.0
         curl_multi_setopt(curlm, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
-        #endif
-        #if LIBCURL_VERSION_NUM >= 0x071e00 // Max connections requires >= 7.30.0
         curl_multi_setopt(curlm, CURLMOPT_MAX_TOTAL_CONNECTIONS,
             fileTransferSettings.httpConnections.get());
-        #endif
-
-        wakeupPipe.create();
-        fcntl(wakeupPipe.readSide.get(), F_SETFL, O_NONBLOCK);
 
         workerThread = std::thread([&]() { workerThreadEntry(); });
     }
@@ -546,6 +503,12 @@ struct curlFileTransfer : public FileTransfer
         if (curlm) curl_multi_cleanup(curlm);
     }
 
+    void wakeup()
+    {
+        if (auto mc = curl_multi_wakeup(curlm))
+            throw nix::Error("unexpected error from curl_multi_wakeup(): %s", curl_multi_strerror(mc));
+    }
+
     void stopWorkerThread()
     {
         /* Signal the worker thread to exit. */
@@ -553,7 +516,7 @@ struct curlFileTransfer : public FileTransfer
             auto state(state_.lock());
             state->quit = true;
         }
-        writeFull(wakeupPipe.writeSide.get(), " ", false);
+        wakeup();
     }
 
     void workerThreadMain()
@@ -595,32 +558,21 @@ struct curlFileTransfer : public FileTransfer
             }
 
             /* Wait for activity, including wakeup events. */
-            int numfds = 0;
-            struct curl_waitfd extraFDs[1];
-            extraFDs[0].fd = wakeupPipe.readSide.get();
-            extraFDs[0].events = CURL_WAIT_POLLIN;
-            extraFDs[0].revents = 0;
             long maxSleepTimeMs = items.empty() ? 10000 : 100;
             auto sleepTimeMs =
                 nextWakeup != std::chrono::steady_clock::time_point()
                 ? std::max(0, (int) std::chrono::duration_cast<std::chrono::milliseconds>(nextWakeup - std::chrono::steady_clock::now()).count())
                 : maxSleepTimeMs;
             vomit("download thread waiting for %d ms", sleepTimeMs);
-            mc = curl_multi_wait(curlm, extraFDs, 1, sleepTimeMs, &numfds);
+            mc = curl_multi_poll(curlm, nullptr, 0, sleepTimeMs, nullptr);
             if (mc != CURLM_OK)
-                throw nix::Error("unexpected error from curl_multi_wait(): %s", curl_multi_strerror(mc));
+                throw nix::Error("unexpected error from curl_multi_poll(): %s", curl_multi_strerror(mc));
 
             nextWakeup = std::chrono::steady_clock::time_point();
 
             /* Add new curl requests from the incoming requests queue,
                except for requests that are embargoed (waiting for a
                retry timeout to expire). */
-            if (extraFDs[0].revents & CURL_WAIT_POLLIN) {
-                char buf[1024];
-                auto res = read(extraFDs[0].fd, buf, sizeof(buf));
-                if (res == -1 && errno != EINTR)
-                    throw SysError("reading curl wakeup socket");
-            }
 
             std::vector<std::shared_ptr<TransferItem>> incoming;
             auto now = std::chrono::steady_clock::now();
@@ -683,7 +635,7 @@ struct curlFileTransfer : public FileTransfer
                 throw nix::Error("cannot enqueue download request because the download thread is shutting down");
             state->incoming.push(item);
         }
-        writeFull(wakeupPipe.writeSide.get(), " ");
+        wakeup();
     }
 
 #if ENABLE_S3
@@ -704,6 +656,13 @@ struct curlFileTransfer : public FileTransfer
 
     void enqueueFileTransfer(const FileTransferRequest & request,
         Callback<FileTransferResult> callback) override
+    {
+        enqueueFileTransfer(request, std::move(callback), {});
+    }
+
+    void enqueueFileTransfer(const FileTransferRequest & request,
+        Callback<FileTransferResult> callback,
+        std::function<void(TransferItem &, std::string_view data)> dataCallback)
     {
         /* Ugly hack to support s3:// URIs. */
         if (request.uri.starts_with("s3://")) {
@@ -733,7 +692,116 @@ struct curlFileTransfer : public FileTransfer
             return;
         }
 
-        enqueueItem(std::make_shared<TransferItem>(*this, request, std::move(callback)));
+        enqueueItem(std::make_shared<TransferItem>(
+            *this, request, std::move(callback), std::move(dataCallback)
+        ));
+    }
+
+    void download(FileTransferRequest && request, Sink & sink) override
+    {
+        /* Note: we can't call 'sink' via request.dataCallback, because
+           that would cause the sink to execute on the fileTransfer
+           thread. If 'sink' is a coroutine, this will fail. Also, if the
+           sink is expensive (e.g. one that does decompression and writing
+           to the Nix store), it would stall the download thread too much.
+           Therefore we use a buffer to communicate data between the
+           download thread and the calling thread. */
+
+        struct State {
+            bool quit = false;
+            std::exception_ptr exc;
+            std::string data;
+            std::condition_variable avail, request;
+            std::unique_ptr<FinishSink> decompressor;
+        };
+
+        auto _state = std::make_shared<Sync<State>>();
+
+        /* In case of an exception, wake up the download thread. FIXME:
+           abort the download request. */
+        Finally finally([&]() {
+            auto state(_state->lock());
+            state->quit = true;
+            state->request.notify_one();
+        });
+
+        enqueueFileTransfer(request,
+            {[_state](std::future<FileTransferResult> fut) {
+                auto state(_state->lock());
+                state->quit = true;
+                try {
+                    fut.get();
+                } catch (...) {
+                    state->exc = std::current_exception();
+                }
+                state->avail.notify_one();
+                state->request.notify_one();
+            }},
+            [_state, &sink](TransferItem & transfer, std::string_view data) {
+                auto state(_state->lock());
+
+                if (state->quit) return;
+
+                if (!state->decompressor) {
+                    state->decompressor = makeDecompressionSink(transfer.encoding, sink);
+                }
+
+                /* If the buffer is full, then go to sleep until the calling
+                thread wakes us up (i.e. when it has removed data from the
+                buffer). We don't wait forever to prevent stalling the
+                download thread. (Hopefully sleeping will throttle the
+                sender.) */
+                if (state->data.size() > 1024 * 1024) {
+                    debug("download buffer is full; going to sleep");
+                    state.wait_for(state->request, std::chrono::seconds(10));
+                }
+
+                /* Append data to the buffer and wake up the calling
+                thread. */
+                state->data.append(data);
+                state->avail.notify_one();
+            });
+
+        while (true) {
+            checkInterrupt();
+
+            std::string chunk;
+            FinishSink * sink = nullptr;
+
+            /* Grab data if available, otherwise wait for the download
+               thread to wake us up. */
+            {
+                auto state(_state->lock());
+
+                if (state->data.empty()) {
+
+                    if (state->quit) {
+                        if (state->exc) std::rethrow_exception(state->exc);
+                        if (state->decompressor) {
+                            state->decompressor->finish();
+                        }
+                        return;
+                    }
+
+                    state.wait(state->avail);
+
+                    if (state->data.empty()) continue;
+                }
+
+                chunk = std::move(state->data);
+                sink = state->decompressor.get();
+                /* Reset state->data after the move, since we check data.empty() */
+                state->data = "";
+
+                state->request.notify_one();
+            }
+
+            /* Flush the data to the sink and wake up the download thread
+               if it's blocked on a full buffer. We don't hold the state
+               lock while doing this to prevent blocking the download
+               thread if sink() takes a long time. */
+            (*sink)(chunk);
+        }
     }
 };
 
@@ -782,105 +850,6 @@ FileTransferResult FileTransfer::upload(const FileTransferRequest & request)
     return enqueueFileTransfer(request).get();
 }
 
-void FileTransfer::download(FileTransferRequest && request, Sink & sink)
-{
-    /* Note: we can't call 'sink' via request.dataCallback, because
-       that would cause the sink to execute on the fileTransfer
-       thread. If 'sink' is a coroutine, this will fail. Also, if the
-       sink is expensive (e.g. one that does decompression and writing
-       to the Nix store), it would stall the download thread too much.
-       Therefore we use a buffer to communicate data between the
-       download thread and the calling thread. */
-
-    struct State {
-        bool quit = false;
-        std::exception_ptr exc;
-        std::string data;
-        std::condition_variable avail, request;
-    };
-
-    auto _state = std::make_shared<Sync<State>>();
-
-    /* In case of an exception, wake up the download thread. FIXME:
-       abort the download request. */
-    Finally finally([&]() {
-        auto state(_state->lock());
-        state->quit = true;
-        state->request.notify_one();
-    });
-
-    request.dataCallback = [_state](std::string_view data) {
-
-        auto state(_state->lock());
-
-        if (state->quit) return;
-
-        /* If the buffer is full, then go to sleep until the calling
-           thread wakes us up (i.e. when it has removed data from the
-           buffer). We don't wait forever to prevent stalling the
-           download thread. (Hopefully sleeping will throttle the
-           sender.) */
-        if (state->data.size() > 1024 * 1024) {
-            debug("download buffer is full; going to sleep");
-            state.wait_for(state->request, std::chrono::seconds(10));
-        }
-
-        /* Append data to the buffer and wake up the calling
-           thread. */
-        state->data.append(data);
-        state->avail.notify_one();
-    };
-
-    enqueueFileTransfer(request,
-        {[_state](std::future<FileTransferResult> fut) {
-            auto state(_state->lock());
-            state->quit = true;
-            try {
-                fut.get();
-            } catch (...) {
-                state->exc = std::current_exception();
-            }
-            state->avail.notify_one();
-            state->request.notify_one();
-        }});
-
-    while (true) {
-        checkInterrupt();
-
-        std::string chunk;
-
-        /* Grab data if available, otherwise wait for the download
-           thread to wake us up. */
-        {
-            auto state(_state->lock());
-
-            if (state->data.empty()) {
-
-                if (state->quit) {
-                    if (state->exc) std::rethrow_exception(state->exc);
-                    return;
-                }
-
-                state.wait(state->avail);
-
-                if (state->data.empty()) continue;
-            }
-
-            chunk = std::move(state->data);
-            /* Reset state->data after the move, since we check data.empty() */
-            state->data = "";
-
-            state->request.notify_one();
-        }
-
-        /* Flush the data to the sink and wake up the download thread
-           if it's blocked on a full buffer. We don't hold the state
-           lock while doing this to prevent blocking the download
-           thread if sink() takes a long time. */
-        sink(chunk);
-    }
-}
-
 template<typename... Args>
 FileTransferError::FileTransferError(FileTransfer::Error error, std::optional<std::string> response, const Args & ... args)
     : Error(args...), error(error), response(response)

src/libstore/filetransfer.hh

@@ -59,10 +59,8 @@ struct FileTransferRequest
     size_t tries = fileTransferSettings.tries;
     unsigned int baseRetryTimeMs = 250;
     ActivityId parentAct;
-    bool decompress = true;
     std::optional<std::string> data;
     std::string mimeType;
-    std::function<void(std::string_view data)> dataCallback;
 
     FileTransferRequest(std::string_view uri)
         : uri(uri), parentAct(getCurActivity()) { }
@@ -116,7 +114,7 @@ struct FileTransfer
      * Download a file, writing its data to a sink. The sink will be
      * invoked on the thread of the caller.
      */
-    void download(FileTransferRequest && request, Sink & sink);
+    virtual void download(FileTransferRequest && request, Sink & sink) = 0;
 
     enum Error { NotFound, Forbidden, Misc, Transient, Interrupted };
 };

src/libstore/gc-store.hh

@@ -7,7 +7,14 @@
 namespace nix {
 
 
+/**
+ * Garbage-collector roots, referring to a store path
+ */
 typedef std::unordered_map<StorePath, std::unordered_set<std::string>> Roots;
+/**
+ * Possible garbage collector roots, referring to any path
+ */
+typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
 
 
 struct GCOptions

src/libstore/gc.cc

@@ -321,105 +321,8 @@ Roots LocalStore::findRoots(bool censor)
     return roots;
 }
 
-typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
-
-static void readProcLink(const std::string & file, UncheckedRoots & roots)
+void LocalStore::findPlatformRoots(UncheckedRoots & unchecked)
 {
-    constexpr auto bufsiz = PATH_MAX;
-    char buf[bufsiz];
-    auto res = readlink(file.c_str(), buf, bufsiz);
-    if (res == -1) {
-        if (errno == ENOENT || errno == EACCES || errno == ESRCH)
-            return;
-        throw SysError("reading symlink");
-    }
-    if (res == bufsiz) {
-        throw Error("overly long symlink starting with '%1%'", std::string_view(buf, bufsiz));
-    }
-    if (res > 0 && buf[0] == '/')
-        roots[std::string(static_cast<char *>(buf), res)]
-            .emplace(file);
-}
-
-static std::string quoteRegexChars(const std::string & raw)
-{
-    static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
-    return std::regex_replace(raw, specialRegex, R"(\$&)");
-}
-
-#if __linux__
-static void readFileRoots(const char * path, UncheckedRoots & roots)
-{
-    try {
-        roots[readFile(path)].emplace(path);
-    } catch (SysError & e) {
-        if (e.errNo != ENOENT && e.errNo != EACCES)
-            throw;
-    }
-}
-#endif
-
-void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
-{
-    UncheckedRoots unchecked;
-
-    auto procDir = AutoCloseDir{opendir("/proc")};
-    if (procDir) {
-        struct dirent * ent;
-        auto digitsRegex = std::regex(R"(^\d+$)");
-        auto mapRegex = std::regex(R"(^\s*\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+(/\S+)\s*$)");
-        auto storePathRegex = std::regex(quoteRegexChars(storeDir) + R"(/[0-9a-z]+[0-9a-zA-Z\+\-\._\?=]*)");
-        while (errno = 0, ent = readdir(procDir.get())) {
-            checkInterrupt();
-            if (std::regex_match(ent->d_name, digitsRegex)) {
-                try {
-                    readProcLink(fmt("/proc/%s/exe" ,ent->d_name), unchecked);
-                    readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
-
-                    auto fdStr = fmt("/proc/%s/fd", ent->d_name);
-                    auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
-                    if (!fdDir) {
-                        if (errno == ENOENT || errno == EACCES)
-                            continue;
-                        throw SysError("opening %1%", fdStr);
-                    }
-                    struct dirent * fd_ent;
-                    while (errno = 0, fd_ent = readdir(fdDir.get())) {
-                        if (fd_ent->d_name[0] != '.')
-                            readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
-                    }
-                    if (errno) {
-                        if (errno == ESRCH)
-                            continue;
-                        throw SysError("iterating /proc/%1%/fd", ent->d_name);
-                    }
-                    fdDir.reset();
-
-                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
-                    auto mapLines = tokenizeString<std::vector<std::string>>(readFile(mapFile), "\n");
-                    for (const auto & line : mapLines) {
-                        auto match = std::smatch{};
-                        if (std::regex_match(line, match, mapRegex))
-                            unchecked[match[1]].emplace(mapFile);
-                    }
-
-                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
-                    auto envString = readFile(envFile);
-                    auto env_end = std::sregex_iterator{};
-                    for (auto i = std::sregex_iterator{envString.begin(), envString.end(), storePathRegex}; i != env_end; ++i)
-                        unchecked[i->str()].emplace(envFile);
-                } catch (SysError & e) {
-                    if (errno == ENOENT || errno == EACCES || errno == ESRCH)
-                        continue;
-                    throw;
-                }
-            }
-        }
-        if (errno)
-            throw SysError("iterating /proc");
-    }
-
-#if !defined(__linux__)
     // lsof is really slow on OS X. This actually causes the gc-concurrent.sh test to fail.
     // See: https://github.com/NixOS/nix/issues/3011
     // Because of this we disable lsof when running the tests.
@@ -437,13 +340,13 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
             /* lsof not installed, lsof failed */
         }
     }
-#endif
+}
 
-#if __linux__
-    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
-    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
-    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
-#endif
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
+{
+    UncheckedRoots unchecked;
+
+    findPlatformRoots(unchecked);
 
     for (auto & [target, links] : unchecked) {
         if (!isInStore(target)) continue;

src/libstore/local-store.cc

@@ -1940,6 +1940,4 @@ std::optional<std::string> LocalStore::getVersion()
     return nixVersion;
 }
 
-static RegisterStoreImplementation<LocalStore, LocalStoreConfig> regLocalStore;
-
 }  // namespace nix

src/libstore/local-store.hh

@@ -127,6 +127,17 @@ private:
 
     const PublicKeys & getPublicKeys();
 
+protected:
+
+    /**
+     * Initialise the local store, upgrading the schema if
+     * necessary.
+     * Protected so that users don't accidentally create a LocalStore
+     * instead of a platform's subclass.
+     */
+    LocalStore(const Params & params);
+    LocalStore(std::string scheme, std::string path, const Params & params);
+
 public:
 
     /**
@@ -134,18 +145,16 @@ public:
      */
     PathSet locksHeld;
 
-    /**
-     * Initialise the local store, upgrading the schema if
-     * necessary.
-     */
-    LocalStore(const Params & params);
-    LocalStore(std::string scheme, std::string path, const Params & params);
-
-    ~LocalStore();
+    virtual ~LocalStore();
 
     static std::set<std::string> uriSchemes()
     { return {}; }
 
+    /**
+     * Create a LocalStore, possibly a platform-specific subclass
+     */
+    static std::shared_ptr<LocalStore> makeLocalStore(const Params & params);
+
     /**
      * Implementations of abstract store API methods.
      */
@@ -330,6 +339,12 @@ private:
 
     void findRootsNoTemp(Roots & roots, bool censor);
 
+    /**
+     * Find possible garbage collector roots in a platform-specific manner,
+     * e.g. by looking in `/proc` or using `lsof`
+     */
+    virtual void findPlatformRoots(UncheckedRoots & unchecked);
+
     void findRuntimeRoots(Roots & roots, bool censor);
 
     std::pair<Path, AutoCloseFD> createTempDirInStore();

src/libstore/local.mk

@@ -5,6 +5,13 @@ libstore_NAME = libnixstore
 libstore_DIR := $(d)
 
 libstore_SOURCES := $(wildcard $(d)/*.cc $(d)/builtins/*.cc $(d)/build/*.cc)
+ifdef HOST_LINUX
+libstore_SOURCES += $(d)/platform/linux.cc
+else ifdef HOST_DARWIN
+libstore_SOURCES += $(d)/platform/darwin.cc
+else
+libstore_SOURCES += $(d)/platform/fallback.cc
+endif
 
 libstore_LIBS = libutil
 

src/libstore/machines.cc

@@ -69,10 +69,10 @@ ref<Store> Machine::openStore() const
     Store::Params storeParams;
     if (storeUri.starts_with("ssh://")) {
         storeParams["max-connections"] = "1";
-        storeParams["log-fd"] = "4";
     }
 
     if (storeUri.starts_with("ssh://") || storeUri.starts_with("ssh-ng://")) {
+        storeParams["log-fd"] = "4";
         if (sshKey != "")
             storeParams["ssh-key"] = sshKey;
         if (sshPublicHostKey != "")

src/libstore/meson.build

@@ -11,7 +11,7 @@ foreach header : [ 'schema.sql', 'ca-specific-schema.sql' ]
 endforeach
 
 if enable_embedded_sandbox_shell
-  hexdump = find_program('hexdump', required : true)
+  hexdump = find_program('hexdump', required : true, native : true)
   embedded_sandbox_shell_gen = custom_target(
     'embedded-sandbox-shell.gen.hh',
     command : [
@@ -66,6 +66,7 @@ libstore_sources = files(
   'path-with-outputs.cc',
   'path.cc',
   'pathlocks.cc',
+  'platform.cc',
   'profiles.cc',
   'realisation.cc',
   'remote-fs-accessor.cc',
@@ -158,6 +159,17 @@ libstore_headers = files(
   'worker-protocol.hh',
 )
 
+if host_machine.system() == 'linux'
+  libstore_sources += files('platform/linux.cc')
+  libstore_headers += files('platform/linux.hh')
+elif host_machine.system() == 'darwin'
+  libstore_sources += files('platform/darwin.cc')
+  libstore_headers += files('platform/darwin.hh')
+else
+  libstore_sources += files('platform/fallback.cc')
+  libstore_headers += files('platform/fallback.hh')
+endif
+
 # These variables (aside from LSOF) are created pseudo-dynamically, near the beginning of
 # the top-level meson.build. Aside from prefix itself, each of these was
 # made into an absolute path by joining it with prefix, unless it was already

src/libstore/parsed-derivations.cc

@@ -151,7 +151,7 @@ std::optional<nlohmann::json> ParsedDerivation::prepareStructuredAttrs(Store & s
         for (auto i = e->begin(); i != e->end(); ++i) {
             StorePathSet storePaths;
             for (auto & p : *i)
-                storePaths.insert(store.parseStorePath(p.get<std::string>()));
+                storePaths.insert(store.toStorePath(p.get<std::string>()).first);
             json[i.key()] = store.pathInfoToJSON(
                 store.exportReferences(storePaths, inputPaths), false, true);
         }

src/libstore/platform.cc

@@ -0,0 +1,22 @@
+#include "local-store.hh"
+
+#if __linux__
+#include "platform/linux.hh"
+#elif __APPLE__
+#include "platform/darwin.hh"
+#else
+#include "platform/fallback.hh"
+#endif
+
+namespace nix {
+std::shared_ptr<LocalStore> LocalStore::makeLocalStore(const Params & params)
+{
+#if __linux__
+    return std::shared_ptr<LocalStore>(new LinuxLocalStore(params));
+#elif __APPLE__
+    return std::shared_ptr<LocalStore>(new DarwinLocalStore(params));
+#else
+    return std::shared_ptr<LocalStore>(new FallbackLocalStore(params));
+#endif
+}
+}

src/libstore/platform/darwin.cc

@@ -0,0 +1,223 @@
+#include "gc-store.hh"
+#include "signals.hh"
+#include "platform/darwin.hh"
+#include "regex.hh"
+
+#include <sys/proc_info.h>
+#include <sys/sysctl.h>
+#include <libproc.h>
+
+#include <regex>
+
+namespace nix {
+
+void DarwinLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
+{
+    auto storePathRegex = regex::storePathRegex(storeDir);
+
+    std::vector<int> pids;
+    int pidBufSize = 1;
+
+    while (pidBufSize > pids.size() * sizeof(int)) {
+        // Reserve some extra size so we don't fail too much
+        pids.resize((pidBufSize + pidBufSize / 8) / sizeof(int));
+        pidBufSize = proc_listpids(PROC_ALL_PIDS, 0, pids.data(), pids.size() * sizeof(int));
+
+        if (pidBufSize <= 0) {
+            throw SysError("Listing PIDs");
+        }
+    }
+
+    pids.resize(pidBufSize / sizeof(int));
+
+    for (auto pid : pids) {
+        // It doesn't make sense to ask about the kernel
+        if (pid == 0) {
+            continue;
+        }
+
+        try {
+            // Process cwd/root directory
+            struct proc_vnodepathinfo vnodeInfo;
+            if (proc_pidinfo(pid, PROC_PIDVNODEPATHINFO, 0, &vnodeInfo, sizeof(vnodeInfo)) <= 0) {
+                throw SysError("Getting pid %1% working directory", pid);
+            }
+
+            unchecked[std::string(vnodeInfo.pvi_cdir.vip_path)].emplace(fmt("{libproc/%d/cwd}", pid)
+            );
+            unchecked[std::string(vnodeInfo.pvi_rdir.vip_path)].emplace(
+                fmt("{libproc/%d/rootdir}", pid)
+            );
+
+            // File descriptors
+            std::vector<struct proc_fdinfo> fds;
+            int fdBufSize = 1;
+            while (fdBufSize > fds.size() * sizeof(struct proc_fdinfo)) {
+                // Reserve some extra size so we don't fail too much
+                fds.resize((fdBufSize + fdBufSize / 8) / sizeof(struct proc_fdinfo));
+                fdBufSize = proc_pidinfo(
+                    pid, PROC_PIDLISTFDS, 0, fds.data(), fds.size() * sizeof(struct proc_fdinfo)
+                );
+
+                if (fdBufSize <= 0) {
+                    throw SysError("Listing pid %1% file descriptors", pid);
+                }
+            }
+            fds.resize(fdBufSize / sizeof(struct proc_fdinfo));
+
+            for (auto fd : fds) {
+                // By definition, only a vnode is on the filesystem
+                if (fd.proc_fdtype != PROX_FDTYPE_VNODE) {
+                    continue;
+                }
+
+                struct vnode_fdinfowithpath fdInfo;
+                if (proc_pidfdinfo(
+                        pid, fd.proc_fd, PROC_PIDFDVNODEPATHINFO, &fdInfo, sizeof(fdInfo)
+                    )
+                    <= 0)
+                {
+                    // They probably just closed this fd, no need to cancel looking at ranges and
+                    // arguments
+                    if (errno == EBADF) {
+                        continue;
+                    }
+                    throw SysError("Getting pid %1% fd %2% path", pid, fd.proc_fd);
+                }
+
+                unchecked[std::string(fdInfo.pvip.vip_path)].emplace(
+                    fmt("{libproc/%d/fd/%d}", pid, fd.proc_fd)
+                );
+            }
+
+            // Regions (e.g. mmapped files, executables, shared libraries)
+            uint64_t nextAddr = 0;
+            while (true) {
+                // Seriously, what are you doing XNU?
+                // There's 3 flavors of PROC_PIDREGIONPATHINFO:
+                // * PROC_PIDREGIONPATHINFO includes all regions
+                // * PROC_PIDREGIONPATHINFO2 includes regions backed by a vnode
+                // * PROC_PIDREGIONPATHINFO3 includes regions backed by a vnode on a specified
+                // filesystem Only PROC_PIDREGIONPATHINFO is documented. Unfortunately, using it
+                // would make finding gcroots take about 100x as long and tests would fail from
+                // timeout. According to the Frida source code, PROC_PIDREGIONPATHINFO2 has been
+                // available since XNU 2782.1.97 in OS X 10.10
+                //
+                // 22 means PROC_PIDREGIONPATHINFO2
+                struct proc_regionwithpathinfo regionInfo;
+                if (proc_pidinfo(pid, 22, nextAddr, &regionInfo, sizeof(regionInfo)) <= 0) {
+                    // PROC_PIDREGIONPATHINFO signals we're done with an error,
+                    // so we're expected to hit this once per process
+                    if (errno == ESRCH || errno == EINVAL) {
+                        break;
+                    }
+                    throw SysError("Getting pid %1% region path", pid);
+                }
+
+                unchecked[std::string(regionInfo.prp_vip.vip_path)].emplace(
+                    fmt("{libproc/%d/region}", pid)
+                );
+
+                nextAddr = regionInfo.prp_prinfo.pri_address + regionInfo.prp_prinfo.pri_size;
+            }
+
+            // Arguments and environment variables
+            // We can't read environment variables of binaries with entitlements unless
+            // nix has the `com.apple.private.read-environment-variables` entitlement or SIP is off
+            // We can read arguments for all applications though.
+
+            // Yes, it's a sysctl, the proc_info and sysctl APIs are mostly similar,
+            // but both have exclusive capabilities
+            int sysctlName[3] = {CTL_KERN, KERN_PROCARGS2, pid};
+            size_t argsSize = 0;
+            if (sysctl(sysctlName, 3, nullptr, &argsSize, nullptr, 0) < 0) {
+                throw SysError("Reading pid %1% arguments", pid);
+            }
+
+            std::vector<char> args(argsSize);
+            if (sysctl(sysctlName, 3, args.data(), &argsSize, nullptr, 0) < 0) {
+                throw SysError("Reading pid %1% arguments", pid);
+            }
+
+            if (argsSize < args.size()) {
+                args.resize(argsSize);
+            }
+
+            // We have these perfectly nice arguments, but have to ignore them because
+            // otherwise we'd see arguments to nix-store commands and
+            // `nix-store --delete /nix/store/whatever` would always fail
+            // First 4 bytes are an int of argc.
+            if (args.size() < sizeof(int)) {
+                continue;
+            }
+            auto argc = reinterpret_cast<int *>(args.data())[0];
+
+            auto argsIter = args.begin();
+            std::advance(argsIter, sizeof(int));
+            // Executable then argc args, each separated by some number of null bytes
+            for (int i = 0; argsIter != args.end() && i < argc + 1; i++) {
+                argsIter = std::find(argsIter, args.end(), '\0');
+                argsIter = std::find_if(argsIter, args.end(), [](char ch) { return ch != '\0'; });
+            }
+
+            if (argsIter != args.end()) {
+                auto env_end = std::sregex_iterator{};
+                for (auto i = std::sregex_iterator{argsIter, args.end(), storePathRegex};
+                     i != env_end;
+                     ++i)
+                {
+                    unchecked[i->str()].emplace(fmt("{libproc/%d/environ}", pid));
+                }
+            };
+
+            // Per-thread working directories
+            struct proc_taskallinfo taskAllInfo;
+            if (proc_pidinfo(pid, PROC_PIDTASKALLINFO, 0, &taskAllInfo, sizeof(taskAllInfo)) <= 0) {
+                throw SysError("Reading pid %1% tasks", pid);
+            }
+
+            // If the process doesn't have the per-thread cwd flag then we already have the
+            // process-wide cwd from PROC_PIDVNODEPATHINFO
+            if (taskAllInfo.pbsd.pbi_flags & PROC_FLAG_THCWD) {
+                std::vector<uint64_t> tids(taskAllInfo.ptinfo.pti_threadnum);
+                int tidBufSize = proc_pidinfo(
+                    pid, PROC_PIDLISTTHREADS, 0, tids.data(), tids.size() * sizeof(uint64_t)
+                );
+                if (tidBufSize <= 0) {
+                    throw SysError("Listing pid %1% threads", pid);
+                }
+
+                for (auto tid : tids) {
+                    struct proc_threadwithpathinfo threadPathInfo;
+                    if (proc_pidinfo(
+                            pid,
+                            PROC_PIDTHREADPATHINFO,
+                            tid,
+                            &threadPathInfo,
+                            sizeof(threadPathInfo)
+                        )
+                        <= 0)
+                    {
+                        throw SysError("Reading pid %1% thread %2% cwd", pid, tid);
+                    }
+
+                    unchecked[std::string(threadPathInfo.pvip.vip_path)].emplace(
+                        fmt("{libproc/%d/thread/%d/cwd}", pid, tid)
+                    );
+                }
+            }
+        } catch (SysError & e) {
+            // ENOENT/ESRCH: Process no longer exists (proc_info)
+            // EINVAL: Process no longer exists (sysctl)
+            // EACCESS/EPERM: We don't have permission to read this field (proc_info)
+            // EIO: Kernel failed to read from target process memory during KERN_PROCARGS2 (sysctl)
+            if (errno == ENOENT || errno == ESRCH || errno == EINVAL || errno == EACCES
+                || errno == EPERM || errno == EIO)
+            {
+                continue;
+            }
+            throw;
+        }
+    }
+}
+}

src/libstore/platform/darwin.hh

@@ -0,0 +1,35 @@
+#pragma once
+///@file
+
+#include "gc-store.hh"
+#include "local-store.hh"
+
+namespace nix {
+
+/**
+ * Darwin-specific implementation of LocalStore
+ */
+class DarwinLocalStore : public LocalStore
+{
+public:
+    DarwinLocalStore(const Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , LocalStoreConfig(params)
+        , Store(params)
+        , LocalFSStore(params)
+        , LocalStore(params)
+    {
+    }
+    DarwinLocalStore(const std::string scheme, std::string path, const Params & params)
+        : DarwinLocalStore(params)
+    {
+        throw UnimplementedError("DarwinLocalStore");
+    }
+
+private:
+
+    void findPlatformRoots(UncheckedRoots & unchecked) override;
+};
+
+}

src/libstore/platform/fallback.cc

@@ -0,0 +1,5 @@
+#include "platform/fallback.hh"
+
+namespace nix {
+static RegisterStoreImplementation<FallbackLocalStore, LocalStoreConfig> regLocalStore;
+}

src/libstore/platform/fallback.hh

@@ -0,0 +1,31 @@
+#pragma once
+///@file
+
+#include "local-store.hh"
+
+namespace nix {
+
+/**
+ * Fallback platform implementation of LocalStore
+ * Exists so we can make LocalStore constructor protected
+ */
+class FallbackLocalStore : public LocalStore
+{
+public:
+    FallbackLocalStore(const Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , LocalStoreConfig(params)
+        , Store(params)
+        , LocalFSStore(params)
+        , LocalStore(params)
+    {
+    }
+    FallbackLocalStore(const std::string scheme, std::string path, const Params & params)
+        : FallbackLocalStore(params)
+    {
+        throw UnimplementedError("FallbackLocalStore");
+    }
+};
+
+}

src/libstore/platform/linux.cc

@@ -0,0 +1,117 @@
+#include "gc-store.hh"
+#include "signals.hh"
+#include "platform/linux.hh"
+#include "regex.hh"
+
+#include <regex>
+
+namespace nix {
+static RegisterStoreImplementation<LinuxLocalStore, LocalStoreConfig> regLocalStore;
+
+static void readProcLink(const std::string & file, UncheckedRoots & roots)
+{
+    constexpr auto bufsiz = PATH_MAX;
+    char buf[bufsiz];
+    auto res = readlink(file.c_str(), buf, bufsiz);
+    if (res == -1) {
+        if (errno == ENOENT || errno == EACCES || errno == ESRCH) {
+            return;
+        }
+        throw SysError("reading symlink");
+    }
+    if (res == bufsiz) {
+        throw Error("overly long symlink starting with '%1%'", std::string_view(buf, bufsiz));
+    }
+    if (res > 0 && buf[0] == '/') {
+        roots[std::string(static_cast<char *>(buf), res)].emplace(file);
+    }
+}
+
+static void readFileRoots(const char * path, UncheckedRoots & roots)
+{
+    try {
+        roots[readFile(path)].emplace(path);
+    } catch (SysError & e) {
+        if (e.errNo != ENOENT && e.errNo != EACCES) {
+            throw;
+        }
+    }
+}
+
+void LinuxLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
+{
+    auto procDir = AutoCloseDir{opendir("/proc")};
+    if (procDir) {
+        struct dirent * ent;
+        auto digitsRegex = std::regex(R"(^\d+$)");
+        auto mapRegex = std::regex(R"(^\s*\S+\s+\S+\s+\S+\s+\S+\s+\S+\s+(/\S+)\s*$)");
+        auto storePathRegex = regex::storePathRegex(storeDir);
+        while (errno = 0, ent = readdir(procDir.get())) {
+            checkInterrupt();
+            if (std::regex_match(ent->d_name, digitsRegex)) {
+                try {
+                    readProcLink(fmt("/proc/%s/exe", ent->d_name), unchecked);
+                    readProcLink(fmt("/proc/%s/cwd", ent->d_name), unchecked);
+
+                    auto fdStr = fmt("/proc/%s/fd", ent->d_name);
+                    auto fdDir = AutoCloseDir(opendir(fdStr.c_str()));
+                    if (!fdDir) {
+                        if (errno == ENOENT || errno == EACCES) {
+                            continue;
+                        }
+                        throw SysError("opening %1%", fdStr);
+                    }
+                    struct dirent * fd_ent;
+                    while (errno = 0, fd_ent = readdir(fdDir.get())) {
+                        if (fd_ent->d_name[0] != '.') {
+                            readProcLink(fmt("%s/%s", fdStr, fd_ent->d_name), unchecked);
+                        }
+                    }
+                    if (errno) {
+                        if (errno == ESRCH) {
+                            continue;
+                        }
+                        throw SysError("iterating /proc/%1%/fd", ent->d_name);
+                    }
+                    fdDir.reset();
+
+                    auto mapFile = fmt("/proc/%s/maps", ent->d_name);
+                    auto mapLines =
+                        tokenizeString<std::vector<std::string>>(readFile(mapFile), "\n");
+                    for (const auto & line : mapLines) {
+                        auto match = std::smatch{};
+                        if (std::regex_match(line, match, mapRegex)) {
+                            unchecked[match[1]].emplace(mapFile);
+                        }
+                    }
+
+                    auto envFile = fmt("/proc/%s/environ", ent->d_name);
+                    auto envString = readFile(envFile);
+                    auto env_end = std::sregex_iterator{};
+                    for (auto i =
+                             std::sregex_iterator{
+                                 envString.begin(), envString.end(), storePathRegex
+                             };
+                         i != env_end;
+                         ++i)
+                    {
+                        unchecked[i->str()].emplace(envFile);
+                    }
+                } catch (SysError & e) {
+                    if (errno == ENOENT || errno == EACCES || errno == ESRCH) {
+                        continue;
+                    }
+                    throw;
+                }
+            }
+        }
+        if (errno) {
+            throw SysError("iterating /proc");
+        }
+    }
+
+    readFileRoots("/proc/sys/kernel/modprobe", unchecked);
+    readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
+    readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
+}
+}

src/libstore/platform/linux.hh

@@ -0,0 +1,35 @@
+#pragma once
+///@file
+
+#include "gc-store.hh"
+#include "local-store.hh"
+
+namespace nix {
+
+/**
+ * Linux-specific implementation of LocalStore
+ */
+class LinuxLocalStore : public LocalStore
+{
+public:
+    LinuxLocalStore(const Params & params)
+        : StoreConfig(params)
+        , LocalFSStoreConfig(params)
+        , LocalStoreConfig(params)
+        , Store(params)
+        , LocalFSStore(params)
+        , LocalStore(params)
+    {
+    }
+    LinuxLocalStore(const std::string scheme, std::string path, const Params & params)
+        : LinuxLocalStore(params)
+    {
+        throw UnimplementedError("LinuxLocalStore");
+    }
+
+private:
+
+    void findPlatformRoots(UncheckedRoots & unchecked) override;
+};
+
+}

src/libstore/ssh-store.cc

@@ -32,6 +32,10 @@ struct SSHStoreConfig : virtual RemoteStoreConfig, virtual CommonSSHStoreConfig
 class SSHStore : public virtual SSHStoreConfig, public virtual RemoteStore
 {
 public:
+    // Hack for getting remote build log output.
+    // Intentionally not in `SSHStoreConfig` so that it doesn't appear in
+    // the documentation
+    const Setting<int> logFD{(StoreConfig*) this, -1, "log-fd", "file descriptor to which SSH's stderr is connected"};
 
     SSHStore(const std::string & scheme, const std::string & host, const Params & params)
         : StoreConfig(params)
@@ -47,7 +51,8 @@ public:
             sshPublicHostKey,
             // Use SSH master only if using more than 1 connection.
             connections->capacity() > 1,
-            compress)
+            compress,
+            logFD)
     {
     }
 

src/libstore/ssh.cc

@@ -88,8 +88,6 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
             addCommonSSHOpts(args);
             if (socketPath != "")
                 args.insert(args.end(), {"-S", socketPath});
-            if (verbosity >= lvlChatty)
-                args.push_back("-v");
         }
 
         args.push_back(command);
@@ -154,8 +152,6 @@ Path SSHMaster::startMaster()
             throw SysError("duping over stdout");
 
         Strings args = { "ssh", host.c_str(), "-M", "-N", "-S", state->socketPath };
-        if (verbosity >= lvlChatty)
-            args.push_back("-v");
         addCommonSSHOpts(args);
         execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());
 

src/libstore/store-api.cc

@@ -1085,8 +1085,6 @@ void copyStorePath(
 
     auto info = srcStore.queryPathInfo(storePath);
 
-    uint64_t total = 0;
-
     // recompute store path on the chance dstStore does it differently
     if (info->ca && info->references.empty()) {
         auto info2 = make_ref<ValidPathInfo>(*info);
@@ -1105,7 +1103,7 @@ void copyStorePath(
     }
 
     auto source = sinkToSource([&](Sink & sink) {
-        LambdaSink progressSink([&](std::string_view data) {
+        LambdaSink progressSink([&, total = 0ULL](std::string_view data) mutable {
             total += data.size();
             act.progress(total, info->narSize);
         });
@@ -1218,9 +1216,6 @@ std::map<StorePath, StorePath> copyPaths(
         return storePathForDst;
     };
 
-    // total is accessed by each copy, which are each handled in separate threads
-    std::atomic<uint64_t> total = 0;
-
     for (auto & missingPath : sortedMissing) {
         auto info = srcStore.queryPathInfo(missingPath);
 
@@ -1241,7 +1236,7 @@ std::map<StorePath, StorePath> copyPaths(
                 {storePathS, srcUri, dstUri});
             PushActivity pact(act.id);
 
-            LambdaSink progressSink([&](std::string_view data) {
+            LambdaSink progressSink([&, total = 0ULL](std::string_view data) mutable {
                 total += data.size();
                 act.progress(total, info->narSize);
             });
@@ -1426,7 +1421,7 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
     if (uri == "" || uri == "auto") {
         auto stateDir = getOr(params, "state", settings.nixStateDir);
         if (access(stateDir.c_str(), R_OK | W_OK) == 0)
-            return std::make_shared<LocalStore>(params);
+            return LocalStore::makeLocalStore(params);
         else if (pathExists(settings.nixDaemonSocketFile))
             return std::make_shared<UDSRemoteStore>(params);
         #if __linux__
@@ -1444,26 +1439,26 @@ std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Para
                 try {
                     createDirs(chrootStore);
                 } catch (Error & e) {
-                    return std::make_shared<LocalStore>(params);
+                    return LocalStore::makeLocalStore(params);
                 }
                 warn("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             } else
                 debug("'%s' does not exist, so Nix will use '%s' as a chroot store", stateDir, chrootStore);
             Store::Params params2;
             params2["root"] = chrootStore;
-            return std::make_shared<LocalStore>(params2);
+            return LocalStore::makeLocalStore(params);
         }
         #endif
         else
-            return std::make_shared<LocalStore>(params);
+            return LocalStore::makeLocalStore(params);
     } else if (uri == "daemon") {
         return std::make_shared<UDSRemoteStore>(params);
     } else if (uri == "local") {
-        return std::make_shared<LocalStore>(params);
+        return LocalStore::makeLocalStore(params);
     } else if (isNonUriPath(uri)) {
         Store::Params params2 = params;
         params2["root"] = absPath(uri);
-        return std::make_shared<LocalStore>(params2);
+        return LocalStore::makeLocalStore(params2);
     } else {
         return nullptr;
     }

src/libutil/meson.build

@@ -22,6 +22,7 @@ libutil_sources = files(
   'position.cc',
   'print-elided.cc',
   'references.cc',
+  'regex.cc',
   'serialise.cc',
   'shlex.cc',
   'signals.cc',
@@ -77,6 +78,7 @@ libutil_headers = files(
   'ref.hh',
   'references.hh',
   'regex-combinators.hh',
+  'regex.hh',
   'repair-flag.hh',
   'serialise.hh',
   'shlex.hh',

src/libutil/regex.cc

@@ -0,0 +1,16 @@
+#include <string>
+#include <regex>
+
+namespace nix::regex {
+std::string quoteRegexChars(const std::string & raw)
+{
+    static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
+    return std::regex_replace(raw, specialRegex, R"(\$&)");
+}
+
+std::regex storePathRegex(const std::string & storeDir)
+{
+    return std::regex(quoteRegexChars(storeDir) + R"(/[0-9a-z]+[0-9a-zA-Z\+\-\._\?=]*)");
+}
+
+}

src/libutil/regex.hh

@@ -0,0 +1,11 @@
+#pragma once
+///@file
+
+#include <string>
+#include <regex>
+
+namespace nix::regex {
+std::string quoteRegexChars(const std::string & raw);
+
+std::regex storePathRegex(const std::string & storeDir);
+}

src/nix-env/user-env.cc

@@ -16,22 +16,6 @@
 namespace nix {
 
 
-DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
-{
-    DrvInfos elems;
-    if (pathExists(userEnv + "/manifest.json"))
-        throw Error("profile '%s' is incompatible with 'nix-env'; please use 'nix profile' instead", userEnv);
-    auto manifestFile = userEnv + "/manifest.nix";
-    if (pathExists(manifestFile)) {
-        Value v;
-        state.evalFile(state.rootPath(CanonPath(manifestFile)), v);
-        Bindings & bindings(*state.allocBindings(0));
-        getDerivations(state, v, "", bindings, elems, false);
-    }
-    return elems;
-}
-
-
 bool createUserEnv(EvalState & state, DrvInfos & elems,
     const Path & profile, bool keepDerivations,
     const std::string & lockToken)

src/nix/diff-closures.cc

@@ -1,4 +1,5 @@
 #include "command.hh"
+#include "cmd-profiles.hh"
 #include "shared.hh"
 #include "store-api.hh"
 #include "common-args.hh"
@@ -43,15 +44,6 @@ GroupedPaths getClosureInfo(ref<Store> store, const StorePath & toplevel)
     return groupedPaths;
 }
 
-std::string showVersions(const std::set<std::string> & versions)
-{
-    if (versions.empty()) return "∅";
-    std::set<std::string> versions2;
-    for (auto & version : versions)
-        versions2.insert(version.empty() ? "ε" : version);
-    return concatStringsSep(", ", versions2);
-}
-
 void printClosureDiff(
     ref<Store> store,
     const StorePath & beforePath,

src/nix/prefetch.cc

@@ -98,7 +98,6 @@ std::tuple<StorePath, Hash> prefetchFile(
             FdSink sink(fd.get());
 
             FileTransferRequest req(url);
-            req.decompress = false;
             getFileTransfer()->download(std::move(req), sink);
         }
 

src/nix/profile.cc

@@ -1,4 +1,5 @@
 #include "command.hh"
+#include "cmd-profiles.hh"
 #include "installable-flake.hh"
 #include "common-args.hh"
 #include "shared.hh"
@@ -17,269 +18,6 @@
 
 using namespace nix;
 
-struct ProfileElementSource
-{
-    FlakeRef originalRef;
-    // FIXME: record original attrpath.
-    FlakeRef lockedRef;
-    std::string attrPath;
-    ExtendedOutputsSpec outputs;
-
-    bool operator < (const ProfileElementSource & other) const
-    {
-        return
-            std::tuple(originalRef.to_string(), attrPath, outputs) <
-            std::tuple(other.originalRef.to_string(), other.attrPath, other.outputs);
-    }
-
-    std::string to_string() const
-    {
-        return fmt("%s#%s%s", originalRef, attrPath, outputs.to_string());
-    }
-};
-
-const int defaultPriority = 5;
-
-struct ProfileElement
-{
-    StorePathSet storePaths;
-    std::optional<ProfileElementSource> source;
-    bool active = true;
-    int priority = defaultPriority;
-
-    std::string identifier() const
-    {
-        if (source)
-            return source->to_string();
-        StringSet names;
-        for (auto & path : storePaths)
-            names.insert(DrvName(path.name()).name);
-        return concatStringsSep(", ", names);
-    }
-
-    /**
-     * Return a string representing an installable corresponding to the current
-     * element, either a flakeref or a plain store path
-     */
-    std::set<std::string> toInstallables(Store & store)
-    {
-        if (source)
-            return {source->to_string()};
-        StringSet rawPaths;
-        for (auto & path : storePaths)
-            rawPaths.insert(store.printStorePath(path));
-        return rawPaths;
-    }
-
-    std::string versions() const
-    {
-        StringSet versions;
-        for (auto & path : storePaths)
-            versions.insert(DrvName(path.name()).version);
-        return showVersions(versions);
-    }
-
-    bool operator < (const ProfileElement & other) const
-    {
-        return std::tuple(identifier(), storePaths) < std::tuple(other.identifier(), other.storePaths);
-    }
-
-    void updateStorePaths(
-        ref<Store> evalStore,
-        ref<Store> store,
-        const BuiltPaths & builtPaths)
-    {
-        storePaths.clear();
-        for (auto & buildable : builtPaths) {
-            std::visit(overloaded {
-                [&](const BuiltPath::Opaque & bo) {
-                    storePaths.insert(bo.path);
-                },
-                [&](const BuiltPath::Built & bfd) {
-                    for (auto & output : bfd.outputs)
-                        storePaths.insert(output.second);
-                },
-            }, buildable.raw());
-        }
-    }
-};
-
-struct ProfileManifest
-{
-    std::vector<ProfileElement> elements;
-
-    ProfileManifest() { }
-
-    ProfileManifest(EvalState & state, const Path & profile)
-    {
-        auto manifestPath = profile + "/manifest.json";
-
-        if (pathExists(manifestPath)) {
-            auto json = nlohmann::json::parse(readFile(manifestPath));
-
-            auto version = json.value("version", 0);
-            std::string sUrl;
-            std::string sOriginalUrl;
-            switch (version) {
-                case 1:
-                    sUrl = "uri";
-                    sOriginalUrl = "originalUri";
-                    break;
-                case 2:
-                    sUrl = "url";
-                    sOriginalUrl = "originalUrl";
-                    break;
-                default:
-                    throw Error("profile manifest '%s' has unsupported version %d", manifestPath, version);
-            }
-
-            for (auto & e : json["elements"]) {
-                ProfileElement element;
-                for (auto & p : e["storePaths"])
-                    element.storePaths.insert(state.store->parseStorePath((std::string) p));
-                element.active = e["active"];
-                if(e.contains("priority")) {
-                    element.priority = e["priority"];
-                }
-                if (e.value(sUrl, "") != "") {
-                    element.source = ProfileElementSource {
-                        parseFlakeRef(e[sOriginalUrl]),
-                        parseFlakeRef(e[sUrl]),
-                        e["attrPath"],
-                        e["outputs"].get<ExtendedOutputsSpec>()
-                    };
-                }
-                elements.emplace_back(std::move(element));
-            }
-        }
-
-        else if (pathExists(profile + "/manifest.nix")) {
-            // FIXME: needed because of pure mode; ugly.
-            state.allowPath(state.store->followLinksToStore(profile));
-            state.allowPath(state.store->followLinksToStore(profile + "/manifest.nix"));
-
-            auto drvInfos = queryInstalled(state, state.store->followLinksToStore(profile));
-
-            for (auto & drvInfo : drvInfos) {
-                ProfileElement element;
-                element.storePaths = {drvInfo.queryOutPath()};
-                elements.emplace_back(std::move(element));
-            }
-        }
-    }
-
-    nlohmann::json toJSON(Store & store) const
-    {
-        auto array = nlohmann::json::array();
-        for (auto & element : elements) {
-            auto paths = nlohmann::json::array();
-            for (auto & path : element.storePaths)
-                paths.push_back(store.printStorePath(path));
-            nlohmann::json obj;
-            obj["storePaths"] = paths;
-            obj["active"] = element.active;
-            obj["priority"] = element.priority;
-            if (element.source) {
-                obj["originalUrl"] = element.source->originalRef.to_string();
-                obj["url"] = element.source->lockedRef.to_string();
-                obj["attrPath"] = element.source->attrPath;
-                obj["outputs"] = element.source->outputs;
-            }
-            array.push_back(obj);
-        }
-        nlohmann::json json;
-        json["version"] = 2;
-        json["elements"] = array;
-        return json;
-    }
-
-    StorePath build(ref<Store> store)
-    {
-        auto tempDir = createTempDir();
-
-        StorePathSet references;
-
-        Packages pkgs;
-        for (auto & element : elements) {
-            for (auto & path : element.storePaths) {
-                if (element.active)
-                    pkgs.emplace_back(store->printStorePath(path), true, element.priority);
-                references.insert(path);
-            }
-        }
-
-        buildProfile(tempDir, std::move(pkgs));
-
-        writeFile(tempDir + "/manifest.json", toJSON(*store).dump());
-
-        /* Add the symlink tree to the store. */
-        StringSink sink;
-        dumpPath(tempDir, sink);
-
-        auto narHash = hashString(htSHA256, sink.s);
-
-        ValidPathInfo info {
-            *store,
-            "profile",
-            FixedOutputInfo {
-                .method = FileIngestionMethod::Recursive,
-                .hash = narHash,
-                .references = {
-                    .others = std::move(references),
-                    // profiles never refer to themselves
-                    .self = false,
-                },
-            },
-            narHash,
-        };
-        info.narSize = sink.s.size();
-
-        StringSource source(sink.s);
-        store->addToStore(info, source);
-
-        return std::move(info.path);
-    }
-
-    static void printDiff(const ProfileManifest & prev, const ProfileManifest & cur, std::string_view indent)
-    {
-        auto prevElems = prev.elements;
-        std::sort(prevElems.begin(), prevElems.end());
-
-        auto curElems = cur.elements;
-        std::sort(curElems.begin(), curElems.end());
-
-        auto i = prevElems.begin();
-        auto j = curElems.begin();
-
-        bool changes = false;
-
-        while (i != prevElems.end() || j != curElems.end()) {
-            if (j != curElems.end() && (i == prevElems.end() || i->identifier() > j->identifier())) {
-                logger->cout("%s%s: ∅ -> %s", indent, j->identifier(), j->versions());
-                changes = true;
-                ++j;
-            }
-            else if (i != prevElems.end() && (j == curElems.end() || i->identifier() < j->identifier())) {
-                logger->cout("%s%s: %s -> ∅", indent, i->identifier(), i->versions());
-                changes = true;
-                ++i;
-            }
-            else {
-                auto v1 = i->versions();
-                auto v2 = j->versions();
-                if (v1 != v2) {
-                    logger->cout("%s%s: %s -> %s", indent, i->identifier(), v1, v2);
-                    changes = true;
-                }
-                ++i;
-                ++j;
-            }
-        }
-
-        if (!changes)
-            logger->cout("%sNo changes.", indent);
-    }
-};
 
 static std::map<Installable *, std::pair<BuiltPaths, ref<ExtraPathInfo>>>
 builtPathsPerInstallable(
@@ -361,8 +99,8 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
                 : ({
                     auto * info2 = dynamic_cast<ExtraPathInfoValue *>(&*info);
                     info2
-                        ? info2->value.priority.value_or(defaultPriority)
-                        : defaultPriority;
+                        ? info2->value.priority.value_or(DEFAULT_PRIORITY)
+                        : DEFAULT_PRIORITY;
                 });
 
             element.updateStorePaths(getEvalStore(), store, res);

src/nix/upgrade-nix.cc

@@ -1,5 +1,11 @@
+#include <algorithm>
+
+#include "cmd-profiles.hh"
 #include "command.hh"
 #include "common-args.hh"
+#include "local-fs-store.hh"
+#include "logging.hh"
+#include "profiles.hh"
 #include "store-api.hh"
 #include "filetransfer.hh"
 #include "eval.hh"
@@ -10,11 +16,13 @@
 
 using namespace nix;
 
-struct CmdUpgradeNix : MixDryRun, StoreCommand
+struct CmdUpgradeNix : MixDryRun, EvalCommand
 {
     Path profileDir;
     std::string storePathsUrl = "https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix";
 
+    std::optional<Path> overrideStorePath;
+
     CmdUpgradeNix()
     {
         addFlag({
@@ -25,6 +33,13 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
             .handler = {&profileDir}
         });
 
+        addFlag({
+            .longName = "store-path",
+            .description = "A specific store path to upgrade Nix to",
+            .labels = {"store-path"},
+            .handler = {&overrideStorePath},
+        });
+
         addFlag({
             .longName = "nix-store-paths-url",
             .description = "The URL of the file that contains the store paths of the latest Nix release.",
@@ -59,12 +74,15 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
     {
         evalSettings.pureEval = true;
 
-        if (profileDir == "")
+        if (profileDir == "") {
             profileDir = getProfileDir(store);
+        }
+
+        auto canonProfileDir = canonPath(profileDir, true);
 
         printInfo("upgrading Nix in profile '%s'", profileDir);
 
-        auto storePath = getLatestNix(store);
+        StorePath storePath = getLatestNix(store);
 
         auto version = DrvName(storePath.name()).version;
 
@@ -89,11 +107,28 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
 
         stopProgressBar();
 
-        {
-            Activity act(*logger, lvlInfo, actUnknown,
-                fmt("installing '%s' into profile '%s'...", store->printStorePath(storePath), profileDir));
-            runProgram(settings.nixBinDir + "/nix-env", false,
-                {"--profile", profileDir, "-i", store->printStorePath(storePath), "--no-sandbox"});
+        auto const fullStorePath = store->printStorePath(storePath);
+
+        if (canonProfileDir.ends_with("user-environment")) {
+
+            std::string nixEnvCmd = settings.nixBinDir + "/nix-env";
+            Strings upgradeArgs = {
+                "--profile",
+                this->profileDir,
+                "--install",
+                fullStorePath,
+                "--no-sandbox",
+            };
+
+            printTalkative("running %s %s", nixEnvCmd, concatStringsSep(" ", upgradeArgs));
+            runProgram(nixEnvCmd, false, upgradeArgs);
+        } else if (canonProfileDir.ends_with("profile")) {
+            this->upgradeNewStyleProfile(store, storePath);
+        } else {
+            // No I will not use std::unreachable.
+            // That is undefined behavior if you're wrong.
+            // This will have a half-decent error message and coredump.
+            assert("unreachable" == nullptr);
         }
 
         printInfo(ANSI_GREEN "upgrade to version %s done" ANSI_NORMAL, version);
@@ -121,26 +156,105 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         Path profileDir = dirOf(where);
 
         // Resolve profile to /nix/var/nix/profiles/<name> link.
-        while (canonPath(profileDir).find("/profiles/") == std::string::npos && isLink(profileDir))
+        while (canonPath(profileDir).find("/profiles/") == std::string::npos && isLink(profileDir)) {
             profileDir = readLink(profileDir);
+        }
 
         printInfo("found profile '%s'", profileDir);
 
         Path userEnv = canonPath(profileDir, true);
 
-        if (baseNameOf(where) != "bin" ||
-            !userEnv.ends_with("user-environment"))
+        if (baseNameOf(where) != "bin") {
+            if (!userEnv.ends_with("user-environment") && !userEnv.ends_with("profile")) {
                 throw Error("directory '%s' does not appear to be part of a Nix profile", where);
+            }
+        }
 
-        if (!store->isValidPath(store->parseStorePath(userEnv)))
+        if (!store->isValidPath(store->parseStorePath(userEnv))) {
             throw Error("directory '%s' is not in the Nix store", userEnv);
+        }
 
         return profileDir;
     }
 
+    // TODO: Is there like, any good naming scheme that distinguishes
+    // "profiles which nix-env can use" and "profiles which nix profile can use"?
+    // You can't just say the manifest version since v2 and v3 are both the latter.
+    void upgradeNewStyleProfile(ref<Store> & store, StorePath const & newNix)
+    {
+        auto fsStore = store.dynamic_pointer_cast<LocalFSStore>();
+        // TODO(Qyriad): this check is here because we need to cast to a LocalFSStore,
+        // to pass to createGeneration(), ...but like, there's no way a remote store
+        // would work with the nix-env based upgrade either right?
+        if (!fsStore) {
+            throw Error("nix upgrade-nix cannot be used on a remote store");
+        }
+
+        // nb: nothing actually gets evaluated here.
+        // The ProfileManifest constructor only evaluates anything for manifest.nix
+        // profiles, which this is not.
+        auto evalState = this->getEvalState();
+
+        ProfileManifest manifest(*evalState, profileDir);
+
+        // Find which profile element has Nix in it.
+        // It should be impossible to *not* have Nix, since we grabbed this
+        // store path by looking for things with bin/nix-env in them anyway.
+        auto findNix = [&](ProfileElement const & elem) -> bool {
+            for (auto const & ePath : elem.storePaths) {
+                auto const nixEnv = store->printStorePath(ePath) + "/bin/nix-env";
+                if (pathExists(nixEnv)) {
+                    return true;
+                }
+            }
+            // We checked each store path in this element. No nixes here boss!
+            return false;
+        };
+        auto elemWithNix = std::find_if(
+            manifest.elements.begin(),
+            manifest.elements.end(),
+            findNix
+        );
+        // *Should* be impossible...
+        assert(elemWithNix != std::end(manifest.elements));
+
+        // Now create a new profile element for the new Nix version...
+        ProfileElement elemForNewNix = {
+            .storePaths = {newNix},
+        };
+
+        // ...and splork it into the manifest where the old profile element was.
+        // (Remember, elemWithNix is an iterator)
+        *elemWithNix = elemForNewNix;
+
+        // Build the new profile, and switch to it.
+        StorePath const newProfile = manifest.build(store);
+        printTalkative("built new profile '%s'", store->printStorePath(newProfile));
+        auto const newGeneration = createGeneration(*fsStore, this->profileDir, newProfile);
+        printTalkative(
+            "switching '%s' to newly created generation '%s'",
+            this->profileDir,
+            newGeneration
+        );
+        // TODO(Qyriad): use switchGeneration?
+        // switchLink's docstring seems to indicate that's preferred, but it's
+        // not used for any other `nix profile`-style profile code except for
+        // rollback, and it assumes you already have a generation number, which
+        // we don't.
+        switchLink(profileDir, newGeneration);
+    }
+
     /* Return the store path of the latest stable Nix. */
     StorePath getLatestNix(ref<Store> store)
     {
+        if (this->overrideStorePath) {
+            printTalkative(
+                "skipping Nix version query and using '%s' as latest Nix",
+                *this->overrideStorePath
+            );
+            return store->parseStorePath(*this->overrideStorePath);
+        }
+
         Activity act(*logger, lvlInfo, actUnknown, "querying latest Nix version");
 
         // FIXME: use nixos.org?

tests/functional/common/vars-and-functions.sh.in

@@ -24,7 +24,6 @@ if [[ -n $NIX_STORE ]]; then
     export _NIX_TEST_NO_SANDBOX=1
 fi
 export _NIX_IN_TEST=$TEST_ROOT/shared
-export _NIX_TEST_NO_LSOF=1
 export NIX_REMOTE=${NIX_REMOTE_-}
 unset NIX_PATH
 export TEST_HOME=$TEST_ROOT/test-home

tests/functional/gc-runtime.nix

@@ -1,7 +1,18 @@
 with import ./config.nix;
 
-mkDerivation {
-  name = "gc-runtime";
+{
+  environ = mkDerivation {
+    name = "gc-runtime-environ";
+    buildCommand = "mkdir $out; echo environ > $out/environ";
+  };
+
+  open = mkDerivation {
+    name = "gc-runtime-open";
+    buildCommand = "mkdir $out; echo open > $out/open";
+  };
+
+  program = mkDerivation {
+    name = "gc-runtime-program";
     builder =
       # Test inline source file definitions.
       builtins.toFile "builder.sh" ''
@@ -9,9 +20,10 @@ mkDerivation {
 
         cat > $out/program <<EOF
         #! ${shell}
-      sleep 10000
+        sleep 10000 < \$1
         EOF
 
         chmod +x $out/program
       '';
+  };
 }

tests/functional/gc-runtime.sh

@@ -1,38 +1,44 @@
 source common.sh
 
-case $system in
-    *linux*)
-        ;;
-    *)
-        skipTest "Not running Linux";
-esac
-
 set -m # enable job control, needed for kill
 
 profiles="$NIX_STATE_DIR"/profiles
 rm -rf $profiles
 
-nix-env -p $profiles/test -f ./gc-runtime.nix -i gc-runtime
+nix-env -p $profiles/test -f ./gc-runtime.nix -i gc-runtime-{program,environ,open}
 
-outPath=$(nix-env -p $profiles/test -q --no-name --out-path gc-runtime)
-echo $outPath
+programPath=$(nix-env -p $profiles/test -q --no-name --out-path gc-runtime-program)
+environPath=$(nix-env -p $profiles/test -q --no-name --out-path gc-runtime-environ)
+openPath=$(nix-env -p $profiles/test -q --no-name --out-path gc-runtime-open)
+echo $programPath $environPath $openPath
 
 echo "backgrounding program..."
-$profiles/test/program &
+export environPath
+$profiles/test/program $openPath/open &
 sleep 2 # hack - wait for the program to get started
 child=$!
 echo PID=$child
 
-nix-env -p $profiles/test -e gc-runtime
+nix-env -p $profiles/test -e gc-runtime-{program,environ,open}
 nix-env -p $profiles/test --delete-generations old
 
 nix-store --gc
 
 kill -- -$child
 
-if ! test -e $outPath; then
+if ! test -e $programPath; then
     echo "running program was garbage collected!"
     exit 1
 fi
 
+if ! test -e $environPath; then
+    echo "file in environment variable was garbage collected!"
+    exit 1
+fi
+
+if ! test -e $openPath; then
+    echo "opened file was garbage collected!"
+    exit 1
+fi
+
 exit 0

tests/nixos/default.nix

@@ -141,6 +141,8 @@ in
 
   nix-copy = runNixOSTestFor "x86_64-linux" ./nix-copy.nix;
 
+  nix-upgrade-nix = runNixOSTestFor "x86_64-linux" ./nix-upgrade-nix.nix;
+
   nssPreload = runNixOSTestFor "x86_64-linux" ./nss-preload.nix;
 
   githubFlakes = runNixOSTestFor "x86_64-linux" ./github-flakes.nix;

tests/nixos/github-flakes.nix

@@ -119,6 +119,9 @@ in
                 [ { urlPath = "/repos/NixOS/nixpkgs";
                     dir = nixpkgs-api;
                   }
+                  { urlPath = "/repos/fork/nixpkgs";
+                    dir = nixpkgs-api;
+                  }
                   { urlPath = "/repos/fancy-enterprise/private-flake";
                     dir = private-flake-api;
                   }
@@ -190,6 +193,10 @@ in
     client.succeed("nix registry pin nixpkgs")
     client.succeed("nix flake metadata nixpkgs --tarball-ttl 0 >&2")
 
+    # fetching a fork with the same commit ID should fail, even if the revision is cached
+    client.succeed("nix flake metadata github:NixOS/nixpkgs")
+    client.fail("nix flake metadata github:fork/nixpkgs")
+
     # Shut down the web server. The flake should be cached on the client.
     github.succeed("systemctl stop httpd.service")
 

tests/nixos/nix-upgrade-nix.nix

@@ -0,0 +1,80 @@
+{ lib, config, ... }:
+
+/**
+ * Test that nix upgrade-nix works regardless of whether /nix/var/nix/profiles/default
+ * is a nix-env style profile or a nix profile style profile.
+ */
+
+let
+  pkgs = config.nodes.machine.nixpkgs.pkgs;
+
+  lix = pkgs.nix;
+  lixVersion = lib.getVersion lix;
+
+  newNix = pkgs.nixVersions.unstable;
+  newNixVersion = lib.getVersion newNix;
+
+in {
+  name = "nix-upgrade-nix";
+
+  nodes = {
+    machine = { config, lib, pkgs, ... }: {
+      virtualisation.writableStore = true;
+      virtualisation.additionalPaths = [ pkgs.hello.drvPath ];
+      nix.settings.substituters = lib.mkForce [ ];
+      nix.settings.experimental-features = [ "nix-command" "flakes" ];
+      services.getty.autologinUser = "root";
+
+    };
+  };
+
+  testScript = { nodes }: ''
+    # fmt: off
+
+    start_all()
+
+    machine.succeed("nix --version >&2")
+
+    # Install Lix into the default profile, overriding /run/current-system/sw/bin/nix,
+    # and thus making Lix think we're not on NixOS.
+    machine.succeed("nix-env --install '${lib.getBin lix}' --profile /nix/var/nix/profiles/default >&2")
+
+    # Make sure that correctly got inserted into our PATH.
+    default_profile_nix_path = machine.succeed("command -v nix")
+    print(default_profile_nix_path)
+    assert default_profile_nix_path.strip() == "/nix/var/nix/profiles/default/bin/nix", \
+      f"{default_profile_nix_path.strip()=} != /nix/var/nix/profiles/default/bin/nix"
+
+    # And that it's the Nix we specified.
+    default_profile_version = machine.succeed("nix --version")
+    assert "${lixVersion}" in default_profile_version, f"${lixVersion} not in {default_profile_version}"
+
+    # Upgrade to a different version of Nix, and make sure that also worked.
+
+    machine.succeed("nix upgrade-nix --store-path ${newNix} >&2")
+    default_profile_version = machine.succeed("nix --version")
+    print(default_profile_version)
+    assert "${newNixVersion}" in default_profile_version, f"${newNixVersion} not in {default_profile_version}"
+
+    # Now 'break' this profile -- use nix profile on it so nix-env will no longer work on it.
+    machine.succeed(
+      "nix profile install --profile /nix/var/nix/profiles/default '${pkgs.hello.drvPath}^*' >&2"
+    )
+
+    # Confirm that nix-env is broken.
+    machine.fail(
+      "nix-env --query --installed --profile /nix/var/nix/profiles/default >&2"
+    )
+
+    # And use nix upgrade-nix one more time, on the `nix profile` style profile.
+    # (Specifying Lix by full path so we can use --store-path.)
+    machine.succeed(
+      "${lib.getBin lix}/bin/nix upgrade-nix --store-path '${lix}' >&2"
+    )
+
+    default_profile_version = machine.succeed("nix --version")
+    print(default_profile_version)
+    assert "${lixVersion}" in default_profile_version, f"${lixVersion} not in {default_profile_version}"
+  '';
+
+}

tests/nixos/remote-builds-ssh-ng.nix

@@ -95,6 +95,10 @@ in
       builder.succeed("mkdir -p -m 700 /root/.ssh")
       builder.copy_from_host("key.pub", "/root/.ssh/authorized_keys")
       builder.wait_for_unit("sshd.service")
+
+      out = client.fail("nix-build ${expr nodes.client 1} 2>&1")
+      assert "error: failed to start SSH connection to 'root@builder': Host key verification failed" in out, f"No host verification error in {out}"
+
       client.succeed(f"ssh -o StrictHostKeyChecking=no {builder.name} 'echo hello world' >&2")
 
       # Perform a build

tests/nixos/tarball-flakes.nix

@@ -64,15 +64,18 @@ in
     info = json.loads(out)
 
     # Check that we got redirected to the immutable URL.
-    assert info["locked"]["url"] == "http://localhost/stable/${nixpkgs.rev}.tar.gz"
+    locked_url = info["locked"]["url"]
+    assert locked_url == "http://localhost/stable/${nixpkgs.rev}.tar.gz", f"{locked_url=} != http://localhost/stable/${nixpkgs.rev}.tar.gz"
 
     # Check that we got the rev and revCount attributes.
-    assert info["revision"] == "${nixpkgs.rev}"
-    assert info["revCount"] == 1234
+    revision = info["revision"]
+    rev_count = info["revCount"]
+    assert revision == "${nixpkgs.rev}", f"{revision=} != ${nixpkgs.rev}"
+    assert rev_count == 1234, f"{rev_count=} != 1234"
 
     # Check that fetching with rev/revCount/narHash succeeds.
-    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?rev=" + info["revision"])
-    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?revCount=" + str(info["revCount"]))
+    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?rev=" + revision)
+    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?revCount=" + str(rev_count))
     machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?narHash=" + info["locked"]["narHash"])
 
     # Check that fetching fails if we provide incorrect attributes.