Move builder execution to store layer

It is not a language topic.

doc/manual/redirects.js

@@ -346,6 +346,9 @@ const redirects = {
     "scoping-rules": "scoping.html",
     "string-literal": "string-literals.html",
   },
+  "language/derivations.md": {
+    "builder-execution": "store/drv/building.md#building"
+  },
   "installation/installing-binary.html": {
     "linux": "uninstall.html#linux",
     "macos": "uninstall.html#macos",

doc/manual/source/language/derivations.md

@@ -235,77 +235,3 @@ It outputs an attribute set, and produces a [derivation] as a side effect of eva
       passed as an empty string.
 
 <!-- FIXME: add a section on output attributes -->
-
-## Builder execution
-
-The [`builder`](#attr-builder) is executed as follows:
-
-- A temporary directory is created under the directory specified by
-  `TMPDIR` (default `/tmp`) where the build will take place. The
-  current directory is changed to this directory.
-
-- The environment is cleared and set to the derivation attributes, as
-  specified above.
-
-- In addition, the following variables are set:
-
-  - `NIX_BUILD_TOP` contains the path of the temporary directory for
-    this build.
-
-  - Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
-    temporary directory. This is to prevent the builder from
-    accidentally writing temporary files anywhere else. Doing so
-    might cause interference by other processes.
-
-  - `PATH` is set to `/path-not-set` to prevent shells from
-    initialising it to their built-in default value.
-
-  - `HOME` is set to `/homeless-shelter` to prevent programs from
-    using `/etc/passwd` or the like to find the user's home
-    directory, which could cause impurity. Usually, when `HOME` is
-    set, it is used as the location of the home directory, even if
-    it points to a non-existent path.
-
-  - `NIX_STORE` is set to the path of the top-level Nix store
-    directory (typically, `/nix/store`).
-
-  - `NIX_ATTRS_JSON_FILE` & `NIX_ATTRS_SH_FILE` if `__structuredAttrs`
-    is set to `true` for the derivation. A detailed explanation of this
-    behavior can be found in the
-    [section about structured attrs](./advanced-attributes.md#adv-attr-structuredAttrs).
-
-  - For each output declared in `outputs`, the corresponding
-    environment variable is set to point to the intended path in the
-    Nix store for that output. Each output path is a concatenation
-    of the cryptographic hash of all build inputs, the `name`
-    attribute and the output name. (The output name is omitted if
-    it’s `out`.)
-
-- If an output path already exists, it is removed. Also, locks are
-  acquired to prevent multiple Nix instances from performing the same
-  build at the same time.
-
-- A log of the combined standard output and error is written to
-  `/nix/var/log/nix`.
-
-- The builder is executed with the arguments specified by the
-  attribute `args`. If it exits with exit code 0, it is considered to
-  have succeeded.
-
-- The temporary directory is removed (unless the `-K` option was
-  specified).
-
-- If the build was successful, Nix scans each output path for
-  references to input paths by looking for the hash parts of the input
-  paths. Since these are potential runtime dependencies, Nix registers
-  them as dependencies of the output paths.
-
-- After the build, Nix sets the last-modified timestamp on all files
-  in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
-  the default group, and sets the mode of the file to 0444 or 0555
-  (i.e., read-only, with execute permission enabled if the file was
-  originally executable). Note that possible `setuid` and `setgid`
-  bits are cleared. Setuid and setgid programs are not currently
-  supported by Nix. This is because the Nix archives used in
-  deployment have no concept of ownership information, and because it
-  makes the build result dependent on the user performing the build.

doc/manual/source/store/drv/building.md

@@ -9,9 +9,79 @@ TODO
 Each input must be [realised] prior to building the derivation in question.
 At that point, the derivation can be *normalized*, by replacing each input deriving path with its store path --- which we now know since we've realised it.
 
-## Building
+## Builder Execution
 
-TODO
+The [`builder`](../drv.md#builder) is executed as follows:
+
+- A temporary directory is created under the directory specified by
+  `TMPDIR` (default `/tmp`) where the build will take place. The
+  current directory is changed to this directory.
+
+- The environment is cleared and set to the derivation attributes, as
+  specified above.
+
+- In addition, the following variables are set:
+
+  - `NIX_BUILD_TOP` contains the path of the temporary directory for
+    this build.
+
+  - Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
+    temporary directory. This is to prevent the builder from
+    accidentally writing temporary files anywhere else. Doing so
+    might cause interference by other processes.
+
+  - `PATH` is set to `/path-not-set` to prevent shells from
+    initialising it to their built-in default value.
+
+  - `HOME` is set to `/homeless-shelter` to prevent programs from
+    using `/etc/passwd` or the like to find the user's home
+    directory, which could cause impurity. Usually, when `HOME` is
+    set, it is used as the location of the home directory, even if
+    it points to a non-existent path.
+
+  - `NIX_STORE` is set to the path of the top-level Nix store
+    directory (typically, `/nix/store`).
+
+  - `NIX_ATTRS_JSON_FILE` & `NIX_ATTRS_SH_FILE` if `__structuredAttrs`
+    is set to `true` for the derivation. A detailed explanation of this
+    behavior can be found in the
+    [section about structured attrs](@docroot@/language/advanced-attributes.md#adv-attr-structuredAttrs).
+
+  - For each output declared in `outputs`, the corresponding
+    environment variable is set to point to the intended path in the
+    Nix store for that output. Each output path is a concatenation
+    of the cryptographic hash of all build inputs, the `name`
+    attribute and the output name. (The output name is omitted if
+    it’s `out`.)
+
+- If an output path already exists, it is removed. Also, locks are
+  acquired to prevent multiple Nix instances from performing the same
+  build at the same time.
+
+- A log of the combined standard output and error is written to
+  `/nix/var/log/nix`.
+
+- The builder is executed with the arguments specified by the
+  attribute `args`. If it exits with exit code 0, it is considered to
+  have succeeded.
+
+- The temporary directory is removed (unless the `-K` option was
+  specified).
+
+- If the build was successful, Nix scans each output path for
+  references to input paths by looking for the hash parts of the input
+  paths. Since these are potential runtime dependencies, Nix registers
+  them as dependencies of the output paths.
+
+- After the build, Nix sets the last-modified timestamp on all files
+  in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
+  the default group, and sets the mode of the file to 0444 or 0555
+  (i.e., read-only, with execute permission enabled if the file was
+  originally executable). Note that possible `setuid` and `setgid`
+  bits are cleared. Setuid and setgid programs are not currently
+  supported by Nix. This is because the Nix archives used in
+  deployment have no concept of ownership information, and because it
+  makes the build result dependent on the user performing the build.
 
 ## Processing outputs and Reference scanning