Add MESONREWRITE to `meson dist` scripts

Fixes #688

7 files changed, 63 insertions, 6 deletions

diff --git a/docs/markdown/Creating-releases.md b/docs/markdown/Creating-releases.md
index 638125c..e0c80af 100644
--- a/docs/markdown/Creating-releases.md
+++ b/docs/markdown/Creating-releases.md
@@ -86,3 +86,30 @@ meson setup builddir
 meson dist -C builddir
 ```
 This produces `builddir/meson-dist/mysubproject-1.0.tar.xz` tarball.
+
+## Cement a version obtained from VCS
+
+*Since 1.4.0* the `meson dist` command enables rewriting the build
+configuration of the distribution tarball. This is needed when the
+configuration depends on metadata from revision control such as in the
+following example.
+
+`meson.build`:
+```meson
+project('tig', 'c',
+  version : run_command('version.sh', 'get-vcs').stdout.strip())
+
+meson.add_dist_script('version.sh', 'set-dist', meson.project_version())
+```
+`version.sh`:
+```sh
+#!/bin/sh
+
+if [ "$1" = "get-vcs" ]; then
+  git -C "$MESON_SOURCE_ROOT" describe --always --dirty
+elif [ "$1" = "set-dist" ]; then
+  $MESONREWRITE --sourcedir="$MESON_PROJECT_DIST_ROOT" kwargs set project / version "$2"
+else
+  exit 1
+fi
+```
diff --git a/docs/markdown/Reference-tables.md b/docs/markdown/Reference-tables.md
index af6a9b9..02ac083 100644
--- a/docs/markdown/Reference-tables.md
+++ b/docs/markdown/Reference-tables.md
@@ -85,6 +85,7 @@ For languages that don't have separate dynamic linkers such as C# and Java, the
 | Value               | Comment                         |
 | -----               | -------                         |
 | MESONINTROSPECT     | Command to run to run the introspection command, may be of the form `python /path/to/meson introspect`, user is responsible for splitting the path if necessary. |
+| MESONREWRITE        | Command to run to run the rewriting command, only set when running `dist` scripts |
 | MESON_BUILD_ROOT    | Absolute path to the build dir  |
 | MESON_DIST_ROOT     | Points to the root of the staging directory, only set when running `dist` scripts |
 | MESON_SOURCE_ROOT   | Absolute path to the source dir |
diff --git a/docs/yaml/builtins/meson.yaml b/docs/yaml/builtins/meson.yaml
index 0d4eacf..516e41c 100644
--- a/docs/yaml/builtins/meson.yaml
+++ b/docs/yaml/builtins/meson.yaml
@@ -32,6 +32,17 @@ methods:
       scripts, but for subproject scripts they have the path to the root of the
       subproject appended, usually `subprojects/<subproject-name>`.
 
+      *(since 1.4.0)* The `MESONREWRITE` environment variable contains the path
+      to the rewrite command that corresponds to the `meson` executable that
+      was used to configure the build. (This might be a different path than the
+      first executable found in `PATH`.) It can be used to remove or replace
+      any [[run_command]] that depends on the revision control system from the
+      build configuration. Note that the value will contain many parts. For
+      example, it may be `python3 /path/to/meson.py introspect`. The user is
+      responsible for splitting the string to an array if needed by splitting
+      lexically like a UNIX shell would. If your script uses Python,
+      `shlex.split()` is the easiest correct way to do this.
+
     posargs:
       script_name:
         type: str | file | external_program
diff --git a/mesonbuild/mdist.py b/mesonbuild/mdist.py
index 93ef44e..23cc580 100644
--- a/mesonbuild/mdist.py
+++ b/mesonbuild/mdist.py
@@ -20,7 +20,7 @@ import typing as T
 from dataclasses import dataclass
 from glob import glob
 from pathlib import Path
-from mesonbuild.environment import detect_ninja
+from mesonbuild.environment import Environment, detect_ninja
 from mesonbuild.mesonlib import (MesonException, RealPathAction, get_meson_command, quiet_git,
                                  windows_proof_rmtree, setup_vsenv, OptionKey)
 from mesonbuild.msetup import add_arguments as msetup_argparse
@@ -102,10 +102,12 @@ class Dist(metaclass=abc.ABCMeta):
 
     def run_dist_scripts(self) -> None:
         assert os.path.isabs(self.distdir)
-        env = {}
-        env['MESON_DIST_ROOT'] = self.distdir
-        env['MESON_SOURCE_ROOT'] = self.src_root
-        env['MESON_BUILD_ROOT'] = self.bld_root
+        mesonrewrite = Environment.get_build_command() + ['rewrite']
+        env = {'MESON_DIST_ROOT': self.distdir,
+               'MESON_SOURCE_ROOT': self.src_root,
+               'MESON_BUILD_ROOT': self.bld_root,
+               'MESONREWRITE': ' '.join(shlex.quote(x) for x in mesonrewrite),
+               }
         for d in self.dist_scripts:
             if d.subproject and d.subproject not in self.subprojects:
                 continue
diff --git a/test cases/unit/35 dist script/subprojects/sub/dist-script.py b/test cases/unit/35 dist script/subprojects/sub/dist-script.py
index 1274f29..5f1b4a1 100644
--- a/test cases/unit/35 dist script/subprojects/sub/dist-script.py
+++ b/test cases/unit/35 dist script/subprojects/sub/dist-script.py
@@ -2,11 +2,18 @@
 
 import os
 import pathlib
+import shlex
+import subprocess
 import sys
 
 assert sys.argv[1] == 'success'
 
 source_root = pathlib.Path(os.environ['MESON_PROJECT_DIST_ROOT'])
+mesonrewrite = shlex.split(os.environ['MESONREWRITE'])
+rewrite_cmd = ['kwargs', 'set', 'project', '/', 'version', 'release']
+
+subprocess.run([*mesonrewrite, '-s', source_root, *rewrite_cmd], check=True)
+
 modfile = source_root / 'prog.c'
 with modfile.open('w') as f:
     f.write('int main(){return 0;}')
diff --git a/test cases/unit/35 dist script/subprojects/sub/meson.build b/test cases/unit/35 dist script/subprojects/sub/meson.build
index a41a3b6..9dc047c 100644
--- a/test cases/unit/35 dist script/subprojects/sub/meson.build
+++ b/test cases/unit/35 dist script/subprojects/sub/meson.build
@@ -1,4 +1,5 @@
-project('sub', 'c')
+project('sub', 'c',
+  version : 'vcs')
 
 if get_option('broken_dist_script')
   # Make sure we can add a dist script in a subproject, but it won't be run
@@ -8,4 +9,7 @@ else
   # The dist script replace prog.c with something that actually build.
   meson.add_dist_script('dist-script.py', 'success')
   executable('prog', 'prog.c')
+
+  versiontest = find_program('version-test.py')
+  test('dist version replacement', versiontest, args : meson.project_version())
 endif
diff --git a/test cases/unit/35 dist script/subprojects/sub/version-test.py b/test cases/unit/35 dist script/subprojects/sub/version-test.py
new file mode 100644
index 0000000..1dcafc4
--- /dev/null
+++ b/test cases/unit/35 dist script/subprojects/sub/version-test.py
@@ -0,0 +1,5 @@
+#!/usr/bin/env python3
+
+from sys import argv
+
+assert argv[1] == 'release'