allow install script to run in dry-run mode

docs/markdown/snippets/run_script_dry_run.md

@@ -0,0 +1,8 @@
+## Allow custom install scripts to run with `--dry-run` option
+
+An new `dry_run` keyword is added to `meson.add_install_script()`
+to allow a custom install script to run when meson is invoked
+with `meson install --dry-run`. 
+
+In dry run mode, the `MESON_INSTALL_DRY_RUN` environment variable
+is set.

docs/yaml/builtins/meson.yaml

@@ -64,6 +64,9 @@ methods:
       *(since 0.54.0)* If `meson install` is called with the `--quiet` option, the
       environment variable `MESON_INSTALL_QUIET` will be set.
 
+      *(since 1.1.0)* If `meson install` is called with the `--dry-run` option, the
+      environment variable `MESON_INSTALL_DRY_RUN` will be set.
+
       Meson uses the `DESTDIR` environment variable as set by the
       inherited environment to determine the (temporary) installation
       location for files. Your install script must be aware of this while
@@ -125,6 +128,15 @@ methods:
           to install only a subset of the files.
           By default the script has no install tag which means it is not being run when
           `meson install --tags` argument is specified.
+      
+      dry_run:
+        type: bool
+        since: 1.1.0
+        default: false
+        description: |
+          If `true` the script will be run even if `--dry-run` option is provided to
+          the `meson install` command. The script can use the `MESON_INSTALL_DRY_RUN`
+          variable to determine if it is in dry run mode or not.
 
   - name: add_postconf_script
     returns: void

mesonbuild/interpreter/mesonmain.py

@@ -38,6 +38,7 @@ if T.TYPE_CHECKING:
 
         skip_if_destdir: bool
         install_tag: str
+        dry_run: bool
 
     class NativeKW(TypedDict):
 
@@ -152,6 +153,7 @@ class MesonMain(MesonInterpreterObject):
         'meson.add_install_script',
         KwargInfo('skip_if_destdir', bool, default=False, since='0.57.0'),
         KwargInfo('install_tag', (str, NoneType), since='0.60.0'),
+        KwargInfo('dry_run', bool, default=False, since='1.1.0'),
     )
     def add_install_script_method(
             self,
@@ -162,6 +164,7 @@ class MesonMain(MesonInterpreterObject):
         script = self._find_source_script('add_install_script', args[0], script_args)
         script.skip_if_destdir = kwargs['skip_if_destdir']
         script.tag = kwargs['install_tag']
+        script.dry_run = kwargs['dry_run']
         self.build.install_scripts.append(script)
 
     @typed_pos_args(

mesonbuild/minstall.py

@@ -361,9 +361,9 @@ class Installer:
             return p.returncode, o, e
         return 0, '', ''
 
-    def run_exe(self, *args: T.Any, **kwargs: T.Any) -> int:
-        if not self.dry_run:
-            return run_exe(*args, **kwargs)
+    def run_exe(self, exe: ExecutableSerialisation, extra_env: T.Optional[T.Dict[str, str]] = None) -> int:
+        if (not self.dry_run) or exe.dry_run:
+            return run_exe(exe, extra_env)
         return 0
 
     def should_install(self, d: T.Union[TargetInstallData, InstallEmptyDir,
@@ -655,6 +655,8 @@ class Installer:
                }
         if self.options.quiet:
             env['MESON_INSTALL_QUIET'] = '1'
+        if self.dry_run:
+            env['MESON_INSTALL_DRY_RUN'] = '1'
 
         for i in d.install_scripts:
             if not self.should_install(i):

mesonbuild/utils/core.py

@@ -152,3 +152,4 @@ class ExecutableSerialisation:
         self.pickled = False
         self.skip_if_destdir = False
         self.subproject = ''
+        self.dry_run = False

test cases/common/53 install script/meson.build

@@ -1,6 +1,6 @@
 project('custom install script', 'c')
 
-meson.add_install_script('myinstall.py', 'diiba/daaba', 'file.dat')
+meson.add_install_script('myinstall.py', 'diiba/daaba', 'file.dat', dry_run: true)
 meson.add_install_script('myinstall.py', 'this/should', 'also-work.dat')
 
 subdir('src')

test cases/common/53 install script/myinstall.py

@@ -5,6 +5,7 @@ import os
 import shutil
 
 prefix = os.environ['MESON_INSTALL_DESTDIR_PREFIX']
+dry_run = bool(os.environ.get('MESON_INSTALL_DRY_RUN'))
 
 
 def main() -> None:
@@ -16,15 +17,24 @@ def main() -> None:
 
     dirname = os.path.join(prefix, args.dirname)
     if not os.path.exists(dirname):
-        os.makedirs(dirname)
+        if dry_run:
+            print(f"DRYRUN: Creating directory {dirname}")
+        else:
+            os.makedirs(dirname)
 
     if args.mode == 'create':
         for name in args.files:
-            with open(os.path.join(dirname, name), 'w') as f:
-                f.write('')
+            if dry_run:
+                print(f'DRYRUN: Writing file {name}')
+            else:
+                with open(os.path.join(dirname, name), 'w') as f:
+                    f.write('')
     else:
         for name in args.files:
-            shutil.copy(name, dirname)
+            if dry_run:
+                print(f"DRYRUN: Copying file {name} to {dirname}")
+            else:
+                shutil.copy(name, dirname)
 
 
 if __name__ == "__main__":

unittests/allplatformstests.py

@@ -4243,6 +4243,20 @@ class AllPlatformTests(BasePlatformTests):
         do_install('runtime,custom', expected_runtime_custom, 1)
         do_install(None, expected_all, 2)
 
+
+    def test_install_script_dry_run(self):
+        testdir = os.path.join(self.common_test_dir, '53 install script')
+        self.init(testdir)
+        self.build()
+
+        cmd = self.meson_command + ['install', '--dry-run', '--destdir', self.installdir]
+        outputs = self._run(cmd, workdir=self.builddir)
+
+        installpath = Path(self.installdir)
+        self.assertFalse((installpath / 'usr/diiba/daaba/file.dat').exists())
+        self.assertIn("DRYRUN: Writing file file.dat", outputs)
+
+
     def test_introspect_install_plan(self):
         testdir = os.path.join(self.unit_test_dir, '98 install all targets')
         introfile = os.path.join(self.builddir, 'meson-info', 'intro-install_plan.json')