add_install_script: add skip_if_destdir kwarg

It is common, at least in GNOME projects, to have scripts that must be
run only in the final destination, to update system icon cache, etc.
Skipping them from Meson ensures we can properly log that they have not
been run instead of relying on such scripts to to it (they don't
always).

5 files changed, 28 insertions, 4 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index 72199df..fa6321a 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -1851,6 +1851,10 @@ the following methods.
   `MESON_BUILD_ROOT`, `MESON_INSTALL_PREFIX`,
   `MESON_INSTALL_DESTDIR_PREFIX`, and `MESONINTROSPECT` set.
   All positional arguments are passed as parameters.
+  *since 0.57.0* `skip_if_destdir` boolean keyword argument (defaults to `false`)
+  can be specified. If `true` the script will not be run if DESTDIR is set during
+  installation. This is useful in the case the script updates system wide
+  cache that is only needed when copying files into final destination.
 
   *(since 0.54.0)* If `meson install` is called with the `--quiet` option, the
   environment variable `MESON_INSTALL_QUIET` will be set.
diff --git a/docs/markdown/snippets/destdir.md b/docs/markdown/snippets/destdir.md
new file mode 100644
index 0000000..d8cf55d
--- /dev/null
+++ b/docs/markdown/snippets/destdir.md
@@ -0,0 +1,11 @@
+## Specify DESTDIR on command line
+
+`meson install` command now has `--destdir` argument that overrides DESTDIR
+from environment.
+
+## Skip install scripts if DESTDIR is set
+
+`meson.add_install_script()` now has `skip_if_destdir` keyword argument. If set
+to `true` the script won't be run if DESTDIR is set during installation. This is
+useful in the case the script updates system wide cache that is only needed when
+copying files into final destination.
diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index caec761..badc2d0 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -137,6 +137,7 @@ class ExecutableSerialisation:
         self.extra_paths = extra_paths
         self.capture = capture
         self.pickled = False
+        self.skip_if_destdir = False
 
 class TestSerialisation:
     def __init__(self, name: str, project: str, suite: str, fname: T.List[str],
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index ceaa29a..0ce0fe8 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2015,15 +2015,20 @@ class MesonMain(InterpreterObject):
                 '0.55.0', self.interpreter.subproject)
         return script_args
 
-    @permittedKwargs(set())
+    @FeatureNewKwargs('add_install_script', '0.57.0', ['skip_if_destdir'])
+    @permittedKwargs({'skip_if_destdir'})
     def add_install_script_method(self, args: 'T.Tuple[T.Union[str, mesonlib.File, ExecutableHolder], T.Union[str, mesonlib.File, CustomTargetHolder, CustomTargetIndexHolder, ConfigureFileHolder], ...]', kwargs):
         if len(args) < 1:
             raise InterpreterException('add_install_script takes one or more arguments')
         if isinstance(args[0], mesonlib.File):
             FeatureNew.single_use('Passing file object to script parameter of add_install_script',
                                   '0.57.0', self.interpreter.subproject)
+        skip_if_destdir = kwargs.get('skip_if_destdir', False)
+        if not isinstance(skip_if_destdir, bool):
+            raise InterpreterException('skip_if_destdir keyword argument must be boolean')
         script_args = self._process_script_args('add_install_script', args[1:], allow_built=True)
         script = self._find_source_script(args[0], script_args)
+        script.skip_if_destdir = skip_if_destdir
         self.build.install_scripts.append(script)
 
     @permittedKwargs(set())
diff --git a/mesonbuild/minstall.py b/mesonbuild/minstall.py
index db08dfe..18dca8b 100644
--- a/mesonbuild/minstall.py
+++ b/mesonbuild/minstall.py
@@ -429,7 +429,7 @@ class Installer:
                 self.install_man(d, dm, destdir, fullprefix)
                 self.install_data(d, dm, destdir, fullprefix)
                 restore_selinux_contexts()
-                self.run_install_script(d, fullprefix)
+                self.run_install_script(d, destdir, fullprefix)
                 if not self.did_install_something:
                     self.log('Nothing to install.')
                 if not self.options.quiet and self.preserved_file_count > 0:
@@ -483,7 +483,7 @@ class Installer:
                 self.did_install_something = True
             set_mode(outfilename, install_mode, d.install_umask)
 
-    def run_install_script(self, d: InstallData, fullprefix: str) -> None:
+    def run_install_script(self, d: InstallData, destdir: str, fullprefix: str) -> None:
         env = {'MESON_SOURCE_ROOT': d.source_dir,
                'MESON_BUILD_ROOT': d.build_dir,
                'MESON_INSTALL_PREFIX': d.prefix,
@@ -494,8 +494,11 @@ class Installer:
             env['MESON_INSTALL_QUIET'] = '1'
 
         for i in d.install_scripts:
-            self.did_install_something = True  # Custom script must report itself if it does nothing.
             name = ' '.join(i.cmd_args)
+            if i.skip_if_destdir and destdir:
+                self.log('Skipping custom install script because DESTDIR is set {!r}'.format(name))
+                continue
+            self.did_install_something = True  # Custom script must report itself if it does nothing.
             self.log('Running custom install script {!r}'.format(name))
             try:
                 rc = run_exe(i, env)