Fix FeatureNew false positive in vcs_tag

Fixes https://github.com/mesonbuild/meson/issues/3904

mesonbuild/interpreter.py

@@ -3098,7 +3098,7 @@ root and issuing %s.
              regex_selector] + vcs_cmd
         kwargs.setdefault('build_by_default', True)
         kwargs.setdefault('build_always_stale', True)
-        return self.func_custom_target(node, [kwargs['output']], kwargs)
+        return self._func_custom_target_impl(node, [kwargs['output']], kwargs)
 
     @FeatureNew('subdir_done', '0.46.0')
     @stringArgs
@@ -3119,6 +3119,10 @@ root and issuing %s.
             raise InterpreterException('custom_target: Only one positional argument is allowed, and it must be a string name')
         if 'depfile' in kwargs and ('@BASENAME@' in kwargs['depfile'] or '@PLAINNAME@' in kwargs['depfile']):
             FeatureNew('substitutions in custom_target depfile', '0.47.0').use(self.subproject)
+        return self._func_custom_target_impl(node, args, kwargs)
+
+    def _func_custom_target_impl(self, node, args, kwargs):
+        'Implementation-only, without FeatureNew checks, for internal use'
         name = args[0]
         kwargs['install_mode'] = self._get_kwarg_install_mode(kwargs)
         tg = CustomTargetHolder(build.CustomTarget(name, self.subdir, self.subproject, kwargs), self)

run_unittests.py

@@ -2761,6 +2761,16 @@ class FailureTests(BasePlatformTests):
                                 ".*WARNING.*Project targetting.*but.*",
                                 meson_version='>= 0.41.0')
 
+    def test_vcs_tag_featurenew_build_always_stale(self):
+        'https://github.com/mesonbuild/meson/issues/3904'
+        vcs_tag = '''version_data = configuration_data()
+        version_data.set('PROJVER', '@VCS_TAG@')
+        vf = configure_file(output : 'version.h.in', configuration: version_data)
+        f = vcs_tag(input : vf, output : 'version.h')
+        '''
+        msg = '.*WARNING:.*feature.*build_always_stale.*custom_target.*'
+        self.assertMesonDoesNotOutput(vcs_tag, msg, meson_version='>=0.43')
+
 
 class WindowsTests(BasePlatformTests):
     '''