modules/gnome: make_native_glib_version an instance var

This removes the need for the use of the global statement. I've also
updated the test that overrides this to use mock.patch instead of hand
monkey patching.

mesonbuild/modules/gnome.py

@@ -269,8 +269,6 @@ class VapiTarget(build.CustomTarget):
 # https://bugzilla.gnome.org/show_bug.cgi?id=774368
 gresource_dep_needed_version = '>= 2.51.1'
 
-native_glib_version: T.Optional[str] = None
-
 class GnomeModule(ExtensionModule):
 
     INFO = ModuleInfo('gnome')
@@ -285,6 +283,7 @@ class GnomeModule(ExtensionModule):
         self.install_gtk_update_icon_cache = False
         self.install_update_desktop_database = False
         self.devenv: T.Optional[build.EnvironmentVariables] = None
+        self.native_glib_version: T.Optional[str] = None
         self.methods.update({
             'post_install': self.post_install,
             'compile_resources': self.compile_resources,
@@ -300,19 +299,17 @@ class GnomeModule(ExtensionModule):
             'generate_vapi': self.generate_vapi,
         })
 
-    @staticmethod
-    def _get_native_glib_version(state: 'ModuleState') -> str:
-        global native_glib_version
-        if native_glib_version is None:
+    def _get_native_glib_version(self, state: 'ModuleState') -> str:
+        if self.native_glib_version is None:
             glib_dep = PkgConfigDependency('glib-2.0', state.environment,
                                            {'native': True, 'required': False})
             if glib_dep.found():
-                native_glib_version = glib_dep.get_version()
+                self.native_glib_version = glib_dep.get_version()
             else:
                 mlog.warning('Could not detect glib version, assuming 2.54. '
                              'You may get build errors if your glib is older.')
-                native_glib_version = '2.54'
-        return native_glib_version
+                self.native_glib_version = '2.54'
+        return self.native_glib_version
 
     @mesonlib.run_once
     def __print_gresources_warning(self, state: 'ModuleState') -> None:

unittests/linuxliketests.py

@@ -1082,15 +1082,12 @@ class LinuxlikeTests(BasePlatformTests):
         also tested.
         '''
         testdir = os.path.join(self.framework_test_dir, '7 gnome')
-        mesonbuild.modules.gnome.native_glib_version = '2.20'
-        env = {'MESON_UNIT_TEST_PRETEND_GLIB_OLD': "1"}
-        try:
+        with mock.patch('mesonbuild.modules.gnome.GnomeModule._get_native_glib_version', mock.Mock(return_value='2.20')):
+            env = {'MESON_UNIT_TEST_PRETEND_GLIB_OLD': "1"}
             self.init(testdir,
                       inprocess=True,
                       override_envvars=env)
             self.build(override_envvars=env)
-        finally:
-            mesonbuild.modules.gnome.native_glib_version = None
 
     @skipIfNoPkgconfig
     def test_pkgconfig_usage(self):