Add unit for the "final" GType flag

Check that we're emitting the correct set of warnings when trying to
derive a final type.

gobject/tests/meson.build

@@ -51,6 +51,7 @@ gobject_tests = {
     'source' : ['signals.c', marshalers_h, marshalers_c],
   },
   'testing' : {},
+  'type-flags' : {},
 }
 
 if cc.get_id() != 'msvc'

gobject/tests/type-flags.c

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// SPDX-FileCopyrightText: 2021  Emmanuele Bassi
+
+#include <glib-object.h>
+
+#define TEST_TYPE_FINAL (test_final_get_type())
+G_DECLARE_FINAL_TYPE (TestFinal, test_final, TEST, FINAL, GObject)
+
+struct _TestFinal
+{
+  GObject parent_instance;
+};
+
+struct _TestFinalClass
+{
+  GObjectClass parent_class;
+};
+
+G_DEFINE_FINAL_TYPE (TestFinal, test_final, G_TYPE_OBJECT)
+
+static void
+test_final_class_init (TestFinalClass *klass)
+{
+}
+
+static void
+test_final_init (TestFinal *self)
+{
+}
+
+#define TEST_TYPE_FINAL2 (test_final2_get_type())
+G_DECLARE_FINAL_TYPE (TestFinal2, test_final2, TEST, FINAL2, TestFinal)
+
+struct _TestFinal2
+{
+  TestFinal parent_instance;
+};
+
+struct _TestFinal2Class
+{
+  TestFinalClass parent_class;
+};
+
+G_DEFINE_TYPE (TestFinal2, test_final2, TEST_TYPE_FINAL)
+
+static void
+test_final2_class_init (TestFinal2Class *klass)
+{
+}
+
+static void
+test_final2_init (TestFinal2 *self)
+{
+}
+
+/* test_type_flags_final: Check that trying to derive from a final class
+ * will result in a warning from the type system
+ */
+static void
+test_type_flags_final (void)
+{
+  GType final2_type;
+
+  /* This is the message we print out when registering the type */
+  g_test_expect_message ("GLib-GObject", G_LOG_LEVEL_WARNING,
+                         "*cannot derive*");
+
+  /* This is the message when we fail to return from the GOnce init
+   * block within the test_final2_get_type() function
+   */
+  g_test_expect_message ("GLib", G_LOG_LEVEL_CRITICAL,
+                         "*g_once_init_leave: assertion*");
+
+  final2_type = TEST_TYPE_FINAL2;
+  g_assert_true (final2_type == G_TYPE_INVALID);
+
+  g_test_assert_expected_messages ();
+}
+
+int
+main (int argc, char *argv[])
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/type/flags/final", test_type_flags_final);
+
+  return g_test_run ();
+}