gobject: forbid finalization-during-construction

If a constructor() implementation created an object but then unreffed
it rather than returning it, that object would get left on the
construction_objects list, which would cause problems later when that
memory location got reused by another object.

"Fix" this by making it fail intentionally, and add a test for it (and
for the normal, working singleton case).

https://bugzilla.gnome.org/show_bug.cgi?id=661576

gobject/tests/.gitignore

@@ -4,6 +4,7 @@ closure
 dynamictests
 enums
 ifaceproperties
+object
 param
 properties
 qdata

gobject/tests/Makefile.am

@@ -21,6 +21,7 @@ test_programs = \
 	type				\
 	private				\
 	closure				\
+	object				\
 	$(NULL)
 
 # -----------------------------------------------------------------------------

gobject/tests/object.c

@@ -0,0 +1,151 @@
+#include <glib-object.h>
+
+/* --------------------------------- */
+/* test_object_constructor_singleton */
+
+typedef GObject MySingletonObject;
+typedef GObjectClass MySingletonObjectClass;
+
+GType my_singleton_object_get_type (void);
+
+G_DEFINE_TYPE (MySingletonObject, my_singleton_object, G_TYPE_OBJECT)
+
+static MySingletonObject *singleton;
+
+static void
+my_singleton_object_init (MySingletonObject *obj)
+{
+}
+
+static GObject *
+my_singleton_object_constructor (GType                  type,
+                                 guint                  n_construct_properties,
+                                 GObjectConstructParam *construct_params)
+{
+  GObject *object;
+
+  if (singleton)
+    return g_object_ref (singleton);
+
+  object = G_OBJECT_CLASS (my_singleton_object_parent_class)->
+    constructor (type, n_construct_properties, construct_params);
+  singleton = (MySingletonObject *)object;
+
+  return object;
+}
+
+static void
+my_singleton_object_finalize (MySingletonObject *obj)
+{
+  singleton = NULL;
+
+  G_OBJECT_CLASS (my_singleton_object_parent_class)->finalize (obj);
+}
+
+static void
+my_singleton_object_class_init (MySingletonObjectClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->constructor = my_singleton_object_constructor;
+  object_class->finalize = my_singleton_object_finalize;
+}
+
+static void
+test_object_constructor_singleton (void)
+{
+  MySingletonObject *one, *two, *three;
+
+  one = g_object_new (my_singleton_object_get_type (), NULL);
+  g_assert_cmpint (G_OBJECT (one)->ref_count, ==, 1);
+
+  two = g_object_new (my_singleton_object_get_type (), NULL);
+  g_assert (one == two);
+  g_assert_cmpint (G_OBJECT (two)->ref_count, ==, 2);
+
+  three = g_object_new (my_singleton_object_get_type (), NULL);
+  g_assert (one == three);
+  g_assert_cmpint (G_OBJECT (three)->ref_count, ==, 3);
+
+  g_object_add_weak_pointer (G_OBJECT (one), (gpointer *)&one);
+
+  g_object_unref (one);
+  g_assert (one != NULL);
+
+  g_object_unref (three);
+  g_object_unref (two);
+
+  g_assert (one == NULL);
+}
+
+/* ----------------------------------- */
+/* test_object_constructor_infanticide */
+
+typedef GObject MyInfanticideObject;
+typedef GObjectClass MyInfanticideObjectClass;
+
+GType my_infanticide_object_get_type (void);
+
+G_DEFINE_TYPE (MyInfanticideObject, my_infanticide_object, G_TYPE_OBJECT)
+
+static void
+my_infanticide_object_init (MyInfanticideObject *obj)
+{
+}
+
+static GObject *
+my_infanticide_object_constructor (GType                  type,
+                                   guint                  n_construct_properties,
+                                   GObjectConstructParam *construct_params)
+{
+  GObject *object;
+
+  object = G_OBJECT_CLASS (my_infanticide_object_parent_class)->
+    constructor (type, n_construct_properties, construct_params);
+
+  g_object_unref (object);
+  g_assert_not_reached ();
+
+  return NULL;
+}
+
+static void
+my_infanticide_object_class_init (MyInfanticideObjectClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->constructor = my_infanticide_object_constructor;
+}
+
+static void
+test_object_constructor_infanticide_subprocess (void)
+{
+  g_object_new (my_infanticide_object_get_type (), NULL);
+  g_assert_not_reached ();
+}
+
+static void
+test_object_constructor_infanticide (void)
+{
+  g_test_bug ("661576");
+
+  g_test_trap_subprocess ("/object/constructor/infanticide/subprocess", 0, 0);
+  g_test_trap_assert_failed ();
+  g_test_trap_assert_stderr ("*finalized while still in-construction*");
+  g_test_trap_assert_stderr_unmatched ("*reached*");
+}
+
+/* --------------------------------- */
+
+int
+main (int argc, char *argv[])
+{
+  g_test_init (&argc, &argv, NULL);
+  g_test_bug_base ("http://bugzilla.gnome.org/");
+
+  g_test_add_func ("/object/constructor/singleton", test_object_constructor_singleton);
+  g_test_add_func ("/object/constructor/infanticide", test_object_constructor_infanticide);
+  g_test_add_func ("/object/constructor/infanticide/subprocess", test_object_constructor_infanticide_subprocess);
+
+  return g_test_run ();
+}