Add G_SIGNAL_MUST_COLLECT

In some cases, signal arguments have to be collected, even if there are i
no signal handlers connected (e.g. for GVariant parameters, where collection
consumes a floating variant).

Based on a patch by Christian Persch.

Bug #643624.

gobject/tests/Makefile.am

@@ -9,6 +9,7 @@ TEST_PROGS += 		\
 	boxed		\
 	enums		\
 	param		\
+	signals		\
 	threadtests	\
 	dynamictests	\
 	binding		\

gobject/tests/signals.c

@@ -0,0 +1,91 @@
+#include <glib-object.h>
+
+typedef struct _Test Test;
+typedef struct _TestClass TestClass;
+
+struct _Test
+{
+  GObject parent_instance;
+};
+
+struct _TestClass
+{
+  GObjectClass parent_class;
+
+  void (* variant_changed) (Test *, GVariant *);
+};
+
+static GType test_get_type (void);
+G_DEFINE_TYPE (Test, test, G_TYPE_OBJECT)
+
+static void
+test_init (Test *test)
+{
+}
+
+static void
+test_class_init (TestClass *klass)
+{
+  g_signal_new ("variant-changed-no-slot",
+                G_TYPE_FROM_CLASS (klass),
+                G_SIGNAL_RUN_LAST | G_SIGNAL_MUST_COLLECT,
+                0,
+                NULL, NULL,
+                g_cclosure_marshal_VOID__VARIANT,
+                G_TYPE_NONE,
+                1,
+                G_TYPE_VARIANT);
+  g_signal_new ("variant-changed",
+                G_TYPE_FROM_CLASS (klass),
+                G_SIGNAL_RUN_LAST | G_SIGNAL_MUST_COLLECT,
+                G_STRUCT_OFFSET (TestClass, variant_changed),
+                NULL, NULL,
+                g_cclosure_marshal_VOID__VARIANT,
+                G_TYPE_NONE,
+                1,
+                G_TYPE_VARIANT);
+}
+
+static void
+test_variant_signal (void)
+{
+  Test *test;
+  GVariant *v;
+
+  /* Tests that the signal emission consumes the variant,
+   * even if there are no handlers connected.
+   */
+
+  test = g_object_new (test_get_type (), NULL);
+
+  v = g_variant_new_boolean (TRUE);
+  g_variant_ref (v);
+  g_assert (g_variant_is_floating (v));
+  g_signal_emit_by_name (test, "variant-changed-no-slot", v);
+  g_assert (!g_variant_is_floating (v));
+  g_variant_unref (v);
+
+  v = g_variant_new_boolean (TRUE);
+  g_variant_ref (v);
+  g_assert (g_variant_is_floating (v));
+  g_signal_emit_by_name (test, "variant-changed", v);
+  g_assert (!g_variant_is_floating (v));
+  g_variant_unref (v);
+
+  g_object_unref (test);
+}
+
+/* --- */
+
+int
+main (int argc,
+     char *argv[])
+{
+  g_type_init ();
+
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/gobject/signals/variant", test_variant_signal);
+
+  return g_test_run ();
+}