Add g_value_take_variant

Turns out we do need g_value_take_variant(), so we can correctly
implement VARIANT:* marshalers.

Bug #621947.

gobject/glib-genmarshal.c

@@ -249,7 +249,7 @@ complete_out_arg (OutArgument *oarg)
     { "BOXED",		"BOXED",	"gpointer",	"g_value_take_boxed",			     },
     { "POINTER",	"POINTER",	"gpointer",	"g_value_set_pointer",			     },
     { "OBJECT",		"OBJECT",	"GObject*",	"g_value_take_object",			     },
-    { "VARIANT",	"VARIANT",	"GVariant*",	"g_value_set_variant",			     },
+    { "VARIANT",	"VARIANT",	"GVariant*",	"g_value_take_variant",			     },
     /* deprecated: */
     { "NONE",		"VOID",		"void",		NULL,					     },
     { "BOOL",		"BOOLEAN",	"gboolean",	"g_value_set_boolean",			     },

gobject/gobject.symbols

@@ -299,6 +299,7 @@ g_value_get_gtype
 g_value_get_variant
 g_value_dup_variant
 g_value_set_variant
+g_value_take_variant
 #endif
 #endif
 

gobject/gtype.h

@@ -184,6 +184,13 @@ G_BEGIN_DECLS
  *
  * The fundamental type corresponding to #GVariant.
  *
+ * All floating #GVariant instances passed through the #GType system are
+ * consumed.
+ * 
+ * Note that callbacks in closures, and signal handlers
+ * for signals of return type %G_TYPE_VARIANT, must never return floating
+ * variants.
+ *
  * Note: GLib 2.24 did include a boxed type with this name. It was replaced
  * with this fundamental type in 2.26.
  *

gobject/gvaluetypes.c

@@ -1206,6 +1206,45 @@ g_value_set_variant (GValue   *value,
     g_variant_unref (old_variant);
 }
 
+/**
+ * g_value_take_variant:
+ * @value: a valid #GValue of %G_TYPE_VARIANT
+ * @variant: a #GVariant, or %NULL
+ *
+ * Set the contents of a variant #GValue to @variant, and takes over
+ * the ownership of the caller's reference to @variant;
+ * the caller doesn't have to unref it any more (i.e. the reference
+ * count of the variant is not increased).
+ * 
+ * It is a programmer error to pass a floating variant to this function.
+ * In particular this means that callbacks in closures, and signal handlers
+ * for signals of return type %G_TYPE_VARIANT, must never return floating
+ * variants.
+ *
+ * If you want the #GValue to hold its own reference to @variant, use
+ * g_value_set_variant() instead.
+ *
+ * This is an internal function introduced mainly for C marshallers.
+ *
+ * Since: 2.26
+ */
+void
+g_value_take_variant (GValue   *value,
+                      GVariant *variant)
+{
+  GVariant *old_variant;
+
+  g_return_if_fail (G_VALUE_HOLDS_VARIANT (value));
+  g_return_if_fail (variant == NULL || !g_variant_is_floating (variant));
+
+  old_variant = value->data[0].v_pointer;
+
+  value->data[0].v_pointer = variant;
+
+  if (old_variant)
+    g_variant_unref (old_variant);
+}
+
 /**
  * g_value_get_variant:
  * @value: a valid #GValue of %G_TYPE_VARIANT

gobject/gvaluetypes.h

@@ -225,6 +225,8 @@ void		      g_value_set_gtype	        (GValue	      *value,
 GType	              g_value_get_gtype	        (const GValue *value);
 void		      g_value_set_variant	(GValue	      *value,
 						 GVariant     *variant);
+void		      g_value_take_variant	(GValue	      *value,
+						 GVariant     *variant);
 GVariant*	      g_value_get_variant	(const GValue *value);
 GVariant*	      g_value_dup_variant	(const GValue *value);