gobject: add 'explicit notify' GParamSpec flag

Add a flag to prevent the automatic emission of the "notify" signal
during g_object_set_property().

If this flag is set then the class must explicitly emit the notify
for themselves.  This is already standard practice on most classes, but
we cannot simply remove the existing behaviour because there are surely
many cases where it is needed.

https://bugzilla.gnome.org/show_bug.cgi?id=731200

2 files changed, 13 insertions, 5 deletions

diff --git a/gobject/gobject.c b/gobject/gobject.c
index 4a35cd065..7e9e46752 100644
--- a/gobject/gobject.c
+++ b/gobject/gobject.c
@@ -1380,14 +1380,17 @@ object_set_property (GObject             *object,
     }
   else
     {
-      GParamSpec *notify_pspec;
-
       class->set_property (object, param_id, &tmp_value, pspec);
 
-      notify_pspec = get_notify_pspec (pspec);
+      if (~pspec->flags & G_PARAM_EXPLICIT_NOTIFY)
+        {
+          GParamSpec *notify_pspec;
+
+          notify_pspec = get_notify_pspec (pspec);
 
-      if (notify_pspec != NULL)
-        g_object_notify_queue_add (object, nqueue, notify_pspec);
+          if (notify_pspec != NULL)
+            g_object_notify_queue_add (object, nqueue, notify_pspec);
+        }
     }
   g_value_unset (&tmp_value);
 }
diff --git a/gobject/gparam.h b/gobject/gparam.h
index fb21f7bae..8f216e4ce 100644
--- a/gobject/gparam.h
+++ b/gobject/gparam.h
@@ -130,6 +130,10 @@ G_BEGIN_DECLS
  *  parameter is guaranteed to remain valid and 
  *  unmodified for the lifetime of the parameter. 
  *  Since 2.8
+ * @G_PARAM_EXPLICIT_NOTIFY: calls to g_object_set_property() for this
+ *   property will not automatically result in a "notify" signal being
+ *   emitted: the implementation must call g_object_notify() themselves
+ *   in case the property actually changes.  Since: 2.42.
  * @G_PARAM_PRIVATE: internal
  * @G_PARAM_DEPRECATED: the parameter is deprecated and will be removed
  *  in a future version. A warning will be generated if it is used
@@ -153,6 +157,7 @@ typedef enum
 #endif
   G_PARAM_STATIC_NICK	      = 1 << 6,
   G_PARAM_STATIC_BLURB	      = 1 << 7,
+  G_PARAM_EXPLICIT_NOTIFY     = 1 << 8,
   /* User defined flags go up to 30 */
   G_PARAM_DEPRECATED          = 1 << 31
 } GParamFlags;