[glib] Add G_DECLARE_INTERFACE

[Ryan Lortie <desrt src gnome org>]

commit 3d39b8eb01aa5590865691a303ee9153b2a35cf5
Author: Xavier Claessens <xavier claessens collabora com>
Date:   Tue Feb 3 10:40:07 2015 -0500

    Add G_DECLARE_INTERFACE
    
    https://bugzilla.gnome.org/show_bug.cgi?id=743939

 docs/reference/gobject/gobject-sections.txt |    1 +
 gobject/gtype.h                             |   74 +++++++++++++++++++++++++++
 2 files changed, 75 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gobject/gobject-sections.txt b/docs/reference/gobject/gobject-sections.txt
index fe322d6..d22b6d1 100644
--- a/docs/reference/gobject/gobject-sections.txt
+++ b/docs/reference/gobject/gobject-sections.txt
@@ -105,6 +105,7 @@ g_type_get_instance_count
 
 G_DECLARE_FINAL_TYPE
 G_DECLARE_DERIVABLE_TYPE
+G_DECLARE_INTERFACE
 G_DEFINE_TYPE
 G_DEFINE_TYPE_WITH_PRIVATE
 G_DEFINE_TYPE_WITH_CODE
diff --git a/gobject/gtype.h b/gobject/gtype.h
index c2624f6..a9dbdc7 100644
--- a/gobject/gtype.h
+++ b/gobject/gtype.h
@@ -1496,6 +1496,80 @@ guint     g_type_get_type_registration_serial (void);
   G_GNUC_END_IGNORE_DEPRECATIONS
 
 /**
+ * G_DECLARE_INTERFACE:
+ * @ModuleObjName: The name of the new type, in camel case (like GtkWidget)
+ * @module_obj_name: The name of the new type in lowercase, with words
+ *  separated by '_' (like 'gtk_widget')
+ * @MODULE: The name of the module, in all caps (like 'GTK')
+ * @OBJ_NAME: The bare name of the type, in all caps (like 'WIDGET')
+ * @PrerequisiteName: the name of the prerequisite type, in camel case (like GtkWidget)
+ *
+ * A convenience macro for emitting the usual declarations in the header file for a GInterface type.
+ *
+ * You might use it in a header as follows:
+ *
+ * |[
+ * #ifndef _my_model_h_
+ * #define _my_model_h_
+ *
+ * #define MY_TYPE_MODEL my_model_get_type ()
+ * GDK_AVAILABLE_IN_3_12
+ * G_DECLARE_INTERFACE (MyModel, my_model, MY, MODEL, GObject)
+ *
+ * struct _MyModelInterface
+ * {
+ *   GTypeInterface g_iface;
+ *
+ *   gpointer (* get_item)  (MyModel *model);
+ * };
+ *
+ * gpointer my_model_get_item (MyModel *model);
+ *
+ * ...
+ *
+ * #endif
+ * ]|
+ *
+ * This results in the following things happening:
+ *
+ * - the usual my_model_get_type() function is declared with a return type of #GType
+ *
+ * - the MyModelInterface type is defined as a typedef to struct _MyModelInterface,
+ *   which is left undefined. You should do this from the header file directly after
+ *   you use the macro.
+ *
+ * - the MY_MODEL() cast is emitted as static inline functions along with
+ *   the MY_IS_MODEL() type checking function and MY_MODEL_GET_IFACE() function.
+ *
+ * - g_autoptr() support being added for your type, based on your prerequisite type.
+ *
+ * You can only use this function if your prerequisite type also supports g_autoptr().
+ *
+ * Because the type macro (MY_TYPE_MODEL in the above example) is not a callable, you must continue to
+ * manually define this as a macro for yourself.
+ *
+ * The declaration of the _get_type() function is the first thing emitted by the macro.  This allows this 
macro
+ * to be used in the usual way with export control and API versioning macros.
+ *
+ * Since: 2.44
+ **/
+#define G_DECLARE_INTERFACE(ModuleObjName, module_obj_name, MODULE, OBJ_NAME, PrerequisiteName) \
+  GType module_obj_name##_get_type (void);                                                                 \
+  G_GNUC_BEGIN_IGNORE_DEPRECATIONS                                                                         \
+  typedef struct _##ModuleObjName ModuleObjName;                                                           \
+  typedef struct _##ModuleObjName##Interface ModuleObjName##Interface;                                     \
+                                                                                                           \
+  _GLIB_DEFINE_AUTOPTR_CHAINUP (ModuleObjName, PrerequisiteName)                                           \
+                                                                                                           \
+  static inline ModuleObjName * MODULE##_##OBJ_NAME (gpointer ptr) {                                       \
+    return G_TYPE_CHECK_INSTANCE_CAST (ptr, module_obj_name##_get_type (), ModuleObjName); }               \
+  static inline gboolean MODULE##_IS_##OBJ_NAME (gpointer ptr) {                                           \
+    return G_TYPE_CHECK_INSTANCE_TYPE (ptr, module_obj_name##_get_type ()); }                              \
+  static inline ModuleObjName##Interface * MODULE##_##OBJ_NAME##_GET_IFACE (gpointer ptr) {                \
+    return G_TYPE_INSTANCE_GET_INTERFACE (ptr, module_obj_name##_get_type (), ModuleObjName##Interface); } \
+  G_GNUC_END_IGNORE_DEPRECATIONS
+
+/**
  * G_DEFINE_TYPE:
  * @TN: The name of the new type, in Camel case.
  * @t_n: The name of the new type, in lowercase, with words