Add the MATRIX_API_CALLBACK_PROTO convenience macro

It can ease creating API callback function headers.

docs/reference/matrix-glib/matrix-glib-sections.txt

@@ -236,6 +236,7 @@ matrix_presence_event_get_type
 <TITLE>MatrixAPI</TITLE>
 MatrixAPIInterface
 MatrixAPICallback
+MATRIX_API_CALLBACK_PROTO
 
 <SUBSECTION>
 matrix_api_set_token

src/matrix-api.c

@@ -120,6 +120,26 @@
  * @raw_content will be set.
  */
 
+/**
+ * MATRIX_API_CALLBACK_PROTO:
+ * @name: the name of the function
+ *
+ * Convenience macro to define a #MatrixAPICallback function. The
+ * parameter names in the defined function will be the same as defined
+ * in #MatrixAPICallback.
+ *
+ * |[<!-- language="C" -->
+ * // Use it for prototypes…
+ * MATRIX_API_CALLBACK_PROTO(my_fancy_callback);
+ *
+ * // …or for the implementation.
+ * MATRIX_API_CALLBACK_PROTO(my_fancy_callback)
+ * {
+ *     do_callback_stuff(api, json_content);
+ * }
+ * ]|
+ */
+
 G_DEFINE_INTERFACE(MatrixAPI, matrix_api, G_TYPE_OBJECT);
 
 static void

src/matrix-api.h

@@ -41,6 +41,14 @@ typedef void (*MatrixAPICallback)(MatrixAPI *api,
                                   gpointer user_data,
                                   GError *err);
 
+#define MATRIX_API_CALLBACK_PROTO(name) static void \
+    name (MatrixAPI *api,                           \
+          const gchar *content_type,                \
+          JsonNode *json_content,                   \
+          GByteArray *raw_content,                  \
+          gpointer user_data,                       \
+          GError *error)
+
 struct _MatrixAPIInterface {
     /*< private >*/
     GTypeInterface g_iface;