Add the MATRIX_API_CALLBACK cast macro

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
 MATRIX_API_CALLBACK_PROTO
 
 <SUBSECTION>

src/matrix-api.c

@@ -120,6 +120,13 @@
  * @raw_content will be set.
  */
 
+/**
+ * MATRIX_API_CALLBACK:
+ * @f: a function pointer
+ *
+ * Cast a function pointer to a #MatrixAPICallback.
+ */
+
 /**
  * MATRIX_API_CALLBACK_PROTO:
  * @name: the name of the function

src/matrix-api.h

@@ -41,6 +41,8 @@ typedef void (*MatrixAPICallback)(MatrixAPI *api,
                                   gpointer user_data,
                                   GError *err);
 
+#define MATRIX_API_CALLBACK(f) ((MatrixAPICallback) (f)
+
 #define MATRIX_API_CALLBACK_PROTO(name) static void \
     name (MatrixAPI *api,                           \
           const gchar *content_type,                \