[glib/wip/otte/interface-types: 34/37] closure: Support generic marshals for interface returns

[Philip Withnall <pwithnall src gnome org>]

commit 3f2a8d53f0277cf5e77c7bfccc4fa51101eb42ef
Author: Benjamin Otte <otte redhat com>
Date:   Mon Nov 25 19:56:47 2019 +0100

    closure: Support generic marshals for interface returns
    
    Use the newly added g_type_interface_instantiable_prerequisite() to
    allow closure return values being interfaces by looking up the
    instantiable type for the interface and using its GValue accessors.

 gobject/gclosure.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/gobject/gclosure.c b/gobject/gclosure.c
index 7caf9c4e6..1d1f2f48a 100644
--- a/gobject/gclosure.c
+++ b/gobject/gclosure.c
@@ -1258,8 +1258,12 @@ static void
 value_from_ffi_type (GValue *gvalue, gpointer *value)
 {
   ffi_arg *int_val = (ffi_arg*) value;
+  GType type;
 
-  switch (g_type_fundamental (G_VALUE_TYPE (gvalue)))
+  type = G_VALUE_TYPE (gvalue);
+
+restart:
+  switch (g_type_fundamental (type))
     {
     case G_TYPE_INT:
       g_value_set_int (gvalue, (gint) *int_val);
@@ -1318,9 +1322,15 @@ value_from_ffi_type (GValue *gvalue, gpointer *value)
     case G_TYPE_VARIANT:
       g_value_take_variant (gvalue, *(gpointer*)value);
       break;
+    case G_TYPE_INTERFACE:
+      type = g_type_interface_instantiatable_prerequisite (type);
+      if (type)
+        goto restart;
+      G_GNUC_FALLTHROUGH;
     default:
-      g_warning ("value_from_ffi_type: Unsupported fundamental type: %s",
-                g_type_name (g_type_fundamental (G_VALUE_TYPE (gvalue))));
+      g_warning ("value_from_ffi_type: Unsupported fundamental type %s for type %s",
+                 g_type_name (g_type_fundamental (G_VALUE_TYPE (gvalue))),
+                 g_type_name (G_VALUE_TYPE (gvalue)));
     }
 }