gi: arg: use instance's gtype rather than the introspection data

When converting a native object to it's JavaScript proxy, we want to
be as precise as possible to map that native object.
Right now we handle different kinds of proxy for native types :
      * GObject proxies
      * GBoxed proxies
      * GParam proxies
      * GError proxies
      * Function proxies
      * Unions proxies
      * GI proxies
      * Fundamental proxies
      * basic types

The introspection data can provide information that helps us map a
GType to one of the items listed above. But there is a case that is
rather painful to deal with : interfaces.

In GObject interfaces can be attached to different kind of GTypes
(that includes GObjects and custom fundamental types and maybe more, I
haven't checked all the twisted cases). Although there is a way to add
a prerequisite for an interface, not all interface properly use this
feature.

In this particular case (native -> JS) we can use the native object's
gtype to figure out the most appropriate proxy, which what this patch
implements.

https://bugzilla.gnome.org/show_bug.cgi?id=727824

2 files changed, 15 insertions, 0 deletions

diff --git a/gi/arg.cpp b/gi/arg.cpp
index ba86c23f..1da4fe61 100644
--- a/gi/arg.cpp
+++ b/gi/arg.cpp
@@ -2598,6 +2598,10 @@ gjs_value_from_g_argument (JSContext  *context,
             }
 
             gtype = g_registered_type_info_get_g_type((GIRegisteredTypeInfo*)interface_info);
+            if (G_TYPE_IS_INSTANTIATABLE(gtype) ||
+                G_TYPE_IS_INTERFACE(gtype))
+                gtype = G_TYPE_FROM_INSTANCE(arg->v_pointer);
+
             gjs_debug_marshal(GJS_DEBUG_GFUNCTION,
                               "gtype of INTERFACE is %s", g_type_name(gtype));
 
@@ -2903,6 +2907,10 @@ gjs_g_arg_release_internal(JSContext  *context,
                 goto out;
 
             gtype = g_registered_type_info_get_g_type((GIRegisteredTypeInfo*)interface_info);
+            if (G_TYPE_IS_INSTANTIATABLE(gtype) ||
+                G_TYPE_IS_INTERFACE(gtype))
+                gtype = G_TYPE_FROM_INSTANCE(arg->v_pointer);
+
             gjs_debug_marshal(GJS_DEBUG_GFUNCTION,
                               "gtype of INTERFACE is %s", g_type_name(gtype));
 
diff --git a/installed-tests/js/testGIMarshalling.js b/installed-tests/js/testGIMarshalling.js
index 4000f9f4..a2e8e35b 100644
--- a/installed-tests/js/testGIMarshalling.js
+++ b/installed-tests/js/testGIMarshalling.js
@@ -401,4 +401,11 @@ function testVFuncs() {
     assertEquals(50, c);
 }
 
+function testInterfaces() {
+    let ifaceImpl = new GIMarshallingTests.InterfaceImpl();
+    let itself = ifaceImpl.get_as_interface();
+
+    assertEquals(ifaceImpl, itself);
+}
+
 gjstestRun();