Don't pass the object as the first argument to a vfunc

The object is already passed as this, there is no need to pass it
as the first argument, and it actually breaks expectations from
API users.

https://bugzilla.gnome.org/show_bug.cgi?id=671833

2 files changed, 8 insertions, 3 deletions

diff --git a/gi/function.c b/gi/function.c
index 96ed0ed1..0e3fc7f0 100644
--- a/gi/function.c
+++ b/gi/function.c
@@ -279,10 +279,13 @@ gjs_callback_closure(ffi_cif *cif,
         }
     }
 
-    if (trampoline->is_vfunc)
+    if (trampoline->is_vfunc) {
         this_object = JSVAL_TO_OBJECT(jsargs[0]);
-    else
+        jsargs++;
+        n_jsargs--;
+    } else {
         this_object = NULL;
+    }
 
     if (!JS_CallFunctionValue(context,
                               this_object,
diff --git a/test/js/testGObjectClass.js b/test/js/testGObjectClass.js
index ec2c79ce..99a408c1 100644
--- a/test/js/testGObjectClass.js
+++ b/test/js/testGObjectClass.js
@@ -142,6 +142,8 @@ const MyInitable = new Lang.Class({
     },
 
     vfunc_init: function(cancellable) { // error?
+        assertTrue(cancellable instanceof Gio.Cancellable);
+
         this.inited = true;
     }
 });
@@ -252,7 +254,7 @@ function testInterface() {
     let instance = new MyInitable();
     assertEquals(false, instance.inited);
 
-    instance.init(null);
+    instance.init(new Gio.Cancellable);
     assertEquals(true, instance.inited);
 
     // assertTrue(instance instanceof Gio.Initable)