js: Add macros for 'this' and private data

This adds two macros, GJS_GET_THIS() to get a function's 'this' value as
a rooted object (and if it was not an object, to box it into one), and
GJS_GET_PRIV() to get our private C data from the 'this' object.

This operation is done over and over again inside most JSNative
functions, and SpiderMonkey code often uses convenience macros like this.
These will come in handy even more when we switch to JSNative property
accessors in a following commit.

At the same time we make things more typesafe by doing a typecheck on
each 'this' object in the native methods as part of GJS_GET_PRIV() and
throwing an error if it is not the correct type. This gets rid of the
args.thisv().toObjectOrNull() idiom which I'm pretty sure is wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=742249

1 files changed, 2 insertions, 6 deletions

diff --git a/modules/cairo-surface.cpp b/modules/cairo-surface.cpp
index 7d2dc674..2b055286 100644
--- a/modules/cairo-surface.cpp
+++ b/modules/cairo-surface.cpp
@@ -61,9 +61,7 @@ writeToPNG_func(JSContext *context,
                 unsigned   argc,
                 JS::Value *vp)
 {
-    JS::CallArgs argv = JS::CallArgsFromVp (argc, vp);
-    JSObject *obj = argv.thisv().toObjectOrNull();
-
+    GJS_GET_THIS(context, argc, vp, argv, obj);
     char *filename;
     cairo_surface_t *surface;
 
@@ -90,9 +88,7 @@ getType_func(JSContext *context,
              unsigned   argc,
              JS::Value *vp)
 {
-    JS::CallReceiver rec = JS::CallReceiverFromVp(vp);
-    JSObject *obj = rec.thisv().toObjectOrNull();
-
+    GJS_GET_THIS(context, argc, vp, rec, obj);
     cairo_surface_t *surface;
     cairo_surface_type_t type;