[gjs/ewlsh/chain-static] Correctly chain constructor prototypes to enable static inheritance

[Evan Welsh <ewlsh src gnome org>]

commit 0a9298a65abdfd78c28dcfdbfdd58d33f66acc45
Author: Evan Welsh <contact evanwelsh com>
Date:   Sun Sep 12 00:26:06 2021 -0700

    Correctly chain constructor prototypes to enable static inheritance
    
    In ES2015+ classes it is expected for constructors to inherit the
    static methods of their parent class, our implementation of
    classes previously did not do this as it was uncommon in ES5 era
    classes.

 gi/object.cpp                  | 47 ++++++++++++++++++++++++++++++++++++------
 gi/object.h                    |  3 +++
 installed-tests/js/testGtk3.js |  4 ++++
 installed-tests/js/testGtk4.js |  4 ++++
 4 files changed, 52 insertions(+), 6 deletions(-)
---
diff --git a/gi/object.cpp b/gi/object.cpp
index cc945d6e..376832b2 100644
--- a/gi/object.cpp
+++ b/gi/object.cpp
@@ -2375,11 +2375,35 @@ JSPropertySpec ObjectBase::proto_properties[] = {
 bool ObjectPrototype::get_parent_proto(JSContext* cx,
                                        JS::MutableHandleObject proto) const {
     GType parent_type = g_type_parent(gtype());
-    if (parent_type != G_TYPE_INVALID) {
-        proto.set(gjs_lookup_object_prototype(cx, parent_type));
-        if (!proto)
-            return false;
+    if (parent_type == G_TYPE_INVALID) {
+        proto.set(nullptr);
+        return true;
     }
+
+    JSObject* prototype = gjs_lookup_object_prototype(cx, parent_type);
+    if (!prototype)
+        return false;
+
+    proto.set(prototype);
+    return true;
+}
+
+bool ObjectPrototype::get_parent_constructor(
+    JSContext* cx, JS::MutableHandleObject constructor) const {
+    GType parent_type = g_type_parent(gtype());
+
+    if (parent_type == G_TYPE_INVALID) {
+        constructor.set(nullptr);
+        return true;
+    }
+
+    JS::RootedValue v_constructor(cx);
+    if (!gjs_lookup_object_constructor(cx, parent_type, &v_constructor))
+        return false;
+
+    // gjs_lookup_object_constructor should always return an object.
+    g_assert(v_constructor.isObject());
+    constructor.set(&v_constructor.toObject());
     return true;
 }
 
@@ -2401,10 +2425,21 @@ bool ObjectPrototype::define_class(JSContext* context,
                                    GIObjectInfo* info, GType gtype,
                                    JS::MutableHandleObject constructor,
                                    JS::MutableHandleObject prototype) {
-    if (!ObjectPrototype::create_class(context, in_object, info, gtype,
-                                       constructor, prototype))
+    ObjectPrototype* priv = ObjectPrototype::create_class(
+        context, in_object, info, gtype, constructor, prototype);
+    if (!priv)
         return false;
 
+    JS::RootedObject parent_constructor(context);
+    if (!priv->get_parent_constructor(context, &parent_constructor))
+        return false;
+    // If this is a fundamental constructor (e.g. GObject.Object) the
+    // parent constructor may be null.
+    if (parent_constructor) {
+        if (!JS_SetPrototype(context, constructor, parent_constructor))
+            return false;
+    }
+
     // hook_up_vfunc and the signal handler matcher functions can't be included
     // in gjs_object_instance_proto_funcs because they are custom symbols.
     const GjsAtoms& atoms = GjsContextPrivate::atoms(context);
diff --git a/gi/object.h b/gi/object.h
index e988189c..044a3e23 100644
--- a/gi/object.h
+++ b/gi/object.h
@@ -211,6 +211,9 @@ class ObjectPrototype
  private:
     GJS_JSAPI_RETURN_CONVENTION
     bool get_parent_proto(JSContext* cx, JS::MutableHandleObject proto) const;
+    GJS_JSAPI_RETURN_CONVENTION
+    bool get_parent_constructor(JSContext* cx,
+                                JS::MutableHandleObject constructor) const;
 
     [[nodiscard]] bool is_vfunc_unchanged(GIVFuncInfo* info);
     static void vfunc_invalidated_notify(void* data, GClosure* closure);
diff --git a/installed-tests/js/testGtk3.js b/installed-tests/js/testGtk3.js
index 27450fea..83ca8247 100644
--- a/installed-tests/js/testGtk3.js
+++ b/installed-tests/js/testGtk3.js
@@ -174,6 +174,10 @@ describe('Gtk overrides', function () {
         expect(Gtk.Widget.get_css_name.call(MyComplexGtkSubclass)).toEqual('complex-subclass');
     });
 
+    it('static inheritance works', function () {
+        expect(MyComplexGtkSubclass.get_css_name()).toEqual('complex-subclass');
+    });
+
     it('avoid crashing when GTK vfuncs are called in garbage collection', function () {
         GLib.test_expect_message('Gjs', GLib.LogLevelFlags.LEVEL_CRITICAL,
             '*during garbage collection*');
diff --git a/installed-tests/js/testGtk4.js b/installed-tests/js/testGtk4.js
index 2d458610..d7fc0028 100644
--- a/installed-tests/js/testGtk4.js
+++ b/installed-tests/js/testGtk4.js
@@ -184,6 +184,10 @@ describe('Gtk overrides', function () {
         expect(Gtk.Widget.get_css_name.call(MyComplexGtkSubclass)).toEqual('complex-subclass');
     });
 
+    it('static inheritance works', function () {
+        expect(MyComplexGtkSubclass.get_css_name()).toEqual('complex-subclass');
+    });
+
     it('can create a Gtk.TreeIter with accessible stamp field', function () {
         const iter = new Gtk.TreeIter();
         iter.stamp = 42;