[gjs: 3/8] object: Use addProperty hook to simplify toggle ref

[Cosimo Cecchi <cosimoc src gnome org>]

commit b88ccfddde9e8d464e3509e78138a9237bc21f1b
Author: Philip Chimento <philip chimento gmail com>
Date:   Fri May 25 00:50:40 2018 -0400

    object: Use addProperty hook to simplify toggle ref
    
    Since the getProperty and setProperty hooks are going away in
    SpiderMonkey 60, we need to find another way to switch an object to
    toggle refs when setting custom state on it. The addProperty hook is
    called during a setProperty operation when all the resolve hooks in the
    prototype chain have failed, so it called when a new property is added to
    the object from JS code: exactly correct for our purposes.
    
    See: #160

 gi/object.cpp | 47 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 37 insertions(+), 10 deletions(-)
---
diff --git a/gi/object.cpp b/gi/object.cpp
index f675c803..37c76c4f 100644
--- a/gi/object.cpp
+++ b/gi/object.cpp
@@ -287,6 +287,37 @@ proto_priv_from_js(JSContext       *context,
     return priv_from_js(context, proto);
 }
 
+/* A hook on adding a property to an object. This is called during a set
+ * property operation after all the resolve hooks on the prototype chain have
+ * failed to resolve. We use this to mark an object as needing toggle refs when
+ * custom state is set on it, because we need to keep the JS GObject wrapper
+ * alive in order not to lose custom "expando" properties.
+ */
+static bool
+object_instance_add_prop(JSContext       *cx,
+                         JS::HandleObject obj,
+                         JS::HandleId     id,
+                         JS::HandleValue  value)
+{
+    ObjectInstance *priv = priv_from_js(cx, obj);
+
+    gjs_debug_jsprop(GJS_DEBUG_GOBJECT,
+                     "Add prop '%s' hook, obj %s, priv %p, gobj %p %s",
+                     gjs_debug_id(id).c_str(), gjs_debug_object(obj).c_str(),
+                     priv,
+                     priv ? priv->gobj : nullptr,
+                     priv ? g_type_name(priv->gtype) : "(type unknown)");
+
+    if (!priv ||        /* during init: property is not being added from JS */
+        !priv->gobj ||  /* prototype, not instance */
+        !priv->info ||  /* custom JS class, already uses toggle ref */
+        priv->g_object_finalized)
+        return true;
+
+    ensure_uses_toggle_ref(cx, priv);
+    return true;
+}
+
 static bool
 get_prop_from_g_param(JSContext             *context,
                       JS::HandleObject       obj,
@@ -474,12 +505,8 @@ set_g_param_from_prop(JSContext          *context,
 
     GType gtype = G_TYPE_FROM_INSTANCE(priv->gobj);
     GParamSpec *param_spec = param_spec_from_js_prop_name(name, gtype);
-    if (!param_spec) {
-        /* We need to keep the wrapper alive in order not to lose custom
-         * "expando" properties */
-        ensure_uses_toggle_ref(context, priv);
+    if (!param_spec)
         return result.succeed();
-    }
 
     /* Do not set JS overridden properties through GObject, to avoid
      * infinite recursion (unless constructing) */
@@ -573,10 +600,6 @@ object_instance_set_prop(JSContext              *context,
 
     GjsAutoJSChar name;
     if (!gjs_get_string_id(context, id, &name)) {
-        /* We need to keep the wrapper alive in order not to lose custom
-         * "expando" properties. In this case if gjs_get_string_id() is false
-         * then a number or symbol property was probably set. */
-        ensure_uses_toggle_ref(context, priv);
         return result.succeed();  /* not resolved, but no error */
     }
 
@@ -1382,6 +1405,10 @@ ensure_uses_toggle_ref(JSContext      *cx,
     if (priv->uses_toggle_ref)
         return;
 
+    gjs_debug_jsprop(GJS_DEBUG_GOBJECT,
+                     "Switching object instance %p, gobj %p %s to toggle ref",
+                     priv, priv->gobj, g_type_name(priv->gtype));
+
     g_assert(!priv->keep_alive.rooted());
 
     /* OK, here is where things get complicated. We want the
@@ -1994,7 +2021,7 @@ to_string_func(JSContext *context,
 }
 
 static const struct JSClassOps gjs_object_class_ops = {
-    NULL,  /* addProperty */
+    object_instance_add_prop,
     NULL,  /* deleteProperty */
     object_instance_get_prop,
     object_instance_set_prop,