Bug 1360715 - Part 1: Hide @@hasInstance for IDL interfaces behind a flag r=edgar

Differential Revision: https://phabricator.services.mozilla.com/D106661

dom/bindings/BindingUtils.cpp

@@ -837,13 +837,16 @@ static JSObject* CreateInterfaceObject(
 
   if (DOMIfaceAndProtoJSClass::FromJSClass(constructorClass)
           ->wantsInterfaceHasInstance) {
-    JS::Rooted<jsid> hasInstanceId(cx, SYMBOL_TO_JSID(JS::GetWellKnownSymbol(
-                                           cx, JS::SymbolCode::hasInstance)));
-    if (!JS_DefineFunctionById(
-            cx, constructor, hasInstanceId, InterfaceHasInstance, 1,
-            // Flags match those of Function[Symbol.hasInstance]
-            JSPROP_READONLY | JSPROP_PERMANENT)) {
-      return nullptr;
+    if (isChrome ||
+        StaticPrefs::dom_webidl_crosscontext_hasinstance_enabled()) {
+      JS::Rooted<jsid> hasInstanceId(cx, SYMBOL_TO_JSID(JS::GetWellKnownSymbol(
+                                             cx, JS::SymbolCode::hasInstance)));
+      if (!JS_DefineFunctionById(
+              cx, constructor, hasInstanceId, InterfaceHasInstance, 1,
+              // Flags match those of Function[Symbol.hasInstance]
+              JSPROP_READONLY | JSPROP_PERMANENT)) {
+        return nullptr;
+      }
     }
 
     if (isChrome && !JS_DefineFunction(cx, constructor, "isInstance",

modules/libpref/init/StaticPrefList.yaml

@@ -3513,6 +3513,11 @@
   value: true
   mirror: always
 
+- name: dom.webidl.crosscontext_hasinstance.enabled
+  type: RelaxedAtomicBool
+  value: @IS_NOT_NIGHTLY_BUILD@
+  mirror: always
+
 # WebShare API - exposes navigator.share()
 - name: dom.webshare.enabled
   type: bool

testing/web-platform/meta/WebIDL/ecmascript-binding/has-instance.html.ini

@@ -1,7 +1,2 @@
 [has-instance.html]
-  [instanceof must return false across different globals, for platform objects]
-    expected: FAIL
-
-  [platform objects do not have Symbol.hasInstance installed]
-    expected: FAIL
-
+  prefs: [dom.webidl.crosscontext_hasinstance.enabled:false]