Bug 1641517 - Don't expose FinalizationRegistry.prototype.cleanupSome in the browser r=mccr8

This adds an extra pref for whether the cleanupSome method is exposed and renames the existing pref. We can turn on the pref to expose cleanupSome to get test262 coverage in the browser.

Differential Revision: https://phabricator.services.mozilla.com/D77267

js/public/RealmOptions.h

@@ -50,6 +50,16 @@ enum class CompartmentSpecifier {
   ExistingCompartment,
 };
 
+/**
+ * Specification for whether weak refs should be enabled and if so whether the
+ * FinalizationRegistry.cleanupSome method should be present.
+ */
+enum class WeakRefSpecifier {
+  Disabled,
+  EnabledWithCleanupSome,
+  EnabledWithoutCleanupSome
+};
+
 /**
  * RealmCreationOptions specifies options relevant to creating a new realm, that
  * are either immutable characteristics of that realm or that are discarded
@@ -208,9 +218,9 @@ class JS_PUBLIC_API RealmCreationOptions {
     return *this;
   }
 
-  bool getWeakRefsEnabled() const { return weakRefs_; }
-  RealmCreationOptions& setWeakRefsEnabled(bool flag) {
-    weakRefs_ = flag;
+  WeakRefSpecifier getWeakRefsEnabled() const { return weakRefs_; }
+  RealmCreationOptions& setWeakRefsEnabled(WeakRefSpecifier spec) {
+    weakRefs_ = spec;
     return *this;
   }
 
@@ -264,6 +274,7 @@ class JS_PUBLIC_API RealmCreationOptions {
     Zone* zone_;
   };
   uint64_t profilerRealmID_ = 0;
+  WeakRefSpecifier weakRefs_ = WeakRefSpecifier::Disabled;
   bool invisibleToDebugger_ = false;
   bool mergeable_ = false;
   bool preserveJitCode_ = false;
@@ -276,7 +287,6 @@ class JS_PUBLIC_API RealmCreationOptions {
   bool byobStreamReaders_ = false;
   bool writableStreams_ = false;
   bool readableStreamPipeTo_ = false;
-  bool weakRefs_ = false;
   bool toSource_ = false;
   bool propertyErrorMessageFix_ = false;
   bool iteratorHelpers_ = false;

js/src/fuzz-tests/tests.cpp

@@ -31,7 +31,8 @@ static const JSClass* getGlobalClass() {
 static JSObject* jsfuzz_createGlobal(JSContext* cx, JSPrincipals* principals) {
   /* Create the global object. */
   JS::RealmOptions options;
-  options.creationOptions().setStreamsEnabled(true).setWeakRefsEnabled(true);
+  options.creationOptions().setStreamsEnabled(true).setWeakRefsEnabled(
+      JS::WeakRefSpecifier::EnabledWithCleanupSome);
   return JS_NewGlobalObject(cx, getGlobalClass(), principals,
                             JS::FireOnNewGlobalHook, options);
 }

js/src/jsapi-tests/tests.cpp

@@ -90,7 +90,7 @@ JSObject* JSAPITest::createGlobal(JSPrincipals* principals) {
   JS::RealmOptions options;
   options.creationOptions()
       .setStreamsEnabled(true)
-      .setWeakRefsEnabled(true)
+      .setWeakRefsEnabled(JS::WeakRefSpecifier::EnabledWithCleanupSome)
       .setSharedMemoryAndAtomicsEnabled(true);
   newGlobal = JS_NewGlobalObject(cx, getGlobalClass(), principals,
                                  JS::FireOnNewGlobalHook, options);

js/src/shell/js.cpp

@@ -3891,7 +3891,9 @@ static void SetStandardRealmOptions(JS::RealmOptions& options) {
       .setBYOBStreamReadersEnabled(enableBYOBStreamReaders)
       .setWritableStreamsEnabled(enableWritableStreams)
       .setReadableStreamPipeToEnabled(enableReadableStreamPipeTo)
-      .setWeakRefsEnabled(enableWeakRefs)
+      .setWeakRefsEnabled(enableWeakRefs
+                              ? JS::WeakRefSpecifier::EnabledWithCleanupSome
+                              : JS::WeakRefSpecifier::Disabled)
       .setToSourceEnabled(enableToSource)
       .setPropertyErrorMessageFixEnabled(enablePropertyErrorMessageFix)
       .setIteratorHelpersEnabled(enableIteratorHelpers)

js/src/tests/user.js

@@ -30,5 +30,6 @@ user_pref("privacy.trackingprotection.enabled", false);
 user_pref("privacy.trackingprotection.pbmode.enabled", false);
 user_pref("general.useragent.updates.enabled", false);
 user_pref("browser.webapps.checkForUpdates", 0);
-user_pref("javascript.options.experimental.weakrefs", true);
+user_pref("javascript.options.experimental.weakrefs.enabled", true);
+user_pref("javascript.options.experimental.weakrefs.expose_cleanupSome", true);
 user_pref("javascript.options.experimental.iterator_helpers", true);

js/src/vm/GlobalObject.cpp

@@ -208,7 +208,8 @@ bool GlobalObject::skipDeselectedConstructor(JSContext* cx, JSProtoKey key) {
 
     case JSProto_WeakRef:
     case JSProto_FinalizationRegistry:
-      return !cx->realm()->creationOptions().getWeakRefsEnabled();
+      return cx->realm()->creationOptions().getWeakRefsEnabled() ==
+             JS::WeakRefSpecifier::Disabled;
 
     case JSProto_Iterator:
       return !cx->realm()->creationOptions().getIteratorHelpersEnabled();

js/src/vm/JSObject.cpp

@@ -2844,6 +2844,12 @@ JS_FRIEND_API bool js::ShouldIgnorePropertyDefinition(JSContext* cx,
            id == NameToId(cx->names().uneval);
   }
 
+  if (key == JSProto_FinalizationRegistry &&
+      cx->realm()->creationOptions().getWeakRefsEnabled() ==
+          JS::WeakRefSpecifier::EnabledWithoutCleanupSome) {
+    return id == NameToId(cx->names().cleanupSome);
+  }
+
   return false;
 }
 

js/xpconnect/src/XPCJSContext.cpp

@@ -758,8 +758,21 @@ static mozilla::Atomic<bool> sStreamsEnabled(false);
 
 static mozilla::Atomic<bool> sPropertyErrorMessageFixEnabled(false);
 static mozilla::Atomic<bool> sWeakRefsEnabled(false);
+static mozilla::Atomic<bool> sWeakRefsExposeCleanupSome(false);
 static mozilla::Atomic<bool> sIteratorHelpersEnabled(false);
 
+static JS::WeakRefSpecifier GetWeakRefsEnabled() {
+  if (!sWeakRefsEnabled) {
+    return JS::WeakRefSpecifier::Disabled;
+  }
+
+  if (sWeakRefsExposeCleanupSome) {
+    return JS::WeakRefSpecifier::EnabledWithCleanupSome;
+  }
+
+  return JS::WeakRefSpecifier::EnabledWithoutCleanupSome;
+}
+
 void xpc::SetPrefableRealmOptions(JS::RealmOptions& options) {
   options.creationOptions()
       .setSharedMemoryAndAtomicsEnabled(sSharedMemoryEnabled)
@@ -770,7 +783,7 @@ void xpc::SetPrefableRealmOptions(JS::RealmOptions& options) {
       .setWritableStreamsEnabled(
           StaticPrefs::javascript_options_writable_streams())
       .setPropertyErrorMessageFixEnabled(sPropertyErrorMessageFixEnabled)
-      .setWeakRefsEnabled(sWeakRefsEnabled)
+      .setWeakRefsEnabled(GetWeakRefsEnabled())
       .setIteratorHelpersEnabled(sIteratorHelpersEnabled);
 }
 
@@ -948,7 +961,9 @@ static void ReloadPrefsCallback(const char* pref, void* aXpccx) {
       Preferences::GetBool(JS_OPTIONS_DOT_STR "property_error_message_fix");
 #ifdef NIGHTLY_BUILD
   sWeakRefsEnabled =
-      Preferences::GetBool(JS_OPTIONS_DOT_STR "experimental.weakrefs");
+      Preferences::GetBool(JS_OPTIONS_DOT_STR "experimental.weakrefs.enabled");
+  sWeakRefsExposeCleanupSome = Preferences::GetBool(
+      JS_OPTIONS_DOT_STR "experimental.weakrefs.expose_cleanupSome");
   sIteratorHelpersEnabled =
       Preferences::GetBool(JS_OPTIONS_DOT_STR "experimental.iterator_helpers");
 #endif

js/xpconnect/tests/mochitest/mochitest.ini

@@ -38,7 +38,7 @@ support-files =
   test2_bug629331.html
   finalizationRegistry_worker.js
 prefs =
-  javascript.options.experimental.weakrefs=true
+  javascript.options.experimental.weakrefs.enabled=true
 
 [test_bug384632.html]
 [test_bug390488.html]

modules/libpref/init/StaticPrefList.yaml

@@ -4722,7 +4722,13 @@
 #ifdef NIGHTLY_BUILD
   # Experimental support for weak references in JavaScript (WeakRef and
   # FinalizationRegistry).
-- name: javascript.options.experimental.weakrefs
+- name: javascript.options.experimental.weakrefs.enabled
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
+  # Whether to expose the FinalizationRegistry.prototype.cleanupSome method.
+- name: javascript.options.experimental.weakrefs.expose_cleanupSome
   type: RelaxedAtomicBool
   value: false
   mirror: always