Bug 1729602 - Remove the magic cx constructor handling in Rooted<TypeConstructibleWithCx> foo(cx); r=tcampbell,jonco

Differential Revision: https://phabricator.services.mozilla.com/D124994

js/public/RootingAPI.h

@@ -1089,12 +1089,6 @@ using RootedPtrTraits =
                        js::RootedTraceableTraits<T>,
                        js::RootedGCThingTraits<T>>;
 
-// Dummy types to make it easier to understand template overload preference
-// ordering.
-struct FallbackOverload {};
-struct PreferredOverload : FallbackOverload {};
-using OverloadSelector = PreferredOverload;
-
 } /* namespace detail */
 
 /**
@@ -1123,38 +1117,17 @@ class MOZ_RAII Rooted : public js::RootedBase<T, Rooted<T>> {
     return rootLists(RootingContext::get(cx));
   }
 
-  // Define either one or two Rooted(cx) constructors: the fallback one, which
-  // constructs a Rooted holding a SafelyInitialized<T>, and a convenience one
-  // for types that can be constructed with a cx, which will give a Rooted
-  // holding a T(cx).
-
-  // Dummy type to distinguish these constructors from Rooted(cx, initial)
-  struct CtorDispatcher {};
-
-  // Normal case: construct an empty Rooted holding a safely initialized but
-  // empty T.
-  template <typename RootingContext>
-  Rooted(const RootingContext& cx, CtorDispatcher, detail::FallbackOverload)
-      : Rooted(cx, SafelyInitialized<T>()) {}
-
-  // If T can be constructed with a cx, then define another constructor for it
-  // that will be preferred.
-  template <
-      typename RootingContext,
-      typename = std::enable_if_t<std::is_constructible_v<T, RootingContext>>>
-  Rooted(const RootingContext& cx, CtorDispatcher, detail::PreferredOverload)
-      : Rooted(cx, T(cx)) {}
-
  public:
   using ElementType = T;
 
-  // Construct an empty Rooted. Delegates to an internal constructor that
-  // chooses a specific meaning of "empty" depending on whether T can be
-  // constructed with a cx.
+  // Construct an empty Rooted holding a safely initialized but empty T.
   template <typename RootingContext>
   explicit Rooted(const RootingContext& cx)
-      : Rooted(cx, CtorDispatcher(), detail::OverloadSelector()) {}
+      : ptr(SafelyInitialized<T>()) {
+    registerWithRootLists(rootLists(cx));
+  }
 
+  // Provide an initial value.
   template <typename RootingContext, typename S>
   Rooted(const RootingContext& cx, S&& initial)
       : ptr(std::forward<S>(initial)) {

js/src/builtin/ModuleObject.cpp

@@ -2495,7 +2495,7 @@ template <XDRMode mode>
 XDRResult js::XDRExportEntries(XDRState<mode>* xdr,
                                MutableHandleArrayObject vec) {
   JSContext* cx = xdr->cx();
-  Rooted<GCVector<ExportEntryObject*>> expVec(cx);
+  Rooted<GCVector<ExportEntryObject*>> expVec(cx, cx);
   RootedExportEntryObject expObj(cx);
   RootedAtom exportName(cx);
   RootedModuleRequestObject moduleRequest(cx);

js/src/builtin/RegExp.cpp

@@ -1631,7 +1631,7 @@ static bool CollectNames(JSContext* cx, HandleLinearString replacement,
 static bool InitNamedCaptures(JSContext* cx, HandleLinearString replacement,
                               HandleObject groups, size_t firstDollarIndex,
                               MutableHandle<CapturesVector> namedCaptures) {
-  Rooted<GCVector<jsid>> names(cx);
+  Rooted<GCVector<jsid>> names(cx, cx);
   if (replacement->hasLatin1Chars()) {
     if (!CollectNames<Latin1Char>(cx, replacement, firstDollarIndex, &names)) {
       return false;
@@ -1766,7 +1766,7 @@ bool js::RegExpGetSubstitution(JSContext* cx, HandleArrayObject matchResult,
     captures.infallibleAppend(StringValue(captureLinear));
   }
 
-  Rooted<CapturesVector> namedCaptures(cx);
+  Rooted<CapturesVector> namedCaptures(cx, cx);
   if (groups.isObject()) {
     RootedObject groupsObj(cx, &groups.toObject());
     if (!InitNamedCaptures(cx, replacement, groupsObj, firstDollarIndex,

js/src/debugger/Debugger.cpp

@@ -5235,7 +5235,7 @@ class MOZ_STACK_CLASS Debugger::ScriptQuery : public Debugger::QueryBase {
       using RealmToScriptMap =
           GCHashMap<Realm*, BaseScript*, DefaultHasher<Realm*>>;
 
-      Rooted<RealmToScriptMap> innermostForRealm(cx);
+      Rooted<RealmToScriptMap> innermostForRealm(cx, cx);
 
       // Visit each candidate script and find innermost in each realm.
       for (BaseScript* script : scriptVector) {

js/src/jsapi-tests/testGCExactRooting.cpp

@@ -255,7 +255,7 @@ END_TEST(testGCHandleHashMap)
 using ShapeVec = GCVector<Shape*>;
 
 BEGIN_TEST(testGCRootedVector) {
-  JS::Rooted<ShapeVec> shapes(cx);
+  JS::Rooted<ShapeVec> shapes(cx, cx);
 
   for (size_t i = 0; i < 10; ++i) {
     RootedObject obj(cx, JS_NewObject(cx, nullptr));

js/src/shell/ModuleLoader.cpp

@@ -500,7 +500,7 @@ JSLinearString* ModuleLoader::normalizePath(JSContext* cx,
 #endif  // XP_WIN
 
   // Normalize the path by removing redundant path components.
-  Rooted<GCVector<JSLinearString*>> components(cx);
+  Rooted<GCVector<JSLinearString*>> components(cx, cx);
   size_t lastSep = 0;
   while (lastSep < path->length()) {
     int32_t i = IndexOf(path, PathSeparator, lastSep);