Bug 1696046 - Factor out implementation of JS_ExtensibleLexicalEnvironment to a non-API static method with a more specific return type. r=mgaudet

Differential Revision: https://phabricator.services.mozilla.com/D107009

js/src/builtin/Eval.cpp

@@ -472,10 +472,8 @@ JS_FRIEND_API bool JS::ExecuteInJSMEnvironment(JSContext* cx,
       ObjectRealm::get(varEnv).getNonSyntacticLexicalEnvironment(varEnv));
   MOZ_DIAGNOSTIC_ASSERT(scriptArg->noScriptRval());
 
-  Rooted<ExtensibleLexicalEnvironmentObject*> env(cx);
-  if (auto* envPtr = JS_ExtensibleLexicalEnvironment(varEnv)) {
-    env = &envPtr->as<ExtensibleLexicalEnvironmentObject>();
-  }
+  Rooted<ExtensibleLexicalEnvironmentObject*> env(
+      cx, ExtensibleLexicalEnvironmentObject::forVarEnvironment(varEnv));
 
   // If the Gecko subscript loader specifies target objects, we need to add
   // them to the environment. These are added after the NSVO environment.

js/src/jsapi.cpp

@@ -1249,14 +1249,7 @@ extern JS_PUBLIC_API bool JS_HasExtensibleLexicalEnvironment(JSObject* obj) {
 }
 
 extern JS_PUBLIC_API JSObject* JS_ExtensibleLexicalEnvironment(JSObject* obj) {
-  JSObject* lexical = nullptr;
-  if (obj->is<GlobalObject>()) {
-    lexical = JS_GlobalLexicalEnvironment(obj);
-  } else {
-    lexical = ObjectRealm::get(obj).getNonSyntacticLexicalEnvironment(obj);
-  }
-  MOZ_ASSERT(lexical);
-  return lexical;
+  return ExtensibleLexicalEnvironmentObject::forVarEnvironment(obj);
 }
 
 JS_PUBLIC_API JSObject* JS::CurrentGlobalOrNull(JSContext* cx) {

js/src/vm/EnvironmentObject.cpp

@@ -1112,6 +1112,19 @@ JSObject* ExtensibleLexicalEnvironmentObject::thisObject() const {
   return obj;
 }
 
+/* static */
+ExtensibleLexicalEnvironmentObject*
+ExtensibleLexicalEnvironmentObject::forVarEnvironment(JSObject* obj) {
+  ExtensibleLexicalEnvironmentObject* lexical = nullptr;
+  if (obj->is<GlobalObject>()) {
+    lexical = &obj->as<GlobalObject>().lexicalEnvironment();
+  } else {
+    lexical = ObjectRealm::get(obj).getNonSyntacticLexicalEnvironment(obj);
+  }
+  MOZ_ASSERT(lexical);
+  return lexical;
+}
+
 /* static */
 GlobalLexicalEnvironmentObject* GlobalLexicalEnvironmentObject::create(
     JSContext* cx, Handle<GlobalObject*> global) {

js/src/vm/EnvironmentObject.h

@@ -619,6 +619,11 @@ class ExtensibleLexicalEnvironmentObject : public LexicalEnvironmentObject {
  public:
   JSObject* thisObject() const;
 
+  // For a given global object or JSMEnvironment `obj`, return the associated
+  // global lexical or non-syntactic lexical environment, where top-level `let`
+  // bindings are added.
+  static ExtensibleLexicalEnvironmentObject* forVarEnvironment(JSObject* obj);
+
  protected:
   void initThisObject(JSObject* obj) {
     MOZ_ASSERT(isGlobal() || !isSyntactic());