Declare the arguments object before creating the function var, to make sure it masks it

BUG=chromium:649067

Review-Url: https://codereview.chromium.org/2362463003
Cr-Commit-Position: refs/heads/master@{#39642}

src/ast/scopes.cc

@@ -1218,7 +1218,6 @@ void DeclarationScope::AnalyzePartially(DeclarationScope* migrate_to,
   DCHECK_EQ(outer_scope_->zone(), migrate_to->zone());
   DCHECK_EQ(NeedsHomeObject(), migrate_to->NeedsHomeObject());
   DCHECK_EQ(asm_function_, migrate_to->asm_function_);
-  DCHECK_EQ(arguments() != nullptr, migrate_to->arguments() != nullptr);
 }
 
 #ifdef DEBUG

src/parsing/parser.cc

@@ -2842,10 +2842,6 @@ FunctionLiteral* Parser::ParseFunctionLiteral(
 
     // Parsing the body may change the language mode in our scope.
     language_mode = scope->language_mode();
-    scope->DeclareArguments(ast_value_factory());
-    if (main_scope != scope) {
-      main_scope->DeclareArguments(ast_value_factory());
-    }
 
     // Validate name and parameter names. We can do this only after parsing the
     // function, since the function can declare itself strict.
@@ -3434,6 +3430,13 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
     }
   }
 
+  if (!IsArrowFunction(kind)) {
+    // Declare arguments after parsing the function since lexical 'arguments'
+    // masks the arguments object. Declare arguments before declaring the
+    // function var since the arguments object masks 'function arguments'.
+    function_scope->DeclareArguments(ast_value_factory());
+  }
+
   if (function_type == FunctionLiteral::kNamedExpression) {
     Statement* statement;
     if (function_scope->LookupLocal(function_name) == nullptr) {

test/mjsunit/regress/regress-649067.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+assertEquals(1, (function arguments() { return eval("arguments"); })(1)[0]);