Lexical arguments for arrow functions

Only allocate 'arguments' if the scope is not an arrow scope.

BUG=v8:2700
LOG=N
R=adamk@chromium.org, wingo@igalia.cmo

Review URL: https://codereview.chromium.org/1078483002

Cr-Commit-Position: refs/heads/master@{#27716}

src/scopes.cc

@@ -328,8 +328,8 @@ void Scope::Initialize() {
     receiver_ = outer_scope()->receiver();
   }
 
-  if (is_function_scope()) {
-    // Declare 'arguments' variable which exists in all functions.
+  if (is_function_scope() && !is_arrow_scope()) {
+    // Declare 'arguments' variable which exists in all non arrow functions.
     // Note that it might never be accessed, in which case it won't be
     // allocated during variable allocation.
     variables_.Declare(this,
@@ -1295,11 +1295,13 @@ void Scope::AllocateHeapSlot(Variable* var) {
 void Scope::AllocateParameterLocals(Isolate* isolate) {
   DCHECK(is_function_scope());
   Variable* arguments = LookupLocal(ast_value_factory_->arguments_string());
-  DCHECK(arguments != NULL);  // functions have 'arguments' declared implicitly
+  // Functions have 'arguments' declared implicitly in all non arrow functions.
+  DCHECK(arguments != nullptr || is_arrow_scope());
 
   bool uses_sloppy_arguments = false;
 
-  if (MustAllocate(arguments) && !HasArgumentsParameter(isolate)) {
+  if (arguments != nullptr && MustAllocate(arguments) &&
+      !HasArgumentsParameter(isolate)) {
     // 'arguments' is used. Unless there is also a parameter called
     // 'arguments', we must be conservative and allocate all parameters to
     // the context assuming they will be captured by the arguments object.

src/scopes.h

@@ -394,7 +394,10 @@ class Scope: public ZoneObject {
   }
 
   // The local variable 'arguments' if we need to allocate it; NULL otherwise.
-  Variable* arguments() const { return arguments_; }
+  Variable* arguments() const {
+    DCHECK(!is_arrow_scope() || arguments_ == nullptr);
+    return arguments_;
+  }
 
   // Declarations list.
   ZoneList<Declaration*>* declarations() { return &decls_; }

test/mjsunit/harmony/arrow-functions-lexical-arguments.js

+// Copyright 2015 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.
+
+// Flags: --harmony-arrow-functions --harmony-classes
+
+
+(function testInFunctionDeclaration() {
+  var calls = 0;
+  function f() {
+    (() => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    })();
+  }
+  f('a', 'b');
+  assertEquals(1, calls);
+
+  calls = 0;
+  new f('a', 'b');
+  assertEquals(1, calls);
+})();
+
+
+(function testInFunctionExpression() {
+  var calls = 0;
+  var f = function() {
+    (() => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    })();
+  }
+  f('a', 'b');
+  assertEquals(1, calls);
+})();
+
+
+(function testInConstructor() {
+  'use strict';
+
+  var calls = 0;
+  class C {
+    constructor() {
+      (() => {
+        calls++;
+        assertEquals(2, arguments.length);
+        assertEquals('a', arguments[0]);
+        assertEquals('b', arguments[1]);
+      })();
+    }
+  }
+  new C('a', 'b');
+  assertEquals(1, calls);
+})();
+
+
+(function testInSetter() {
+  'use strict';
+
+  var calls = 0;
+  var o = {
+    set x(_) {
+      (() => {
+        calls++;
+        assertEquals(1, arguments.length);
+        assertEquals('a', arguments[0]);
+      })();
+    }
+  }
+  o.x = 'a';
+  assertEquals(1, calls);
+})();
+
+
+(function testMappedArguments() {
+  var calls = 0;
+  function f(x) {
+    x = 'c';
+    (() => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('c', arguments[0]);
+      x = 'a';
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    })();
+  }
+  f('a', 'b');
+  assertEquals(1, calls);
+})();
+
+
+(function testUnMappedArguments() {
+  'use strict';
+
+  var calls = 0;
+  function f(x) {
+    x = 'c';
+    (() => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    })();
+  }
+  f('a', 'b');
+  assertEquals(1, calls);
+})();
+
+
+(function testClosure() {
+  var calls = 0;
+  function f(x) {
+    return () => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    };
+  }
+  f('a', 'b')();
+  assertEquals(1, calls);
+})();
+
+
+(function testClosureMappedArguments() {
+  var calls = 0;
+  function f(x) {
+    x = 'c';
+    return () => {
+      calls++;
+      assertEquals(2, arguments.length);
+      assertEquals('c', arguments[0]);
+      x = 'a';
+      assertEquals('a', arguments[0]);
+      assertEquals('b', arguments[1]);
+    };
+  }
+  f('a', 'b')();
+  assertEquals(1, calls);
+})();
+
+
+(function testParamNamedArguments() {
+  var calls = 0;
+  function f(arguments) {
+    (() => {
+      calls++;
+      assertEquals('a', arguments);
+    })();
+  }
+  f('a');
+  assertEquals(1, calls);
+})();