Fix legacy const for-of/in destructuring

src/parser.cc

 // Copyright 2012 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.
 
 #include "src/parser.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/ast-literal-reindexer.h"
 #include "src/bailout-reason.h"
@@ skipping 2535 matching lines @@
     const AstRawString* single_name =
         pattern->IsVariableProxy() ? pattern->AsVariableProxy()->raw_name()
                                    : nullptr;
     if (single_name != nullptr) {
       if (fni_ != NULL) fni_->PushVariableName(single_name);
     }
 
     is_for_iteration_variable =
         var_context == kForStatement &&
         (peek() == Token::IN || PeekContextualKeyword(CStrVector("of")));
     if (is_for_iteration_variable && parsing_result->descriptor.mode == CONST) {

[adamk, 2015/10/05 20:13:19]

Could you fix this here instead, by resetting needs_init to false for
CONST_LEGACY as well as CONST?

       parsing_result->descriptor.needs_init = false;
     }
 
     Expression* value = NULL;
     // Harmony consts have non-optional initializers.
     int initializer_position = RelocInfo::kNoPosition;
     if (peek() == Token::ASSIGN || (parsing_result->descriptor.mode == CONST &&
                                     !is_for_iteration_variable)) {
       Expect(Token::ASSIGN, ok);
       if (!*ok) return;
@@ skipping 19 matching lines @@
         }
       }
       // End position of the initializer is after the assignment expression.
       initializer_position = scanner()->location().end_pos;
     } else {
       // End position of the initializer is after the variable.
       initializer_position = position();
     }
 
     // Make sure that 'const x' and 'let x' initialize 'x' to undefined.
-    if (value == NULL && parsing_result->descriptor.needs_init) {
+    // If in a for-of/in loop, no need to initialize here.
+    if (value == NULL && parsing_result->descriptor.needs_init &&
+        !is_for_iteration_variable) {
       value = GetLiteralUndefined(position());
     }
 
     if (single_name && fni_ != NULL) fni_->Leave();
     parsing_result->declarations.Add(DeclarationParsingResult::Declaration(
         pattern, initializer_position, value));
     first_declaration = false;
   } while (peek() == Token::COMMA);
 
   parsing_result->bindings_loc =
@@ skipping 3712 matching lines @@
 
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(Context::REFLECT_CONSTRUCT_INDEX, args, pos);
 }
 }  // namespace internal
 }  // namespace v8