Defer CONST_LEGACY redeclaration errors until runtime in harmony mode

src/parsing/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/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-literal-reindexer.h"
 #include "src/ast/scopeinfo.h"
@@ skipping 2075 matching lines @@
       // functions. The function CheckConflictingVarDeclarations checks for
       // var and let bindings from different scopes whereas this is a check for
       // conflicting declarations within the same scope. This check also covers
       // the special case
       //
       // function () { let x; { var x; } }
       //
       // because the var declaration is hoisted to the function scope where 'x'
       // is already bound.
       DCHECK(IsDeclaredVariableMode(var->mode()));
-      if (is_strict(language_mode()) || allow_harmony_sloppy()) {
+      if (is_strict(language_mode()) ||
+          (allow_harmony_sloppy() && mode != CONST_LEGACY &&
+           var->mode() != CONST_LEGACY)) {
         // In harmony we treat re-declarations as early errors. See
         // ES5 16 for a definition of early errors.
         if (declaration_kind == DeclarationDescriptor::NORMAL) {
           ParserTraits::ReportMessage(MessageTemplate::kVarRedeclaration, name);
         } else {
           ParserTraits::ReportMessage(MessageTemplate::kParamDupe);
         }
         *ok = false;
         return nullptr;
       }
@@ skipping 4348 matching lines @@
 }
 
 
 void Parser::RaiseLanguageMode(LanguageMode mode) {
   SetLanguageMode(scope_,
                   static_cast<LanguageMode>(scope_->language_mode() | mode));
 }
 
 }  // namespace internal
 }  // namespace v8