[destructuring] Refactor duplicate parameter name detection.

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/v8.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/bailout-reason.h"
 #include "src/base/platform/platform.h"
@@ skipping 3787 matching lines @@
   const AstRawString* raw_name = expr->AsVariableProxy()->raw_name();
   Scanner::Location param_location(expr->position(),
                                    expr->position() + raw_name->length());
 
   // When the formal parameter was originally seen, it was parsed as a
   // VariableProxy and recorded as unresolved in the scope.  Here we undo that
   // parse-time side-effect.
   parser_->scope_->RemoveUnresolved(expr->AsVariableProxy());
 
   bool is_rest = false;
-  bool is_duplicate = DeclareFormalParameter(scope, raw_name, is_rest);
-
-  if (is_duplicate && !duplicate_loc->IsValid()) {
-    *duplicate_loc = param_location;
-  }
+  ExpressionClassifier classifier;
+  DeclareFormalParameter(scope, raw_name, &classifier, is_rest);
+  *duplicate_loc = classifier.duplicate_formal_parameter_error().location;
 }
 
 
 void ParserTraits::ParseArrowFunctionFormalParameters(
     Scope* scope, Expression* params, const Scanner::Location& params_loc,
     bool* is_rest, Scanner::Location* duplicate_loc, bool* ok) {
   DeclareArrowFunctionParameters(scope, params, params_loc, duplicate_loc, ok);
 }
 
 
@@ skipping 1998 matching lines @@
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(
       ast_value_factory()->reflect_construct_string(), NULL, args, pos);
 }
 }  // namespace internal
 }  // namespace v8