Introduce a flag to disable string operator +

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/flags.h"
 #include "vm/growable_array.h"
 #include "vm/longjump.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/resolver.h"
 #include "vm/scopes.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, enable_asserts, false, "Enable assert statements.");
 DEFINE_FLAG(bool, enable_type_checks, false, "Enable type checks.");
 DEFINE_FLAG(bool, trace_parser, false, "Trace parser operations.");
 DEFINE_FLAG(bool, warning_as_error, false, "Treat warnings as errors.");
 DEFINE_FLAG(bool, silent_warnings, false, "Silence warnings.");
+DEFINE_FLAG(bool, allow_string_plus, true, "Allow + operator on strings.");
 
 static void CheckedModeHandler(bool value) {
   FLAG_enable_asserts = value;
   FLAG_enable_type_checks = value;
 }
 
 DEFINE_FLAG_HANDLER(CheckedModeHandler,
                     enable_checked_mode,
                     "Enabled checked mode.");
 
@@ skipping 5656 matching lines @@
           || Token::IsEqualityOperator(op_kind)) {
         left_operand = new ComparisonNode(
             op_pos, op_kind, left_operand, right_operand);
         break;  // Equality and relational operators cannot be chained.
       } else {
         StringConcatNode* str_concat = NULL;
         if (op_kind == Token::kADD) {
           if (left_operand->IsLiteralNode()) {
             LiteralNode* lit = left_operand->AsLiteralNode();
             if (lit->literal().IsString()) {
-              str_concat = new StringConcatNode(lit->token_index());
-              str_concat->AddExpr(lit);
+              if (FLAG_allow_string_plus) {
+                str_concat = new StringConcatNode(lit->token_index());
+                str_concat->AddExpr(lit);
+              } else {
+                ErrorMsg(op_pos, "operator + on strings no longer allowed");
+              }
             }
           } else if (left_operand->IsStringConcatNode()) {
             str_concat = left_operand->AsStringConcatNode();
           }
         }
         if (str_concat != NULL) {
           str_concat->AddExpr(right_operand);
           left_operand = str_concat;
         } else {
           left_operand = OptimizeBinaryOpNode(
@@ skipping 2562 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart