Always evaluate e in (e is T)

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 "lib/invocation_mirror.h"
 #include "platform/utils.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 7590 matching lines @@
             (current_block_->scope->function_level() > 0)) {
           // Make sure that the instantiator is captured.
           CaptureInstantiator();
         }
         right_operand = new TypeNode(type_pos, type);
         // In production mode, the type may be malformed.
         // In checked mode, the type may be malformed or malbounded.
         if (((op_kind == Token::kIS) || (op_kind == Token::kISNOT) ||
              (op_kind == Token::kAS)) &&
             type.IsMalformedOrMalbounded()) {
-          // Note that a type error is thrown even if the tested value is null
-          // in a type test or in a type cast.
-          // TODO(hausner): We drop the left operand. We need to
-          // evaluate it in case there are side effects.
-          left_operand = ThrowTypeError(type_pos, type);
+          // Note that a type error is thrown in a type test or in
+          // a type cast even if the tested value is null.
+          // We need to evaluate the left operand for potential
+          // side effects.
+          LetNode* let = new LetNode(left_operand->token_pos());
+          let->AddNode(left_operand);
+          let->AddNode(ThrowTypeError(type_pos, type));
+          left_operand = let;
           break;  // Type checks and casts can't be chained.
         }
       }
       if (Token::IsRelationalOperator(op_kind)
           || Token::IsTypeTestOperator(op_kind)
           || Token::IsTypeCastOperator(op_kind)
           || Token::IsEqualityOperator(op_kind)) {
         if (Token::IsTypeTestOperator(op_kind) ||
             Token::IsTypeCastOperator(op_kind)) {
           if (!right_operand->AsTypeNode()->type().IsInstantiated()) {
@@ skipping 3159 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart