Do not ignore side effects of a type test or type cast as expression, such

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 14183 matching lines @@
 bool TypeParameter::CheckBound(const AbstractType& bounded_type,
                                const AbstractType& upper_bound,
                                Error* bound_error) const {
   ASSERT((bound_error != NULL) && bound_error->IsNull());
   ASSERT(bounded_type.IsFinalized());
   ASSERT(upper_bound.IsFinalized());
   ASSERT(!bounded_type.IsMalformed());
   if (bounded_type.IsSubtypeOf(upper_bound, bound_error)) {
     return true;
   }
-  if (bound_error->IsNull()) {
+  // Set bound_error if the caller is interested and if this is the first error.
+  if ((bound_error != NULL) && bound_error->IsNull()) {
     // Report the bound error only if both the bounded type and the upper bound
     // are instantiated. Otherwise, we cannot tell yet it is a bound error.
     if (bounded_type.IsInstantiated() && upper_bound.IsInstantiated()) {
       const String& bounded_type_name = String::Handle(
           bounded_type.UserVisibleName());
       const String& upper_bound_name = String::Handle(
           upper_bound.UserVisibleName());
       const AbstractType& declared_bound = AbstractType::Handle(bound());
       const String& declared_bound_name = String::Handle(
           declared_bound.UserVisibleName());
@@ skipping 208 matching lines @@
     const TypeArguments& instantiator_type_arguments,
     Error* bound_error,
     GrowableObjectArray* trail) const {
   ASSERT(IsFinalized());
   AbstractType& bounded_type = AbstractType::Handle(type());
   if (!bounded_type.IsInstantiated()) {
     bounded_type = bounded_type.InstantiateFrom(instantiator_type_arguments,
                                                 bound_error,
                                                 trail);
   }
-  if (FLAG_enable_type_checks && bound_error->IsNull()) {
+  if (FLAG_enable_type_checks &&
+      (bound_error != NULL) && bound_error->IsNull()) {
     AbstractType& upper_bound = AbstractType::Handle(bound());
     ASSERT(!upper_bound.IsObjectType() && !upper_bound.IsDynamicType());
     const TypeParameter& type_param = TypeParameter::Handle(type_parameter());
     if (!upper_bound.IsInstantiated()) {
       upper_bound = upper_bound.InstantiateFrom(instantiator_type_arguments,
                                                 bound_error,
                                                 trail);
     }
     if (bound_error->IsNull()) {
       if (!type_param.CheckBound(bounded_type, upper_bound, bound_error) &&
@@ skipping 4018 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintToJSONStream(JSONStream* stream, bool ref) const {
   Instance::PrintToJSONStream(stream, ref);
 }
 
 
 }  // namespace dart