Hide MirroredCompilationErrror behind a flag until post-1.0.

runtime/lib/mirrors.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 "lib/invocation_mirror.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/port.h"
 #include "vm/resolver.h"
 #include "vm/symbols.h"
 
 namespace dart {
 
+DEFINE_FLAG(bool, use_mirrored_compilation_error, false,
+    "Wrap compilation errors that occur during reflective access in a "
+    "MirroredCompilationError, rather than suspending the isolate.");
+
 static RawInstance* CreateMirror(const String& mirror_class_name,
                                  const Array& constructor_arguments) {
   const Library& mirrors_lib = Library::Handle(Library::MirrorsLibrary());
   const String& constructor_name = Symbols::Dot();
 
   const Object& result = Object::Handle(
       DartLibraryCalls::InstanceCreate(mirrors_lib,
                                        mirror_class_name,
                                        constructor_name,
                                        constructor_arguments));
   ASSERT(!result.IsError());
   return Instance::Cast(result).raw();
 }
 
 
 static void ThrowMirroredCompilationError(const String& message) {
   Array& args = Array::Handle(Array::New(1));
   args.SetAt(0, message);
 
   Exceptions::ThrowByType(Exceptions::kMirroredCompilationError, args);
   UNREACHABLE();
 }
 
 
 static void ThrowInvokeError(const Error& error) {
-  if (error.IsLanguageError()) {
+  if (FLAG_use_mirrored_compilation_error && error.IsLanguageError()) {
     // A compilation error that was delayed by lazy compilation.
     const LanguageError& compilation_error = LanguageError::Cast(error);
     String& message = String::Handle(compilation_error.message());
     ThrowMirroredCompilationError(message);
     UNREACHABLE();
   }
   Exceptions::PropagateError(error);
   UNREACHABLE();
 }
 
@@ skipping 1917 matching lines @@
 }
 
 
 DEFINE_NATIVE_ENTRY(VariableMirror_type, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Field& field = Field::Handle(ref.GetFieldReferent());
   return field.type();
 }
 
 }  // namespace dart