Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/helpers/helpers.dart

 // Copyright (c) 2014, 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.
 
 /// Library for debugging helpers. The unittest analyze_unused_test checks that
 /// the helper are not used in production code.
 
 library dart2js.helpers;
 
 import 'dart:async' show EventSink;
 import 'dart:collection';
 import 'dart:convert';
 
 import '../../compiler.dart';
 import '../dart2jslib.dart';
 import '../util/util.dart';
 
 part 'debug_collection.dart';
 part 'trace.dart';
 part 'expensive_map.dart';
 part 'expensive_set.dart';
 part 'stats.dart';
 part 'track_map.dart';
 
 /// Global flag to enable [debugPrint]. This should always be `true` by default
 /// and be set to `false` as a means to temporarily turn off all debugging
 /// printouts.
 const bool DEBUG_PRINT_ENABLED = true;
 
+/// Enables debug mode.

[karlklose, 2014/09/25 08:43:25]

Why do we need this mode?

We already test that the helpers are not used in production and we only use it
for a hint that (IMHO) could do with a comment.

[Johnni Winther, 2014/09/29 08:24:44]

See comment on Constant.toString()

+///
+/// Sets the [DEBUG_MODE] to `true`.
+void enableDebugMode() {
+  DEBUG_MODE = true;
+}
+
 class _DebugIndentation extends Indentation {
   final String indentationUnit = " ";
 }
 _DebugIndentation _indentation = new _DebugIndentation();
 
+/// Function signature of [debugPrint].
+typedef DebugPrint(s);
+
 /// If [DEBUG_PRINT_ENABLED] is `true` print [s] using the current identation.
-debugPrint(s) {
+DebugPrint get debugPrint {
+  enableDebugMode();
+  return _debugPrint;
+}
+
+/// Implementation of [debugPrint].
+_debugPrint(s) {
   if (DEBUG_PRINT_ENABLED) print('${_indentation.indentation}$s');
 }
 
+/// Function signature of [debugWrapPrint].
+typedef DebugWrapPrint(s, f());
+
 /// Wraps the call to [f] with a print of 'start:$s' and 'end:$s' incrementing
 /// the current indentation used by [debugPrint] during the execution of [f].
 ///
 /// Use this to get a tree-like debug printout for nested calls.
-debugWrapPrint(s, f()) {
+DebugWrapPrint get debugWrapPrint {
+  enableDebugMode();
+  return _debugWrapPrint;
+}
+
+/// Implementation of [debugWrapPrint].
+DebugWrapPrint _debugWrapPrint(s, f()) {
   debugPrint('start:$s');
   var result = _indentation.indentBlock(f);
   debugPrint('end:$s');
   return result;
 }
 
 /// Dummy method to mark breakpoints.
-debugBreak() {}
+debugBreak() {
+  enableDebugMode();
+}
+
+/// Function signature of [reportHere].
+typedef ReportHere(Compiler compiler, Spannable node, String debugMessage);
 
 /// Print a message with a source location.
-reportHere(Compiler compiler, Spannable node, String debugMessage) {
+ReportHere get reportHere {
+  enableDebugMode();

[sigurdm, 2014/09/25 08:44:56]

Maybe ensure that debug mode is disabled after debug printing.

[Johnni Winther, 2014/09/29 08:24:44]

TODO added.

+  return _reportHere;
+}
+
+/// Implementation of [reportHere]
+_reportHere(Compiler compiler, Spannable node, String debugMessage) {
   compiler.reportInfo(node,
       MessageKind.GENERIC, {'text': 'HERE: $debugMessage'});
 }