Add support for null-aware operators to the CPS-IR.

pkg/compiler/lib/src/resolution/operators.dart

 // Copyright (c) 2015, 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 dart2js.operators;
 
 import '../elements/elements.dart';
 import '../universe/universe.dart';
 
 enum UnaryOperatorKind {
@@ skipping 152 matching lines @@
   /// The logical && operator.
   static const BinaryOperator LOGICAL_AND =
       const _LogicalOperator(BinaryOperatorKind.LOGICAL_AND, '&&');
 
   /// The binary | operator.
   static const BinaryOperator LOGICAL_OR =
       const _LogicalOperator(BinaryOperatorKind.LOGICAL_OR, '||');
 
   /// The if-null ?? operator.
   static const BinaryOperator IF_NULL =
-      const _LogicalOperator(BinaryOperatorKind.IF_NULL, '??');
+      const _IfNullOperator(BinaryOperatorKind.IF_NULL, '??');
 
   static BinaryOperator parse(String value) {
     switch (value) {
       case '==': return EQ;
       case '!=': return NOT_EQ;
       case '[]': return INDEX;
       case '*': return MUL;
       case '/': return DIV;
       case '%': return MOD;
       case '~/': return IDIV;
@@ skipping 30 matching lines @@
 /// structures.
 class _LogicalOperator extends BinaryOperator {
   const _LogicalOperator(BinaryOperatorKind kind, String name)
       : super._(kind, name);
 
   bool get isUserDefinable => false;
 
   String get selectorName => null;
 }
 
+/// The operators ?? is not user definable.
+class _IfNullOperator extends BinaryOperator {

[Siggi Cherem (dart-lang), 2015/05/28 02:15:34]

technically this cleanup is not needed for this CL. It just didn't seem
appropriate to keep it together with _LogicalOperator.

[Johnni Winther, 2015/05/29 10:23:24]

Acknowledged.

+  const _IfNullOperator(BinaryOperatorKind kind, String name)
+      : super._(kind, name);
+
+  bool get isUserDefinable => false;
+
+  String get selectorName => '??';
+}
+
 enum AssignmentOperatorKind {
   ASSIGN,
   IF_NULL,
   ADD,
   SUB,
   MUL,
   DIV,
   IDIV,
   MOD,
   SHL,
@@ skipping 129 matching lines @@
       const IncDecOperator._(IncDecOperatorKind.DEC, '--', BinaryOperator.SUB);
 
   static IncDecOperator parse(String value) {
     switch (value) {
       case '++': return INC;
       case '--': return DEC;
       default: return null;
     }
   }
 }