Implementation of null-aware operators.

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

Index: pkg/compiler/lib/src/resolution/operators.dart
diff --git a/pkg/compiler/lib/src/resolution/operators.dart b/pkg/compiler/lib/src/resolution/operators.dart
index e862c30e89d48e06c9562cbbe912bc9cf7e8b839..e903b10281c4876d4a240820099430f8b25c9f5d 100644
--- a/pkg/compiler/lib/src/resolution/operators.dart
+++ b/pkg/compiler/lib/src/resolution/operators.dart
@@ -66,6 +66,7 @@ enum BinaryOperatorKind {
   XOR,
   LOGICAL_AND,
   LOGICAL_OR,
+  IF_NULL,
 }
 
 class BinaryOperator {
@@ -161,6 +162,10 @@ class BinaryOperator {
   static const BinaryOperator LOGICAL_OR =
       const _LogicalOperator(BinaryOperatorKind.LOGICAL_OR, '||');
 
+  /// The if-null ?? operator.
+  static const BinaryOperator IF_NULL =
+      const _LogicalOperator(BinaryOperatorKind.IF_NULL, '??');
+
   static BinaryOperator parse(String value) {
     switch (value) {
       case '==': return EQ;
@@ -183,6 +188,7 @@ class BinaryOperator {
       case '|': return OR;
       case '&&': return LOGICAL_AND;
       case '||': return LOGICAL_OR;
+      case '??': return IF_NULL;
       default: return null;
     }
   }
@@ -211,6 +217,7 @@ class _LogicalOperator extends BinaryOperator {
 
 enum AssignmentOperatorKind {
   ASSIGN,
+  IF_NULL,
   ADD,
   SUB,
   MUL,
@@ -244,6 +251,12 @@ class AssignmentOperator {
       const AssignmentOperator._(AssignmentOperatorKind.ASSIGN, '=',
                                  null, isUserDefinable: false);
 
+  /// The ??= operator.
+  static const AssignmentOperator IF_NULL =
+      const AssignmentOperator._(AssignmentOperatorKind.IF_NULL, '??=',
+                                 BinaryOperator.IF_NULL,
+                                 isUserDefinable: false);
+
   /// The += assignment operator.
   static const AssignmentOperator ADD =
       const AssignmentOperator._(AssignmentOperatorKind.ADD, '+=',
@@ -302,6 +315,7 @@ class AssignmentOperator {
   static AssignmentOperator parse(String value) {
     switch (value) {
       case '=': return ASSIGN;
+      case '??=': return IF_NULL;
       case '*=': return MUL;
       case '/=': return DIV;
       case '%=': return MOD;
@@ -349,4 +363,4 @@ class IncDecOperator {
       default: return null;
     }
   }
-}
+}