Implementation of null-aware operators.

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

Index: pkg/compiler/lib/src/resolution/members.dart
diff --git a/pkg/compiler/lib/src/resolution/members.dart b/pkg/compiler/lib/src/resolution/members.dart
index 762c6f223b6ca06e6575e3d694e0215f77ad6646..5e90ff7f0ed21994e19f3cf8c223e03a9718f414 100644
--- a/pkg/compiler/lib/src/resolution/members.dart
+++ b/pkg/compiler/lib/src/resolution/members.dart
@@ -2597,7 +2597,24 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
 
     var oldCategory = allowedCategory;
     allowedCategory |= ElementCategory.PREFIX | ElementCategory.SUPER;
+
+    bool oldSendIsMemberAccess = sendIsMemberAccess;
+    int oldAllowedCategory = allowedCategory;
+
+    // Conditional sends like `e?.foo` treat the receiver as an expression.  So
+    // `C?.foo` needs to be treated like `(C).foo`, not like C.foo. Prefixes and
+    // super are not allowed on their own in that context.
+    if (node.isConditional) {
+      sendIsMemberAccess = false;
+      allowedCategory = ElementCategory.VARIABLE | ElementCategory.FUNCTION
+          | ElementCategory.IMPLIES_TYPE;

[Johnni Winther, 2015/05/22 12:39:49]

Format like this:

allowedCategory =
    ElementCategory.VARIABLE |
    ElementCategory.FUNCTION |
    ElementCategory.IMPLIES_TYPE;

[Siggi Cherem (dart-lang), 2015/05/22 19:49:54]

Done.

+    }
     ResolutionResult resolvedReceiver = visit(node.receiver);
+    if (node.isConditional) {
+      sendIsMemberAccess = oldSendIsMemberAccess;
+      allowedCategory = oldAllowedCategory;
+    }
+
     allowedCategory = oldCategory;
 
     Element target;
@@ -3029,9 +3046,16 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
           registry.registerThrowNoSuchMethod();
         }
       } else if (target.impliesType) {
-        setter = reportAndCreateErroneousElement(node.selector, target.name,
-            MessageKind.ASSIGNING_TYPE, const {});
-        registry.registerThrowNoSuchMethod();
+        if (node.isIfNullAssignment) {
+          setter = reportAndCreateErroneousElement(node.selector, target.name,
+              MessageKind.IF_NULL_ASSIGNING_TYPE, const {});
+          // In this case, no assignment happens, the rest of the compiler can
+          // treat the expression `C ??= e` as if it's just reading `C`.
+        } else {
+          setter = reportAndCreateErroneousElement(node.selector, target.name,
+              MessageKind.ASSIGNING_TYPE, const {});
+          registry.registerThrowNoSuchMethod();
+        }
         registerTypeLiteralAccess(node, target);

[Siggi Cherem (dart-lang), 2015/05/22 03:50:49]

funny thing that you just added this - I was doing the exact same refactoring
because I needed the TypeLiteal here :)

       } else if (target.isFinal || target.isConst) {
         if (Elements.isStaticOrTopLevelField(target) || target.isLocal) {