Implementation of null-aware operators.

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

 // 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.
 
 part of resolution;
 
 abstract class TreeElements {
   AnalyzableElement get analyzedElement;
   Iterable<Node> get superUses;
 
@@ skipping 2579 matching lines @@
         }
         registry.registerAssert(node);
         return const AssertResult();
       }
 
       return node.selector.accept(this);
     }
 
     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;
     String name = node.selector.asIdentifier().source;
     if (identical(name, 'this')) {
       // TODO(ahe): Why is this using GENERIC?
       error(node.selector, MessageKind.GENERIC,
             {'text': "expected an identifier"});
       return null;
     } else if (node.isSuperCall) {
@@ skipping 411 matching lines @@
                 MessageKind.CANNOT_RESOLVE_SETTER, const {});
             registry.registerThrowNoSuchMethod();
           }
         }
         if (isComplex && getter == null && !inInstanceContext) {
           getter = reportAndCreateErroneousElement(node.selector, field.name,
               MessageKind.CANNOT_RESOLVE_GETTER, const {});
           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) {
           setter = reportAndCreateErroneousElement(
               node.selector, target.name, MessageKind.CANNOT_RESOLVE_SETTER,
               const {});
         } else if (node.isSuperCall) {
           setter = reportAndCreateErroneousElement(
               node.selector, target.name, MessageKind.SETTER_NOT_FOUND_IN_SUPER,
               {'name': target.name, 'className': currentClass.name});
           registry.registerSuperNoSuchMethod();
@@ skipping 2124 matching lines @@
 }
 
 /// The result for the resolution of the `assert` method.
 class AssertResult implements ResolutionResult {
   const AssertResult();
 
   Element get element => null;
 
   String toString() => 'AssertResult()';
 }