Implementation of null-aware operators.

pkg/compiler/lib/src/resolution/send_resolver.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.
 
 part of dart2js.semantics_visitor;
 
 enum SendStructureKind {
   GET,
   SET,
   INVOKE,
@@ skipping 207 matching lines @@
 
     if (node.isOperator) {
       String operatorText = node.selector.asOperator().source;
       if (operatorText == 'is') {
         return internalError(node, "Unexpected is test.");
       } else if (operatorText == 'as') {
         return internalError(node, "Unexpected as cast.");
         return new AsStructure(elements.getType(node.arguments.single));
       } else if (operatorText == '&&') {
         return internalError(node, "Unexpected logical and.");
-        return const LogicalAndStructure();
       } else if (operatorText == '||') {
         return internalError(node, "Unexpected logical or.");
+      } else if (operatorText == '??') {
+        return internalError(node, "Unexpected if-null.");
       }
     }
 
     SendStructureKind kind;
 
     if (node.asSendSet() != null) {
       SendSet sendSet = node.asSendSet();
       String operatorText = sendSet.assignmentOperator.source;
       if (sendSet.isPrefix || sendSet.isPostfix) {
         kind = sendSet.isPrefix
@@ skipping 266 matching lines @@
           }
           return new CompoundAccessSemantics(accessKind, getter, element);
         }
         return new StaticAccess.superSetter(element);
       } else if (isCompound) {
         return new CompoundAccessSemantics(
             CompoundAccessKind.SUPER_GETTER_SETTER, getter, element);
       } else {
         return new StaticAccess.superMethod(element);
       }
-    } else if (node.isOperator) {
+    } else if (node.isOperator || node.isConditional) {
+      // Conditional sends (e?.x) are treated as dynamic property reads because
+      // they are equivalent to do ((a) => a == null ? null : a.x)(e). If `e` is
+      // a type `A`, this is equivalent to write `(A).x`.
+      // TODO(johnniwinther): maybe add DynamicAccess.conditionalDynamicProperty
       return new DynamicAccess.dynamicProperty(node.receiver);
     } else if (Elements.isClosureSend(node, element)) {
       if (element == null) {
         if (node.selector.isThis()) {
           return new AccessSemantics.thisAccess();
         } else {
           return new AccessSemantics.expression();
         }
       } else if (Elements.isErroneous(element)) {
         return new StaticAccess.unresolved(element);
@@ skipping 407 matching lines @@
       return internalError(node, "Unexpected variable $element.");
     }
     if (element.isConst) {
       ConstantExpression constant = elements.getConstant(element.initializer);
       return new ConstantVariableStructure(kind, node, element, constant);
     } else {
       return new NonConstantVariableStructure(kind, node, element);
     }
   }
 }