Handle parenthesized expression in type promotion.

sdk/lib/_internal/compiler/implementation/typechecker.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 dart2js;
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
@@ skipping 167 matching lines @@
     messages.add(new TypePromotionMessage(api.Diagnostic.HINT,
         spannable, kind, arguments));
   }
 
   void addInfo(Spannable spannable, MessageKind kind, [Map arguments]) {
     messages.add(new TypePromotionMessage(api.Diagnostic.INFO,
         spannable, kind, arguments));
   }
 
   String toString() {
-    return 'Promote ${variable} to ${type}';
+    return 'Promote ${variable} to ${type}${isValid ? '' : ' (invalid)'}';
   }
 }
 
 /// A hint or info message attached to a type promotion.
 class TypePromotionMessage {
   api.Diagnostic diagnostic;
   Spannable spannable;
   MessageKind messageKind;
   Map messageArguments;
 
@@ skipping 204 matching lines @@
         }
         for (Node mutation in mutations) {
           typePromotion.addInfo(mutation,
               MessageKind.POTENTIAL_MUTATION_HERE,
               {'variableName': variableName});
         }
       }
     }
   }
 
-  void reshowTypePromotions(Node node, Node receiver, Node argument) {
-    for (TypePromotion typePromotion in  getShownTypePromotionsFor(receiver)) {
+  /// Show type promotions from [left] and [right] in [node] given that the
+  /// promoted variables are not potentially mutated in [right].
+  void reshowTypePromotions(Node node, Node left, Node right) {
+    for (TypePromotion typePromotion in  getShownTypePromotionsFor(left)) {
       typePromotion = typePromotion.copy();
-      checkTypePromotion(argument, typePromotion);
+      checkTypePromotion(right, typePromotion);
       showTypePromotion(node, typePromotion);
     }
 
-    for (TypePromotion typePromotion in getShownTypePromotionsFor(argument)) {
+    for (TypePromotion typePromotion in getShownTypePromotionsFor(right)) {
       typePromotion = typePromotion.copy();
-      checkTypePromotion(argument, typePromotion);
+      checkTypePromotion(right, typePromotion);
       showTypePromotion(node, typePromotion);
     }
   }
 
   /// Analyze [node] in the context of the known types shown in [context].
   DartType analyzeInPromotedContext(Node context, Node node) {
     Link<TypePromotion> knownForNode = const Link<TypePromotion>();
     for (TypePromotion typePromotion in  getShownTypePromotionsFor(context)) {
       typePromotion = typePromotion.copy();
       checkTypePromotion(node, typePromotion, checkAccesses: true);
@@ skipping 491 matching lines @@
       }
     }
 
     Identifier selector = node.selector.asIdentifier();
     String name = selector.source;
 
     if (node.isOperator && identical(name, 'is')) {
       analyze(node.receiver);
       if (!node.isIsNotCheck) {
         Element variable = elements[node.receiver];
+        if (variable == null) {
+          // Look for the variable element within parenthesized expressions.
+          ParenthesizedExpression parentheses =
+              node.receiver.asParenthesizedExpression();
+          while (parentheses != null) {
+            variable = elements[parentheses.expression];
+            if (variable != null) break;
+            parentheses = parentheses.expression.asParenthesizedExpression();
+          }
+        }
+
         if (variable != null &&
             (variable.isVariable() || variable.isParameter())) {
           DartType knownType = getKnownType(variable);
           if (!knownType.isDynamic) {
             DartType shownType = elements.getType(node.arguments.head);
             TypePromotion typePromotion =
                 new TypePromotion(node, variable, shownType);
             if (!types.isMoreSpecific(shownType, knownType)) {
               String variableName = variable.name;
               // TODO(johnniwinther): Provide a how-to-fix in the case one tries
@@ skipping 459 matching lines @@
       // TODO(karlklose): this should be StatementType.RETURNING unless there
       // is a break in the loop body that has the loop or a label outside the
       // loop as a target.
       return bodyType;
     } else {
       return bodyType.join(StatementType.NOT_RETURNING);
     }
   }
 
   DartType visitParenthesizedExpression(ParenthesizedExpression node) {
-    return analyze(node.expression);
+    Expression expression = node.expression;
+    DartType type = analyze(expression);
+    for (TypePromotion typePromotion in getShownTypePromotionsFor(expression)) {
+      showTypePromotion(node, typePromotion);
+    }
+    return type;
   }
 
   DartType visitConditional(Conditional node) {
     Expression condition = node.condition;
     Expression thenExpression = node.thenExpression;
 
     checkCondition(condition);
 
     DartType thenType = analyzeInPromotedContext(condition, thenExpression);
 
@@ skipping 154 matching lines @@
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     compiler.internalError(
         'Unexpected node ${node.getObjectDescription()} in the type checker.',
         node: node);
   }
 }