Await cancellation in the Kernel await transformer

pkg/kernel/lib/transformations/continuation.dart

 // Copyright (c) 2016, 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.
 
 library kernel.transformations.continuation;
 
 import 'dart:math' as math;
 
 import '../ast.dart';
 import '../core_types.dart';
@@ skipping 536 matching lines @@
       // To:
       //
       //   {
       //     var :for-iterator = new StreamIterator(<stream-expression>);
       //     try {
       //       while (await :for-iterator.moveNext()) {
       //         var <variable> = :for-iterator.current;
       //         ...
       //       }
       //     } finally {
-      //       :for-iterator.cancel();
+      //       await :for-iterator.cancel();
       //     }
       //   }
       var iteratorVariable = new VariableDeclaration(':for-iterator',
           initializer: new ConstructorInvocation(
               helper.streamIteratorConstructor,
               new Arguments(<Expression>[stmt.iterable],
                   types: [const DynamicType()])));
 
       // await iterator.moveNext()
       var condition = new AwaitExpression(new MethodInvocation(
           new VariableGet(iteratorVariable),
           new Name('moveNext'),
           new Arguments(<Expression>[])))..fileOffset = stmt.fileOffset;
 
       // var <variable> = iterator.current;
       var valueVariable = stmt.variable;
       valueVariable.initializer = new PropertyGet(
           new VariableGet(iteratorVariable), new Name('current'));
       valueVariable.initializer.parent = valueVariable;
 
       var whileBody = new Block(<Statement>[valueVariable, stmt.body]);
       var tryBody = new WhileStatement(condition, whileBody);
 
       // iterator.cancel();
-      var tryFinalizer = new ExpressionStatement(new MethodInvocation(
-          new VariableGet(iteratorVariable),
-          new Name('cancel'),
-          new Arguments(<Expression>[])));
+      var tryFinalizer = new ExpressionStatement(new AwaitExpression(
+          new MethodInvocation(new VariableGet(iteratorVariable),
+              new Name('cancel'), new Arguments(<Expression>[]))));
 
       var tryFinally = new TryFinally(tryBody, tryFinalizer);
 
       var block = new Block(<Statement>[iteratorVariable, tryFinally]);
       block.accept(this);
     } else {
       stmt.iterable = expressionRewriter.rewrite(stmt.iterable, statements)
         ..parent = stmt;
       stmt.body = visitDelimited(stmt.body)..parent = stmt;
       statements.add(stmt);
@@ skipping 318 matching lines @@
         coreTypes.getMember('dart:core', '_SyncIterable', ''),
         coreTypes.getMember('dart:async', '_StreamIterator', ''),
         coreTypes.getMember('dart:async', 'Future', 'microtask'),
         coreTypes.getMember('dart:async', '_AsyncStarStreamController', ''),
         coreTypes.getTopLevelMember('dart:async', '_asyncThenWrapperHelper'),
         coreTypes.getTopLevelMember('dart:async', '_asyncErrorWrapperHelper'),
         coreTypes.getTopLevelMember('dart:async', '_awaitHelper'),
         coreTypes);
   }
 }