[kernel] set dartAsyncMarker to Sync for continuations

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 110 matching lines @@
         super(helper, enclosingFunction);
 
   FunctionNode rewrite() {
     // :sync_body(:iterator) {
     //     modified <node.body>;
     // }
     final nestedClosureVariable = new VariableDeclaration(":sync_op");
     final function = new FunctionNode(buildClosureBody(),
         positionalParameters: [iteratorVariable],
         requiredParameterCount: 1,
-        asyncMarker: AsyncMarker.SyncYielding)
+        asyncMarker: AsyncMarker.SyncYielding,
+        dartAsyncMarker: AsyncMarker.Sync)

[Kevin Millikin (Google), 2017/03/13 11:20:35]

This is a fresh function that doesn't correspond directly to any Dart function,
so thinking about its async marker is weird.

We need a comment here explaining why we chose sync and what the consequences
are.  You could say: "SyncYielding functions have no Dart equivalent.  Since
they are synchronous, we use Sync.  (The Dart VM backend uses the Dart async
marker to decide if functions are debuggable.)

Really, this suggests to me that we should consider bringing back is_debuggable
as a separate bit on functions, if we want to hide some but not all of them from
the debugger.

       ..fileOffset = enclosingFunction.fileOffset
       ..fileEndOffset = enclosingFunction.fileEndOffset
       ..returnType = helper.coreTypes.boolClass.rawType;
 
     final closureFunction =
         new FunctionDeclaration(nestedClosureVariable, function)
           ..fileOffset = enclosingFunction.parent.fileOffset;
 
     // return new _SyncIterable(:sync_body);
     final arguments = new Arguments([new VariableGet(nestedClosureVariable)]);
@@ skipping 77 matching lines @@
     //     modified <node.body>;
     // }
     final parameters = <VariableDeclaration>[
       expressionRewriter.asyncResult,
       new VariableDeclaration(':exception'),
       new VariableDeclaration(':stack_trace'),
     ];
     final function = new FunctionNode(buildWrappedBody(),
         positionalParameters: parameters,
         requiredParameterCount: 0,
-        asyncMarker: AsyncMarker.SyncYielding)
+        asyncMarker: AsyncMarker.SyncYielding,
+        dartAsyncMarker: AsyncMarker.Sync)
       ..fileOffset = enclosingFunction.fileOffset
       ..fileEndOffset = enclosingFunction.fileEndOffset;
 
     // The await expression lifter might have created a number of
     // [VariableDeclarations].
     // TODO(kustermann): If we didn't need any variables we should not emit
     // these.
     statements.addAll(variableDeclarations());
     statements.addAll(expressionRewriter.variables);
 
@@ skipping 664 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);
   }
 }