Fix summary type inference of async closures.

pkg/analyzer/lib/src/summary/link.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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 2844 matching lines @@
       _functions ??= _variable.unlinkedVariable.initializer.localFunctions
           .map((UnlinkedExecutable ex) =>
               new FunctionElementForLink_Local_NonSynthetic(
                   _variable.compilationUnit, this, ex))
           .toList();
 
   @override
   String get identifier => '';
 
   @override
+  bool get isAsynchronous => _unlinkedExecutable.isAsynchronous;
+
+  @override
   DartType get returnType {
     // If this is a variable whose type needs inferring, infer it.
     if (_variable.hasImplicitType) {
       return _variable.inferredType;
     } else {
       // There's no reason linking should need to access the type of
       // this FunctionElement, since the variable doesn't need its
       // type inferred.
       assert(false);
       // But for robustness, return the dynamic type.
@@ skipping 115 matching lines @@
     Element enclosing = this.enclosingElement;
     if (enclosing is ExecutableElement) {
       int id =
           ElementImpl.findElementIndexUsingIdentical(enclosing.functions, this);
       identifier += "@$id";
     }
     return identifier;
   }
 
   @override
+  bool get isAsynchronous => _unlinkedExecutable.isAsynchronous;
+
+  @override
   bool get _hasTypeBeenInferred => _inferredReturnType != null;
 
   @override
   DartType buildType(
       DartType getTypeArgument(int i), List<int> implicitFunctionTypeIndices) {
     assert(implicitFunctionTypeIndices.isEmpty);
     return type;
   }
 
   @override
@@ skipping 1632 matching lines @@
     List<TypeInferenceNode> dependencies = <TypeInferenceNode>[];
     collectDependencies(dependencies, functionElement._unlinkedExecutable,
         functionElement.compilationUnit);
     return dependencies;
   }
 
   void evaluate(bool inCycle) {
     if (inCycle) {
       functionElement._setInferredType(DynamicTypeImpl.instance);
     } else {
-      functionElement
-          ._setInferredType(new ExprTypeComputer(functionElement).compute());
+      var bodyType = new ExprTypeComputer(functionElement).compute();
+      if (functionElement.isAsynchronous) {
+        var linker = functionElement.compilationUnit.library._linker;
+        var typeProvider = linker.typeProvider;
+        var typeSystem = linker.typeSystem;
+        bodyType = typeProvider.futureType
+            .instantiate([bodyType.flattenFutures(typeSystem)]);
+      }
+      functionElement._setInferredType(bodyType);
     }
   }
 
   @override
   String toString() => 'TypeInferenceNode($functionElement)';
 }
 
 class TypeProviderForLink extends TypeProviderBase {
   final Linker _linker;
 
@@ skipping 306 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }