Stop propagating return types for top-level function declarations

pkg/analyzer/test/generated/incremental_resolver_test.dart

 // Copyright (c) 2014, 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 engine.incremental_resolver_test;
 
 import 'package:analyzer/src/context/cache.dart' as task;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 2328 matching lines @@
 }
 ''',
         r'''
 class A {
   final field;
   A(this.field(int a, String b));
 }
 ''');
   }
 
+  void test_true_functionExpression() {
+    _assertMatches(r'''
+import 'dart:async';
+
+class A {
+  Future<int> mmm() async {
+    return 42;
+  }
+
+  a() {
+    mmm().then((p1) {
+      return p1.toString();
+    }).then((p2) {
+      print(p2);
+    });
+  }
+}
+''', r'''import 'dart:async';
+
+class A {
+  Future<int> mmm() async {
+    return 42;
+  }
+
+  a() {
+    mmm().then((int p1) {
+      return p1.toString();
+    }).then((String p2) {
+      print(p2);
+    });
+  }
+}
+''');
+  }
+
   void test_true_functionTypeAlias_list_reorder() {
     _assertMatches(
         r'''
 typedef A(int pa);
 typedef B(String pb);
 typedef C(pc);
 ''',
         r'''
 typedef C(pc);
 typedef A(int pa);
@@ skipping 2331 matching lines @@
     return ResolutionContextBuilder.contextFor(node, listener).scope;
   }
 }
 
 class _Edit {
   final int offset;
   final int length;
   final String replacement;
   _Edit(this.offset, this.length, this.replacement);
 }