Infer Null for return type of functions with empty returns.

pkg/analyzer/lib/src/task/strong/checker.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 35 matching lines @@
 DartType _elementType(Element e) {
   if (e == null) {
     // Malformed code - just return dynamic.
     return DynamicTypeImpl.instance;
   }
   return (e as dynamic).type;
 }
 
 Element _getKnownElement(Expression expression) {
   if (expression is ParenthesizedExpression) {
-    expression = (expression as ParenthesizedExpression).expression;
-  }
-  if (expression is FunctionExpression) {
+    return _getKnownElement(expression.expression);
+  } else if (expression is NamedExpression) {

[Leaf, 2017/02/06 18:27:15]

This fixes 28630, where we were not treating named parameters as concrete
functions.

[Jennifer Messerly, 2017/02/06 20:08:09]

wow this bug has been here for like ever. nice fix!

+    return _getKnownElement(expression.expression);
+  } else if (expression is FunctionExpression) {
     return expression.element;
   } else if (expression is PropertyAccess) {
     return expression.propertyName.staticElement;
   } else if (expression is Identifier) {
     return expression.staticElement;
   }
   return null;
 }
 
 /// Return the field on type corresponding to member, or null if none
@@ skipping 1423 matching lines @@
     var visited = new Set<InterfaceType>();
     do {
       visited.add(current);
       current.mixins.reversed.forEach(
           (m) => _checkIndividualOverridesFromClass(node, m, seen, true));
       _checkIndividualOverridesFromClass(node, current.superclass, seen, true);
       current = current.superclass;
     } while (!current.isObject && !visited.contains(current));
   }
 }