Better hints for await in non-async functions

pkg/compiler/lib/src/typechecker.dart

 // Copyright (c) 2012, 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.
 
 part of dart2js;
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
@@ skipping 799 matching lines @@
           case MemberKind.OPERATOR:
             reportTypeWarning(node, MessageKind.OPERATOR_NOT_FOUND,
                 {'className': receiverType.name, 'memberName': name});
             break;
           case MemberKind.GETTER:
             if (lookupMemberSignature(memberName.setter, interface) != null) {
               // A setter is present so warn explicitly about the missing
               // getter.
               reportTypeWarning(node, MessageKind.GETTER_NOT_FOUND,
                   {'className': receiverType.name, 'memberName': name});
+            } else if (name == 'await') {
+              var enclosingFunctionName = executableContext.name;
+              reportTypeWarning(node, MessageKind.AWAIT_MEMBER_NOT_FOUND,
+                  {'className': receiverType.name,
+                   'enclosingFunctionText': enclosingFunctionName == ''
+                       ? 'the enclosing function'
+                       : "'$enclosingFunctionName'"
+                  });
             } else {
               reportTypeWarning(node, MessageKind.MEMBER_NOT_FOUND,
                   {'className': receiverType.name, 'memberName': name});
             }
             break;
           case MemberKind.SETTER:
             reportTypeWarning(node, MessageKind.SETTER_NOT_FOUND,
                 {'className': receiverType.name, 'memberName': name});
             break;
         }
@@ skipping 1017 matching lines @@
 
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     compiler.internalError(node,
         'Unexpected node ${node.getObjectDescription()} in the type checker.');
   }
 }