Introduce element categories and move resolver towards being more compositional.

dart/frog/leg/warnings.dart

 // Copyright (c) 2011, 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.
 
 class MessageKind {
   final String template;
   const MessageKind(this.template);
 
   static final GENERIC = const MessageKind('#{1}');
 
@@ skipping 28 matching lines @@
   static final CANNOT_RESOLVE = const MessageKind(
       'cannot resolve #{1}');
   static final CANNOT_RESOLVE_CONSTRUCTOR = const MessageKind(
       'cannot resolve constructor #{1}');
   static final CANNOT_RESOLVE_TYPE = const MessageKind(
       'cannot resolve type #{1}');
   static final DUPLICATE_DEFINITION = const MessageKind(
       'duplicate definition of #{1}');
   static final NOT_A_TYPE = const MessageKind(
       '#{1} is not a type');
+  static final NOT_A_PREFIX = const MessageKind(
+      '#{1} is not a prefix');
   static final NO_SUPER_IN_OBJECT = const MessageKind(
       "'Object' does not have a superclass");
   static final CANNOT_FIND_CONSTRUCTOR = const MessageKind(
       'cannot find constructor #{1}');
   static final CANNOT_FIND_CONSTRUCTOR2 = const MessageKind(
       'cannot find constructor #{1} or #{2}');
   static final CYCLIC_CLASS_HIERARCHY = const MessageKind(
       '#{1} creates a cycle in the class hierarchy');
   static final INVALID_RECEIVER_IN_INITIALIZER = const MessageKind(
       'field initializer expected');
@@ skipping 48 matching lines @@
   static final NO_CONTINUE_TARGET = const MessageKind(
       'continue statement not inside loop');
   static final EXISTING_LABEL = const MessageKind(
       'original declaration of duplicate label #{1}');
   static final DUPLICATE_LABEL = const MessageKind(
       'duplicate declaration of label #{1}');
   static final UNUSED_LABEL = const MessageKind(
       'unused label #{1}');
   static final INVALID_CONTINUE = const MessageKind(
       'target of continue is not a loop or switch case');
+  static final INVALID_USE_OF_SUPER = const MessageKind(
+      'super not allowed here');
 
   static final NOT_A_COMPILE_TIME_CONSTANT = const MessageKind(
       'not a compile-time constant');
 
   static final NO_SUCH_LIBRARY_MEMBER = const MessageKind(
       '#{1} has no member named #{2}');
 
   static final CANNOT_INSTANTIATE_INTERFACE = const MessageKind(
       "cannot instantiate interface '#{1}'");
 
@@ skipping 63 matching lines @@
   String toString() => message.toString();
 }
 
 class CompileTimeConstantError {
   final Message message;
   CompileTimeConstantError.message(this.message);
   CompileTimeConstantError(MessageKind kind, List<Type> arguments)
     : message = new Message(kind, arguments);
   String toString() => message.toString();
 }