Refactor fuzzy arrow hints.

pkg/analyzer/lib/src/dart/error/hint_codes.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 analyzer.src.dart.error.hint_codes;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 
 /**
@@ skipping 20 matching lines @@
    *
    * Parameters:
    * 0: the name of the actual argument type
    * 1: the name of the expected type
    */
   static const HintCode ARGUMENT_TYPE_NOT_ASSIGNABLE = const HintCode(
       'ARGUMENT_TYPE_NOT_ASSIGNABLE',
       "The argument type '{0}' can't be assigned to the parameter type '{1}'.");
 
   /**
+   * This hint is generated when a function type is assigned to a function
+   * typed location, and the assignment will be invalid after fuzzy arrows
+   * (the treatment of dynamic as bottom in certain locations) is removed.
+   *
+   */
+  static const HintCode USES_DYNAMIC_AS_BOTTOM = const HintCode(
+      'USES_DYNAMIC_AS_BOTTOM',
+      "A function of type '{0}' can't be assigned to a variable of type '{1}'.",
+      "Try changing the type of the function, or "
+      "casting the right-hand type to '{1}'.");
+
+  /**
    * When the target expression uses '?.' operator, it can be `null`, so all the
    * subsequent invocations should also use '?.' operator.
    */
   static const HintCode CAN_BE_NULL_AFTER_NULL_AWARE = const HintCode(
       'CAN_BE_NULL_AFTER_NULL_AWARE',
       "The target expression uses '?.', so its value can be null.",
       "Replace the '.' with a '?.' in the invocation.");
 
   /**
    * Dead code is code that is never reached, this can happen for instance if a
@@ skipping 622 matching lines @@
    */
   const HintCode(String name, String message, [String correction])
       : super(name, message, correction);
 
   @override
   ErrorSeverity get errorSeverity => ErrorType.HINT.severity;
 
   @override
   ErrorType get type => ErrorType.HINT;
 }