Error code validation for error filters.

pkg/analysis_server/lib/src/services/linter/linter.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 services.src.linter;
 
 import 'package:analyzer/plugin/options.dart';
 import 'package:analyzer/analyzer.dart';
 import 'package:yaml/yaml.dart';
 import 'package:linter/src/rules.dart';
 import 'package:linter/src/linter.dart';
 
 /**
  * An error code indicating an undefined lint rule.
  *
  * Parameters:
  * 0: the rule name
  */
 const AnalysisOptionsWarningCode UNDEFINED_LINT_WARNING =
     const AnalysisOptionsWarningCode(
-        'UNDEFINED_LINT_WARNING', "Undefined lint rule '{0}'");
+        'UNDEFINED_LINT_WARNING', "'{0}' is not a recognized lint rule");
 
 /// Validates `linter` rule configurations.
 class LinterRuleOptionsValidator extends OptionsValidator {
   static const linter = 'linter';
   static const rulesKey = 'rules';
   @override
   List<AnalysisError> validate(
       ErrorReporter reporter, Map<String, YamlNode> options) {
     List<AnalysisError> errors = <AnalysisError>[];
     var node = options[linter];
@@ skipping 10 matching lines @@
       Iterable<String> registeredLints = ruleRegistry.map((r) => r.name);
       rules.nodes.forEach((YamlNode ruleNode) {
         if (!registeredLints.contains(ruleNode.value)) {
           reporter.reportErrorForSpan(
               UNDEFINED_LINT_WARNING, ruleNode.span, [ruleNode.value]);
         }
       });
     }
   }
 }