OptionsValidator plugin extension and linter service.

pkg/analyzer/lib/src/plugin/options_plugin.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.
 
 library analyzer.src.plugin.options;
 
 import 'package:analyzer/plugin/options.dart';
 import 'package:analyzer/plugin/task.dart';
 import 'package:analyzer/src/task/options.dart';
 import 'package:plugin/plugin.dart';
 
 /// A plugin that defines the extension points and extensions that are defined
 /// by applications that want to consume options defined in the analysis
 /// options file.
 class OptionsPlugin implements Plugin {
   /// The simple identifier of the extension point that allows plugins to
   /// register new options processors.
   static const String OPTIONS_PROCESSOR_EXTENSION_POINT = 'optionsProcessor';
 
+  /// The simple identifier of the extension point that allows plugins to
+  /// register new options validators.
+  static const String OPTIONS_VALIDATOR_EXTENSION_POINT = 'optionsValidator';
+
   /// The unique identifier of this plugin.
   static const String UNIQUE_IDENTIFIER = 'options.core';
 
-  /// The extension point that allows plugins to register new options processors.
+  /// The extension point that allows plugins to register new options
+  /// processors.
   ExtensionPoint optionsProcessorExtensionPoint;
 
+  /// The extension point that allows plugins to register new options
+  /// validators.
+  ExtensionPoint optionsValidatorExtensionPoint;
+
   /// All contributed options processors.
   List<OptionsProcessor> get optionsProcessors =>
-      optionsProcessorExtensionPoint == null
-          ? const []
-          : optionsProcessorExtensionPoint.extensions;
+      optionsProcessorExtensionPoint?.extensions ?? const [];
+
+  /// All contributed options validators.
+  List<OptionsValidator> get optionsValidators =>
+      optionsValidatorExtensionPoint?.extensions ?? const [];
 
   @override
   String get uniqueIdentifier => UNIQUE_IDENTIFIER;
 
   @override
   void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
     optionsProcessorExtensionPoint = registerExtensionPoint(
         OPTIONS_PROCESSOR_EXTENSION_POINT, _validateOptionsProcessorExtension);
+    optionsValidatorExtensionPoint = registerExtensionPoint(
+        OPTIONS_VALIDATOR_EXTENSION_POINT, _validateOptionsValidatorExtension);
   }
 
   @override
   void registerExtensions(RegisterExtension registerExtension) {
     // Analyze options files.
     registerExtension(
         TASK_EXTENSION_POINT_ID, GenerateOptionsErrorsTask.DESCRIPTOR);
+    // Validate analyzer analysis options.
+    registerExtension(
+        OPTIONS_VALIDATOR_EXTENSION_POINT_ID, new AnalyzerOptionsValidator());
   }
 
-  /// Validate the given extension by throwing an [ExtensionError] if it is not a
-  /// valid options processor.
+  /// Validate the given extension by throwing an [ExtensionError] if it is not
+  /// a valid options processor.
   void _validateOptionsProcessorExtension(Object extension) {
     if (extension is! OptionsProcessor) {
       String id = optionsProcessorExtensionPoint.uniqueIdentifier;
       throw new ExtensionError('Extensions to $id must be an OptionsProcessor');
     }
   }
+
+  /// Validate the given extension by throwing an [ExtensionError] if it is not
+  /// a valid options validator.
+  void _validateOptionsValidatorExtension(Object extension) {
+    if (extension is! OptionsValidator) {
+      String id = optionsValidatorExtensionPoint.uniqueIdentifier;
+      throw new ExtensionError('Extensions to $id must be an OptionsValidator');
+    }
+  }
 }