Options plugin API.

pkg/analyzer/lib/src/plugin/options_plugin.dart

Index: pkg/analyzer/lib/src/plugin/options_plugin.dart
diff --git a/pkg/analyzer/lib/src/plugin/options_plugin.dart b/pkg/analyzer/lib/src/plugin/options_plugin.dart
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+// 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: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 unique identifier of this plugin.
+  static const String UNIQUE_IDENTIFIER = 'options.core';
+
+  /// The extension point that allows plugins to register new options processors.
+  ExtensionPoint optionsProcessorExtensionPoint;
+
+  /// All contributed options processors.
+  List<OptionsProcessor> get optionsProcessors =>
+      optionsProcessorExtensionPoint.extensions;
+
+  @override
+  String get uniqueIdentifier => UNIQUE_IDENTIFIER;
+
+  @override
+  void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
+    optionsProcessorExtensionPoint = registerExtensionPoint(
+        OPTIONS_PROCESSOR_EXTENSION_POINT, _validateOptionsProcessorExtension);
+  }
+
+  @override
+  void registerExtensions(RegisterExtension registerExtension) {
+    // There are no default extensions.
+  }
+
+  /// 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');
+    }
+  }
+}