Add plugin support for command-line access

pkg/analyzer/lib/src/plugin/command_line_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.command_line_plugin;
+
+import 'package:analyzer/plugin/command_line.dart';
+import 'package:plugin/plugin.dart';
+
+/**
+ * A plugin that defines the extension points and extensions that are defined by
+ * command-line applications using the analysis engine.
+ */
+class CommandLinePlugin implements Plugin {
+  /**
+   * The simple identifier of the extension point that allows plugins to
+   * register new parser contributors.
+   */
+  static const String PARSER_CONTRIBUTOR_EXTENSION_POINT = 'parserContributor';
+
+  /**
+   * The simple identifier of the extension point that allows plugins to
+   * register new result processors.
+   */
+  static const String RESULT_PROCESSOR_EXTENSION_POINT = 'resultProcessor';
+
+  /**
+   * The unique identifier of this plugin.
+   */
+  static const String UNIQUE_IDENTIFIER = 'command_line.core';
+
+  /**
+   * The extension point that allows plugins to register new parser
+   * contributors.
+   */
+  ExtensionPoint parserContributorExtensionPoint;
+
+  /**
+   * The extension point that allows plugins to register new result processors.
+   */
+  ExtensionPoint resultProcessorExtensionPoint;
+
+  /**
+   * Initialize a newly created plugin.
+   */
+  CommandLinePlugin();
+
+  /**
+   * Return a list containing all of the parser contributors that were
+   * contributed.
+   */
+  List<ArgParserContributor> get parserContributors =>
+      parserContributorExtensionPoint.extensions;
+
+  /**
+   * Return a list containing all of the result processors that were
+   * contributed.
+   */
+  List<ArgParserContributor> get resultProcessors =>
+      resultProcessorExtensionPoint.extensions;
+
+  @override
+  String get uniqueIdentifier => UNIQUE_IDENTIFIER;
+
+  @override
+  void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
+    parserContributorExtensionPoint = registerExtensionPoint(
+        PARSER_CONTRIBUTOR_EXTENSION_POINT,
+        _validateParserContributorExtension);
+    resultProcessorExtensionPoint = registerExtensionPoint(
+        RESULT_PROCESSOR_EXTENSION_POINT, _validateResultProcessorExtension);
+  }
+
+  @override
+  void registerExtensions(RegisterExtension registerExtension) {
+    // There are no default extensions.
+  }
+
+  /**
+   * Validate the given extension by throwing an [ExtensionError] if it is not a
+   * valid parser contributor.
+   */
+  void _validateParserContributorExtension(Object extension) {
+    if (extension is! ArgParserContributor) {
+      String id = parserContributorExtensionPoint.uniqueIdentifier;
+      throw new ExtensionError(
+          'Extensions to $id must be an ArgParserContributor');
+    }
+  }
+
+  /**
+   * Validate the given extension by throwing an [ExtensionError] if it is not a
+   * valid result processor.
+   */
+  void _validateResultProcessorExtension(Object extension) {
+    if (extension is! ArgResultsProcessor) {
+      String id = resultProcessorExtensionPoint.uniqueIdentifier;
+      throw new ExtensionError(
+          'Extensions to $id must be an ArgResultsProcessor');
+    }
+  }
+}