refactor DDC to support --ignore-unrecognized-flags

pkg/analyzer/lib/src/command_line/command_line_parser.dart

-// Copyright (c) 2016, 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.
-
-import 'package:args/args.dart';
-
-/**
- * Commandline argument parser.
- *
- * TODO(pq): when the args package supports ignoring unrecognized options/flags,
- * this class can be replaced with a simple [ArgParser] instance.
- */
-class CommandLineParser {
-  static const String IGNORE_UNRECOGNIZED_FLAG = 'ignore-unrecognized-flags';
-
-  final List<String> _knownFlags;
-  final bool _alwaysIgnoreUnrecognized;
-  final ArgParser _parser;
-
-  /// Creates a new command line parser.
-  CommandLineParser({bool alwaysIgnoreUnrecognized: false})
-      : _knownFlags = <String>[],
-        _alwaysIgnoreUnrecognized = alwaysIgnoreUnrecognized,
-        _parser = new ArgParser(allowTrailingOptions: true) {
-    addFlag(IGNORE_UNRECOGNIZED_FLAG,
-        help: 'Ignore unrecognized command line flags.',
-        defaultsTo: false,
-        negatable: false);
-  }
-
-  ArgParser get parser => _parser;
-
-  /// Defines a flag.
-  /// See [ArgParser.addFlag()].
-  void addFlag(String name,
-      {String abbr,
-      String help,
-      bool defaultsTo: false,
-      bool negatable: true,
-      void callback(bool value),
-      bool hide: false}) {
-    _knownFlags.add(name);
-    _parser.addFlag(name,
-        abbr: abbr,
-        help: help,
-        defaultsTo: defaultsTo,
-        negatable: negatable,
-        callback: callback,
-        hide: hide);
-  }
-
-  /// Defines a value-taking option.
-  /// See [ArgParser.addOption()].
-  void addOption(String name,
-      {String abbr,
-      String help,
-      List<String> allowed,
-      Map<String, String> allowedHelp,
-      String defaultsTo,
-      void callback(value),
-      bool allowMultiple: false,
-      bool splitCommas,
-      bool hide: false}) {
-    _knownFlags.add(name);
-    _parser.addOption(name,
-        abbr: abbr,
-        help: help,
-        allowed: allowed,
-        allowedHelp: allowedHelp,
-        defaultsTo: defaultsTo,
-        callback: callback,
-        allowMultiple: allowMultiple,
-        splitCommas: splitCommas,
-        hide: hide);
-  }
-
-  /// Parses [args], a list of command-line arguments, matches them against the
-  /// flags and options defined by this parser, and returns the result.
-  /// See [ArgParser].
-  ArgResults parse(List<String> args) => _parser.parse(_filterUnknowns(args));
-
-  List<String> _filterUnknowns(List<String> args) {
-    if (!_alwaysIgnoreUnrecognized &&
-        !args.contains('--$IGNORE_UNRECOGNIZED_FLAG')) {
-      return args;
-    }
-
-    //TODO(pquitslund): replace w/ the following once library skew issues are
-    // sorted out
-    //return args.where((arg) => !arg.startsWith('--') ||
-    //  _knownFlags.contains(arg.substring(2)));
-
-    // Filter all unrecognized flags and options.
-    List<String> filtered = <String>[];
-    for (int i = 0; i < args.length; ++i) {
-      String arg = args[i];
-      if (arg.startsWith('--') && arg.length > 2) {
-        String option = arg.substring(2);
-        // strip the last '=value'
-        int equalsOffset = option.lastIndexOf('=');
-        if (equalsOffset != -1) {
-          option = option.substring(0, equalsOffset);
-        }
-        // Check the option
-        if (!_knownFlags.contains(option)) {
-          //"eat" params by advancing to the next flag/option
-          i = _getNextFlagIndex(args, i);
-        } else {
-          filtered.add(arg);
-        }
-      } else {
-        filtered.add(arg);
-      }
-    }
-
-    return filtered;
-  }
-
-  int _getNextFlagIndex(args, i) {
-    for (; i < args.length; ++i) {
-      if (args[i].startsWith('--')) {
-        return i;
-      }
-    }
-    return i;
-  }
-}