Fix for filtering unknown options.

pkg/analyzer/lib/options.dart

 // Copyright (c) 2013, 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 options;
 
 import 'dart:io';
 
 import 'package:args/args.dart';
 
@@ skipping 378 matching lines @@
         }
       } else if (arg.startsWith("-D")) {
         definedVariables[arg.substring(2)] = args[++i];
       } else {
         remainingArgs.add(arg);
       }
     }
     return remainingArgs;
   }
 
-  List<String> _filterUnknowns(args) {
+  List<String> _filterUnknowns(List<String> args) {
 
     // Only filter args if the ignore flag is specified, or if
     // _alwaysIgnoreUnrecognized was set to true
     if (_alwaysIgnoreUnrecognized ||
         args.contains('--ignore-unrecognized-flags')) {
 
       //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.
-      var filtered = <String>[];
-      for (var i = 0; i < args.length; ++i) {
-        var arg = args[i];
+      List<String> filtered = <String>[];
+      for (int i = 0; i < args.length; ++i) {
+        String arg = args[i];
         if (arg.startsWith('--') && arg.length > 2) {
-          if (!_knownFlags.contains(arg.substring(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)) {
             //print('remove: $arg');
             //"eat" params by advancing to the next flag/option
             i = _getNextFlagIndex(args, i);
           } else {
             filtered.add(arg);
           }
         } else {
           filtered.add(arg);
         }
       }
 
       return filtered;
     } else {
       return args;
     }
   }
 
   _getNextFlagIndex(args, i) {
     for ( ; i < args.length; ++i) {
       if (args[i].startsWith('--')) {
         return i;
       }
     }
     return i;
   }
 }