Load instances of the same transformer from the same isolate.

sdk/lib/_internal/pub/test/serve/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 80 matching lines @@
 /// rewrites Dart files.
 ///
 /// The transformer defines a constant named TOKEN whose value is [id]. When the
 /// transformer transforms another Dart file, it will look for a "TOKEN"
 /// constant definition there and modify it to include *this* transformer's
 /// TOKEN value as well.
 ///
 /// If [import] is passed, it should be the name of a package that defines its
 /// own TOKEN constant. The primary library of that package will be imported
 /// here and its TOKEN value will be added to this library's.
+///
+/// This transformer takes one configuration field: "addition". This is
+/// concatenated to its TOKEN value before adding it to the output library.
 String dartTransformer(String id, {String import}) {
   if (import != null) {
     id = '$id imports \${$import.TOKEN}';
     import = 'import "package:$import/$import.dart" as $import;';
   } else {
     import = '';
   }
 
   return """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 $import
 
+import 'dart:io';
+
 const TOKEN = "$id";
 
 final _tokenRegExp = new RegExp(r'^const TOKEN = "(.*?)";\$', multiLine: true);
 
 class DartTransformer extends Transformer {
-  DartTransformer.asPlugin();
+  final BarbackSettings _settings;
+
+  DartTransformer.asPlugin(this._settings);
 
   String get allowedExtensions => '.dart';
 
   Future apply(Transform transform) {
     return transform.primaryInput.readAsString().then((contents) {
       transform.addOutput(new Asset.fromString(transform.primaryInput.id,
           contents.replaceAllMapped(_tokenRegExp, (match) {
-        return 'const TOKEN = "(\${match[1]}, \$TOKEN)";';
+        var token = TOKEN;
+        var addition = _settings.configuration["addition"];
+        if (addition != null) token += addition;
+        return 'const TOKEN = "(\${match[1]}, \$token)";';
       })));
     });
   }
 }
 """;
 }
 
 /// Schedules starting the `pub serve` process.
 ///
 /// Unlike [pubServe], this doesn't determine the port number of the server, and
@@ skipping 338 matching lines @@
 /// included. Unlike [getServerUrl], this should only be called after the ports
 /// are known.
 String _getServerUrlSync([String root, String path]) {
   if (root == null) root = 'web';
   expect(_ports, contains(root));
   var url = "http://localhost:${_ports[root]}";
   if (path != null) url = "$url/$path";
   return url;
 }