Support transformers that depend on other transformers.

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 'package:http/http.dart' as http;
 import 'package:scheduled_test/scheduled_process.dart';
@@ skipping 21 matching lines @@
 
   Future apply(Transform transform) {
     return transform.primaryInput.readAsString().then((contents) {
       var id = transform.primaryInput.id.changeExtension(".out");
       transform.addOutput(new Asset.fromString(id, "\$contents.out"));
     });
   }
 }
 """;
 
+/// Returns the source code for a Dart library defining a Transformer that
+/// 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.
+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
+
+const TOKEN = "$id";
+
+final _tokenRegExp = new RegExp(r'^const TOKEN = "(.*?)";\$', multiLine: true);
+
+class DartTransformer extends Transformer {
+  DartTransformer();
+
+  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)";';
+      })));
+    });
+  }
+}
+""";
+}
+
 /// Schedules starting the "pub serve" process.
 ///
 /// If [shouldInstallFirst] is `true`, validates that pub install is run first.
 ///
 /// Returns the `pub serve` process.
 ScheduledProcess startPubServe({bool shouldInstallFirst: false}) {
   // Use port 0 to get an ephemeral port.
   _pubServer = startPub(args: ["serve", "--port=0"]);
 
   if (shouldInstallFirst) {
@@ skipping 61 matching lines @@
     return _pubServer.nextLine().then((line) {
       if (line.contains("successfully")) return;
 
       // This line wasn't it, so ignore it and keep trying.
       return nextLine();
     });
   }
 
   schedule(nextLine);
 }