add support for x-dart-test link tags in the new test package

lib/build/test_compatibility.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.
+
+/// Some Transformers to maintain compatibility with the new `test` package,
+/// since it doesn't use normal dart script tags in html. We get around this by
+/// using two transformers:
+///   - A transformer to convert <lint rel="x-dart-test"> intro dart script tags
+///     so that they can be processed by the rest of the transformers normally.
+///   - A second transformer to convert the output back, so that the `test`
+///     package can find a <link rel="x-dart-test"> tag after all the
+///     transformations are done.
+library web_components.build.test_compatability.dart;
+
+import 'dart:async';
+import 'package:barback/barback.dart';
+import 'package:html/dom.dart';
+import 'package:html/parser.dart';
+
+/// The name of the attribute that will be added to script tags that started out
+/// as <link rel="x-dart-test"> tags.
+const testAttribute = '_was_test';
+
+/// The first transformer that should be ran, this does a query selector for
+/// link[rel="x-dart-test"] and changes them to a normal dart script tag with a
+/// special `_was_test` attribute so we know to change it back later on.
+class RewriteXDartTestToScript extends _EntryPointOnlyTransformer {
+  RewriteXDartTestToScript(List<String> entryPoints) : super(entryPoints);
+
+  Future apply(Transform transform) {
+    return transform.primaryInput.readAsString().then((String html) {
+      var doc = parse(html);
+      for (var tag in doc.querySelectorAll('link[rel="x-dart-test"]')) {
+        tag.replaceWith(new Element.tag('script')
+          ..attributes['type'] = 'application/dart'
+          ..attributes['src'] = tag.attributes['href']
+          ..attributes[testAttribute] = '');
+      }
+      transform.addOutput(
+          new Asset.fromString(transform.primaryInput.id, doc.outerHtml));
+    });
+  }
+}
+
+/// The last transformer that should be ran, this does a query selector for
+/// `script[type="application/dart"][_was_test]` and changes matching elements
+/// back to `<link rel="x-dart-test">` tags.
+class RewriteScriptToXDartTest extends _EntryPointOnlyTransformer {
+  RewriteScriptToXDartTest(List<String> entryPoints) : super(entryPoints);
+
+  Future apply(Transform transform) {
+    return transform.primaryInput.readAsString().then((String html) {
+      var doc = parse(html);
+      var scripts = doc.querySelectorAll(
+          'script[type="application/dart"][$testAttribute]');
+      for (var tag in scripts) {
+        tag.replaceWith(new Element.tag('link')
+          ..attributes['rel'] = 'x-dart-test'
+          ..attributes['href'] = tag.attributes['src']);
+      }
+      transform.addOutput(
+          new Asset.fromString(transform.primaryInput.id, doc.outerHtml));
+    });
+  }
+}
+
+/// Internal base class to encapsulate the isPrimary logic.
+abstract class _EntryPointOnlyTransformer extends Transformer {
+  final List<String> entryPoints;
+
+  _EntryPointOnlyTransformer(this.entryPoints) : super();
+
+  bool isPrimary(AssetId id) {
+    if (!id.path.startsWith('test/')) return false;
+    if (entryPoints != null) return entryPoints.contains(id.path);
+    // If no entry point is supplied, then any html file is an entry point.
+    return id.path.endsWith('.html');
+  }
+}