add initWebComponents

lib/src/mirror_initializer.dart

Index: lib/src/mirror_initializer.dart
diff --git a/lib/src/mirror_initializer.dart b/lib/src/mirror_initializer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..652031f71349a7677c3cd460fe398fb61c65ee4f
--- /dev/null
+++ b/lib/src/mirror_initializer.dart
@@ -0,0 +1,130 @@
+// Copyright (c) 2014, 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.
+
+/// Contains logic to initialize web_components apps during development. This
+/// implementation uses dart:mirrors to load each library as they are discovered
+/// through HTML imports. This is only meant to be used during development in
+/// dartium, and the web_components transformers replace this implementation
+/// for deployment.
+library web_components.src.mirror_initializer;
+
+import 'dart:async';
+import 'dart:collection' show LinkedHashMap;
+import 'dart:mirrors';
+import 'dart:html';
+import 'package:initialize/initialize.dart' as init;
+
+Future run({List<Type> typeFilter, init.InitializerFilter customFilter}) async {
+  var libraryUris = _discoverLibrariesToLoad(document, window.location.href)
+      .map(Uri.parse);
+
+  for (var uri in libraryUris) {
+    await init.run(
+        typeFilter: typeFilter, customFilter: customFilter, from: uri);
+  }
+  return null;
+}
+
+/// Walks the HTML import structure to discover all script tags that are
+/// implicitly loaded. This code is only used in Dartium and should only be
+/// called after all HTML imports are resolved. Polymer ensures this by asking
+/// users to put their Dart script tags after all HTML imports (this is checked
+/// by the linter, and Dartium will otherwise show an error message).
+Iterable<_ScriptInfo> _discoverScripts(
+    Document doc, String baseUri, [_State state]) {
+  if (state == null) state = new _State();
+  if (doc == null) {
+    print('warning: $baseUri not found.');
+    return state.scripts.values;
+  }
+  if (!state.seen.add(doc)) return state.scripts.values;
+
+  for (var node in doc.querySelectorAll('script,link[rel="import"]')) {
+    if (node is LinkElement) {
+      _discoverScripts(node.import, node.href, state);
+    } else if (node is ScriptElement && node.type == 'application/dart') {
+      var info = _scriptInfoFor(node, baseUri);
+      if (state.scripts.containsKey(info.resolvedUrl)) {
+        // TODO(jakemac): Move this to a web_components uri.
+        print('warning: Script `${info.resolvedUrl}` included more than once. '
+            'See http://goo.gl/5HPeuP#polymer_44 for more details.');
+      } else {
+        state.scripts[info.resolvedUrl] = info;
+      }
+    }
+  }
+  return state.scripts.values;
+}
+
+/// Internal state used in [_discoverScripts].
+class _State {
+  /// Documents that we have visited thus far.
+  final Set<Document> seen = new Set();
+
+  /// Scripts that have been discovered, in tree order.
+  final LinkedHashMap<String, _ScriptInfo> scripts = {};
+}
+
+/// Holds information about a Dart script tag.
+class _ScriptInfo {
+  /// The original URL seen in the tag fully resolved.
+  final String resolvedUrl;
+
+  /// Whether it seems to be a 'package:' URL (starts with the package-root).
+  bool get isPackage => packageUrl != null;
+
+  /// The equivalent 'package:' URL, if any.
+  final String packageUrl;
+
+  _ScriptInfo(this.resolvedUrl, {this.packageUrl});
+}
+
+
+// TODO(sigmund): explore other (cheaper) ways to resolve URIs relative to the
+// root library (see dartbug.com/12612)
+final _rootUri = currentMirrorSystem().isolate.rootLibrary.uri;
+
+/// Returns [_ScriptInfo] for [script] which was seen in [baseUri].
+_ScriptInfo _scriptInfoFor(script, baseUri) {
+  var uriString = script.src;
+  if (uriString != '') {
+    var uri = _rootUri.resolve(uriString);
+    if (!_isHttpStylePackageUrl(uri)) return new _ScriptInfo('$uri');
+    // Use package: urls if available. This rule here is more permissive than
+    // how we translate urls in polymer-build, but we expect Dartium to limit
+    // the cases where there are differences. The polymer-build issues an error
+    // when using packages/ inside lib without properly stepping out all the way
+    // to the packages folder. If users don't create symlinks in the source
+    // tree, then Dartium will also complain because it won't find the file seen
+    // in an HTML import.
+    var packagePath = uri.path.substring(
+        uri.path.lastIndexOf('packages/') + 'packages/'.length);
+    return new _ScriptInfo('$uri', packageUrl: 'package:$packagePath');
+  }
+
+  // Even in the case of inline scripts its ok to just use the baseUri since
+  // there can only be one per page.
+  return new _ScriptInfo(baseUri);
+}
+
+/// Whether [uri] is an http URI that contains a 'packages' segment, and
+/// therefore could be converted into a 'package:' URI.
+bool _isHttpStylePackageUrl(Uri uri) {
+  var uriPath = uri.path;
+  return uri.scheme == _rootUri.scheme &&
+      // Don't process cross-domain uris.
+      uri.authority == _rootUri.authority &&
+      uriPath.endsWith('.dart') &&
+      (uriPath.contains('/packages/') || uriPath.startsWith('packages/'));
+}
+
+Iterable<String> _discoverLibrariesToLoad(Document doc, String baseUri) =>
+    _discoverScripts(doc, baseUri).map(
+        (info) => _packageUrlExists(info) ? info.packageUrl : info.resolvedUrl);
+
+/// All libraries in the current isolate.
+final _libs = currentMirrorSystem().libraries;
+
+bool _packageUrlExists(_ScriptInfo info) =>
+    info.isPackage && _libs[Uri.parse(info.packageUrl)] != null;