Introduce boot.js: this finally makes it possible to load and run Todomvc

lib/polymer.dart

Index: lib/polymer.dart
diff --git a/lib/polymer.dart b/lib/polymer.dart
index b81a01d3001886e591acfc09832317ca57c5e804..c949a496aef00d73ddcebf859d63c681413efd17 100644
--- a/lib/polymer.dart
+++ b/lib/polymer.dart
@@ -11,10 +11,131 @@
  */
 library polymer;
 
-export 'custom_element.dart';
+import 'dart:async';
+import 'dart:mirrors';
+
+import 'package:mdv/mdv.dart' as mdv;
+import 'package:observe/observe.dart' show Observable;
+import 'package:path/path.dart' as path;
+import 'polymer_element.dart' show registerPolymerElement;
+
+export 'package:custom_element/custom_element.dart';
+export 'package:observe/observe.dart';
+
 export 'event.dart';
 export 'observe.dart';
 export 'observe_html.dart';
 export 'polymer_element.dart';
 export 'safe_html.dart';
 export 'scoped_css.dart';
+
+
+/** Annotation used to automatically register polymer elements. */
+class CustomTag {
+  final String tagName;
+  const CustomTag(this.tagName);
+}
+
+/**
+ * Metadata used to label static or top-level methods that are called
+ * automatically when loading the library of a custom element.
+ */
+const polymerInitMethod = const _InitPolymerAnnotation();
+
+/**
+ * Initializes a polymer application by: setting up polling for observable
+ * changes, initializing MDV, registering and initializing custom elements from
+ * each library in [elementLibraries], and finally invoking [userMain].
+ *
+ * There are two mechanisms by which custom elements can be initialized:
+ * annotating the class that declares a custom element with [CustomTag] or
+ * programatically registering the element in a static or top-level function and
+ * annotating that function with [polymerInitMethod].
+ *
+ * The urls in [elementLibraries] can be absolute or relative to [srcUrl].
+ */
+initPolymer(List<String> elementLibraries, void userMain(), [String srcUrl]) {
+  new Timer.periodic(new Duration(milliseconds: 125),
+      (_) => Observable.dirtyCheck());
+
+  // TODO(jmesserly): mdv should use initMdv instead of mdv.initialize.
+  mdv.initialize();
+  for (var lib in elementLibraries) {
+    _registerPolymerElementsOf(lib, srcUrl);
+  }
+  userMain();
+}
+
+/** All libraries in the current isolate. */
+var _libs = currentMirrorSystem().libraries;
+
+/**
+ * Reads the library at [uriString] (which can be an absolute URI or a relative
+ * URI from [srcUrl]), and:
+ *
+ *   * Invokes top-level and static functions marked with the
+ *     [polymerInitMethod] annotation.
+ *
+ *   * Registers any [PolymerElement] that is marked with the [CustomTag]
+ *     annotation.
+ */
+void _registerPolymerElementsOf(String uriString, [String srcUrl]) {
+  var uri = Uri.parse(uriString);
+  if (uri.scheme == '' && srcUrl != null) {
+    uri = Uri.parse(path.normalize(path.join(path.dirname(srcUrl), uriString)));
+  }
+  var lib = _libs[uri];
+  if (lib == null) {
+    print('warning: $uri library not found');
+    return;
+  }
+
+  // Search top-level functions marked with @polymerInitMethod
+  for (var f in lib.functions.values) {
+    _maybeInvoke(lib, f);
+  }
+
+  for (var c in lib.classes.values) {
+    // Search for @CustomTag on classes
+    for (var m in c.metadata) {
+      var meta = m.reflectee;
+      if (meta is CustomTag) {
+        registerPolymerElement(meta.tagName,
+            () => c.newInstance(const Symbol(''), const []).reflectee);
+      }
+    }
+
+    // TODO(sigmund): check also static methods marked with @polymerInitMethod.
+    // This is blocked on two bugs:
+    //  - dartbug.com/12133 (static methods are incorrectly listed as top-level
+    //    in dart2js, so they end up being called twice)
+    //  - dartbug.com/12134 (sometimes "method.metadata" throws an exception,
+    //    we could wrap and hide those exceptions, but it's not ideal).
+  }
+}
+
+void _maybeInvoke(ObjectMirror obj, MethodMirror method) {
+  var annotationFound = false;
+  for (var meta in method.metadata) {
+    if (identical(meta.reflectee, polymerInitMethod)) {
+      annotationFound = true;
+      break;
+    }
+  }
+  if (!annotationFound) return;
+  if (!method.isStatic) {
+    print("warning: methods marked with @polymerInitMethod should be static,"
+        " ${method.simpleName} is not.");
+    return;
+  }
+  if (!method.parameters.where((p) => !p.isOptional).isEmpty) {
+    print("warning: methods marked with @polymerInitMethod should take no "
+        "arguments, ${method.simpleName} expects some.");
+    return;
+  }
+  obj.invoke(method.simpleName, const []);
+}
+
+class _InitPolymerAnnotation {
+  const _InitPolymerAnnotation();
+}