Rationalize Dart mojo and sky package structure

sky/framework/fn.dart

Index: sky/framework/fn.dart
diff --git a/sky/framework/fn.dart b/sky/framework/fn.dart
deleted file mode 100644
index 427e4da8fd7f9cc7691af7965176ad4e42867970..0000000000000000000000000000000000000000
--- a/sky/framework/fn.dart
+++ /dev/null
@@ -1,924 +0,0 @@
-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-library fn;
-
-import 'dart:async';
-import 'dart:collection';
-import 'dart:sky' as sky;
-import 'reflect.dart' as reflect;
-import 'layout.dart';
-
-export 'layout.dart' show Style;
-
-final sky.Tracing _tracing = sky.window.tracing;
-
-final bool _shouldLogRenderDuration = false;
-final bool _shouldTrace = false;
-
-enum _SyncOperation { IDENTICAL, INSERTION, STATEFUL, STATELESS, REMOVAL }
-
-/*
- * All Effen nodes derive from UINode. All nodes have a _parent, a _key and
- * can be sync'd.
- */
-abstract class UINode {
-  String _key;
-  UINode _parent;
-  UINode get parent => _parent;
-  RenderCSS _root;
-  bool _defunct = false;
-
-  UINode({ Object key }) {
-    _key = key == null ? "$runtimeType" : "$runtimeType-$key";
-  }
-
-  // Subclasses which implements Nodes that become stateful may return true
-  // if the |old| node has become stateful and should be retained.
-  bool _willSync(UINode old) => false;
-
-  bool get interchangeable => false; // if true, then keys can be duplicated
-
-  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore);
-
-  void _remove() {
-    _defunct = true;
-    _root = null;
-    handleRemoved();
-  }
-  void handleRemoved() { }
-
-  int _nodeDepth;
-  void _ensureDepth() {
-    if (_nodeDepth == null) {
-      if (_parent != null) {
-        _parent._ensureDepth();
-        _nodeDepth = _parent._nodeDepth + 1;
-      } else {
-        _nodeDepth = 0;
-      }
-    }
-  }
-
-  void _trace(String message) {
-    if (!_shouldTrace)
-      return;
-
-    _ensureDepth();
-    print((' ' * _nodeDepth) + message);
-  }
-
-  void _traceSync(_SyncOperation op, String key) {
-    if (!_shouldTrace)
-      return;
-
-    String opString = op.toString().toLowerCase();
-    String outString = opString.substring(opString.indexOf('.') + 1);
-    _trace('_sync($outString) $key');
-  }
-
-  void _removeChild(UINode node) {
-    _traceSync(_SyncOperation.REMOVAL, node._key);
-    node._remove();
-  }
-
-  // Returns the child which should be retained as the child of this node.
-  UINode _syncChild(UINode node, UINode oldNode, RenderCSSContainer host,
-      RenderCSS insertBefore) {
-
-    assert(oldNode == null || node._key == oldNode._key);
-
-    if (node == oldNode) {
-      _traceSync(_SyncOperation.IDENTICAL, node._key);
-      return node; // Nothing to do. Subtrees must be identical.
-    }
-
-    // TODO(rafaelw): This eagerly removes the old DOM. It may be that a
-    // new component was built that could re-use some of it. Consider
-    // syncing the new VDOM against the old one.
-    if (oldNode != null && node._key != oldNode._key) {
-      _removeChild(oldNode);
-    }
-
-    if (node._willSync(oldNode)) {
-      _traceSync(_SyncOperation.STATEFUL, node._key);
-      oldNode._sync(node, host, insertBefore);
-      node._defunct = true;
-      assert(oldNode._root is RenderCSS);
-      return oldNode;
-    }
-
-    node._parent = this;
-
-    if (oldNode == null) {
-      _traceSync(_SyncOperation.INSERTION, node._key);
-    } else {
-      _traceSync(_SyncOperation.STATELESS, node._key);
-    }
-    node._sync(oldNode, host, insertBefore);
-    if (oldNode != null)
-      oldNode._defunct = true;
-
-    assert(node._root is RenderCSS);
-    return node;
-  }
-}
-
-abstract class ContentNode extends UINode {
-  UINode content;
-
-  ContentNode(UINode content) : this.content = content, super(key: content._key);
-
-  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore) {
-    UINode oldContent = old == null ? null : (old as ContentNode).content;
-    content = _syncChild(content, oldContent, host, insertBefore);
-    assert(content._root != null);
-    _root = content._root;
-  }
-
-  void _remove() {
-    if (content != null)
-      _removeChild(content);
-    super._remove();
-  }
-}
-
-class StyleNode extends ContentNode {
-  final Style style;
-
-  StyleNode(UINode content, this.style): super(content);
-}
-
-class ParentDataNode extends ContentNode {
-  final ParentData parentData;
-
-  ParentDataNode(UINode content, this.parentData): super(content);
-}
-
-/*
- * SkyNodeWrappers correspond to a desired state of a RenderCSS. They are fully
- * immutable, with one exception: A UINode which is a Component which lives within
- * an SkyElementWrapper's children list, may be replaced with the "old" instance if it
- * has become stateful.
- */
-abstract class SkyNodeWrapper extends UINode {
-
-  static final Map<RenderCSS, SkyNodeWrapper> _nodeMap =
-      new HashMap<RenderCSS, SkyNodeWrapper>();
-
-  static SkyNodeWrapper _getMounted(RenderCSS node) => _nodeMap[node];
-
-  SkyNodeWrapper({ Object key }) : super(key: key);
-
-  SkyNodeWrapper get _emptyNode;
-
-  RenderCSS _createNode();
-
-  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore) {
-    if (old == null) {
-      _root = _createNode();
-      assert(_root != null);
-      host.add(_root, before: insertBefore);
-      old = _emptyNode;
-    } else {
-      _root = old._root;
-      assert(_root != null);
-    }
-
-    _nodeMap[_root] = this;
-    _syncNode(old);
-  }
-
-  void _syncNode(SkyNodeWrapper old);
-
-  void _removeChild(UINode node) {
-    assert(_root is RenderCSSContainer);
-    _root.remove(node._root);
-    super._removeChild(node);
-  }
-
-  void _remove() {
-    assert(_root != null);
-    _nodeMap.remove(_root);
-    super._remove();
-  }
-}
-
-typedef GestureEventListener(sky.GestureEvent e);
-typedef PointerEventListener(sky.PointerEvent e);
-typedef EventListener(sky.Event e);
-
-class EventListenerNode extends ContentNode  {
-  final Map<String, sky.EventListener> listeners;
-
-  static final Set<String> _registeredEvents = new HashSet<String>();
-
-  static Map<String, sky.EventListener> _createListeners({
-    EventListener onWheel,
-    GestureEventListener onGestureFlingCancel,
-    GestureEventListener onGestureFlingStart,
-    GestureEventListener onGestureScrollStart,
-    GestureEventListener onGestureScrollUpdate,
-    GestureEventListener onGestureTap,
-    GestureEventListener onGestureTapDown,
-    PointerEventListener onPointerCancel,
-    PointerEventListener onPointerDown,
-    PointerEventListener onPointerMove,
-    PointerEventListener onPointerUp,
-    Map<String, sky.EventListener> custom
-  }) {
-    var listeners = custom != null ?
-        new HashMap<String, sky.EventListener>.from(custom) :
-        new HashMap<String, sky.EventListener>();
-
-    if (onWheel != null)
-      listeners['wheel'] = onWheel;
-    if (onGestureFlingCancel != null)
-      listeners['gestureflingcancel'] = onGestureFlingCancel;
-    if (onGestureFlingStart != null)
-      listeners['gestureflingstart'] = onGestureFlingStart;
-    if (onGestureScrollStart != null)
-      listeners['gesturescrollstart'] = onGestureScrollStart;
-    if (onGestureScrollUpdate != null)
-      listeners['gesturescrollupdate'] = onGestureScrollUpdate;
-    if (onGestureTap != null)
-      listeners['gesturetap'] = onGestureTap;
-    if (onGestureTapDown != null)
-      listeners['gesturetapdown'] = onGestureTapDown;
-    if (onPointerCancel != null)
-      listeners['pointercancel'] = onPointerCancel;
-    if (onPointerDown != null)
-      listeners['pointerdown'] = onPointerDown;
-    if (onPointerMove != null)
-      listeners['pointermove'] = onPointerMove;
-    if (onPointerUp != null)
-      listeners['pointerup'] = onPointerUp;
-
-    return listeners;
-  }
-
-  EventListenerNode(UINode content, {
-    EventListener onWheel,
-    GestureEventListener onGestureFlingCancel,
-    GestureEventListener onGestureFlingStart,
-    GestureEventListener onGestureScrollStart,
-    GestureEventListener onGestureScrollUpdate,
-    GestureEventListener onGestureTap,
-    GestureEventListener onGestureTapDown,
-    PointerEventListener onPointerCancel,
-    PointerEventListener onPointerDown,
-    PointerEventListener onPointerMove,
-    PointerEventListener onPointerUp,
-    Map<String, sky.EventListener> custom
-  }) : listeners = _createListeners(
-         onWheel: onWheel,
-         onGestureFlingCancel: onGestureFlingCancel,
-         onGestureFlingStart: onGestureFlingStart,
-         onGestureScrollUpdate: onGestureScrollUpdate,
-         onGestureScrollStart: onGestureScrollStart,
-         onGestureTap: onGestureTap,
-         onGestureTapDown: onGestureTapDown,
-         onPointerCancel: onPointerCancel,
-         onPointerDown: onPointerDown,
-         onPointerMove: onPointerMove,
-         onPointerUp: onPointerUp,
-         custom: custom
-       ),
-       super(content);
-
-  void _handleEvent(sky.Event e) {
-    sky.EventListener listener = listeners[e.type];
-    if (listener != null) {
-      listener(e);
-    }
-  }
-
-  static void _dispatchEvent(sky.Event e) {
-    UINode target = SkyNodeWrapper._getMounted(bridgeEventTargetToRenderNode(e.target));
-
-    // TODO(rafaelw): StopPropagation?
-    while (target != null) {
-      if (target is EventListenerNode) {
-        target._handleEvent(e);
-      }
-
-      target = target._parent;
-    }
-  }
-
-  static void _ensureDocumentListener(String eventType) {
-    if (_registeredEvents.add(eventType)) {
-      sky.document.addEventListener(eventType, _dispatchEvent);
-    }
-  }
-
-  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore) {
-    for (var type in listeners.keys) {
-      _ensureDocumentListener(type);
-    }
-
-    super._sync(old, host, insertBefore);
-  }
-}
-
-final List<UINode> _emptyList = new List<UINode>();
-
-abstract class SkyElementWrapper extends SkyNodeWrapper {
-
-  final List<UINode> children;
-  final Style style;
-  final String inlineStyle;
-
-  SkyElementWrapper({
-    Object key,
-    List<UINode> children,
-    this.style,
-    this.inlineStyle
-  }) : this.children = children == null ? _emptyList : children,
-       super(key: key) {
-
-    assert(!_debugHasDuplicateIds());
-  }
-
-  void _remove() {
-    assert(children != null);
-    for (var child in children) {
-      assert(child != null);
-      _removeChild(child);
-    }
-    super._remove();
-  }
-
-  bool _debugHasDuplicateIds() {
-    var idSet = new HashSet<String>();
-    for (var child in children) {
-      assert(child != null);
-      if (child.interchangeable)
-        continue; // when these nodes are reordered, we just reassign the data
-
-      if (!idSet.add(child._key)) {
-        throw '''If multiple non-interchangeable nodes of the same type exist as children
-                of another node, they must have unique keys.
-                Duplicate: "${child._key}"''';
-      }
-    }
-    return false;
-  }
-
-  void _syncNode(SkyNodeWrapper old) {
-    SkyElementWrapper oldSkyElementWrapper = old as SkyElementWrapper;
-
-    List<Style> styles = new List<Style>();
-    if (style != null)
-      styles.add(style);
-    ParentData parentData = null;
-    UINode parent = _parent;
-    while (parent != null && parent is! SkyNodeWrapper) {
-      if (parent is StyleNode && parent.style != null)
-        styles.add(parent.style);
-      else
-      if (parent is ParentDataNode && parent.parentData != null) {
-        if (parentData != null)
-          parentData.merge(parent.parentData); // this will throw if the types aren't the same
-        else
-          parentData = parent.parentData;
-      }
-      parent = parent._parent;
-    }
-    _root.updateStyles(styles);
-    if (parentData != null) {
-      assert(_root.parentData != null);
-      _root.parentData.merge(parentData); // this will throw if the types aren't approriate
-      assert(parent != null);
-      assert(parent._root != null);
-      parent._root.markNeedsLayout();
-    }
-    _root.updateInlineStyle(inlineStyle);
-
-    _syncChildren(oldSkyElementWrapper);
-  }
-
-  void _syncChildren(SkyElementWrapper oldSkyElementWrapper) {
-    if (_root is! RenderCSSContainer)
-      return;
-
-    var startIndex = 0;
-    var endIndex = children.length;
-
-    var oldChildren = oldSkyElementWrapper.children;
-    var oldStartIndex = 0;
-    var oldEndIndex = oldChildren.length;
-
-    RenderCSS nextSibling = null;
-    UINode currentNode = null;
-    UINode oldNode = null;
-
-    void sync(int atIndex) {
-      children[atIndex] = _syncChild(currentNode, oldNode, _root, nextSibling);
-      assert(children[atIndex] != null);
-    }
-
-    // Scan backwards from end of list while nodes can be directly synced
-    // without reordering.
-    while (endIndex > startIndex && oldEndIndex > oldStartIndex) {
-      currentNode = children[endIndex - 1];
-      oldNode = oldChildren[oldEndIndex - 1];
-
-      if (currentNode._key != oldNode._key) {
-        break;
-      }
-
-      endIndex--;
-      oldEndIndex--;
-      sync(endIndex);
-    }
-
-    HashMap<String, UINode> oldNodeIdMap = null;
-
-    bool oldNodeReordered(String key) {
-      return oldNodeIdMap != null &&
-             oldNodeIdMap.containsKey(key) &&
-             oldNodeIdMap[key] == null;
-    }
-
-    void advanceOldStartIndex() {
-      oldStartIndex++;
-      while (oldStartIndex < oldEndIndex &&
-             oldNodeReordered(oldChildren[oldStartIndex]._key)) {
-        oldStartIndex++;
-      }
-    }
-
-    void ensureOldIdMap() {
-      if (oldNodeIdMap != null)
-        return;
-
-      oldNodeIdMap = new HashMap<String, UINode>();
-      for (int i = oldStartIndex; i < oldEndIndex; i++) {
-        var node = oldChildren[i];
-        if (!node.interchangeable)
-          oldNodeIdMap.putIfAbsent(node._key, () => node);
-      }
-    }
-
-    bool searchForOldNode() {
-      if (currentNode.interchangeable)
-        return false; // never re-order these nodes
-
-      ensureOldIdMap();
-      oldNode = oldNodeIdMap[currentNode._key];
-      if (oldNode == null)
-        return false;
-
-      oldNodeIdMap[currentNode._key] = null; // mark it reordered
-      assert(_root is RenderCSSContainer);
-      assert(oldNode._root is RenderCSSContainer);
-      oldSkyElementWrapper._root.remove(oldNode._root);
-      _root.add(oldNode._root, before: nextSibling);
-      return true;
-    }
-
-    // Scan forwards, this time we may re-order;
-    nextSibling = _root.firstChild;
-    while (startIndex < endIndex && oldStartIndex < oldEndIndex) {
-      currentNode = children[startIndex];
-      oldNode = oldChildren[oldStartIndex];
-
-      if (currentNode._key == oldNode._key) {
-        assert(currentNode.runtimeType == oldNode.runtimeType);
-        nextSibling = _root.childAfter(nextSibling);
-        sync(startIndex);
-        startIndex++;
-        advanceOldStartIndex();
-        continue;
-      }
-
-      oldNode = null;
-      searchForOldNode();
-      sync(startIndex);
-      startIndex++;
-    }
-
-    // New insertions
-    oldNode = null;
-    while (startIndex < endIndex) {
-      currentNode = children[startIndex];
-      sync(startIndex);
-      startIndex++;
-    }
-
-    // Removals
-    currentNode = null;
-    while (oldStartIndex < oldEndIndex) {
-      oldNode = oldChildren[oldStartIndex];
-      _removeChild(oldNode);
-      advanceOldStartIndex();
-    }
-  }
-}
-
-class Container extends SkyElementWrapper {
-
-  RenderCSSContainer _root;
-  RenderCSSContainer _createNode() => new RenderCSSContainer(this);
-
-  static final Container _emptyContainer = new Container();
-
-  SkyNodeWrapper get _emptyNode => _emptyContainer;
-
-  Container({
-    Object key,
-    List<UINode> children,
-    Style style,
-    String inlineStyle
-  }) : super(
-    key: key,
-    children: children,
-    style: style,
-    inlineStyle: inlineStyle
-  );
-}
-
-class Paragraph extends SkyElementWrapper {
-
-  RenderCSSParagraph _root;
-  RenderCSSParagraph _createNode() => new RenderCSSParagraph(this);
-
-  static final Paragraph _emptyContainer = new Paragraph();
-
-  SkyNodeWrapper get _emptyNode => _emptyContainer;
-
-  Paragraph({
-    Object key,
-    List<UINode> children,
-    Style style,
-    String inlineStyle
-  }) : super(
-    key: key,
-    children: children,
-    style: style,
-    inlineStyle: inlineStyle
-  );
-}
-
-class FlexContainer extends SkyElementWrapper {
-
-  RenderCSSFlex _root;
-  RenderCSSFlex _createNode() => new RenderCSSFlex(this, this.direction);
-
-  static final FlexContainer _emptyContainer = new FlexContainer();
-    // direction doesn't matter if it's empty
-
-  SkyNodeWrapper get _emptyNode => _emptyContainer;
-
-  final FlexDirection direction;
-
-  FlexContainer({
-    Object key,
-    List<UINode> children,
-    Style style,
-    String inlineStyle,
-    this.direction: FlexDirection.Row
-  }) : super(
-    key: key,
-    children: children,
-    style: style,
-    inlineStyle: inlineStyle
-  );
-
-  void _syncNode(UINode old) {
-    super._syncNode(old);
-    _root.direction = direction;
-  }
-}
-
-class FillStackContainer extends SkyElementWrapper {
-
-  RenderCSSStack _root;
-  RenderCSSStack _createNode() => new RenderCSSStack(this);
-
-  static final FillStackContainer _emptyContainer = new FillStackContainer();
-
-  SkyNodeWrapper get _emptyNode => _emptyContainer;
-
-  FillStackContainer({
-    Object key,
-    List<UINode> children,
-    Style style,
-    String inlineStyle
-  }) : super(
-    key: key,
-    children: _positionNodesToFill(children),
-    style: style,
-    inlineStyle: inlineStyle
-  );
-
-  static StackParentData _fillParentData = new StackParentData()
-                                                 ..top = 0.0
-                                                 ..left = 0.0
-                                                 ..right = 0.0
-                                                 ..bottom = 0.0;
-
-  static List<UINode> _positionNodesToFill(List<UINode> input) {
-    if (input == null)
-      return null;
-    return input.map((node) {
-      return new ParentDataNode(node, _fillParentData);
-    }).toList();
-  }
-}
-
-class TextFragment extends SkyElementWrapper {
-
-  RenderCSSInline _root;
-  RenderCSSInline _createNode() => new RenderCSSInline(this, this.data);
-
-  static final TextFragment _emptyText = new TextFragment('');
-
-  SkyNodeWrapper get _emptyNode => _emptyText;
-
-  final String data;
-
-  TextFragment(this.data, {
-    Object key,
-    Style style,
-    String inlineStyle
-  }) : super(
-    key: key,
-    style: style,
-    inlineStyle: inlineStyle
-  );
-
-  void _syncNode(UINode old) {
-    super._syncNode(old);
-    _root.data = data;
-  }
-}
-
-class Image extends SkyElementWrapper {
-
-  RenderCSSImage _root;
-  RenderCSSImage _createNode() => new RenderCSSImage(this, this.src, this.width, this.height);
-
-  static final Image _emptyImage = new Image();
-
-  SkyNodeWrapper get _emptyNode => _emptyImage;
-
-  final String src;
-  final int width;
-  final int height;
-
-  Image({
-    Object key,
-    Style style,
-    String inlineStyle,
-    this.width,
-    this.height,
-    this.src
-  }) : super(
-    key: key,
-    style: style,
-    inlineStyle: inlineStyle
-  );
-
-  void _syncNode(UINode old) {
-    super._syncNode(old);
-    _root.configure(this.src, this.width, this.height);
-  }
-}
-
-
-Set<Component> _mountedComponents = new HashSet<Component>();
-Set<Component> _unmountedComponents = new HashSet<Component>();
-
-void _enqueueDidMount(Component c) {
-  assert(!_notifingMountStatus);
-  _mountedComponents.add(c);
-}
-
-void _enqueueDidUnmount(Component c) {
-  assert(!_notifingMountStatus);
-  _unmountedComponents.add(c);
-}
-
-bool _notifingMountStatus = false;
-
-void _notifyMountStatusChanged() {
-  try {
-    _notifingMountStatus = true;
-    _unmountedComponents.forEach((c) => c._didUnmount());
-    _mountedComponents.forEach((c) => c._didMount());
-    _mountedComponents.clear();
-    _unmountedComponents.clear();
-  } finally {
-    _notifingMountStatus = false;
-  }
-}
-
-List<Component> _dirtyComponents = new List<Component>();
-bool _buildScheduled = false;
-bool _inRenderDirtyComponents = false;
-
-void _buildDirtyComponents() {
-  _tracing.begin('fn::_buildDirtyComponents');
-
-  Stopwatch sw;
-  if (_shouldLogRenderDuration)
-    sw = new Stopwatch()..start();
-
-  try {
-    _inRenderDirtyComponents = true;
-
-    _dirtyComponents.sort((a, b) => a._order - b._order);
-    for (var comp in _dirtyComponents) {
-      comp._buildIfDirty();
-    }
-
-    _dirtyComponents.clear();
-    _buildScheduled = false;
-  } finally {
-    _inRenderDirtyComponents = false;
-  }
-
-  _notifyMountStatusChanged();
-
-  if (_shouldLogRenderDuration) {
-    sw.stop();
-    print('Render took ${sw.elapsedMicroseconds} microseconds');
-  }
-
-  _tracing.end('fn::_buildDirtyComponents');
-}
-
-void _scheduleComponentForRender(Component c) {
-  assert(!_inRenderDirtyComponents);
-  _dirtyComponents.add(c);
-
-  if (!_buildScheduled) {
-    _buildScheduled = true;
-    new Future.microtask(_buildDirtyComponents);
-  }
-}
-
-abstract class Component extends UINode {
-  bool get _isBuilding => _currentlyBuilding == this;
-  bool _dirty = true;
-
-  UINode _built;
-  final int _order;
-  static int _currentOrder = 0;
-  bool _stateful;
-  static Component _currentlyBuilding;
-  List<Function> _mountCallbacks;
-  List<Function> _unmountCallbacks;
-
-  void onDidMount(Function fn) {
-    if (_mountCallbacks == null)
-      _mountCallbacks = new List<Function>();
-
-    _mountCallbacks.add(fn);
-  }
-
-  void onDidUnmount(Function fn) {
-    if (_unmountCallbacks == null)
-      _unmountCallbacks = new List<Function>();
-
-    _unmountCallbacks.add(fn);
-  }
-
-
-  Component({ Object key, bool stateful })
-      : _stateful = stateful != null ? stateful : false,
-        _order = _currentOrder + 1,
-        super(key: key);
-
-  Component.fromArgs(Object key, bool stateful)
-      : this(key: key, stateful: stateful);
-
-  void _didMount() {
-    if (_mountCallbacks != null)
-      _mountCallbacks.forEach((fn) => fn());
-  }
-
-  void _didUnmount() {
-    if (_unmountCallbacks != null)
-      _unmountCallbacks.forEach((fn) => fn());
-  }
-
-  // TODO(rafaelw): It seems wrong to expose DOM at all. This is presently
-  // needed to get sizing info.
-  RenderCSS getRoot() => _root;
-
-  void _remove() {
-    assert(_built != null);
-    assert(_root != null);
-    _removeChild(_built);
-    _built = null;
-    _enqueueDidUnmount(this);
-    super._remove();
-  }
-
-  bool _willSync(UINode old) {
-    Component oldComponent = old as Component;
-    if (oldComponent == null || !oldComponent._stateful)
-      return false;
-
-    // Make |this| the "old" Component
-    _stateful = false;
-    _built = oldComponent._built;
-    assert(_built != null);
-
-    // Make |oldComponent| the "new" component
-    reflect.copyPublicFields(this, oldComponent);
-    oldComponent._built = null;
-    oldComponent._dirty = true;
-    return true;
-  }
-
-  /* There are three cases here:
-   * 1) Building for the first time:
-   *      assert(_built == null && old == null)
-   * 2) Re-building (because a dirty flag got set):
-   *      assert(_built != null && old == null)
-   * 3) Syncing against an old version
-   *      assert(_built == null && old != null)
-   */
-  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore) {
-    assert(!_defunct);
-    assert(_built == null || old == null);
-
-    Component oldComponent = old as Component;
-
-    var oldBuilt;
-    if (oldComponent == null) {
-      oldBuilt = _built;
-    } else {
-      assert(_built == null);
-      oldBuilt = oldComponent._built;
-    }
-
-    if (oldBuilt == null)
-      _enqueueDidMount(this);
-
-    int lastOrder = _currentOrder;
-    _currentOrder = _order;
-    _currentlyBuilding = this;
-    _built = build();
-    _currentlyBuilding = null;
-    _currentOrder = lastOrder;
-
-    _built = _syncChild(_built, oldBuilt, host, insertBefore);
-    _dirty = false;
-    _root = _built._root;
-    assert(_root != null);
-  }
-
-  void _buildIfDirty() {
-    if (!_dirty || _defunct)
-      return;
-
-    _trace('$_key rebuilding...');
-    _sync(null, null, null); // TODO(ianh): figure out how passing "null, null, null" here is ok
-  }
-
-  void scheduleBuild() {
-    setState(() {});
-  }
-
-  void setState(Function fn()) {
-    _stateful = true;
-    fn();
-    if (_isBuilding || _dirty || _defunct)
-      return;
-
-    _dirty = true;
-    _scheduleComponentForRender(this);
-  }
-
-  UINode build();
-}
-
-abstract class App extends Component {
-  RenderCSS _host;
-
-  App() : super(stateful: true) {
-    _host = new RenderCSSRoot(this);
-    _scheduleComponentForRender(this);
-  }
-
-  void _buildIfDirty() {
-    if (!_dirty || _defunct)
-      return;
-
-    _trace('$_key rebuilding...');
-    _sync(null, _host, _root);
-  }
-}
-
-class Text extends Component {
-  Text(this.data) : super(key: '*text*');
-  final String data;
-  bool get interchangeable => true;
-  UINode build() => new Paragraph(children: [new TextFragment(data)]);
-}