Prototype of fn3

This patch contains a prototype of a new widget framework. In this framework,
Components can be reused in the tree as many times as the author desires. Also,
StatefulComponent is split into two pieces, a ComponentConfiguration and a
ComponentState. The ComponentConfiguration is created by the author and can be
reused as many times as desired. When mounted into the tree, the
ComponentConfiguration creates a ComponentState to hold the state for the
component. The state remains in the tree and cannot be reused.

packages/flutter/lib/src/fn3.dart

@@ -0,0 +1,8 @@
+// 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 fn3;
+
+export 'fn3/basic.dart';
+export 'fn3/framework.dart';

packages/flutter/lib/src/fn3/basic.dart

@@ -0,0 +1,57 @@
+// 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.
+
+import 'package:sky/rendering.dart';
+import 'package:sky/src/fn3/framework.dart';
+
+export 'package:sky/rendering.dart' show
+    BackgroundImage,
+    BlockDirection,
+    Border,
+    BorderSide,
+    BoxConstraints,
+    BoxDecoration,
+    BoxDecorationPosition,
+    BoxShadow,
+    Color,
+    EdgeDims,
+    EventDisposition,
+    FlexAlignItems,
+    FlexDirection,
+    FlexJustifyContent,
+    Offset,
+    Paint,
+    Path,
+    Point,
+    Rect,
+    ScrollDirection,
+    Shape,
+    ShrinkWrap,
+    Size,
+    ValueChanged;
+
+class DecoratedBox extends OneChildRenderObjectWidget {
+  DecoratedBox({
+    Key key,
+    this.decoration,
+    this.position: BoxDecorationPosition.background,
+    Widget child
+  }) : super(key: key, child: child) {
+    assert(decoration != null);
+    assert(position != null);
+  }
+
+  final BoxDecoration decoration;
+  final BoxDecorationPosition position;
+
+  RenderObject createRenderObject() => new RenderDecoratedBox(
+    decoration: decoration,
+    position: position
+  );
+
+  void updateRenderObject(RenderDecoratedBox renderObject) {
+    renderObject.decoration = decoration;
+    renderObject.position = position;
+  }
+}

packages/flutter/lib/src/fn3/framework.dart

@@ -0,0 +1,340 @@
+// 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.
+
+import 'package:sky/rendering.dart';
+
+abstract class Key {
+}
+
+abstract class Widget {
+  Widget(this.key);
+  final Key key;
+
+  Element createElement();
+}
+
+typedef Widget WidgetBuilder();
+
+abstract class RenderObjectWidget extends Widget {
+  RenderObjectWidget({ Key key }) : super(key);
+
+  Element createElement() => new RenderObjectElement(this);
+
+  RenderObject createRenderObject();
+  void updateRenderObject(RenderObject renderObject);
+}
+
+abstract class OneChildRenderObjectWidget extends RenderObjectWidget {
+  OneChildRenderObjectWidget({ Key key, Widget this.child }) : super(key: key);
+
+  final Widget child;
+
+  Element createElement() => new OneChildRenderObjectElement(this);
+}
+
+abstract class MultiChildRenderObjectWidget extends RenderObjectWidget {
+  MultiChildRenderObjectWidget({ Key key, List<Widget> this.children })
+    : super(key: key);
+
+  final List<Widget> children;
+
+  Element createElement() => new MultiChildRenderObjectElement(this);
+}
+
+abstract class Component extends Widget {
+  Component({ Key key }) : super(key);
+  Element createElement() => new ComponentElement(this);
+
+  Widget build();
+}
+
+abstract class ComponentState<T extends ComponentConfiguration> {
+  ComponentStateElement _holder;
+
+  void setState(void fn()) {
+    fn();
+    _holder.scheduleBuild();
+  }
+
+  T get config => _config;
+  T _config;
+
+  /// Override this setter to update additional state when the config changes.
+  void set config(T config) {
+    _config = config;
+  }
+
+  /// Called when this object is removed from the tree
+  void didUnmount() { }
+
+  Widget build();
+}
+
+abstract class ComponentConfiguration extends Widget {
+  ComponentConfiguration({ Key key }) : super(key);
+
+  ComponentStateElement createElement() => new ComponentStateElement(this);
+
+  ComponentState createState();
+}
+
+bool _canUpdate(Widget oldWidget, Widget newWidget) {
+  return oldWidget.runtimeType == newWidget.runtimeType
+    && oldWidget.key == newWidget.key;
+}
+
+void _debugReportException(String context, dynamic exception, StackTrace stack) {
+  print('------------------------------------------------------------------------');
+  'Exception caught while $context'.split('\n').forEach(print);
+  print('$exception');
+  print('Stack trace:');
+  '$stack'.split('\n').forEach(print);
+  print('------------------------------------------------------------------------');
+}
+
+enum _ElementLifecycle {
+  initial,
+  mounted,
+  defunct,
+}
+
+typedef void ElementVisitor(Element element);
+
+abstract class Element<T extends Widget> {
+  Element(T widget) : _widget = widget {
+    assert(_widget != null);
+  }
+
+  Element _parent;
+  T _widget;
+
+  _ElementLifecycle _lifecycleState = _ElementLifecycle.initial;
+
+  void visitChildren(ElementVisitor visitor) { }
+
+  void visitDescendants(ElementVisitor visitor) {
+    void walk(Element element) {
+      visitor(element);
+      element.visitChildren(walk);
+    }
+    visitChildren(walk);
+  }
+
+  void mount(dynamic slot) {
+    assert(_lifecycleState == _ElementLifecycle.initial);
+    assert(_widget != null);
+    _lifecycleState = _ElementLifecycle.mounted;
+    assert(_parent == null || _parent._lifecycleState == _ElementLifecycle.mounted);
+  }
+
+  void update(T updated, dynamic slot) {
+    assert(_lifecycleState == _ElementLifecycle.mounted);
+    assert(_widget != null);
+    assert(updated != null);
+    assert(_canUpdate(_widget, updated));
+    _widget = updated;
+  }
+
+  void unmount() {
+    assert(_lifecycleState == _ElementLifecycle.mounted);
+    assert(_widget != null);
+    _lifecycleState = _ElementLifecycle.defunct;
+  }
+
+  void _detachChild(Element child) {
+    if (child == null)
+      return;
+    child._parent = null;
+
+    bool haveDetachedRenderObject = false;
+    void detach(Element descendant) {
+      if (!haveDetachedRenderObject && descendant is RenderObjectElement) {
+        descendant.detachRenderObject();
+        haveDetachedRenderObject = true;
+      }
+      descendant.unmount();
+    }
+
+    detach(child);
+    child.visitDescendants(detach);
+  }
+
+  Element _updateChild(Element child, Widget updated, dynamic slot) {
+    if (updated == null) {
+      _detachChild(child);
+      return null;
+    }
+
+    if (child != null) {
+      if (_canUpdate(child._widget, updated)) {
+        child.update(updated, slot);
+        return child;
+      }
+      _detachChild(child);
+      assert(child._parent == null);
+    }
+
+    Element newChild = updated.createElement();
+    newChild._parent = this;
+    newChild.mount(slot);
+    return newChild;
+  }
+
+}
+
+abstract class BuildableElement<T extends Widget> extends Element<T> {
+  BuildableElement(T widget) : super(widget);
+
+  WidgetBuilder _builder;
+  Element _child;
+
+  void _rebuild(dynamic slot) {
+    Widget built;
+    try {
+      built = _builder();
+      assert(built != null);
+    } catch (e, stack) {
+      _debugReportException('building $this', e, stack);
+    }
+    _child = _updateChild(_child, built, slot);
+  }
+
+  void visitChildren(ElementVisitor visitor) {
+    if (_child != null)
+      visitor(_child);
+  }
+
+  void mount(dynamic slot) {
+    super.mount(slot);
+    assert(_child == null);
+    _rebuild(slot);
+    assert(_child != null);
+  }
+}
+
+class ComponentElement extends BuildableElement<Component> {
+  ComponentElement(Component component) : super(component) {
+    _builder = component.build;
+  }
+
+  void update(Component updated, dynamic slot) {
+    super.update(updated, slot);
+    assert(_widget == updated);
+    _builder = _widget.build;
+    _rebuild(slot);
+  }
+}
+
+class ComponentStateElement extends BuildableElement<ComponentConfiguration> {
+  ComponentStateElement(ComponentConfiguration configuration)
+    : _state = configuration.createState(), super(configuration) {
+    _builder = _state.build;
+    _state._holder = this;
+    _state.config = configuration;
+  }
+
+  ComponentState _state;
+
+  void update(ComponentConfiguration updated, dynamic slot) {
+    super.update(updated, slot);
+    assert(_widget == updated);
+    _state.config = _widget;
+    _rebuild(slot);
+  }
+
+  void unmount() {
+    super.unmount();
+    _state.didUnmount();
+    _state = null;
+  }
+
+  void scheduleBuild() {
+    // TODO(abarth): Implement rebuilding.
+  }
+}
+
+RenderObjectElement _findAncestorRenderObjectElement(Element ancestor) {
+  while (ancestor != null && ancestor is! RenderObjectElement)
+    ancestor = ancestor._parent;
+  return ancestor;
+}
+
+class RenderObjectElement<T extends RenderObjectWidget> extends Element<T> {
+  RenderObjectElement(T widget)
+    : renderObject = widget.createRenderObject(), super(widget);
+
+  final RenderObject renderObject;
+  RenderObjectElement _ancestorRenderObjectElement;
+
+  void mount(dynamic slot) {
+    super.mount(slot);
+    assert(_ancestorRenderObjectElement == null);
+    _ancestorRenderObjectElement = _findAncestorRenderObjectElement(_parent);
+    if (_ancestorRenderObjectElement != null)
+      _ancestorRenderObjectElement.insertChildRenderObject(renderObject, slot);
+  }
+
+  void update(T updated, dynamic slot) {
+    super.update(updated, slot);
+    assert(_widget == updated);
+    _widget.updateRenderObject(renderObject);
+  }
+
+  void detachRenderObject() {
+    if (_ancestorRenderObjectElement != null) {
+      _ancestorRenderObjectElement.removeChildRenderObject(renderObject);
+      _ancestorRenderObjectElement = null;
+    }
+  }
+
+  void insertChildRenderObject(RenderObject child, dynamic slot) {
+    assert(false);
+  }
+
+  void removeChildRenderObject(RenderObject child) {
+    assert(false);
+  }
+}
+
+class OneChildRenderObjectElement<T extends OneChildRenderObjectWidget> extends RenderObjectElement<T> {
+  OneChildRenderObjectElement(T widget) : super(widget);
+
+  Element _child;
+
+  void visitChildren(ElementVisitor visitor) {
+    if (_child != null)
+      visitor(_child);
+  }
+
+  void mount(dynamic slot) {
+    super.mount(slot);
+    _child = _updateChild(_child, _widget.child, null);
+  }
+
+  void update(T updated, dynamic slot) {
+    super.update(updated, slot);
+    assert(_widget == updated);
+    _child = _updateChild(_child, _widget.child, null);
+  }
+
+  void insertChildRenderObject(RenderObject child, dynamic slot) {
+    final renderObject = this.renderObject; // TODO(ianh): Remove this once the analyzer is cleverer
+    assert(renderObject is RenderObjectWithChildMixin);
+    assert(slot == null);
+    renderObject.child = child;
+    assert(renderObject == this.renderObject); // TODO(ianh): Remove this once the analyzer is cleverer
+  }
+
+  void removeChildRenderObject(RenderObject child) {
+    final renderObject = this.renderObject; // TODO(ianh): Remove this once the analyzer is cleverer
+    assert(renderObject is RenderObjectWithChildMixin);
+    assert(renderObject.child == child);
+    renderObject.child = null;
+    assert(renderObject == this.renderObject); // TODO(ianh): Remove this once the analyzer is cleverer
+  }
+}
+
+class MultiChildRenderObjectElement<T extends MultiChildRenderObjectWidget> extends RenderObjectElement<T> {
+  MultiChildRenderObjectElement(T widget) : super(widget);
+}

packages/flutter/lib/src/widgets/framework.dart

@@ -22,7 +22,7 @@ export 'package:sky/src/rendering/object.dart' show Point, Offset, Size, Rect, C
 final bool _shouldLogRenderDuration = false; // see also 'enableProfilingLoop' argument to runApp()
 
 typedef Widget Builder();
-typedef void WidgetTreeWalker(Widget);
+typedef void WidgetTreeWalker(Widget widget);
 
 abstract class Key {
   const Key.constructor(); // so that subclasses can call us, since the Key() factory constructor shadows the implicit constructor

packages/unit/test/fn3/render_object_widget_test.dart

@@ -0,0 +1,160 @@
+import 'package:sky/rendering.dart';
+import 'package:sky/src/fn3.dart';
+import 'package:test/test.dart';
+
+import 'widget_tester.dart';
+
+final BoxDecoration kBoxDecorationA = new BoxDecoration();
+final BoxDecoration kBoxDecorationB = new BoxDecoration();
+final BoxDecoration kBoxDecorationC = new BoxDecoration();
+
+void main() {
+  test('RenderObjectWidget smoke test', () {
+    WidgetTester tester = new WidgetTester();
+
+    tester.pumpFrame(new DecoratedBox(decoration: kBoxDecorationA));
+    OneChildRenderObjectElement element =
+        tester.findElement((element) => element is OneChildRenderObjectElement);
+    expect(element, isNotNull);
+    expect(element.renderObject is RenderDecoratedBox, isTrue);
+    RenderDecoratedBox renderObject = element.renderObject;
+    expect(renderObject.decoration, equals(kBoxDecorationA));
+    expect(renderObject.position, equals(BoxDecorationPosition.background));
+
+    tester.pumpFrame(new DecoratedBox(decoration: kBoxDecorationB));
+    element = tester.findElement((element) => element is OneChildRenderObjectElement);
+    expect(element, isNotNull);
+    expect(element.renderObject is RenderDecoratedBox, isTrue);
+    renderObject = element.renderObject;
+    expect(renderObject.decoration, equals(kBoxDecorationB));
+    expect(renderObject.position, equals(BoxDecorationPosition.background));
+  });
+
+  test('RenderObjectWidget can add and remove children', () {
+    WidgetTester tester = new WidgetTester();
+
+    void checkFullTree() {
+      OneChildRenderObjectElement element =
+          tester.findElement((element) => element is OneChildRenderObjectElement);
+      expect(element, isNotNull);
+      expect(element.renderObject is RenderDecoratedBox, isTrue);
+      RenderDecoratedBox renderObject = element.renderObject;
+      expect(renderObject.decoration, equals(kBoxDecorationA));
+      expect(renderObject.position, equals(BoxDecorationPosition.background));
+      expect(renderObject.child, isNotNull);
+      expect(renderObject.child is RenderDecoratedBox, isTrue);
+      RenderDecoratedBox child = renderObject.child;
+      expect(child.decoration, equals(kBoxDecorationB));
+      expect(child.position, equals(BoxDecorationPosition.background));
+      expect(child.child, isNull);
+    }
+
+    void childBareTree() {
+      OneChildRenderObjectElement element =
+          tester.findElement((element) => element is OneChildRenderObjectElement);
+      expect(element, isNotNull);
+      expect(element.renderObject is RenderDecoratedBox, isTrue);
+      RenderDecoratedBox renderObject = element.renderObject;
+      expect(renderObject.decoration, equals(kBoxDecorationA));
+      expect(renderObject.position, equals(BoxDecorationPosition.background));
+      expect(renderObject.child, isNull);
+    }
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA,
+      child: new DecoratedBox(
+        decoration: kBoxDecorationB
+      )
+    ));
+
+    checkFullTree();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA,
+      child: new TestComponent(
+        child: new DecoratedBox(
+          decoration: kBoxDecorationB
+        )
+      )
+    ));
+
+    checkFullTree();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA,
+      child: new DecoratedBox(
+        decoration: kBoxDecorationB
+      )
+    ));
+
+    checkFullTree();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA
+    ));
+
+    childBareTree();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA,
+      child: new TestComponent(
+        child: new TestComponent(
+          child: new DecoratedBox(
+            decoration: kBoxDecorationB
+          )
+        )
+      )
+    ));
+
+    checkFullTree();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA
+    ));
+
+    childBareTree();
+  });
+
+  test('Detached render tree is intact', () {
+    WidgetTester tester = new WidgetTester();
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA,
+      child: new DecoratedBox(
+        decoration: kBoxDecorationB,
+        child: new DecoratedBox(
+          decoration: kBoxDecorationC
+        )
+      )
+    ));
+
+    OneChildRenderObjectElement element =
+        tester.findElement((element) => element is OneChildRenderObjectElement);
+    expect(element.renderObject is RenderDecoratedBox, isTrue);
+    RenderDecoratedBox parent = element.renderObject;
+    expect(parent.child is RenderDecoratedBox, isTrue);
+    RenderDecoratedBox child = parent.child;
+    expect(child.decoration, equals(kBoxDecorationB));
+    expect(child.child is RenderDecoratedBox, isTrue);
+    RenderDecoratedBox grandChild = child.child;
+    expect(grandChild.decoration, equals(kBoxDecorationC));
+    expect(grandChild.child, isNull);
+
+    tester.pumpFrame(new DecoratedBox(
+      decoration: kBoxDecorationA
+    ));
+
+    element =
+        tester.findElement((element) => element is OneChildRenderObjectElement);
+    expect(element.renderObject is RenderDecoratedBox, isTrue);
+    expect(element.renderObject, equals(parent));
+    expect(parent.child, isNull);
+
+    expect(child.parent, isNull);
+    expect(child.decoration, equals(kBoxDecorationB));
+    expect(child.child, equals(grandChild));
+    expect(grandChild.parent, equals(child));
+    expect(grandChild.decoration, equals(kBoxDecorationC));
+    expect(grandChild.child, isNull);
+  });
+}

packages/unit/test/fn3/widget_tester.dart

@@ -0,0 +1,44 @@
+import 'package:sky/src/fn3/framework.dart';
+
+class TestComponent extends Component {
+  TestComponent({ this.child });
+  final Widget child;
+  Widget build() => child;
+}
+
+class WidgetTester {
+  ComponentElement _rootElement;
+
+  void walkElements(ElementVisitor visitor) {
+    void walk(Element element) {
+      visitor(element);
+      element.visitChildren(walk);
+    }
+
+    _rootElement.visitChildren(walk);
+  }
+
+  Element findElement(bool predicate(Element widget)) {
+    try {
+      walkElements((Element widget) {
+        if (predicate(widget))
+          throw widget;
+      });
+    } catch (e) {
+      if (e is Element)
+        return e;
+      rethrow;
+    }
+    return null;
+  }
+
+  void pumpFrame(Widget widget) {
+    if (_rootElement == null) {
+      _rootElement = new ComponentElement(new TestComponent(child: widget));
+      _rootElement.mount(null);
+    } else {
+      _rootElement.update(new TestComponent(child: widget), null);
+    }
+  }
+
+}