Rationalise the overflow render boxes

New RenderAligningShiftedBox abstract class for render boxes with
"alignment", which as of now is:

 - RenderPositionedBox
 - RenderConstrainedOverflowBox (ex RenderOverflowBox)
 - RenderSizedOverflowBox
 - RenderFractionallySizedOverflowBox (ex RenderFractionallySizedBox)

(The respective widgets are Align, OverflowBox, SizedOverflowBox, and
FractionallySizedBox. They haven't been renamed.)

Also I added some toString details.

packages/flutter/lib/src/rendering/overflow.dart

@@ -5,79 +5,6 @@
 import 'box.dart';
 import 'object.dart';
 
-export 'package:flutter/src/painting/box_painter.dart';
-
-/// A render box that's a specific size but passes its original constraints through to its child, which will probably overflow
-class RenderSizedOverflowBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
-  RenderSizedOverflowBox({
-    RenderBox child,
-    Size requestedSize
-  }) : _requestedSize = requestedSize {
-    assert(requestedSize != null);
-    this.child = child;
-  }
-
-  /// The size this render box should attempt to be.
-  Size get requestedSize => _requestedSize;
-  Size _requestedSize;
-  void set requestedSize (Size value) {
-    assert(value != null);
-    if (_requestedSize == value)
-      return;
-    _requestedSize = value;
-    markNeedsLayout();
-  }
-
-  @override
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    return constraints.constrainWidth(_requestedSize.width);
-  }
-
-  @override
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    return constraints.constrainWidth(_requestedSize.width);
-  }
-
-  @override
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    return constraints.constrainHeight(_requestedSize.height);
-  }
-
-  @override
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    return constraints.constrainHeight(_requestedSize.height);
-  }
-
-  @override
-  double computeDistanceToActualBaseline(TextBaseline baseline) {
-    if (child != null)
-      return child.getDistanceToActualBaseline(baseline);
-    return super.computeDistanceToActualBaseline(baseline);
-  }
-
-  @override
-  void performLayout() {
-    size = constraints.constrain(_requestedSize);
-    if (child != null)
-      child.layout(constraints);
-  }
-
-  @override
-  bool hitTestChildren(HitTestResult result, { Point position }) {
-    return child?.hitTest(result, position: position) ?? false;
-  }
-
-  @override
-  void paint(PaintingContext context, Offset offset) {
-    if (child != null)
-      context.paintChild(child, offset);
-  }
-}
-
 /// Lays the child out as if it was in the tree, but without painting anything,
 /// without making the child available for hit testing, and without taking any
 /// room in the parent.

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -29,7 +29,6 @@ export 'package:flutter/gestures.dart' show
 /// for render objects that wish to mimic most, but not all, of the properties
 /// of their child.
 class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
-
   RenderProxyBox([RenderBox child = null]) {
     this.child = child;
   }
@@ -247,128 +246,6 @@ class RenderConstrainedBox extends RenderProxyBox {
   }
 }
 
-/// Sizes its child to a fraction of the total available space.
-///
-/// For both its width and height, this render object imposes a tight
-/// constraint on its child that is a multiple (typically less than 1.0) of the
-/// maximum constraint it received from its parent on that axis. If the factor
-/// for a given axis is null, then the constraints from the parent are just
-/// passed through instead.
-///
-/// It then tries to size itself to the size of its child.
-class RenderFractionallySizedBox extends RenderProxyBox {
-  RenderFractionallySizedBox({
-    RenderBox child,
-    double widthFactor,
-    double heightFactor
-  }) : _widthFactor = widthFactor, _heightFactor = heightFactor, super(child) {
-    assert(_widthFactor == null || _widthFactor >= 0.0);
-    assert(_heightFactor == null || _heightFactor >= 0.0);
-  }
-
-  /// If non-null, the factor of the incoming width to use.
-  ///
-  /// If non-null, the child is given a tight width constraint that is the max
-  /// incoming width constraint multipled by this factor.  If null, the child is
-  /// given the incoming width constraings.
-  double get widthFactor => _widthFactor;
-  double _widthFactor;
-  void set widthFactor (double value) {
-    assert(value == null || value >= 0.0);
-    if (_widthFactor == value)
-      return;
-    _widthFactor = value;
-    markNeedsLayout();
-  }
-
-  /// If non-null, the factor of the incoming height to use.
-  ///
-  /// If non-null, the child is given a tight height constraint that is the max
-  /// incoming width constraint multipled by this factor.  If null, the child is
-  /// given the incoming width constraings.
-  double get heightFactor => _heightFactor;
-  double _heightFactor;
-  void set heightFactor (double value) {
-    assert(value == null || value >= 0.0);
-    if (_heightFactor == value)
-      return;
-    _heightFactor = value;
-    markNeedsLayout();
-  }
-
-  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
-    double minWidth = constraints.minWidth;
-    double maxWidth = constraints.maxWidth;
-    if (_widthFactor != null) {
-      double width = maxWidth * _widthFactor;
-      minWidth = width;
-      maxWidth = width;
-    }
-    double minHeight = constraints.minHeight;
-    double maxHeight = constraints.maxHeight;
-    if (_heightFactor != null) {
-      double height = maxHeight * _heightFactor;
-      minHeight = height;
-      maxHeight = height;
-    }
-    return new BoxConstraints(
-      minWidth: minWidth,
-      maxWidth: maxWidth,
-      minHeight: minHeight,
-      maxHeight: maxHeight
-    );
-  }
-
-  @override
-  double getMinIntrinsicWidth(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    if (child != null)
-      return constraints.constrainWidth(child.getMinIntrinsicWidth(_getInnerConstraints(constraints)));
-    return constraints.constrainWidth(_getInnerConstraints(constraints).constrainWidth(0.0));
-  }
-
-  @override
-  double getMaxIntrinsicWidth(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    if (child != null)
-      return constraints.constrainWidth(child.getMaxIntrinsicWidth(_getInnerConstraints(constraints)));
-    return constraints.constrainWidth(_getInnerConstraints(constraints).constrainWidth(0.0));
-  }
-
-  @override
-  double getMinIntrinsicHeight(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    if (child != null)
-      return constraints.constrainHeight(child.getMinIntrinsicHeight(_getInnerConstraints(constraints)));
-    return constraints.constrainHeight(_getInnerConstraints(constraints).constrainHeight(0.0));
-  }
-
-  @override
-  double getMaxIntrinsicHeight(BoxConstraints constraints) {
-    assert(constraints.debugAssertIsNormalized);
-    if (child != null)
-      return constraints.constrainHeight(child.getMaxIntrinsicHeight(_getInnerConstraints(constraints)));
-    return constraints.constrainHeight(_getInnerConstraints(constraints).constrainHeight(0.0));
-  }
-
-  @override
-  void performLayout() {
-    if (child != null) {
-      child.layout(_getInnerConstraints(constraints), parentUsesSize: true);
-      size = constraints.constrain(child.size);
-    } else {
-      size = constraints.constrain(_getInnerConstraints(constraints).constrain(Size.zero));
-    }
-  }
-
-  @override
-  void debugFillDescription(List<String> description) {
-    super.debugFillDescription(description);
-    description.add('widthFactor: ${_widthFactor ?? "pass-through"}');
-    description.add('heightFactor: ${_heightFactor ?? "pass-through"}');
-  }
-}
-
 /// Attempts to size the child to a specific aspect ratio.
 ///
 /// The render object first tries the largest width permited by the layout

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

@@ -293,7 +293,7 @@ class Transform extends SingleChildRenderObjectWidget {
   /// The alignment of the origin, relative to the size of the box.
   ///
   /// This is equivalent to setting an origin based on the size of the box.
-  /// If it is specificed at the same time as an offset, both are applied.
+  /// If it is specified at the same time as an offset, both are applied.
   final FractionalOffset alignment;
 
   /// Whether to apply the translation when performing hit tests.
@@ -443,6 +443,16 @@ class Align extends SingleChildRenderObjectWidget {
       ..widthFactor = widthFactor
       ..heightFactor = heightFactor;
   }
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('alignment: $alignment');
+    if (widthFactor != null)
+      description.add('widthFactor: $widthFactor');
+    if (heightFactor != null)
+      description.add('heightFactor: $heightFactor');
+  }
 }
 
 /// Centers its child within itself.
@@ -610,10 +620,17 @@ class ConstrainedBox extends SingleChildRenderObjectWidget {
 
 /// Sizes itself to a fraction of the total available space.
 ///
-/// See [RenderFractionallySizedBox] for details.
+/// See [RenderFractionallySizedOverflowBox] for details.
 class FractionallySizedBox extends SingleChildRenderObjectWidget {
-  FractionallySizedBox({ Key key, this.width, this.height, Widget child })
-    : super(key: key, child: child);
+  FractionallySizedBox({
+    Key key,
+    this.alignment: const FractionalOffset(0.5, 0.5),
+    this.width,
+    this.height,
+    Widget child
+  }) : super(key: key, child: child) {
+    assert(alignment != null && alignment.dx != null && alignment.dy != null);
+  }
 
   /// If non-null, the factor of the incoming width to use.
   ///
@@ -627,15 +644,28 @@ class FractionallySizedBox extends SingleChildRenderObjectWidget {
   /// incoming height constraint multipled by this factor.
   final double height;
 
+  /// How to align the child.
+  ///
+  /// The x and y values of the alignment control the horizontal and vertical
+  /// alignment, respectively.  An x value of 0.0 means that the left edge of
+  /// the child is aligned with the left edge of the parent whereas an x value
+  /// of 1.0 means that the right edge of the child is aligned with the right
+  /// edge of the parent. Other values interpolate (and extrapolate) linearly.
+  /// For example, a value of 0.5 means that the center of the child is aligned
+  /// with the center of the parent.
+  final FractionalOffset alignment;
+
   @override
-  RenderFractionallySizedBox createRenderObject(BuildContext context) => new RenderFractionallySizedBox(
+  RenderFractionallySizedOverflowBox createRenderObject(BuildContext context) => new RenderFractionallySizedOverflowBox(
+    alignment: alignment,
     widthFactor: width,
     heightFactor: height
   );
 
   @override
-  void updateRenderObject(BuildContext context, RenderFractionallySizedBox renderObject) {
+  void updateRenderObject(BuildContext context, RenderFractionallySizedOverflowBox renderObject) {
     renderObject
+      ..alignment = alignment
       ..widthFactor = width
       ..heightFactor = height;
   }
@@ -643,6 +673,7 @@ class FractionallySizedBox extends SingleChildRenderObjectWidget {
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
+    description.add('alignment: $alignment');
     if (width != null)
       description.add('width: $width');
     if (height != null)
@@ -657,14 +688,25 @@ class FractionallySizedBox extends SingleChildRenderObjectWidget {
 class OverflowBox extends SingleChildRenderObjectWidget {
   OverflowBox({
     Key key,
+    this.alignment: const FractionalOffset(0.5, 0.5),
     this.minWidth,
     this.maxWidth,
     this.minHeight,
     this.maxHeight,
-    this.alignment: const FractionalOffset(0.5, 0.5),
     Widget child
   }) : super(key: key, child: child);
 
+  /// How to align the child.
+  ///
+  /// The x and y values of the alignment control the horizontal and vertical
+  /// alignment, respectively.  An x value of 0.0 means that the left edge of
+  /// the child is aligned with the left edge of the parent whereas an x value
+  /// of 1.0 means that the right edge of the child is aligned with the right
+  /// edge of the parent. Other values interpolate (and extrapolate) linearly.
+  /// For example, a value of 0.5 means that the center of the child is aligned
+  /// with the center of the parent.
+  final FractionalOffset alignment;
+
   /// The minimum width constraint to give the child. Set this to null (the
   /// default) to use the constraint from the parent instead.
   final double minWidth;
@@ -681,39 +723,29 @@ class OverflowBox extends SingleChildRenderObjectWidget {
   /// default) to use the constraint from the parent instead.
   final double maxHeight;
 
-  /// How to align the child.
-  ///
-  /// The x and y values of the alignment control the horizontal and vertical
-  /// alignment, respectively.  An x value of 0.0 means that the left edge of
-  /// the child is aligned with the left edge of the parent whereas an x value
-  /// of 1.0 means that the right edge of the child is aligned with the right
-  /// edge of the parent. Other values interpolate (and extrapolate) linearly.
-  /// For example, a value of 0.5 means that the center of the child is aligned
-  /// with the center of the parent.
-  final FractionalOffset alignment;
-
   @override
-  RenderOverflowBox createRenderObject(BuildContext context) => new RenderOverflowBox(
+  RenderConstrainedOverflowBox createRenderObject(BuildContext context) => new RenderConstrainedOverflowBox(
+    alignment: alignment,
     minWidth: minWidth,
     maxWidth: maxWidth,
     minHeight: minHeight,
-    maxHeight: maxHeight,
-    alignment: alignment
+    maxHeight: maxHeight
   );
 
   @override
-  void updateRenderObject(BuildContext context, RenderOverflowBox renderObject) {
+  void updateRenderObject(BuildContext context, RenderConstrainedOverflowBox renderObject) {
     renderObject
+      ..alignment = alignment
       ..minWidth = minWidth
       ..maxWidth = maxWidth
       ..minHeight = minHeight
-      ..maxHeight = maxHeight
-      ..alignment = alignment;
+      ..maxHeight = maxHeight;
   }
 
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
+    description.add('alignment: $alignment');
     if (minWidth != null)
       description.add('minWidth: $minWidth');
     if (maxWidth != null)
@@ -726,17 +758,49 @@ class OverflowBox extends SingleChildRenderObjectWidget {
 }
 
 class SizedOverflowBox extends SingleChildRenderObjectWidget {
-  SizedOverflowBox({ Key key, this.size, Widget child })
-    : super(key: key, child: child);
+  SizedOverflowBox({
+    Key key,
+    this.alignment: const FractionalOffset(0.5, 0.5),
+    this.size,
+    Widget child
+  }) : super(key: key, child: child) {
+    assert(alignment != null && alignment.dx != null && alignment.dy != null);
+  }
+
+  /// How to align the child.
+  ///
+  /// The x and y values of the alignment control the horizontal and vertical
+  /// alignment, respectively.  An x value of 0.0 means that the left edge of
+  /// the child is aligned with the left edge of the parent whereas an x value
+  /// of 1.0 means that the right edge of the child is aligned with the right
+  /// edge of the parent. Other values interpolate (and extrapolate) linearly.
+  /// For example, a value of 0.5 means that the center of the child is aligned
+  /// with the center of the parent.
+  final FractionalOffset alignment;
 
   final Size size;
 
   @override
-  RenderSizedOverflowBox createRenderObject(BuildContext context) => new RenderSizedOverflowBox(requestedSize: size);
+  RenderSizedOverflowBox createRenderObject(BuildContext context) {
+    return new RenderSizedOverflowBox(
+      alignment: alignment,
+      requestedSize: size
+    );
+  }
 
   @override
   void updateRenderObject(BuildContext context, RenderSizedOverflowBox renderObject) {
-    renderObject.requestedSize = size;
+    renderObject
+      ..alignment = alignment
+      ..requestedSize = size;
+  }
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('alignment: $alignment');
+    if (size != null)
+      description.add('size: $size');
   }
 }
 

packages/flutter/test/rendering/constraints_test.dart

@@ -13,7 +13,7 @@ void main() {
     root = new RenderPositionedBox(
       child: new RenderConstrainedBox(
         additionalConstraints: new BoxConstraints.tight(const Size(200.0, 200.0)),
-        child: test = new RenderFractionallySizedBox(
+        child: test = new RenderFractionallySizedOverflowBox(
           widthFactor: 2.0,
           heightFactor: 0.5,
           child: leaf = new RenderConstrainedBox(

packages/flutter/test/rendering/overflow_test.dart

@@ -28,7 +28,7 @@ void main() {
 
     root = new RenderPositionedBox(
       child: new RenderCustomPaint(
-        child: child = new RenderOverflowBox(
+        child: child = new RenderConstrainedOverflowBox(
           child: text = new RenderParagraph(new TextSpan(text: 'Hello World')),
           maxHeight: height1 / 2.0,
           alignment: const FractionalOffset(0.0, 0.0)

packages/flutter/test/widget/overflow_box_test.dart

@@ -42,6 +42,7 @@ void main() {
       maxHeight: 4.0
     ).debugFillDescription(description);
     expect(description, [
+      'alignment: FractionalOffset(0.5, 0.5)',
       'minWidth: 1.0',
       'maxWidth: 2.0',
       'minHeight: 3.0',