Get more debug info into the rendering layer

- change how we expose settings at the RenderObject layer so that it's
  easier to maintain.
- expose the Widget owner chain in the RenderObject layer debug output
- add debug info to RenderOpacity, RenderIgnorePointer, RenderListener
- make the output for text nodes prettier

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

@@ -118,7 +118,10 @@ abstract class RenderBlockBase extends RenderBox with ContainerRenderObjectMixin
     assert(!size.isInfinite);
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}direction: $direction\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('direction: $direction');
+  }
 }
 
 /// A block layout with a concrete set of children
@@ -427,5 +430,8 @@ class RenderBlockViewport extends RenderBlockBase {
       defaultHitTestChildren(result, position: position + new Offset(-startOffset, 0.0));
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}startOffset: $startOffset\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('startOffset: $startOffset');
+  }
 }

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

@@ -683,7 +683,10 @@ abstract class RenderBox extends RenderObject {
     }
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}size: ${ hasSize ? size : "MISSING" }\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('size: ${ hasSize ? size : "MISSING" }');
+  }
 }
 
 /// A mixin that provides useful default behaviors for boxes with children

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

@@ -597,6 +597,12 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     return header;
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}direction: $_direction\n${prefix}justifyContent: $_justifyContent\n${prefix}alignItems: $_alignItems\n${prefix}textBaseline: $_textBaseline\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('direction: $_direction');
+    settings.add('justifyContent: $_justifyContent');
+    settings.add('alignItems: $_alignItems');
+    settings.add('textBaseline: $_textBaseline');
+  }
 
 }

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

@@ -197,5 +197,9 @@ class RenderImage extends RenderBox {
     );
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}width: $width\n${prefix}height: $height\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('width: $width');
+    settings.add('height: $height');
+  }
 }

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

@@ -475,7 +475,7 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// Override in subclasses with children and call the visitor for each child
   void visitChildren(RenderObjectVisitor visitor) { }
 
-  dynamic debugExceptionContext = '';
+  dynamic debugOwner = '';
   void _debugReportException(String method, dynamic exception, StackTrace stack) {
     debugPrint('-- EXCEPTION --');
     debugPrint('The following exception was raised during $method():');
@@ -483,8 +483,8 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     debugPrint('Stack trace:');
     debugPrint('$stack');
     debugPrint('The following RenderObject was being processed when the exception was fired:\n${this}');
-    if (debugExceptionContext != '')
-      debugPrint('That RenderObject had the following exception context:\n$debugExceptionContext');
+    if (debugOwner != '')
+      debugPrint('That RenderObject had the following owner:\n$debugOwner');
     if (debugRenderingExceptionHandler != null)
       debugRenderingExceptionHandler(this, method, exception, stack);
   }
@@ -1134,20 +1134,25 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     String result = '$prefixLineOne$this\n';
     final String childrenDescription = debugDescribeChildren(prefixOtherLines);
     final String settingsPrefix = childrenDescription != '' ? '$prefixOtherLines \u2502 ' : '$prefixOtherLines   ';
-    result += debugDescribeSettings(settingsPrefix);
-    if (childrenDescription != '')
-      result += '$prefixOtherLines \u2502\n';
-    else
+    List<String> settings = <String>[];
+    debugDescribeSettings(settings);
+    result += settings.map((String setting) => "$settingsPrefix$setting\n").join();
+    if (childrenDescription == '')
       result += '$prefixOtherLines\n';
     result += childrenDescription;
     _debugActiveLayout = debugPreviousActiveLayout;
     return result;
   }
 
-  /// Returns a string describing the current node's fields, one field per line,
-  /// with each line prefixed by the prefix argument. Subclasses should override
-  /// this to have their information included in toStringDeep().
-  String debugDescribeSettings(String prefix) => '${prefix}parentData: $parentData\n${prefix}constraints: $constraints\n';
+  /// Returns a list of strings describing the current node's fields, one field
+  /// per string. Subclasses should override this to have their information
+  /// included in toStringDeep().
+  void debugDescribeSettings(List<String> settings) {
+    settings.add('parentData: $parentData');
+    settings.add('constraints: $constraints');
+    if (debugOwner != '')
+      settings.add('owner: $debugOwner');
+  }
 
   /// Returns a string describing the current node's descendants. Each line of
   /// the subtree in the output should be indented by the prefix argument.
@@ -1194,7 +1199,7 @@ abstract class RenderObjectWithChildMixin<ChildType extends RenderObject> implem
   }
   String debugDescribeChildren(String prefix) {
     if (child != null)
-      return '${child.toStringDeep("$prefix \u2514\u2500child: ", "$prefix  ")}';
+      return '$prefix \u2502\n${child.toStringDeep('$prefix \u2514\u2500child: ', '$prefix  ')}';
     return '';
   }
 }
@@ -1437,7 +1442,7 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
   }
 
   String debugDescribeChildren(String prefix) {
-    String result = '';
+    String result = '$prefix \u2502\n';
     if (_firstChild != null) {
       ChildType child = _firstChild;
       int count = 1;

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

@@ -137,12 +137,12 @@ class RenderOverflowBox extends RenderBox with RenderObjectWithChildMixin<Render
       context.paintChild(child, offset.toPoint());
   }
 
-  String debugDescribeSettings(String prefix) {
-    return '${super.debugDescribeSettings(prefix)}' +
-           '${prefix}minWidth: ${minWidth ?? "use parent minWidth constraint"}\n' +
-           '${prefix}maxWidth: ${maxWidth ?? "use parent maxWidth constraint"}\n' +
-           '${prefix}minHeight: ${minHeight ?? "use parent minHeight constraint"}\n' +
-           '${prefix}maxHeight: ${maxHeight ?? "use parent maxHeight constraint"}\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('minWidth: ${minWidth ?? "use parent minWidth constraint"}');
+    settings.add('maxWidth: ${maxWidth ?? "use parent maxWidth constraint"}');
+    settings.add('minHeight: ${minHeight ?? "use parent minHeight constraint"}');
+    settings.add('maxHeight: ${maxHeight ?? "use parent maxHeight constraint"}');
   }
 }
 

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

@@ -115,9 +115,10 @@ class RenderParagraph extends RenderBox {
 
   // we should probably expose a way to do precise (inter-glpyh) hit testing
 
-  String debugDescribeSettings(String prefix) {
-    String result = '${super.debugDescribeSettings(prefix)}';
-    result += '${prefix}text:\n${text.toString("$prefix  ")}\n';
-    return result;
+  String debugDescribeChildren(String prefix) {
+    return '$prefix \u2558\u2550\u2566\u2550\u2550 text \u2550\u2550\u2550\n'
+           '${text.toString("$prefix   \u2551 ")}\n'
+           '$prefix   \u255A\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\u2550\n'
+           '$prefix\n';
   }
 }

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

@@ -144,7 +144,10 @@ class RenderConstrainedBox extends RenderProxyBox {
     }
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}additionalConstraints: $additionalConstraints\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('additionalConstraints: $additionalConstraints');
+  }
 }
 
 /// A render object that, for both width and height, imposes a tight constraint
@@ -232,10 +235,10 @@ class RenderFractionallySizedBox extends RenderProxyBox {
     }
   }
 
-  String debugDescribeSettings(String prefix) {
-    return '${super.debugDescribeSettings(prefix)}' +
-           '${prefix}widthFactor: ${_widthFactor ?? "pass-through"}\n' +
-           '${prefix}heightFactor: ${_heightFactor ?? "pass-through"}\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('widthFactor: ${_widthFactor ?? "pass-through"}');
+    settings.add('heightFactor: ${_heightFactor ?? "pass-through"}');
   }
 }
 
@@ -302,7 +305,10 @@ class RenderAspectRatio extends RenderProxyBox {
       child.layout(new BoxConstraints.tight(size));
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}aspectRatio: $aspectRatio\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('aspectRatio: $aspectRatio');
+  }
 }
 
 /// Sizes its child to the child's intrinsic width
@@ -397,8 +403,11 @@ class RenderIntrinsicWidth extends RenderProxyBox {
     }
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}stepWidth: $stepWidth\n${prefix}stepHeight: $stepHeight\n';
-
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('stepWidth: $stepWidth');
+    settings.add('stepHeight: $stepHeight');
+  }
 }
 
 /// Sizes its child to the child's intrinsic height
@@ -500,6 +509,11 @@ class RenderOpacity extends RenderProxyBox {
         context.paintChildWithOpacity(child, offset.toPoint(), null, a);
     }
   }
+
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('opacity: ${opacity.toStringAsFixed(1)}');
+  }
 }
 
 class RenderShaderMask extends RenderProxyBox {
@@ -702,7 +716,11 @@ class RenderDecoratedBox extends RenderProxyBox {
       _painter.paint(context.canvas, offset & size);
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}decoration:\n${_painter.decoration.toString(prefix + "  ")}\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('decoration:');
+    settings.addAll(_painter.decoration.toString("  ").split('\n'));
+  }
 }
 
 /// Applies a transformation before painting its child
@@ -833,10 +851,14 @@ class RenderTransform extends RenderProxyBox {
     transform.multiply(_effectiveTransform);
   }
 
-  String debugDescribeSettings(String prefix) {
-    List<String> result = _transform.toString().split('\n').map((String s) => '$prefix  $s\n').toList();
-    result.removeLast();
-    return '${super.debugDescribeSettings(prefix)}${prefix}transform matrix:\n${result.join()}\n${prefix}origin: $origin\n${prefix}alignment: $alignment\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    List<String> matrix = _transform.toString().split('\n').map((String s) => '  $s').toList();
+    matrix.removeLast();
+    settings.add('transform matrix:');
+    settings.addAll(matrix);
+    settings.add('origin: $origin');
+    settings.add('alignment: $alignment');
   }
 }
 
@@ -952,6 +974,22 @@ class RenderPointerListener extends RenderProxyBox {
     if (onPointerCancel != null && event.type == 'pointercancel')
       return onPointerCancel(event);
   }
+
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    List<String> listeners = <String>[];
+    if (onPointerDown != null)
+      listeners.add('down');
+    if (onPointerMove != null)
+      listeners.add('move');
+    if (onPointerUp != null)
+      listeners.add('up');
+    if (onPointerCancel != null)
+      listeners.add('cancel');
+    if (listeners.isEmpty)
+      listeners.add('<none>');
+    settings.add('listeners: ${listeners.join(", ")}');
+  }
 }
 
 /// Is invisible during hit testing.
@@ -968,6 +1006,11 @@ class RenderIgnorePointer extends RenderProxyBox {
   bool hitTest(HitTestResult result, { Point position }) {
     return ignoring ? false : super.hitTest(result, position: position);
   }
+
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('ignoring: $ignoring');
+  }
 }
 
 /// Holds opaque meta data in the render tree

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

@@ -135,7 +135,10 @@ class RenderPadding extends RenderShiftedBox {
     ));
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}padding: $padding\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('padding: $padding');
+  }
 }
 
 enum ShrinkWrap {
@@ -202,7 +205,10 @@ class RenderPositionedBox extends RenderShiftedBox {
     }
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}alignment: $alignment\n';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('alignment: $alignment');
+  }
 }
 
 /// A delegate for computing the layout of a render object with a single child.
@@ -315,5 +321,9 @@ class RenderBaseline extends RenderShiftedBox {
     }
   }
 
-  String debugDescribeSettings(String prefix) => '${super.debugDescribeSettings(prefix)}${prefix}baseline: $baseline\nbaselineType: $baselineType';
+  void debugDescribeSettings(List<String> settings) {
+    super.debugDescribeSettings(settings);
+    settings.add('baseline: $baseline');
+    settings.add('baselineType: $baselineType');
+  }
 }

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

@@ -130,6 +130,10 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
 
   Rect get paintBounds => Point.origin & size;
 
-  String debugDescribeSettings(String prefix) => '${prefix}window size: ${ui.window.size} (in device pixels)\n${prefix}device pixel ratio: ${ui.window.devicePixelRatio} (device pixels per logical pixel)\n${prefix}root constraints: $rootConstraints (in logical pixels)\n';
-  // call to ${super.debugDescribeSettings(prefix)} is omitted because the root superclasses don't include any interesting information for this class
+  void debugDescribeSettings(List<String> settings) {
+    // call to ${super.debugDescribeSettings(prefix)} is omitted because the root superclasses don't include any interesting information for this class
+    settings.add('window size: ${ui.window.size} (in device pixels)');
+    settings.add('device pixel ratio: ${ui.window.devicePixelRatio} (device pixels per logical pixel)');
+    settings.add('root constraints: $rootConstraints (in logical pixels)');
+  }
 }

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

@@ -829,6 +829,10 @@ abstract class Element<T extends Widget> implements BuildContext {
     assert(false);
   }
 
+  String toStringShort() {
+    return widget != null ? '${widget.toStringShort()}' : '[$runtimeType]';
+  }
+
   String toString() {
     final List<String> data = <String>[];
     debugFillDescription(data);
@@ -1240,7 +1244,9 @@ class InheritedElement extends ProxyElement<InheritedWidget> {
 /// Base class for instantiations of RenderObjectWidget subclasses
 abstract class RenderObjectElement<T extends RenderObjectWidget> extends BuildableElement<T> {
   RenderObjectElement(T widget)
-    : _renderObject = widget.createRenderObject(), super(widget);
+    : _renderObject = widget.createRenderObject(), super(widget) {
+    assert(() { debugUpdateRenderObjectOwner(); return true; });
+  }
 
   /// The underlying [RenderObject] for this element
   RenderObject get renderObject => _renderObject;
@@ -1279,10 +1285,23 @@ abstract class RenderObjectElement<T extends RenderObjectWidget> extends Buildab
     T oldWidget = widget;
     super.update(newWidget);
     assert(widget == newWidget);
+    assert(() { debugUpdateRenderObjectOwner(); return true; });
     widget.updateRenderObject(renderObject, oldWidget);
     _dirty = false;
   }
 
+  void debugUpdateRenderObjectOwner() {
+    List<String> chain = <String>[];
+    Element node = this;
+    while (chain.length < 4 && node != null) {
+      chain.add(node.toStringShort());
+      node = node._parent;
+    }
+    if (node != null)
+      chain.add('\u22EF');
+    _renderObject.debugOwner = chain.join(' \u2190 ');
+  }
+
   void performRebuild() {
     reinvokeBuilders();
     _dirty = false;