Add asserts to catch potential misuses of the rendering framework.

sky/sdk/lib/rendering/object.dart

 // 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 'dart:math' as math;
 import 'dart:sky' as sky;
 import 'dart:sky' show Point, Size, Rect, Color, Paint, Path;
 
 import '../base/hit_test.dart';
 import '../base/node.dart';
@@ skipping 62 matching lines @@
     assert(child.parentData != null);
     child.parentData.detach();
     child._cleanRelayoutSubtreeRoot();
     super.dropChild(child);
     markNeedsLayout();
   }
 
   static List<RenderObject> _nodesNeedingLayout = new List<RenderObject>();
   static bool _debugDoingLayout = false;
   static bool get debugDoingLayout => _debugDoingLayout;
+  bool _debugDoingThisResize = false;
+  bool get debugDoingThisResize => _debugDoingThisResize;
+  bool _debugDoingThisLayout = false;
+  bool get debugDoingThisLayout => _debugDoingThisLayout;
+  static RenderObject _debugActiveLayout = null;
+  static RenderObject get debugActiveLayout => _debugActiveLayout;
+  bool _debugCanParentUseSize;
+  bool get debugCanParentUseSize => _debugCanParentUseSize;
   bool _needsLayout = true;
   bool get needsLayout => _needsLayout;
   RenderObject _relayoutSubtreeRoot;
   Constraints _constraints;
   Constraints get constraints => _constraints;
+  bool debugDoesMeetConstraints(); // override this in a subclass to verify that your state matches the constraints object
   bool debugAncestorsAlreadyMarkedNeedsLayout() {
     if (_relayoutSubtreeRoot == null)
       return true; // we haven't yet done layout even once, so there's nothing for us to do
     RenderObject node = this;
     while (node != _relayoutSubtreeRoot) {
       assert(node._relayoutSubtreeRoot == _relayoutSubtreeRoot);
       assert(node.parent != null);
       node = node.parent as RenderObject;
       if (!node._needsLayout)
         return false;
@@ skipping 47 matching lines @@
           node.layoutWithoutResize();
       });
     } finally {
       _debugDoingLayout = false;
       sky.tracing.end('RenderObject.flushLayout');
     }
   }
   void layoutWithoutResize() {
     try {
       assert(_relayoutSubtreeRoot == this);
+      _debugCanParentUseSize = false;
+      _debugDoingThisLayout = true;
+      RenderObject debugPreviousActiveLayout = _debugActiveLayout;
+      _debugActiveLayout = this;
       performLayout();
+      _debugActiveLayout = debugPreviousActiveLayout;
+      _debugDoingThisLayout = false;
+      _debugCanParentUseSize = null;
     } catch (e, stack) {
       print('Exception raised during layout of ${this}: ${e}');
       print(stack);
       return;
     }
     _needsLayout = false;
   }
   void layout(Constraints constraints, { bool parentUsesSize: false }) {
     final parent = this.parent; // TODO(ianh): Remove this once the analyzer is cleverer
     RenderObject relayoutSubtreeRoot;
     if (!parentUsesSize || sizedByParent || constraints.isTight || parent is! RenderObject)
       relayoutSubtreeRoot = this;
     else
       relayoutSubtreeRoot = parent._relayoutSubtreeRoot;
     assert(parent == this.parent); // TODO(ianh): Remove this once the analyzer is cleverer
     if (!needsLayout && constraints == _constraints && relayoutSubtreeRoot == _relayoutSubtreeRoot)
       return;
     _constraints = constraints;
     _relayoutSubtreeRoot = relayoutSubtreeRoot;
-    if (sizedByParent)
+    _debugCanParentUseSize = parentUsesSize;
+    if (sizedByParent) {
+      _debugDoingThisResize = true;
       performResize();
+      _debugDoingThisResize = false;
+    }
+    _debugDoingThisLayout = true;
+    RenderObject debugPreviousActiveLayout = _debugActiveLayout;
+    _debugActiveLayout = this;
     performLayout();
+    _debugActiveLayout = debugPreviousActiveLayout;
+    _debugDoingThisLayout = false;
+    _debugCanParentUseSize = null;
+    assert(debugDoesMeetConstraints());
     _needsLayout = false;
     markNeedsPaint();
     assert(parent == this.parent); // TODO(ianh): Remove this once the analyzer is cleverer
   }
   bool get sizedByParent => false; // return true if the constraints are the only input to the sizing algorithm (in particular, child nodes have no impact)
   void performResize(); // set the local dimensions, using only the constraints (only called if sizedByParent is true)
   void performLayout();
     // Override this to perform relayout without your parent's
     // involvement.
     //
@@ skipping 55 matching lines @@
   //   // For each child that intersects x,y, in z-order starting from the top,
   //   // call hitTest() for that child, passing it /result/, and the coordinates
   //   // converted to the child's coordinate origin, and stop at the first child
   //   // that returns true.
   //   // Then, add yourself to /result/, and return true.
   // }
   // You must not add yourself to /result/ if you return false.
 
 
   String toString([String prefix = '']) {
+    RenderObject debugPreviousActiveLayout = _debugActiveLayout;
+    _debugActiveLayout = null;
     String header = '${runtimeType}';
     if (_relayoutSubtreeRoot != null && _relayoutSubtreeRoot != this) {
       int count = 1;
       RenderObject target = parent;
       while (target != null && target != _relayoutSubtreeRoot) {
         target = target.parent as RenderObject;
         count += 1;
       }
       header += ' relayoutSubtreeRoot=up$count';
     }
     if (_needsLayout)
       header += ' NEEDS-LAYOUT';
     if (!attached)
       header += ' DETACHED';
     prefix += '  ';
-    return '${header}\n${debugDescribeSettings(prefix)}${debugDescribeChildren(prefix)}';
+    String result = '${header}\n${debugDescribeSettings(prefix)}${debugDescribeChildren(prefix)}';
+    _debugActiveLayout = debugPreviousActiveLayout;
+    return result;
   }
   String debugDescribeSettings(String prefix) => '${prefix}parentData: ${parentData}\n${prefix}constraints: ${constraints}\n';
   String debugDescribeChildren(String prefix) => '';
 
 }
 
 double clamp({ double min: 0.0, double value: 0.0, double max: double.INFINITY }) {
   assert(min != null);
   assert(value != null);
   assert(max != null);
@@ skipping 215 matching lines @@
     int count = 1;
     ChildType child = _firstChild;
     while (child != null) {
       result += '${prefix}child ${count}: ${child.toString(prefix)}';
       count += 1;
       child = child.parentData.nextSibling;
     }
     return result;
   }
 }