Factor out debugPaintPadding and test it (#7598)

I plan to use this to implement similar logic in SliverPadding.

To make this easier to test I extended the paints matcher to accept a
function that takes a canvas. While I was at it I also made it accept
a Finder, it'll go and find the render object for you.

Also added support for paints..path and fixed some grammar in the
error messages.

Also improved the docs for debugPaint*.

packages/flutter/lib/src/painting/basic_types.dart

@@ -17,6 +17,7 @@ export 'dart:ui' show
   Paint,
   PaintingStyle,
   Path,
+  PathFillType,
   Point,
   Radius,
   RRect,

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

@@ -31,12 +31,22 @@ Color debugPaintSizeColor = _kDebugPaintSizeColor;
 
 /// The color to use when painting some boxes that just add space (e.g. an empty
 /// RenderConstrainedBox or RenderPadding).
+///
+/// Used by, among other methods, [debugPaintPadding], which is called by
+/// [RenderPadding.debugPaintSize] when [debugPaintSizeEnabled] is true.
 Color debugPaintSpacingColor = _kDebugPaintSpacingColor;
 
 /// The color to use when painting RenderPadding edges.
+///
+/// Used by, among other methods, [debugPaintPadding], which is called by
+/// [RenderPadding.debugPaintSize] when [debugPaintSizeEnabled] is true.
 Color debugPaintPaddingColor = _kDebugPaintPaddingColor;
 
-/// The color to use when painting RenderPadding edges.
+/// The color to use when painting RenderPadding edges. This color is painted on
+/// top of [debugPaintPaddingColor].
+///
+/// Used by, among other methods, [debugPaintPadding], which is called by
+/// [RenderPadding.debugPaintSize] when [debugPaintSizeEnabled] is true.
 Color debugPaintPaddingInnerEdgeColor = _kDebugPaintPaddingInnerEdgeColor;
 
 /// The color to use when painting the arrows used to show RenderPositionedBox alignment.
@@ -105,6 +115,35 @@ List<String> debugDescribeTransform(Matrix4 transform) {
   return matrix;
 }
 
+void _debugDrawDoubleRect(Canvas canvas, Rect outerRect, Rect innerRect, Color color) {
+  final Path path = new Path()
+    ..fillType = PathFillType.evenOdd
+    ..addRect(outerRect)
+    ..addRect(innerRect);
+  final Paint paint = new Paint()
+    ..color = color;
+  canvas.drawPath(path, paint);
+}
+
+/// Paint padding using the [debugPaintPaddingColor],
+/// [debugPaintPaddingInnerEdgeColor], and [debugPaintSpacingColor] colors.
+///
+/// Called by [RenderPadding.debugPaintSize] when [debugPaintSizeEnabled] is
+/// true.
+void debugPaintPadding(Canvas canvas, Rect outerRect, Rect innerRect, { double outlineWidth: 2.0 }) {
+  assert(() {
+    if (innerRect != null && !innerRect.isEmpty) {
+      _debugDrawDoubleRect(canvas, outerRect, innerRect, debugPaintPaddingColor);
+      _debugDrawDoubleRect(canvas, innerRect.inflate(outlineWidth).intersect(outerRect), innerRect, debugPaintPaddingInnerEdgeColor);
+    } else {
+      final Paint paint = new Paint()
+        ..color = debugPaintSpacingColor;
+      canvas.drawRect(outerRect, paint);
+    }
+    return true;
+  });
+}
+
 /// Returns true if none of the rendering library debug variables have been changed.
 ///
 /// This function is used by the test framework to ensure that debug variables

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

@@ -172,43 +172,8 @@ class RenderPadding extends RenderShiftedBox {
   void debugPaintSize(PaintingContext context, Offset offset) {
     super.debugPaintSize(context, offset);
     assert(() {
-      Paint paint;
-      if (child != null && !child.size.isEmpty) {
-        Path path;
-        paint = new Paint()
-          ..color = debugPaintPaddingColor;
-        path = new Path()
-          ..moveTo(offset.dx, offset.dy)
-          ..lineTo(offset.dx + size.width, offset.dy)
-          ..lineTo(offset.dx + size.width, offset.dy + size.height)
-          ..lineTo(offset.dx, offset.dy + size.height)
-          ..close()
-          ..moveTo(offset.dx + padding.left, offset.dy + padding.top)
-          ..lineTo(offset.dx + padding.left, offset.dy + size.height - padding.bottom)
-          ..lineTo(offset.dx + size.width - padding.right, offset.dy + size.height - padding.bottom)
-          ..lineTo(offset.dx + size.width - padding.right, offset.dy + padding.top)
-          ..close();
-        context.canvas.drawPath(path, paint);
-        paint = new Paint()
-          ..color = debugPaintPaddingInnerEdgeColor;
-        const double kOutline = 2.0;
-        path = new Path()
-          ..moveTo(offset.dx + math.max(padding.left - kOutline, 0.0), offset.dy + math.max(padding.top - kOutline, 0.0))
-          ..lineTo(offset.dx + math.min(size.width - padding.right + kOutline, size.width), offset.dy + math.max(padding.top - kOutline, 0.0))
-          ..lineTo(offset.dx + math.min(size.width - padding.right + kOutline, size.width), offset.dy + math.min(size.height - padding.bottom + kOutline, size.height))
-          ..lineTo(offset.dx + math.max(padding.left - kOutline, 0.0), offset.dy + math.min(size.height - padding.bottom + kOutline, size.height))
-          ..close()
-          ..moveTo(offset.dx + padding.left, offset.dy + padding.top)
-          ..lineTo(offset.dx + padding.left, offset.dy + size.height - padding.bottom)
-          ..lineTo(offset.dx + size.width - padding.right, offset.dy + size.height - padding.bottom)
-          ..lineTo(offset.dx + size.width - padding.right, offset.dy + padding.top)
-          ..close();
-        context.canvas.drawPath(path, paint);
-      } else {
-        paint = new Paint()
-          ..color = debugPaintSpacingColor;
-        context.canvas.drawRect(offset & size, paint);
-      }
+      final Rect outerRect = offset & size;
+      debugPaintPadding(context.canvas, outerRect, child != null ? padding.deflateRect(outerRect) : null);
       return true;
     });
   }

packages/flutter/test/material/mergeable_material_test.dart

@@ -203,13 +203,14 @@ void main() {
       )
     );
 
-    RenderBox box = tester.renderObject(find.byType(MergeableMaterial));
-
     final BoxShadow boxShadow = kElevationToShadow[2][0];
     final RRect rrect = kMaterialEdges[MaterialType.card].toRRect(
       new Rect.fromLTRB(0.0, 0.0, 800.0, 100.0)
     );
-    expect(box, paints..rrect(rrect: rrect, color: boxShadow.color, hasMaskFilter: true));
+    expect(
+      find.byType(MergeableMaterial),
+      paints..rrect(rrect: rrect, color: boxShadow.color, hasMaskFilter: true),
+    );
   });
 
   testWidgets('MergeableMaterial merge gap', (WidgetTester tester) async {

packages/flutter/test/rendering/debug_test.dart

@@ -6,8 +6,10 @@ import 'package:flutter/rendering.dart';
 import 'package:test/test.dart';
 import 'package:vector_math/vector_math_64.dart';
 
+import 'mock_canvas.dart';
+
 void main() {
-  test("Describe transform control test", () {
+  test('Describe transform control test', () {
     Matrix4 identity = new Matrix4.identity();
     List<String> description = debugDescribeTransform(identity);
     expect(description, equals(<String>[
@@ -17,4 +19,16 @@ void main() {
       '  [3] 0.0,0.0,0.0,1.0',
     ]));
   });
+
+  test('debugPaintPadding', () {
+    expect((Canvas canvas) {
+      debugPaintPadding(canvas, new Rect.fromLTRB(10.0, 10.0, 20.0, 20.0), null);
+    }, paints..rect(color: debugPaintSpacingColor));
+    expect((Canvas canvas) {
+      debugPaintPadding(canvas, new Rect.fromLTRB(10.0, 10.0, 20.0, 20.0), new Rect.fromLTRB(11.0, 11.0, 19.0, 19.0));
+    }, paints..path(color: debugPaintPaddingColor)..path(color: debugPaintPaddingInnerEdgeColor));
+    expect((Canvas canvas) {
+      debugPaintPadding(canvas, new Rect.fromLTRB(10.0, 10.0, 20.0, 20.0), new Rect.fromLTRB(15.0, 15.0, 15.0, 15.0));
+    }, paints..rect(rect: new Rect.fromLTRB(10.0, 10.0, 20.0, 20.0), color: debugPaintSpacingColor));
+  });
 }

packages/flutter/test/rendering/mock_canvas.dart

@@ -4,10 +4,22 @@
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
-import 'package:test/test.dart';
+import 'package:flutter_test/flutter_test.dart';
 
-/// Matches [RenderObject]s that paint a display list that matches the canvas
-/// calls described by the pattern.
+/// Matches objects or functions that paint a display list that matches the
+/// canvas calls described by the pattern.
+///
+/// Specifically, this can be applied to [RenderObject]s, [Finder]s that
+/// correspond to a single [RenderObject], and functions that have either of the
+/// following signatures:
+///
+/// ```dart
+/// void function(PaintingContext context, Offset offset);
+/// void function(Canvas canvas);
+/// ```
+///
+/// In the case of functions that take a [PaintingContext] and an [Offset], the
+/// [paints] matcher will always pass a zero offset.
 ///
 /// To specify the pattern, call the methods on the returned object. For example:
 ///
@@ -34,6 +46,12 @@ PaintPattern get paints => new _TestRecordingCanvasPatternMatcher();
 /// ```
 typedef bool PaintPatternPredicate(Symbol methodName, List<dynamic> arguments);
 
+/// The signature of [RenderObject.paint] functions.
+typedef void _ContextPainterFunction(PaintingContext context, Offset offset);
+
+/// The signature of functions that paint directly on a canvas.
+typedef void _CanvasPainterFunction(Canvas canvas);
+
 /// Builder interface for patterns used to match display lists (canvas calls).
 ///
 /// The [paints] matcher returns a [PaintPattern] so that you can build the
@@ -125,6 +143,21 @@ abstract class PaintPattern {
   /// [Canvas.drawCircle] call are ignored.
   void circle({ double x, double y, double radius, Color color, bool hasMaskFilter, PaintingStyle style });
 
+  /// Indicates that a path is expected next.
+  ///
+  /// The next path is examined. Any arguments that are passed to this method
+  /// are compared to the actual [Canvas.drawPath] call's `paint` argument, and
+  /// any mismatches result in failure.
+  ///
+  /// There is currently no way to check the actual path itself.
+  // See https://github.com/flutter/flutter/issues/93 which tracks that issue.
+  ///
+  /// If no call to [Canvas.drawPath] was made, then this results in failure.
+  ///
+  /// Any calls made between the last matched call (if any) and the
+  /// [Canvas.drawPath] call are ignored.
+  void path({ Color color, bool hasMaskFilter, PaintingStyle style });
+
   /// Provides a custom matcher.
   ///
   /// Each method call after the last matched call (if any) will be passed to
@@ -192,12 +225,16 @@ class _TestRecordingCanvasPatternMatcher extends Matcher implements PaintPattern
     _predicates.add(new _RRectPaintPredicate(rrect: rrect, color: color, hasMaskFilter: hasMaskFilter, style: style));
   }
 
-
   @override
   void circle({ double x, double y, double radius, Color color, bool hasMaskFilter, PaintingStyle style }) {
     _predicates.add(new _CirclePaintPredicate(x: x, y: y, radius: radius, color: color, hasMaskFilter: hasMaskFilter, style: style));
   }
 
+  @override
+  void path({ Color color, bool hasMaskFilter, PaintingStyle style }) {
+    _predicates.add(new _PathPaintPredicate(color: color, hasMaskFilter: hasMaskFilter, style: style));
+  }
+
   @override
   void something(PaintPatternPredicate predicate) {
     _predicates.add(new _SomethingPaintPredicate(predicate));
@@ -205,12 +242,28 @@ class _TestRecordingCanvasPatternMatcher extends Matcher implements PaintPattern
 
   @override
   bool matches(Object object, Map<dynamic, dynamic> matchState) {
-    if (object is! RenderObject)
-      return false;
     final _TestRecordingCanvas canvas = new _TestRecordingCanvas();
     final _TestRecordingPaintingContext context = new _TestRecordingPaintingContext(canvas);
-    final RenderObject renderObject = object;
-    renderObject.paint(context, Offset.zero);
+    if (object is _ContextPainterFunction) {
+      final _ContextPainterFunction function = object;
+      function(context, Offset.zero);
+    } else if (object is _CanvasPainterFunction) {
+      final _CanvasPainterFunction function = object;
+      function(canvas);
+    } else {
+      if (object is Finder) {
+        TestAsyncUtils.guardSync();
+        final Finder finder = object;
+        object = finder.evaluate().single.renderObject;
+      }
+      if (object is RenderObject) {
+        final RenderObject renderObject = object;
+        renderObject.paint(context, Offset.zero);
+      } else {
+        matchState[this] = 'was not one of the supported objects for the "paints" matcher.';
+        return false;
+      }
+    }
     final StringBuffer description = new StringBuffer();
     final bool result = _evaluatePredicates(canvas._invocations, description);
     if (!result) {
@@ -226,7 +279,7 @@ class _TestRecordingCanvasPatternMatcher extends Matcher implements PaintPattern
 
   @override
   Description describe(Description description) {
-    description.add('RenderObject painting: ');
+    description.add('Object or closure painting: ');
     return description.addAll(
       '', ', ', '',
       _predicates.map((_PaintPredicate predicate) => predicate.toString()),
@@ -387,7 +440,7 @@ abstract class _DrawCommandPaintPredicate extends _PaintPredicate {
       if (hasMaskFilter)
         throw 'called $methodName with a paint that did not have a mask filter, despite expecting one.';
       else
-        throw 'called $methodName with a paint that did had a mask filter, despite not expecting one.';
+        throw 'called $methodName with a paint that did have a mask filter, despite not expecting one.';
     }
     if (style != null && paintArgument.style != style)
       throw 'called $methodName with a paint whose style, ${paintArgument.style}, was not exactly the expected style ($style).';
@@ -437,8 +490,13 @@ class _OneParameterPaintPredicate<T> extends _DrawCommandPaintPredicate {
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
-    if (expected != null)
-      description.add('${T.runtimeType}: $expected');
+    if (expected != null) {
+      if (expected.toString().contains(T.toString())) {
+        description.add('$expected');
+      } else {
+        description.add('$T: $expected');
+      }
+    }
   }
 }
 
@@ -509,6 +567,12 @@ class _CirclePaintPredicate extends _DrawCommandPaintPredicate {
   }
 }
 
+class _PathPaintPredicate extends _DrawCommandPaintPredicate {
+  _PathPaintPredicate({ Color color, bool hasMaskFilter, PaintingStyle style }) : super(
+    #drawPath, 'a path', 2, 1, color: color, hasMaskFilter: hasMaskFilter, style: style
+  );
+}
+
 class _SomethingPaintPredicate extends _PaintPredicate {
   _SomethingPaintPredicate(this.predicate);