Provide toStrings for Native objects (flutter#50168)

This hides the "Instance of _Native" bit that you get in debug output otherwise.

lib/ui/compositing.dart

@@ -80,6 +80,9 @@ base class _NativeScene extends NativeFieldWrapperClass1 implements Scene {
   @override
   @Native<Void Function(Pointer<Void>)>(symbol: 'Scene::dispose')
   external void dispose();
+
+  @override
+  String toString() => 'Scene';
 }
 
 // Lightweight wrapper of a native layer object.
@@ -951,4 +954,7 @@ base class _NativeSceneBuilder extends NativeFieldWrapperClass1 implements Scene
 
   @Native<Void Function(Pointer<Void>, Handle)>(symbol: 'SceneBuilder::build')
   external void _build(Scene outScene);
+
+  @override
+  String toString() => 'SceneBuilder';
 }

lib/ui/painting.dart

@@ -2131,6 +2131,9 @@ base class _NativeCodec extends NativeFieldWrapperClass1 implements Codec {
   @override
   @Native<Void Function(Pointer<Void>)>(symbol: 'Codec::dispose')
   external void dispose();
+
+  @override
+  String toString() => 'Codec(${_cachedFrameCount == null ? "" : "$_cachedFrameCount frames"})';
 }
 
 /// Instantiates an image [Codec].
@@ -3110,6 +3113,9 @@ base class _NativePath extends NativeFieldWrapperClass1 implements Path {
   PathMetrics computeMetrics({bool forceClosed = false}) {
     return PathMetrics._(this, forceClosed);
   }
+
+  @override
+  String toString() => 'Path';
 }
 
 /// The geometric description of a tangent: the angle at a point.
@@ -6238,6 +6244,9 @@ base class _NativeCanvas extends NativeFieldWrapperClass1 implements Canvas {
 
   @Native<Void Function(Pointer<Void>, Pointer<Void>, Uint32, Double, Bool)>(symbol: 'Canvas::drawShadow')
   external void _drawShadow(_NativePath path, int color, double elevation, bool transparentOccluder);
+
+  @override
+  String toString() => 'Canvas(recording: ${_recorder != null})';
 }
 
 /// Signature for [Picture] lifecycle events.
@@ -6381,6 +6390,9 @@ base class _NativePicture extends NativeFieldWrapperClass1 implements Picture {
   @override
   @Native<Uint64 Function(Pointer<Void>)>(symbol: 'Picture::GetAllocationSize', isLeaf: true)
   external int get approximateBytesUsed;
+
+  @override
+  String toString() => 'Picture';
 }
 
 /// Records a [Picture] containing a sequence of graphical operations.
@@ -6438,6 +6450,9 @@ base class _NativePictureRecorder extends NativeFieldWrapperClass1 implements Pi
   external void _endRecording(_NativePicture outPicture);
 
   _NativeCanvas? _canvas;
+
+  @override
+  String toString() => 'PictureRecorder(recording: $isRecording)';
 }
 
 /// A single shadow.
@@ -6895,6 +6910,9 @@ base class _NativeImageDescriptor extends NativeFieldWrapperClass1 implements Im
 
   @Native<Void Function(Pointer<Void>, Handle, Int32, Int32)>(symbol: 'ImageDescriptor::instantiateCodec')
   external void _instantiateCodec(Codec outCodec, int targetWidth, int targetHeight);
+
+  @override
+  String toString() => 'ImageDescriptor(width: ${_width ?? '?'}, height: ${_height ?? '?'}, bytes per pixel: ${_bytesPerPixel ?? '?'})';
 }
 
 /// Generic callback signature, used by [_futurize].

lib/ui/semantics.dart

@@ -1027,6 +1027,9 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
   }
   @Native<Void Function(Pointer<Void>, Handle)>(symbol: 'SemanticsUpdateBuilder::build')
   external void _build(_NativeSemanticsUpdate outSemanticsUpdate);
+
+  @override
+  String toString() => 'SemanticsUpdateBuilder';
 }
 
 /// An opaque object representing a batch of semantics updates.
@@ -1056,4 +1059,7 @@ base class _NativeSemanticsUpdate extends NativeFieldWrapperClass1 implements Se
   @override
   @Native<Void Function(Pointer<Void>)>(symbol: 'SemanticsUpdate::dispose')
   external void dispose();
+
+  @override
+  String toString() => 'SemanticsUpdate';
 }

lib/ui/text.dart

@@ -3334,6 +3334,27 @@ base class _NativeParagraph extends NativeFieldWrapperClass1 implements Paragrap
     }());
     return disposed ?? (throw StateError('$runtimeType.debugDisposed is only available when asserts are enabled.'));
   }
+
+  @override
+  String toString() {
+    String? result;
+    assert(() {
+      if (_disposed && _needsLayout) {
+        result = 'Paragraph(DISPOSED while dirty)';
+      }
+      if (_disposed && !_needsLayout) {
+        result = 'Paragraph(DISPOSED)';
+      }
+      return true;
+    }());
+    if (result != null) {
+      return result!;
+    }
+    if (_needsLayout) {
+      return 'Paragraph(dirty)';
+    }
+    return 'Paragraph()';
+  }
 }
 
 /// Builds a [Paragraph] containing text with the given styling information.
@@ -3657,6 +3678,9 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
 
   @Native<Void Function(Pointer<Void>, Handle)>(symbol: 'ParagraphBuilder::build')
   external void _build(_NativeParagraph outParagraph);
+
+  @override
+  String toString() => 'ParagraphBuilder';
 }
 
 /// Loads a font from a buffer and makes it available for rendering text.

testing/dart/BUILD.gn

@@ -45,6 +45,7 @@ tests = [
   "serial_gc_test.dart",
   "spawn_helper.dart",
   "spawn_test.dart",
+  "stringification_test.dart",
   "task_order_test.dart",
   "text_test.dart",
   "window_test.dart",

testing/dart/stringification_test.dart

@@ -0,0 +1,43 @@
+// Copyright 2013 The Flutter 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:typed_data';
+import 'dart:ui';
+
+import 'package:litetest/litetest.dart';
+
+final Uint8List imageData = Uint8List.fromList(<int>[ // Small WebP file
+  0x52, 0x49, 0x46, 0x46, 0x12, 0x00, 0x00, 0x00,  0x57, 0x45, 0x42, 0x50, 0x56, 0x50, 0x38, 0x4c, // |RIFF....WEBPVP8L|
+  0x06, 0x00, 0x00, 0x00, 0x2f, 0x41, 0x6c, 0x6f,  0x00, 0x6b,                                     // |..../Alo.k|
+]);
+
+void main() {
+  test('Stringification of native objects exposed in Dart', () async {
+    expect(SemanticsUpdateBuilder().toString(), 'SemanticsUpdateBuilder');
+    expect(SemanticsUpdateBuilder().build().toString(), 'SemanticsUpdate');
+    expect(ParagraphBuilder(ParagraphStyle()).toString(), 'ParagraphBuilder');
+    expect(ParagraphBuilder(ParagraphStyle()).build().toString(), 'Paragraph(dirty)');
+    expect((await instantiateImageCodec(imageData)).toString(), 'Codec()');
+    expect(Path().toString(), 'Path');
+    final PictureRecorder recorder = PictureRecorder();
+    expect(recorder.toString(), 'PictureRecorder(recording: false)');
+    final Canvas canvas = Canvas(recorder);
+    expect(recorder.toString(), 'PictureRecorder(recording: true)');
+    expect(canvas.toString(), 'Canvas(recording: true)');
+    final Picture picture = recorder.endRecording();
+    expect(recorder.toString(), 'PictureRecorder(recording: false)');
+    expect(canvas.toString(), 'Canvas(recording: false)');
+    expect(picture.toString(), 'Picture');
+    expect(
+      ImageDescriptor.raw(
+        await ImmutableBuffer.fromUint8List(Uint8List.fromList(<int>[0, 0, 0, 0])),
+        width: 1,
+        height: 1,
+        pixelFormat: PixelFormat.rgba8888,
+      ).toString(), 'ImageDescriptor(width: 1, height: 1, bytes per pixel: 4)',
+    );
+    expect(SceneBuilder().toString(), 'SceneBuilder');
+    expect(SceneBuilder().build().toString(), 'Scene');
+  });
+}