Add debugDisposed to Image (flutter/engine#21547)

engine/src/flutter/lib/ui/painting.dart

@@ -1632,6 +1632,19 @@ class Image {
     }
   }
 
+  /// Whether this reference to the underlying image is [dispose]d.
+  ///
+  /// This only returns a valid value if asserts are enabled, and must not be
+  /// used otherwise.
+  bool get debugDisposed {
+    bool? disposed;
+    assert(() {
+      disposed = _disposed;
+      return true;
+    }());
+    return disposed ?? (throw StateError('Image.debugDisposed is only available when asserts are enabled.'));
+  }
+
   /// Converts the [Image] object into a byte array.
   ///
   /// The [format] argument specifies the format in which the bytes will be

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/image.dart

@@ -54,12 +54,21 @@ class CkAnimatedImage implements ui.Image {
     }
   }
 
+  bool _disposed = false;
   @override
   void dispose() {
     box.delete();
+    _disposed = true;
   }
 
   @override
+  bool get debugDisposed {
+    if (assertionsEnabled) {
+      return _disposed;
+    }
+    throw StateError('Image.debugDisposed is only available when asserts are enabled.');
+  }
+
   ui.Image clone() => CkAnimatedImage._(_skAnimatedImage, box);
 
   @override
@@ -138,9 +147,22 @@ class CkImage implements ui.Image {
     }
   }
 
+  bool _disposed = false;
   @override
   void dispose() {
     box.delete();
+    assert(() {
+      _disposed = true;
+      return true;
+    }());
+  }
+
+  @override
+  bool get debugDisposed {
+    if (assertionsEnabled) {
+      return _disposed;
+    }
+    throw StateError('Image.debugDisposed is only available when asserts are enabled.');
   }
 
   @override

engine/src/flutter/lib/web_ui/lib/src/engine/html_image_codec.dart

@@ -116,12 +116,25 @@ class HtmlImage implements ui.Image {
   bool _requiresClone = false;
   HtmlImage(this.imgElement, this.width, this.height);
 
+  bool _disposed = false;
   @override
   void dispose() {
     // Do nothing. The codec that owns this image should take care of
     // releasing the object url.
+    if (assertionsEnabled) {
+      _disposed = true;
+    }
   }
 
+  @override
+  bool get debugDisposed {
+    if (assertionsEnabled) {
+      return _disposed;
+    }
+    return throw StateError('Image.debugDisposed is only available when asserts are enabled.');
+  }
+
+
   @override
   ui.Image clone() => this;
 

engine/src/flutter/lib/web_ui/lib/src/ui/painting.dart

@@ -329,6 +329,7 @@ abstract class Image {
   int get height;
   Future<ByteData?> toByteData({ImageByteFormat format = ImageByteFormat.rawRgba});
   void dispose();
+  bool get debugDisposed;
 
   Image clone() => this;
 

engine/src/flutter/lib/web_ui/test/canvaskit/image_test.dart

@@ -32,10 +32,13 @@ void testMain() {
       final SkAnimatedImage skAnimatedImage = canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage);
       final CkAnimatedImage image = CkAnimatedImage(skAnimatedImage);
       expect(image.box.isDeleted, false);
+      expect(image.debugDisposed, false);
       image.dispose();
       expect(image.box.isDeleted, true);
+      expect(image.debugDisposed, true);
       image.dispose();
       expect(image.box.isDeleted, true);
+      expect(image.debugDisposed, true);
     });
 
     test('CkAnimatedImage can be cloned and explicitly disposed of', () async {
@@ -69,10 +72,13 @@ void testMain() {
     test('CkImage can be explicitly disposed of', () {
       final SkImage skImage = canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage).getCurrentFrame();
       final CkImage image = CkImage(skImage);
+      expect(image.debugDisposed, false);
       expect(image.box.isDeleted, false);
       image.dispose();
+      expect(image.debugDisposed, true);
       expect(image.box.isDeleted, true);
       image.dispose();
+      expect(image.debugDisposed, true);
       expect(image.box.isDeleted, true);
     });
 

engine/src/flutter/lib/web_ui/test/engine/image/html_image_codec_test.dart

@@ -63,6 +63,14 @@ void testMain() async {
       expect(frameInfo.image.width, 100);
       expect(frameInfo.image.toString(), '[100×100]');
     });
+    test('dispose image image', () async {
+      final HtmlCodec codec = HtmlCodec('sample_image1.png');
+      final ui.FrameInfo frameInfo = await codec.getNextFrame();
+      expect(frameInfo.image, isNotNull);
+      expect(frameInfo.image.debugDisposed, false);
+      frameInfo.image.dispose();
+      expect(frameInfo.image.debugDisposed, true);
+    });
     test('provides image loading progress', () async {
       StringBuffer buffer = new StringBuffer();
       final HtmlCodec codec = HtmlCodec('sample_image1.png',

engine/src/flutter/lib/web_ui/test/golden_tests/engine/recording_canvas_golden_test.dart

@@ -723,6 +723,9 @@ class TestImage implements Image {
   @override
   void dispose() {}
 
+  @override
+  bool get debugDisposed => false;
+
   @override
   Image clone() => this;
 

engine/src/flutter/testing/dart/image_dispose_test.dart

@@ -126,6 +126,25 @@ void main() {
     expect(frame2.image.clone()..dispose(), isNotNull);
     frame2.image.dispose();
   });
+
+  test('debugDisposed works', () async {
+    final Uint8List bytes = await readFile('2x2.png');
+    final Codec codec = await instantiateImageCodec(bytes);
+    final FrameInfo frame = await codec.getNextFrame();
+
+    if (assertsEnabled) {
+      expect(frame.image.debugDisposed, false);
+    } else {
+      expect(() => frame.image.debugDisposed, throwsStateError);
+    }
+
+    frame.image.dispose();
+    if (assertsEnabled) {
+      expect(frame.image.debugDisposed, true);
+    } else {
+      expect(() => frame.image.debugDisposed, throwsStateError);
+    }
+  });
 }
 
 Future<Uint8List> readFile(String fileName) async {