migrate part of painting to nullsafety (#62696)

* migrate part of painting to nullsafety

* address review comments

* address review comment

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:ui' as ui show lerpDouble;
 
@@ -88,12 +87,12 @@ abstract class AlignmentGeometry {
   /// into a concrete [Alignment] using [resolve].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static AlignmentGeometry lerp(AlignmentGeometry a, AlignmentGeometry b, double t) {
+  static AlignmentGeometry? lerp(AlignmentGeometry? a, AlignmentGeometry? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b * t;
+      return b! * t;
     if (b == null)
       return a * (1.0 - t);
     if (a is Alignment && b is Alignment)
@@ -101,9 +100,9 @@ abstract class AlignmentGeometry {
     if (a is AlignmentDirectional && b is AlignmentDirectional)
       return AlignmentDirectional.lerp(a, b, t);
     return _MixedAlignment(
-      ui.lerpDouble(a._x, b._x, t),
-      ui.lerpDouble(a._start, b._start, t),
-      ui.lerpDouble(a._y, b._y, t),
+      ui.lerpDouble(a._x, b._x, t)!,
+      ui.lerpDouble(a._start, b._start, t)!,
+      ui.lerpDouble(a._y, b._y, t)!,
     );
   }
 
@@ -116,7 +115,7 @@ abstract class AlignmentGeometry {
   ///  * [Alignment], for which this is a no-op (returns itself).
   ///  * [AlignmentDirectional], which flips the horizontal direction
   ///    based on the `direction` argument.
-  Alignment resolve(TextDirection direction);
+  Alignment resolve(TextDirection? direction);
 
   @override
   String toString() {
@@ -333,19 +332,19 @@ class Alignment extends AlignmentGeometry {
   /// If either is null, this function interpolates from [Alignment.center].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static Alignment lerp(Alignment a, Alignment b, double t) {
+  static Alignment? lerp(Alignment? a, Alignment? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return Alignment(ui.lerpDouble(0.0, b.x, t), ui.lerpDouble(0.0, b.y, t));
+      return Alignment(ui.lerpDouble(0.0, b!.x, t)!, ui.lerpDouble(0.0, b.y, t)!);
     if (b == null)
-      return Alignment(ui.lerpDouble(a.x, 0.0, t), ui.lerpDouble(a.y, 0.0, t));
-    return Alignment(ui.lerpDouble(a.x, b.x, t), ui.lerpDouble(a.y, b.y, t));
+      return Alignment(ui.lerpDouble(a.x, 0.0, t)!, ui.lerpDouble(a.y, 0.0, t)!);
+    return Alignment(ui.lerpDouble(a.x, b.x, t)!, ui.lerpDouble(a.y, b.y, t)!);
   }
 
   @override
-  Alignment resolve(TextDirection direction) => this;
+  Alignment resolve(TextDirection? direction) => this;
 
   static String _stringify(double x, double y) {
     if (x == -1.0 && y == -1.0)
@@ -514,27 +513,26 @@ class AlignmentDirectional extends AlignmentGeometry {
   /// If either is null, this function interpolates from [AlignmentDirectional.center].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static AlignmentDirectional lerp(AlignmentDirectional a, AlignmentDirectional b, double t) {
+  static AlignmentDirectional? lerp(AlignmentDirectional? a, AlignmentDirectional? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return AlignmentDirectional(ui.lerpDouble(0.0, b.start, t), ui.lerpDouble(0.0, b.y, t));
+      return AlignmentDirectional(ui.lerpDouble(0.0, b!.start, t)!, ui.lerpDouble(0.0, b.y, t)!);
     if (b == null)
-      return AlignmentDirectional(ui.lerpDouble(a.start, 0.0, t), ui.lerpDouble(a.y, 0.0, t));
-    return AlignmentDirectional(ui.lerpDouble(a.start, b.start, t), ui.lerpDouble(a.y, b.y, t));
+      return AlignmentDirectional(ui.lerpDouble(a.start, 0.0, t)!, ui.lerpDouble(a.y, 0.0, t)!);
+    return AlignmentDirectional(ui.lerpDouble(a.start, b.start, t)!, ui.lerpDouble(a.y, b.y, t)!);
   }
 
   @override
-  Alignment resolve(TextDirection direction) {
+  Alignment resolve(TextDirection? direction) {
     assert(direction != null, 'Cannot resolve $runtimeType without a TextDirection.');
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return Alignment(-start, y);
       case TextDirection.ltr:
         return Alignment(start, y);
     }
-    return null;
   }
 
   static String _stringify(double start, double y) {
@@ -622,15 +620,14 @@ class _MixedAlignment extends AlignmentGeometry {
   }
 
   @override
-  Alignment resolve(TextDirection direction) {
+  Alignment resolve(TextDirection? direction) {
     assert(direction != null, 'Cannot resolve $runtimeType without a TextDirection.');
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return Alignment(_x - _start, _y);
       case TextDirection.ltr:
         return Alignment(_x + _start, _y);
     }
-    return null;
   }
 }
 
@@ -652,7 +649,7 @@ class _MixedAlignment extends AlignmentGeometry {
 class TextAlignVertical {
   /// Creates a TextAlignVertical from any y value between -1.0 and 1.0.
   const TextAlignVertical({
-    @required this.y,
+    required this.y,
   }) : assert(y != null),
        assert(y >= -1.0 && y <= 1.0);
 

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:ui' show TextDirection;
 
@@ -143,7 +142,6 @@ Axis flipAxis(Axis direction) {
     case Axis.vertical:
       return Axis.horizontal;
   }
-  return null;
 }
 
 /// A direction in which boxes flow vertically.
@@ -214,7 +212,6 @@ Axis axisDirectionToAxis(AxisDirection axisDirection) {
     case AxisDirection.right:
       return Axis.horizontal;
   }
-  return null;
 }
 
 /// Returns the [AxisDirection] in which reading occurs in the given [TextDirection].
@@ -229,7 +226,6 @@ AxisDirection textDirectionToAxisDirection(TextDirection textDirection) {
     case TextDirection.ltr:
       return AxisDirection.right;
   }
-  return null;
 }
 
 /// Returns the opposite of the given [AxisDirection].
@@ -253,7 +249,6 @@ AxisDirection flipAxisDirection(AxisDirection axisDirection) {
     case AxisDirection.left:
       return AxisDirection.right;
   }
-  return null;
 }
 
 /// Returns whether traveling along the given axis direction visits coordinates
@@ -271,5 +266,4 @@ bool axisDirectionIsReversed(AxisDirection axisDirection) {
     case AxisDirection.right:
       return false;
   }
-  return null;
 }

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:typed_data' show Uint8List;
 import 'dart:ui' as ui show instantiateImageCodec, Codec;
@@ -23,14 +22,12 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
     super.initInstances();
     _instance = this;
     _imageCache = createImageCache();
-    if (shaderWarmUp != null) {
-      shaderWarmUp.execute();
-    }
+    shaderWarmUp?.execute();
   }
 
   /// The current [PaintingBinding], if one has been created.
-  static PaintingBinding get instance => _instance;
-  static PaintingBinding _instance;
+  static PaintingBinding? get instance => _instance;
+  static PaintingBinding? _instance;
 
   /// [ShaderWarmUp] to be executed during [initInstances].
   ///
@@ -53,7 +50,7 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   /// See also:
   ///
   ///  * [ShaderWarmUp], the interface of how this warm up works.
-  static ShaderWarmUp shaderWarmUp = const DefaultShaderWarmUp();
+  static ShaderWarmUp? shaderWarmUp = const DefaultShaderWarmUp();
 
   /// The singleton that implements the Flutter framework's image cache.
   ///
@@ -62,8 +59,8 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   ///
   /// The image cache is created during startup by the [createImageCache]
   /// method.
-  ImageCache get imageCache => _imageCache;
-  ImageCache _imageCache;
+  ImageCache? get imageCache => _imageCache;
+  ImageCache? _imageCache;
 
   /// Creates the [ImageCache] singleton (accessible via [imageCache]).
   ///
@@ -90,8 +87,8 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   /// above its native resolution should prefer scaling the canvas the image is
   /// drawn into.
   Future<ui.Codec> instantiateImageCodec(Uint8List bytes, {
-    int cacheWidth,
-    int cacheHeight,
+    int? cacheWidth,
+    int? cacheHeight,
     bool allowUpscaling = false,
   }) {
     assert(cacheWidth == null || cacheWidth > 0);
@@ -108,8 +105,8 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   @override
   void evict(String asset) {
     super.evict(asset);
-    imageCache.clear();
-    imageCache.clearLiveImages();
+    imageCache!.clear();
+    imageCache!.clearLiveImages();
   }
 
   @override
@@ -170,4 +167,4 @@ class _SystemFontsNotifier extends Listenable {
 ///
 /// The image cache is created during startup by the [PaintingBinding]'s
 /// [PaintingBinding.createImageCache] method.
-ImageCache get imageCache => PaintingBinding.instance.imageCache;
+ImageCache? get imageCache => PaintingBinding.instance!.imageCache;

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:math' as math;
 import 'dart:ui' show Color, lerpDouble, hashValues;
@@ -10,7 +9,7 @@ import 'dart:ui' show Color, lerpDouble, hashValues;
 import 'package:flutter/foundation.dart';
 
 double _getHue(double red, double green, double blue, double max, double delta) {
-  double hue;
+  late double hue;
   if (max == 0.0) {
     hue = 0.0;
   } else if (max == red) {
@@ -199,19 +198,19 @@ class HSVColor {
   /// {@macro dart.ui.shadow.lerp}
   ///
   /// Values outside of the valid range for each channel will be clamped.
-  static HSVColor lerp(HSVColor a, HSVColor b, double t) {
+  static HSVColor? lerp(HSVColor? a, HSVColor? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b._scaleAlpha(t);
+      return b!._scaleAlpha(t);
     if (b == null)
       return a._scaleAlpha(1.0 - t);
     return HSVColor.fromAHSV(
-      lerpDouble(a.alpha, b.alpha, t).clamp(0.0, 1.0) as double,
-      lerpDouble(a.hue, b.hue, t) % 360.0,
-      lerpDouble(a.saturation, b.saturation, t).clamp(0.0, 1.0) as double,
-      lerpDouble(a.value, b.value, t).clamp(0.0, 1.0) as double,
+      lerpDouble(a.alpha, b.alpha, t)!.clamp(0.0, 1.0) as double,
+      lerpDouble(a.hue, b.hue, t)! % 360.0,
+      lerpDouble(a.saturation, b.saturation, t)!.clamp(0.0, 1.0) as double,
+      lerpDouble(a.value, b.value, t)!.clamp(0.0, 1.0) as double,
     );
   }
 
@@ -383,19 +382,19 @@ class HSLColor {
   ///
   /// Values for `t` are usually obtained from an [Animation<double>], such as
   /// an [AnimationController].
-  static HSLColor lerp(HSLColor a, HSLColor b, double t) {
+  static HSLColor? lerp(HSLColor? a, HSLColor? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b._scaleAlpha(t);
+      return b!._scaleAlpha(t);
     if (b == null)
       return a._scaleAlpha(1.0 - t);
     return HSLColor.fromAHSL(
-      lerpDouble(a.alpha, b.alpha, t).clamp(0.0, 1.0) as double,
-      lerpDouble(a.hue, b.hue, t) % 360.0,
-      lerpDouble(a.saturation, b.saturation, t).clamp(0.0, 1.0) as double,
-      lerpDouble(a.lightness, b.lightness, t).clamp(0.0, 1.0) as double,
+      lerpDouble(a.alpha, b.alpha, t)!.clamp(0.0, 1.0) as double,
+      lerpDouble(a.hue, b.hue, t)! % 360.0,
+      lerpDouble(a.saturation, b.saturation, t)!.clamp(0.0, 1.0) as double,
+      lerpDouble(a.lightness, b.lightness, t)!.clamp(0.0, 1.0) as double,
     );
   }
 
@@ -441,7 +440,7 @@ class ColorSwatch<T> extends Color {
   final Map<T, Color> _swatch;
 
   /// Returns an element of the swatch table.
-  Color operator [](T index) => _swatch[index];
+  Color? operator [](T index) => _swatch[index];
 
   @override
   bool operator ==(Object other) {
@@ -468,9 +467,9 @@ class ColorProperty extends DiagnosticsProperty<Color> {
   /// The [showName], [style], and [level] arguments must not be null.
   ColorProperty(
     String name,
-    Color value, {
+    Color? value, {
     bool showName = true,
-    Object defaultValue = kNoDefaultValue,
+    Object? defaultValue = kNoDefaultValue,
     DiagnosticsTreeStyle style = DiagnosticsTreeStyle.singleLine,
     DiagnosticLevel level = DiagnosticLevel.info,
   }) : assert(showName != null),
@@ -484,14 +483,14 @@ class ColorProperty extends DiagnosticsProperty<Color> {
        );
 
   @override
-  Map<String, Object> toJsonMap(DiagnosticsSerializationDelegate delegate) {
-    final Map<String, Object> json = super.toJsonMap(delegate);
+  Map<String, Object?> toJsonMap(DiagnosticsSerializationDelegate delegate) {
+    final Map<String, Object?> json = super.toJsonMap(delegate);
     if (value != null) {
       json['valueProperties'] = <String, Object>{
-        'red': value.red,
-        'green': value.green,
-        'blue': value.blue,
-        'alpha': value.alpha,
+        'red': value!.red,
+        'green': value!.green,
+        'blue': value!.blue,
+        'alpha': value!.alpha,
       };
     }
     return json;

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:io';
 import 'dart:ui' show Size, hashValues;
@@ -30,7 +29,7 @@ typedef HttpClientProvider = HttpClient Function();
 /// a mock client that hasn't been affected by other tests.
 ///
 /// This value is ignored in non-debug builds.
-HttpClientProvider debugNetworkImageHttpClientProvider;
+HttpClientProvider? debugNetworkImageHttpClientProvider;
 
 typedef PaintImageCallback = void Function(ImageSizeInfo);
 
@@ -44,20 +43,20 @@ class ImageSizeInfo {
   /// This class is used by the framework when it paints an image to a canvas
   /// to report to `dart:developer`'s [postEvent], as well as to the
   /// [debugOnPaintImage] callback if it is set.
-  const ImageSizeInfo({this.source, this.displaySize, this.imageSize});
+  const ImageSizeInfo({this.source, this.displaySize, required this.imageSize});
 
   /// A unique identifier for this image, for example its asset path or network
   /// URL.
-  final String source;
+  final String? source;
 
   /// The size of the area the image will be rendered in.
-  final Size displaySize;
+  final Size? displaySize;
 
   /// The size the image has been decoded to.
   final Size imageSize;
 
   /// The number of bytes needed to render the image without scaling it.
-  int get displaySizeInBytes => _sizeToBytes(displaySize);
+  int get displaySizeInBytes => _sizeToBytes(displaySize!);
 
   /// The number of bytes used by the image in memory.
   int get decodedSizeInBytes => _sizeToBytes(imageSize);
@@ -69,14 +68,15 @@ class ImageSizeInfo {
   }
 
   /// Returns a JSON encodable representation of this object.
-  Map<String, Object> toJson() {
-    return <String, Object>{
+  Map<String, Object?> toJson() {
+    return <String, Object?>{
       'source': source,
-      'displaySize': <String, double>{
-        'width': displaySize.width,
-        'height': displaySize.height,
-      },
-      'imageSize': <String, double>{
+      if (displaySize != null)
+        'displaySize': <String, Object?>{
+          'width': displaySize!.width,
+          'height': displaySize!.height,
+        },
+      'imageSize': <String, Object?>{
         'width': imageSize.width,
         'height': imageSize.height,
       },
@@ -125,7 +125,7 @@ class ImageSizeInfo {
 /// a higher resolution while animating, but it would be problematic to have
 /// a grid or list of such thumbnails all be at the full resolution at the same
 /// time.
-PaintImageCallback debugOnPaintImage;
+PaintImageCallback? debugOnPaintImage;
 
 /// If true, the framework will color invert and horizontally flip images that
 /// have been decoded to a size taking at least [debugImageOverheadAllowance]

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:developer';
 import 'dart:ui' show hashValues;
@@ -103,7 +102,7 @@ class ImageCache {
     assert(value >= 0);
     if (value == maximumSize)
       return;
-    TimelineTask timelineTask;
+    TimelineTask? timelineTask;
     if (!kReleaseMode) {
        timelineTask = TimelineTask()..start(
         'ImageCache.setMaximumSize',
@@ -117,7 +116,7 @@ class ImageCache {
       _checkCacheSize(timelineTask);
     }
     if (!kReleaseMode) {
-      timelineTask.finish();
+      timelineTask!.finish();
     }
   }
 
@@ -142,7 +141,7 @@ class ImageCache {
     assert(value >= 0);
     if (value == _maximumSizeBytes)
       return;
-    TimelineTask timelineTask;
+    TimelineTask? timelineTask;
     if (!kReleaseMode) {
       timelineTask = TimelineTask()..start(
         'ImageCache.setMaximumSizeBytes',
@@ -156,7 +155,7 @@ class ImageCache {
       _checkCacheSize(timelineTask);
     }
     if (!kReleaseMode) {
-      timelineTask.finish();
+      timelineTask!.finish();
     }
   }
 
@@ -239,10 +238,10 @@ class ImageCache {
       // will never complete, e.g. it was loaded in a FakeAsync zone.
       // In such a case, we need to make sure subsequent calls to
       // putIfAbsent don't return this image that may never complete.
-      final _LiveImage image = _liveImages.remove(key);
+      final _LiveImage? image = _liveImages.remove(key);
       image?.removeListener();
     }
-    final _PendingImage pendingImage = _pendingImages.remove(key);
+    final _PendingImage? pendingImage = _pendingImages.remove(key);
     if (pendingImage != null) {
       if (!kReleaseMode) {
         Timeline.instantSync('ImageCache.evict', arguments: <String, dynamic>{
@@ -252,7 +251,7 @@ class ImageCache {
       pendingImage.removeListener();
       return true;
     }
-    final _CachedImage image = _cache.remove(key);
+    final _CachedImage? image = _cache.remove(key);
     if (image != null) {
       if (!kReleaseMode) {
         Timeline.instantSync('ImageCache.evict', arguments: <String, dynamic>{
@@ -260,7 +259,7 @@ class ImageCache {
           'sizeInBytes': image.sizeBytes,
         });
       }
-      _currentSizeBytes -= image.sizeBytes;
+      _currentSizeBytes -= image.sizeBytes!;
       return true;
     }
     if (!kReleaseMode) {
@@ -276,13 +275,13 @@ class ImageCache {
   ///
   /// Resizes the cache as appropriate to maintain the constraints of
   /// [maximumSize] and [maximumSizeBytes].
-  void _touch(Object key, _CachedImage image, TimelineTask timelineTask) {
+  void _touch(Object key, _CachedImage image, TimelineTask? timelineTask) {
     // TODO(dnfield): Some customers test in release mode with asserts enabled.
     // This is bound to cause problems, b/150295238 is tracking that. For now,
     // avoid this being a point of failure.
     assert(kReleaseMode || timelineTask != null);
-    if (image.sizeBytes != null && image.sizeBytes <= maximumSizeBytes) {
-      _currentSizeBytes += image.sizeBytes;
+    if (image.sizeBytes != null && image.sizeBytes! <= maximumSizeBytes) {
+      _currentSizeBytes += image.sizeBytes!;
       _cache[key] = image;
       _checkCacheSize(timelineTask);
     }
@@ -310,11 +309,11 @@ class ImageCache {
   /// `onError` is also provided. When an exception is caught resolving an image,
   /// no completers are cached and `null` is returned instead of a new
   /// completer.
-  ImageStreamCompleter putIfAbsent(Object key, ImageStreamCompleter loader(), { ImageErrorListener onError }) {
+  ImageStreamCompleter? putIfAbsent(Object key, ImageStreamCompleter loader(), { ImageErrorListener? onError }) {
     assert(key != null);
     assert(loader != null);
-    TimelineTask timelineTask;
-    TimelineTask listenerTask;
+    TimelineTask? timelineTask;
+    TimelineTask? listenerTask;
     if (!kReleaseMode) {
       timelineTask = TimelineTask()..start(
         'ImageCache.putIfAbsent',
@@ -323,11 +322,11 @@ class ImageCache {
         },
       );
     }
-    ImageStreamCompleter result = _pendingImages[key]?.completer;
+    ImageStreamCompleter? result = _pendingImages[key]?.completer;
     // Nothing needs to be done because the image hasn't loaded yet.
     if (result != null) {
       if (!kReleaseMode) {
-        timelineTask.finish(arguments: <String, dynamic>{'result': 'pending'});
+        timelineTask!.finish(arguments: <String, dynamic>{'result': 'pending'});
       }
       return result;
     }
@@ -335,10 +334,10 @@ class ImageCache {
     // recently used position below.
     // Don't use _touch here, which would trigger a check on cache size that is
     // not needed since this is just moving an existing cache entry to the head.
-    final _CachedImage image = _cache.remove(key);
+    final _CachedImage? image = _cache.remove(key);
     if (image != null) {
       if (!kReleaseMode) {
-        timelineTask.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
+        timelineTask!.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
       }
       // The image might have been keptAlive but had no listeners (so not live).
       // Make sure the cache starts tracking it as live again.
@@ -347,11 +346,11 @@ class ImageCache {
       return image.completer;
     }
 
-    final _CachedImage liveImage = _liveImages[key];
+    final _CachedImage? liveImage = _liveImages[key];
     if (liveImage != null) {
       _touch(key, liveImage, timelineTask);
       if (!kReleaseMode) {
-        timelineTask.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
+        timelineTask!.finish(arguments: <String, dynamic>{'result': 'keepAlive'});
       }
       return liveImage.completer;
     }
@@ -361,7 +360,7 @@ class ImageCache {
       _trackLiveImage(key, _LiveImage(result, null, () => _liveImages.remove(key)));
     } catch (error, stackTrace) {
       if (!kReleaseMode) {
-        timelineTask.finish(arguments: <String, dynamic>{
+        timelineTask!.finish(arguments: <String, dynamic>{
           'result': 'error',
           'error': error.toString(),
           'stackTrace': stackTrace.toString(),
@@ -387,12 +386,12 @@ class ImageCache {
     // will have to listen to the image at least once so we don't leak it in
     // the live image tracking.
     // If the cache is disabled, this variable will be set.
-    _PendingImage untrackedPendingImage;
-    void listener(ImageInfo info, bool syncCall) {
+    _PendingImage? untrackedPendingImage;
+    void listener(ImageInfo? info, bool syncCall) {
       // Images that fail to load don't contribute to cache size.
-      final int imageSize = info?.image == null ? 0 : info.image.height * info.image.width * 4;
+      final int imageSize = info == null || info.image == null ? 0 : info.image.height * info.image.width * 4;
 
-      final _CachedImage image = _CachedImage(result, imageSize);
+      final _CachedImage image = _CachedImage(result!, imageSize);
 
       _trackLiveImage(
         key,
@@ -403,7 +402,7 @@ class ImageCache {
         ),
       );
 
-      final _PendingImage pendingImage = untrackedPendingImage ?? _pendingImages.remove(key);
+      final _PendingImage? pendingImage = untrackedPendingImage ?? _pendingImages.remove(key);
       if (pendingImage != null) {
         pendingImage.removeListener();
       }
@@ -413,11 +412,11 @@ class ImageCache {
       }
 
       if (!kReleaseMode && !listenedOnce) {
-        listenerTask.finish(arguments: <String, dynamic>{
+        listenerTask!.finish(arguments: <String, dynamic>{
           'syncCall': syncCall,
           'sizeInBytes': imageSize,
         });
-        timelineTask.finish(arguments: <String, dynamic>{
+        timelineTask!.finish(arguments: <String, dynamic>{
           'currentSizeBytes': currentSizeBytes,
           'currentSize': currentSize,
         });
@@ -481,9 +480,9 @@ class ImageCache {
 
   // Remove images from the cache until both the length and bytes are below
   // maximum, or the cache is empty.
-  void _checkCacheSize(TimelineTask timelineTask) {
+  void _checkCacheSize(TimelineTask? timelineTask) {
     final Map<String, dynamic> finishArgs = <String, dynamic>{};
-    TimelineTask checkCacheTask;
+    TimelineTask? checkCacheTask;
     if (!kReleaseMode) {
       checkCacheTask = TimelineTask(parent: timelineTask)..start('checkCacheSize');
       finishArgs['evictedKeys'] = <String>[];
@@ -492,8 +491,8 @@ class ImageCache {
     }
     while (_currentSizeBytes > _maximumSizeBytes || _cache.length > _maximumSize) {
       final Object key = _cache.keys.first;
-      final _CachedImage image = _cache[key];
-      _currentSizeBytes -= image.sizeBytes;
+      final _CachedImage image = _cache[key]!;
+      _currentSizeBytes -= image.sizeBytes!;
       _cache.remove(key);
       if (!kReleaseMode) {
         finishArgs['evictedKeys'].add(key.toString());
@@ -502,7 +501,7 @@ class ImageCache {
     if (!kReleaseMode) {
       finishArgs['endSize'] = currentSize;
       finishArgs['endSizeBytes'] = currentSizeBytes;
-      checkCacheTask.finish(arguments: finishArgs);
+      checkCacheTask!.finish(arguments: finishArgs);
     }
     assert(_currentSizeBytes >= 0);
     assert(_cache.length <= maximumSize);
@@ -585,11 +584,11 @@ class _CachedImage {
   _CachedImage(this.completer, this.sizeBytes);
 
   final ImageStreamCompleter completer;
-  int sizeBytes;
+  int? sizeBytes;
 }
 
 class _LiveImage extends _CachedImage {
-  _LiveImage(ImageStreamCompleter completer, int sizeBytes, this.handleRemove)
+  _LiveImage(ImageStreamCompleter completer, int? sizeBytes, this.handleRemove)
       : super(completer, sizeBytes);
 
   final VoidCallback handleRemove;

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:developer';