migrate part of painting to nullsafety (#62951)

packages/flutter/lib/src/painting/_network_image_io.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:io';
@@ -33,7 +32,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
   final double scale;
 
   @override
-  final Map<String, String> headers;
+  final Map<String, String>? headers;
 
   @override
   Future<NetworkImage> obtainKey(image_provider.ImageConfiguration configuration) {
@@ -71,7 +70,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
     HttpClient client = _sharedHttpClient;
     assert(() {
       if (debugNetworkImageHttpClientProvider != null)
-        client = debugNetworkImageHttpClientProvider();
+        client = debugNetworkImageHttpClientProvider!();
       return true;
     }());
     return client;
@@ -102,7 +101,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
 
       final Uint8List bytes = await consolidateHttpClientResponseBytes(
         response,
-        onBytesReceived: (int cumulative, int total) {
+        onBytesReceived: (int cumulative, int? total) {
           chunkEvents.add(ImageChunkEvent(
             cumulativeBytesLoaded: cumulative,
             expectedTotalBytes: total,
@@ -118,7 +117,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
       // have had a chance to track the key in the cache at all.
       // Schedule a microtask to give the cache a chance to add the key.
       scheduleMicrotask(() {
-        PaintingBinding.instance.imageCache.evict(key);
+        PaintingBinding.instance!.imageCache!.evict(key);
       });
       rethrow;
     } finally {

packages/flutter/lib/src/painting/_network_image_web.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:ui' as ui;
@@ -33,7 +32,7 @@ class NetworkImage
   final double scale;
 
   @override
-  final Map<String, String> headers;
+  final Map<String, String>? headers;
 
   @override
   Future<NetworkImage> obtainKey(
@@ -58,9 +57,9 @@ class NetworkImage
         informationCollector: _imageStreamInformationCollector(key));
   }
 
-  InformationCollector _imageStreamInformationCollector(
+  InformationCollector? _imageStreamInformationCollector(
       image_provider.NetworkImage key) {
-    InformationCollector collector;
+    InformationCollector? collector;
     assert(() {
       collector = () {
         return <DiagnosticsNode>[

packages/flutter/lib/src/painting/beveled_rectangle_border.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;
 
@@ -57,24 +56,24 @@ class BeveledRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     assert(t != null);
     if (a is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!,
       );
     }
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     assert(t != null);
     if (b is BeveledRectangleBorder) {
       return BeveledRectangleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
+        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t)!,
       );
     }
     return super.lerpTo(b, t);
@@ -83,7 +82,7 @@ class BeveledRectangleBorder extends OutlinedBorder {
   /// Returns a copy of this RoundedRectangleBorder with the given fields
   /// replaced with the new values.
   @override
-  BeveledRectangleBorder copyWith({ BorderSide side, BorderRadius borderRadius }) {
+  BeveledRectangleBorder copyWith({ BorderSide? side, BorderRadius? borderRadius }) {
     return BeveledRectangleBorder(
       side: side ?? this.side,
       borderRadius: borderRadius ?? this.borderRadius,
@@ -120,17 +119,17 @@ class BeveledRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     return _getPath(borderRadius.resolve(textDirection).toRRect(rect).deflate(side.width));
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return _getPath(borderRadius.resolve(textDirection).toRRect(rect));
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     if (rect.isEmpty)
       return;
     switch (side.style) {

packages/flutter/lib/src/painting/border_radius.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 'package:flutter/foundation.dart';
 
@@ -130,7 +129,7 @@ abstract class BorderRadiusGeometry {
   /// into a concrete [BorderRadius] using [resolve].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadiusGeometry lerp(BorderRadiusGeometry a, BorderRadiusGeometry b, double t) {
+  static BorderRadiusGeometry? lerp(BorderRadiusGeometry? a, BorderRadiusGeometry? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
@@ -148,11 +147,11 @@ abstract class BorderRadiusGeometry {
   ///  * [BorderRadius], for which this is a no-op (returns itself).
   ///  * [BorderRadiusDirectional], which flips the horizontal direction
   ///    based on the `direction` argument.
-  BorderRadius resolve(TextDirection direction);
+  BorderRadius resolve(TextDirection? direction);
 
   @override
   String toString() {
-    String visual, logical;
+    String? visual, logical;
     if (_topLeft == _topRight &&
         _topRight == _bottomLeft &&
         _bottomLeft == _bottomRight) {
@@ -474,24 +473,24 @@ class BorderRadius extends BorderRadiusGeometry {
   /// If either is null, this function interpolates from [BorderRadius.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadius lerp(BorderRadius a, BorderRadius b, double t) {
+  static BorderRadius? lerp(BorderRadius? a, BorderRadius? 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);
     return BorderRadius.only(
-      topLeft: Radius.lerp(a.topLeft, b.topLeft, t),
-      topRight: Radius.lerp(a.topRight, b.topRight, t),
-      bottomLeft: Radius.lerp(a.bottomLeft, b.bottomLeft, t),
-      bottomRight: Radius.lerp(a.bottomRight, b.bottomRight, t),
+      topLeft: Radius.lerp(a.topLeft, b.topLeft, t)!,
+      topRight: Radius.lerp(a.topRight, b.topRight, t)!,
+      bottomLeft: Radius.lerp(a.bottomLeft, b.bottomLeft, t)!,
+      bottomRight: Radius.lerp(a.bottomRight, b.bottomRight, t)!,
     );
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) => this;
+  BorderRadius resolve(TextDirection? direction) => this;
 }
 
 /// An immutable set of radii for each corner of a rectangle, but with the
@@ -691,26 +690,26 @@ class BorderRadiusDirectional extends BorderRadiusGeometry {
   /// If either is null, this function interpolates from [BorderRadiusDirectional.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderRadiusDirectional lerp(BorderRadiusDirectional a, BorderRadiusDirectional b, double t) {
+  static BorderRadiusDirectional? lerp(BorderRadiusDirectional? a, BorderRadiusDirectional? 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);
     return BorderRadiusDirectional.only(
-      topStart: Radius.lerp(a.topStart, b.topStart, t),
-      topEnd: Radius.lerp(a.topEnd, b.topEnd, t),
-      bottomStart: Radius.lerp(a.bottomStart, b.bottomStart, t),
-      bottomEnd: Radius.lerp(a.bottomEnd, b.bottomEnd, t),
+      topStart: Radius.lerp(a.topStart, b.topStart, t)!,
+      topEnd: Radius.lerp(a.topEnd, b.topEnd, t)!,
+      bottomStart: Radius.lerp(a.bottomStart, b.bottomStart, t)!,
+      bottomEnd: Radius.lerp(a.bottomEnd, b.bottomEnd, t)!,
     );
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) {
+  BorderRadius resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return BorderRadius.only(
           topLeft: topEnd,
@@ -726,7 +725,6 @@ class BorderRadiusDirectional extends BorderRadiusGeometry {
           bottomRight: bottomEnd,
         );
     }
-    return null;
   }
 }
 
@@ -838,9 +836,9 @@ class _MixedBorderRadius extends BorderRadiusGeometry {
   }
 
   @override
-  BorderRadius resolve(TextDirection direction) {
+  BorderRadius resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return BorderRadius.only(
           topLeft: _topLeft + _topEnd,
@@ -856,6 +854,5 @@ class _MixedBorderRadius extends BorderRadiusGeometry {
           bottomRight: _bottomRight + _bottomEnd,
         );
     }
-    return null;
   }
 }

packages/flutter/lib/src/painting/borders.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' as ui show lerpDouble;
@@ -130,9 +129,9 @@ class BorderSide {
 
   /// Creates a copy of this border but with the given fields replaced with the new values.
   BorderSide copyWith({
-    Color color,
-    double width,
-    BorderStyle style,
+    Color? color,
+    double? width,
+    BorderStyle? style,
   }) {
     assert(width == null || width >= 0.0);
     return BorderSide(
@@ -186,7 +185,6 @@ class BorderSide {
           ..strokeWidth = 0.0
           ..style = PaintingStyle.stroke;
     }
-    return null;
   }
 
   /// Whether the two given [BorderSide]s can be merged using [new
@@ -219,12 +217,12 @@ class BorderSide {
       return a;
     if (t == 1.0)
       return b;
-    final double width = ui.lerpDouble(a.width, b.width, t);
+    final double width = ui.lerpDouble(a.width, b.width, t)!;
     if (width < 0.0)
       return BorderSide.none;
     if (a.style == b.style) {
       return BorderSide(
-        color: Color.lerp(a.color, b.color, t),
+        color: Color.lerp(a.color, b.color, t)!,
         width: width,
         style: a.style, // == b.style
       );
@@ -247,7 +245,7 @@ class BorderSide {
         break;
     }
     return BorderSide(
-      color: Color.lerp(colorA, colorB, t),
+      color: Color.lerp(colorA, colorB, t)!,
       width: width,
       style: BorderStyle.solid,
     );
@@ -319,7 +317,7 @@ abstract class ShapeBorder {
   /// The `reversed` argument is true if this object was the right operand of
   /// the `+` operator, and false if it was the left operand.
   @protected
-  ShapeBorder add(ShapeBorder other, { bool reversed = false }) => null;
+  ShapeBorder? add(ShapeBorder other, { bool reversed = false }) => null;
 
   /// Creates a new border consisting of the two borders on either side of the
   /// operator.
@@ -382,7 +380,7 @@ abstract class ShapeBorder {
   ///
   /// Instead of calling this directly, use [ShapeBorder.lerp].
   @protected
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a == null)
       return scale(t);
     return null;
@@ -414,7 +412,7 @@ abstract class ShapeBorder {
   ///
   /// Instead of calling this directly, use [ShapeBorder.lerp].
   @protected
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b == null)
       return scale(1.0 - t);
     return null;
@@ -428,9 +426,9 @@ abstract class ShapeBorder {
   /// and `b` after `t=0.5`.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static ShapeBorder lerp(ShapeBorder a, ShapeBorder b, double t) {
+  static ShapeBorder? lerp(ShapeBorder? a, ShapeBorder? b, double t) {
     assert(t != null);
-    ShapeBorder result;
+    ShapeBorder? result;
     if (b != null)
       result = b.lerpFrom(a, t);
     if (result == null && a != null)
@@ -457,7 +455,7 @@ abstract class ShapeBorder {
   ///
   ///  * [getInnerPath], which creates the path for the inner edge.
   ///  * [Path.contains], which can tell if an [Offset] is within a [Path].
-  Path getOuterPath(Rect rect, { TextDirection textDirection });
+  Path getOuterPath(Rect rect, { TextDirection? textDirection });
 
   /// Create a [Path] that describes the inner edge of the border.
   ///
@@ -478,7 +476,7 @@ abstract class ShapeBorder {
   ///
   ///  * [getOuterPath], which creates the path for the outer edge.
   ///  * [Path.contains], which can tell if an [Offset] is within a [Path].
-  Path getInnerPath(Rect rect, { TextDirection textDirection });
+  Path getInnerPath(Rect rect, { TextDirection? textDirection });
 
   /// Paints the border within the given [Rect] on the given [Canvas].
   ///
@@ -486,7 +484,7 @@ abstract class ShapeBorder {
   /// has a text direction dependency (for example if it is expressed in terms
   /// of "start" and "end" instead of "left" and "right"). It may be null if
   /// the border will not need the text direction to paint itself.
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection });
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection });
 
   @override
   String toString() {
@@ -548,7 +546,7 @@ class _CompoundBorder extends ShapeBorder {
       // border, and "merged" is the result of attempting to merge it with the
       // new border. If it's null, it couldn't be merged.
       final ShapeBorder ours = reversed ? borders.last : borders.first;
-      final ShapeBorder merged = ours.add(other, reversed: reversed)
+      final ShapeBorder? merged = ours.add(other, reversed: reversed)
                              ?? other.add(ours, reversed: !reversed);
       if (merged != null) {
         final List<ShapeBorder> result = <ShapeBorder>[...borders];
@@ -574,27 +572,27 @@ class _CompoundBorder extends ShapeBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     return _CompoundBorder.lerp(a, this, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     return _CompoundBorder.lerp(this, b, t);
   }
 
-  static _CompoundBorder lerp(ShapeBorder a, ShapeBorder b, double t) {
+  static _CompoundBorder lerp(ShapeBorder? a, ShapeBorder? b, double t) {
     assert(t != null);
     assert(a is _CompoundBorder || b is _CompoundBorder); // Not really necessary, but all call sites currently intend this.
-    final List<ShapeBorder> aList = a is _CompoundBorder ? a.borders : <ShapeBorder>[a];
-    final List<ShapeBorder> bList = b is _CompoundBorder ? b.borders : <ShapeBorder>[b];
+    final List<ShapeBorder?> aList = a is _CompoundBorder ? a.borders : <ShapeBorder?>[a];
+    final List<ShapeBorder?> bList = b is _CompoundBorder ? b.borders : <ShapeBorder?>[b];
     final List<ShapeBorder> results = <ShapeBorder>[];
     final int length = math.max(aList.length, bList.length);
     for (int index = 0; index < length; index += 1) {
-      final ShapeBorder localA = index < aList.length ? aList[index] : null;
-      final ShapeBorder localB = index < bList.length ? bList[index] : null;
+      final ShapeBorder? localA = index < aList.length ? aList[index] : null;
+      final ShapeBorder? localB = index < bList.length ? bList[index] : null;
       if (localA != null && localB != null) {
-        final ShapeBorder localResult = localA.lerpTo(localB, t) ?? localB.lerpFrom(localA, t);
+        final ShapeBorder? localResult = localA.lerpTo(localB, t) ?? localB.lerpFrom(localA, t);
         if (localResult != null) {
           results.add(localResult);
           continue;
@@ -613,19 +611,19 @@ class _CompoundBorder extends ShapeBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     for (int index = 0; index < borders.length - 1; index += 1)
       rect = borders[index].dimensions.resolve(textDirection).deflateRect(rect);
     return borders.last.getInnerPath(rect, textDirection: textDirection);
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return borders.first.getOuterPath(rect, textDirection: textDirection);
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     for (final ShapeBorder border in borders) {
       border.paint(canvas, rect, textDirection: textDirection);
       rect = border.dimensions.resolve(textDirection).deflateRect(rect);

packages/flutter/lib/src/painting/box_border.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 'package:flutter/foundation.dart';
 
@@ -85,7 +84,7 @@ abstract class BoxBorder extends ShapeBorder {
   // We override this to tighten the return value, so that callers can assume
   // that we'll return a [BoxBorder].
   @override
-  BoxBorder add(ShapeBorder other, { bool reversed = false }) => null;
+  BoxBorder? add(ShapeBorder other, { bool reversed = false }) => null;
 
   /// Linearly interpolate between two borders.
   ///
@@ -104,12 +103,12 @@ abstract class BoxBorder extends ShapeBorder {
   /// instead [add] the two sets of sides and interpolate them simultaneously.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BoxBorder lerp(BoxBorder a, BoxBorder b, double t) {
+  static BoxBorder? lerp(BoxBorder? a, BoxBorder? b, double t) {
     assert(t != null);
-    if ((a is Border || a == null) && (b is Border || b == null))
-      return Border.lerp(a as Border, b as Border, t);
-    if ((a is BorderDirectional || a == null) && (b is BorderDirectional || b == null))
-      return BorderDirectional.lerp(a as BorderDirectional, b as BorderDirectional, t);
+    if ((a is Border?) && (b is Border?))
+      return Border.lerp(a, b, t);
+    if ((a is BorderDirectional?) && (b is BorderDirectional?))
+      return BorderDirectional.lerp(a, b, t);
     if (b is Border && a is BorderDirectional) {
       final BoxBorder c = b;
       b = a;
@@ -167,14 +166,14 @@ abstract class BoxBorder extends ShapeBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { @required TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     assert(textDirection != null, 'The textDirection argument to $runtimeType.getInnerPath must not be null.');
     return Path()
       ..addRect(dimensions.resolve(textDirection).deflateRect(rect));
   }
 
   @override
-  Path getOuterPath(Rect rect, { @required TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     assert(textDirection != null, 'The textDirection argument to $runtimeType.getOuterPath must not be null.');
     return Path()
       ..addRect(rect);
@@ -203,9 +202,9 @@ abstract class BoxBorder extends ShapeBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   });
 
   static void _paintUniformBorderWithRadius(Canvas canvas, Rect rect, BorderSide side, BorderRadius borderRadius) {
@@ -414,7 +413,7 @@ class Border extends BoxBorder {
   }
 
   @override
-  Border add(ShapeBorder other, { bool reversed = false }) {
+  Border? add(ShapeBorder other, { bool reversed = false }) {
     if (other is Border &&
         BorderSide.canMerge(top, other.top) &&
         BorderSide.canMerge(right, other.right) &&
@@ -436,14 +435,14 @@ class Border extends BoxBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a is Border)
       return Border.lerp(a, this, t);
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b is Border)
       return Border.lerp(this, b, t);
     return super.lerpTo(b, t);
@@ -455,12 +454,12 @@ class Border extends BoxBorder {
   /// borders.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static Border lerp(Border a, Border b, double t) {
+  static Border? lerp(Border? a, Border? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return Border(
@@ -494,9 +493,9 @@ class Border extends BoxBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   }) {
     if (isUniform) {
       switch (top.style) {
@@ -694,7 +693,7 @@ class BorderDirectional extends BoxBorder {
   }
 
   @override
-  BoxBorder add(ShapeBorder other, { bool reversed = false }) {
+  BoxBorder? add(ShapeBorder other, { bool reversed = false }) {
     if (other is BorderDirectional) {
       final BorderDirectional typedOther = other;
       if (BorderSide.canMerge(top, typedOther.top) &&
@@ -747,14 +746,14 @@ class BorderDirectional extends BoxBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     if (a is BorderDirectional)
       return BorderDirectional.lerp(a, this, t);
     return super.lerpFrom(a, t);
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     if (b is BorderDirectional)
       return BorderDirectional.lerp(this, b, t);
     return super.lerpTo(b, t);
@@ -766,12 +765,12 @@ class BorderDirectional extends BoxBorder {
   /// borders.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BorderDirectional lerp(BorderDirectional a, BorderDirectional b, double t) {
+  static BorderDirectional? lerp(BorderDirectional? a, BorderDirectional? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return BorderDirectional(
@@ -808,9 +807,9 @@ class BorderDirectional extends BoxBorder {
   void paint(
     Canvas canvas,
     Rect rect, {
-    TextDirection textDirection,
+    TextDirection? textDirection,
     BoxShape shape = BoxShape.rectangle,
-    BorderRadius borderRadius,
+    BorderRadius? borderRadius,
   }) {
     if (isUniform) {
       switch (top.style) {
@@ -839,7 +838,7 @@ class BorderDirectional extends BoxBorder {
 
     BorderSide left, right;
     assert(textDirection != null, 'Non-uniform BorderDirectional objects require a TextDirection when painting.');
-    switch (textDirection) {
+    switch (textDirection!) {
       case TextDirection.rtl:
         left = end;
         right = start;

packages/flutter/lib/src/painting/box_fit.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;
 

packages/flutter/lib/src/painting/box_shadow.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' as ui show Shadow, lerpDouble;
@@ -79,19 +78,19 @@ class BoxShadow extends ui.Shadow {
   /// offset and a zero blurRadius.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BoxShadow lerp(BoxShadow a, BoxShadow b, double t) {
+  static BoxShadow? lerp(BoxShadow? a, BoxShadow? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
     if (a == null)
-      return b.scale(t);
+      return b!.scale(t);
     if (b == null)
       return a.scale(1.0 - t);
     return BoxShadow(
-      color: Color.lerp(a.color, b.color, t),
-      offset: Offset.lerp(a.offset, b.offset, t),
-      blurRadius: ui.lerpDouble(a.blurRadius, b.blurRadius, t),
-      spreadRadius: ui.lerpDouble(a.spreadRadius, b.spreadRadius, t),
+      color: Color.lerp(a.color, b.color, t)!,
+      offset: Offset.lerp(a.offset, b.offset, t)!,
+      blurRadius: ui.lerpDouble(a.blurRadius, b.blurRadius, t)!,
+      spreadRadius: ui.lerpDouble(a.spreadRadius, b.spreadRadius, t)!,
     );
   }
 
@@ -100,7 +99,7 @@ class BoxShadow extends ui.Shadow {
   /// If the lists differ in length, excess items are lerped with null.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static List<BoxShadow> lerpList(List<BoxShadow> a, List<BoxShadow> b, double t) {
+  static List<BoxShadow>? lerpList(List<BoxShadow>? a, List<BoxShadow>? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;
@@ -108,7 +107,7 @@ class BoxShadow extends ui.Shadow {
     b ??= <BoxShadow>[];
     final int commonLength = math.min(a.length, b.length);
     return <BoxShadow>[
-      for (int i = 0; i < commonLength; i += 1) BoxShadow.lerp(a[i], b[i], t),
+      for (int i = 0; i < commonLength; i += 1) BoxShadow.lerp(a[i], b[i], t)!,
       for (int i = commonLength; i < a.length; i += 1) a[i].scale(1.0 - t),
       for (int i = commonLength; i < b.length; i += 1) b[i].scale(t),
     ];

packages/flutter/lib/src/painting/edge_insets.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, WindowPadding;
 
@@ -73,7 +72,6 @@ abstract class EdgeInsetsGeometry {
       case Axis.vertical:
         return vertical;
     }
-    return null;
   }
 
   /// The size that this [EdgeInsets] would occupy with an empty interior.
@@ -218,12 +216,12 @@ abstract class EdgeInsetsGeometry {
   /// into a concrete [EdgeInsets] using [resolve].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsetsGeometry lerp(EdgeInsetsGeometry a, EdgeInsetsGeometry b, double t) {
+  static EdgeInsetsGeometry? lerp(EdgeInsetsGeometry? a, EdgeInsetsGeometry? 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 EdgeInsets && b is EdgeInsets)
@@ -231,12 +229,12 @@ abstract class EdgeInsetsGeometry {
     if (a is EdgeInsetsDirectional && b is EdgeInsetsDirectional)
       return EdgeInsetsDirectional.lerp(a, b, t);
     return _MixedEdgeInsets.fromLRSETB(
-      ui.lerpDouble(a._left, b._left, t),
-      ui.lerpDouble(a._right, b._right, t),
-      ui.lerpDouble(a._start, b._start, t),
-      ui.lerpDouble(a._end, b._end, t),
-      ui.lerpDouble(a._top, b._top, t),
-      ui.lerpDouble(a._bottom, b._bottom, t),
+      ui.lerpDouble(a._left, b._left, t)!,
+      ui.lerpDouble(a._right, b._right, t)!,
+      ui.lerpDouble(a._start, b._start, t)!,
+      ui.lerpDouble(a._end, b._end, t)!,
+      ui.lerpDouble(a._top, b._top, t)!,
+      ui.lerpDouble(a._bottom, b._bottom, t)!,
     );
   }
 
@@ -249,7 +247,7 @@ abstract class EdgeInsetsGeometry {
   ///  * [EdgeInsets], for which this is a no-op (returns itself).
   ///  * [EdgeInsetsDirectional], which flips the horizontal direction
   ///    based on the `direction` argument.
-  EdgeInsets resolve(TextDirection direction);
+  EdgeInsets resolve(TextDirection? direction);
 
   @override
   String toString() {
@@ -597,32 +595,32 @@ class EdgeInsets extends EdgeInsetsGeometry {
   /// If either is null, this function interpolates from [EdgeInsets.zero].
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsets lerp(EdgeInsets a, EdgeInsets b, double t) {
+  static EdgeInsets? lerp(EdgeInsets? a, EdgeInsets? 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);
     return EdgeInsets.fromLTRB(
-      ui.lerpDouble(a.left, b.left, t),
-      ui.lerpDouble(a.top, b.top, t),
-      ui.lerpDouble(a.right, b.right, t),
-      ui.lerpDouble(a.bottom, b.bottom, t),
+      ui.lerpDouble(a.left, b.left, t)!,
+      ui.lerpDouble(a.top, b.top, t)!,
+      ui.lerpDouble(a.right, b.right, t)!,
+      ui.lerpDouble(a.bottom, b.bottom, t)!,
     );
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) => this;
+  EdgeInsets resolve(TextDirection? direction) => this;
 
   /// Creates a copy of this EdgeInsets but with the given fields replaced
   /// with the new values.
   EdgeInsets copyWith({
-    double left,
-    double top,
-    double right,
-    double bottom,
+    double? left,
+    double? top,
+    double? right,
+    double? bottom,
   }) {
     return EdgeInsets.only(
       left: left ?? this.left,
@@ -822,32 +820,31 @@ class EdgeInsetsDirectional extends EdgeInsetsGeometry {
   /// [EdgeInsetsGeometry.lerp] static method.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static EdgeInsetsDirectional lerp(EdgeInsetsDirectional a, EdgeInsetsDirectional b, double t) {
+  static EdgeInsetsDirectional? lerp(EdgeInsetsDirectional? a, EdgeInsetsDirectional? 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);
     return EdgeInsetsDirectional.fromSTEB(
-      ui.lerpDouble(a.start, b.start, t),
-      ui.lerpDouble(a.top, b.top, t),
-      ui.lerpDouble(a.end, b.end, t),
-      ui.lerpDouble(a.bottom, b.bottom, t),
+      ui.lerpDouble(a.start, b.start, t)!,
+      ui.lerpDouble(a.top, b.top, t)!,
+      ui.lerpDouble(a.end, b.end, t)!,
+      ui.lerpDouble(a.bottom, b.bottom, t)!,
     );
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) {
+  EdgeInsets resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return EdgeInsets.fromLTRB(end, top, start, bottom);
       case TextDirection.ltr:
         return EdgeInsets.fromLTRB(start, top, end, bottom);
     }
-    return null;
   }
 }
 
@@ -943,14 +940,13 @@ class _MixedEdgeInsets extends EdgeInsetsGeometry {
   }
 
   @override
-  EdgeInsets resolve(TextDirection direction) {
+  EdgeInsets resolve(TextDirection? direction) {
     assert(direction != null);
-    switch (direction) {
+    switch (direction!) {
       case TextDirection.rtl:
         return EdgeInsets.fromLTRB(_end + _left, _top, _start + _right, _bottom);
       case TextDirection.ltr:
         return EdgeInsets.fromLTRB(_start + _left, _top, _end + _right, _bottom);
     }
-    return null;
   }
 }