migrate painting to nullsafety (#63703)

* migrate painting to nullsafety

* address review comments

packages/flutter/lib/painting.dart

@@ -2,8 +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
-
 /// The Flutter painting library.
 ///
 /// To use, import `package:flutter/painting.dart`.

packages/flutter/lib/src/painting/flutter_logo.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:typed_data';
@@ -107,7 +106,7 @@ class FlutterLogoDecoration extends Decoration {
   /// See also:
   ///
   ///  * [Decoration.lerp], which interpolates between arbitrary decorations.
-  static FlutterLogoDecoration lerp(FlutterLogoDecoration a, FlutterLogoDecoration b, double t) {
+  static FlutterLogoDecoration? lerp(FlutterLogoDecoration? a, FlutterLogoDecoration? b, double t) {
     assert(t != null);
     assert(a == null || a.debugAssertIsValid());
     assert(b == null || b.debugAssertIsValid());
@@ -115,7 +114,7 @@ class FlutterLogoDecoration extends Decoration {
       return null;
     if (a == null) {
       return FlutterLogoDecoration._(
-        b.textColor,
+        b!.textColor,
         b.style,
         b.margin * t,
         b._position,
@@ -136,40 +135,40 @@ class FlutterLogoDecoration extends Decoration {
     if (t == 1.0)
       return b;
     return FlutterLogoDecoration._(
-      Color.lerp(a.textColor, b.textColor, t),
+      Color.lerp(a.textColor, b.textColor, t)!,
       t < 0.5 ? a.style : b.style,
-      EdgeInsets.lerp(a.margin, b.margin, t),
+      EdgeInsets.lerp(a.margin, b.margin, t)!,
       a._position + (b._position - a._position) * t,
       (a._opacity + (b._opacity - a._opacity) * t).clamp(0.0, 1.0) as double,
     );
   }
 
   @override
-  FlutterLogoDecoration lerpFrom(Decoration a, double t) {
+  FlutterLogoDecoration? lerpFrom(Decoration? a, double t) {
     assert(debugAssertIsValid());
     if (a == null || a is FlutterLogoDecoration) {
       assert(a == null || a.debugAssertIsValid());
       return FlutterLogoDecoration.lerp(a as FlutterLogoDecoration, this, t);
     }
-    return super.lerpFrom(a, t) as FlutterLogoDecoration;
+    return super.lerpFrom(a, t) as FlutterLogoDecoration?;
   }
 
   @override
-  FlutterLogoDecoration lerpTo(Decoration b, double t) {
+  FlutterLogoDecoration? lerpTo(Decoration? b, double t) {
     assert(debugAssertIsValid());
     if (b == null || b is FlutterLogoDecoration) {
       assert(b == null || b.debugAssertIsValid());
       return FlutterLogoDecoration.lerp(this, b as FlutterLogoDecoration, t);
     }
-    return super.lerpTo(b, t) as FlutterLogoDecoration;
+    return super.lerpTo(b, t) as FlutterLogoDecoration?;
   }
 
   @override
   // TODO(ianh): better hit testing
-  bool hitTest(Size size, Offset position, { TextDirection textDirection }) => true;
+  bool hitTest(Size size, Offset position, { TextDirection? textDirection }) => true;
 
   @override
-  BoxPainter createBoxPainter([ VoidCallback onChanged ]) {
+  BoxPainter createBoxPainter([ VoidCallback? onChanged ]) {
     assert(debugAssertIsValid());
     return _FlutterLogoPainter(this);
   }
@@ -218,8 +217,8 @@ class _FlutterLogoPainter extends BoxPainter {
   final FlutterLogoDecoration _config;
 
   // these are configured assuming a font size of 100.0.
-  TextPainter _textPainter;
-  Rect _textBoundingRect;
+  late TextPainter _textPainter;
+  late Rect _textBoundingRect;
 
   void _prepareText() {
     const String kLabel = 'Flutter';
@@ -323,7 +322,7 @@ class _FlutterLogoPainter extends BoxPainter {
   @override
   void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
     offset += _config.margin.topLeft;
-    final Size canvasSize = _config.margin.deflateSize(configuration.size);
+    final Size canvasSize = _config.margin.deflateSize(configuration.size!);
     if (canvasSize.isEmpty)
       return;
     Size logoSize;
@@ -365,7 +364,7 @@ class _FlutterLogoPainter extends BoxPainter {
       // only the mark
       logoTargetSquare = centerSquare;
     }
-    final Rect logoSquare = Rect.lerp(centerSquare, logoTargetSquare, _config._position.abs());
+    final Rect logoSquare = Rect.lerp(centerSquare, logoTargetSquare, _config._position.abs())!;
 
     if (_config._opacity < 1.0) {
       canvas.saveLayer(
@@ -388,7 +387,7 @@ class _FlutterLogoPainter extends BoxPainter {
         final double initialLeftTextPosition = // position of text when just starting the animation
           rect.width / 2.0 - _textBoundingRect.width * scale;
         final Offset textOffset = Offset(
-          rect.left + ui.lerpDouble(initialLeftTextPosition, finalLeftTextPosition, _config._position),
+          rect.left + ui.lerpDouble(initialLeftTextPosition, finalLeftTextPosition, _config._position)!,
           rect.top + (rect.height - _textBoundingRect.height * scale) / 2.0,
         );
         canvas.save();

packages/flutter/lib/src/painting/inline_span.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 ParagraphBuilder;
 
@@ -71,10 +70,10 @@ class InlineSpanSemanticsInformation {
   final String text;
 
   /// The semanticsLabel, if any.
-  final String semanticsLabel;
+  final String? semanticsLabel;
 
   /// The gesture recognizer, if any, for this span.
-  final GestureRecognizer recognizer;
+  final GestureRecognizer? recognizer;
 
   /// Whether this is for a placeholder span.
   final bool isPlaceholder;
@@ -155,7 +154,7 @@ abstract class InlineSpan extends DiagnosticableTree {
   ///
   /// The [style] is also applied to any child spans when this is an instance
   /// of [TextSpan].
-  final TextStyle style;
+  final TextStyle? style;
 
   // TODO(garyq): Remove the deprecated visitTextSpan, text, and children.
   /// Returns the text associated with this span if this is an instance of [TextSpan],
@@ -164,7 +163,7 @@ abstract class InlineSpan extends DiagnosticableTree {
     'InlineSpan does not innately have text. Use TextSpan.text instead. '
     'This feature was deprecated after v1.7.3.'
   )
-  String get text => null;
+  String? get text => null;
 
   // TODO(garyq): Remove the deprecated visitTextSpan, text, and children.
   /// Returns the [InlineSpan] children list associated with this span if this is an
@@ -173,7 +172,7 @@ abstract class InlineSpan extends DiagnosticableTree {
     'InlineSpan does not innately have children. Use TextSpan.children instead. '
     'This feature was deprecated after v1.7.3.'
   )
-  List<InlineSpan> get children => null;
+  List<InlineSpan>? get children => null;
 
   /// Returns the [GestureRecognizer] associated with this span if this is an
   /// instance of [TextSpan], otherwise returns null.
@@ -181,7 +180,7 @@ abstract class InlineSpan extends DiagnosticableTree {
     'InlineSpan does not innately have a recognizer. Use TextSpan.recognizer instead. '
     'This feature was deprecated after v1.7.3.'
   )
-  GestureRecognizer get recognizer => null;
+  GestureRecognizer? get recognizer => null;
 
   /// Apply the properties of this object to the given [ParagraphBuilder], from
   /// which a [Paragraph] can be obtained.
@@ -195,7 +194,7 @@ abstract class InlineSpan extends DiagnosticableTree {
   /// in the same order as defined in the [InlineSpan] tree.
   ///
   /// [Paragraph] objects can be drawn on [Canvas] objects.
-  void build(ui.ParagraphBuilder builder, { double textScaleFactor = 1.0, List<PlaceholderDimensions> dimensions });
+  void build(ui.ParagraphBuilder builder, { double textScaleFactor = 1.0, List<PlaceholderDimensions>? dimensions });
 
   // TODO(garyq): Remove the deprecated visitTextSpan, text, and children.
   /// Walks this [TextSpan] and any descendants in pre-order and calls `visitor`
@@ -217,10 +216,10 @@ abstract class InlineSpan extends DiagnosticableTree {
   bool visitChildren(InlineSpanVisitor visitor);
 
   /// Returns the [InlineSpan] that contains the given position in the text.
-  InlineSpan getSpanForPosition(TextPosition position) {
+  InlineSpan? getSpanForPosition(TextPosition position) {
     assert(debugAssertIsValid());
     final Accumulator offset = Accumulator();
-    InlineSpan result;
+    InlineSpan? result;
     visitChildren((InlineSpan span) {
       result = span.getSpanForPositionVisitor(position, offset);
       return result == null;
@@ -237,7 +236,7 @@ abstract class InlineSpan extends DiagnosticableTree {
   ///
   /// This method should not be directly called. Use [getSpanForPosition] instead.
   @protected
-  InlineSpan getSpanForPositionVisitor(TextPosition position, Accumulator offset);
+  InlineSpan? getSpanForPositionVisitor(TextPosition position, Accumulator offset);
 
   /// Flattens the [InlineSpan] tree into a single string.
   ///
@@ -297,11 +296,11 @@ abstract class InlineSpan extends DiagnosticableTree {
   /// This only accounts for the [TextSpan.text] values and ignores [PlaceholderSpan]s.
   ///
   /// Returns null if the `index` is out of bounds.
-  int codeUnitAt(int index) {
+  int? codeUnitAt(int index) {
     if (index < 0)
       return null;
     final Accumulator offset = Accumulator();
-    int result;
+    int? result;
     visitChildren((InlineSpan span) {
       result = span.codeUnitAtVisitor(index, offset);
       return result == null;
@@ -318,7 +317,7 @@ abstract class InlineSpan extends DiagnosticableTree {
   ///
   /// This method should not be directly called. Use [codeUnitAt] instead.
   @protected
-  int codeUnitAtVisitor(int index, Accumulator offset);
+  int? codeUnitAtVisitor(int index, Accumulator offset);
 
   /// Populates the `semanticsOffsets` and `semanticsElements` with the appropriate data
   /// to be able to construct a [SemanticsNode].
@@ -375,7 +374,7 @@ abstract class InlineSpan extends DiagnosticableTree {
     properties.defaultDiagnosticsTreeStyle = DiagnosticsTreeStyle.whitespace;
 
     if (style != null) {
-      style.debugFillProperties(properties);
+      style!.debugFillProperties(properties);
     }
   }
 }

packages/flutter/lib/src/painting/notched_shapes.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;
 
@@ -30,7 +29,7 @@ abstract class NotchedShape {
   ///
   /// The `guest` is the bounding rectangle of the shape for which a notch will
   /// be made. It is null when there is no guest.
-  Path getOuterPath(Rect host, Rect guest);
+  Path getOuterPath(Rect host, Rect? guest);
 }
 
 /// A rectangle with a smooth circular notch.
@@ -57,7 +56,7 @@ class CircularNotchedRectangle extends NotchedShape {
   /// the guest circle.
   // TODO(amirh): add an example diagram here.
   @override
-  Path getOuterPath(Rect host, Rect guest) {
+  Path getOuterPath(Rect host, Rect? guest) {
     if (guest == null || !host.overlaps(guest))
       return Path()..addRect(host);
 
@@ -86,7 +85,7 @@ class CircularNotchedRectangle extends NotchedShape {
     final double p2yA = math.sqrt(r * r - p2xA * p2xA);
     final double p2yB = math.sqrt(r * r - p2xB * p2xB);
 
-    final List<Offset> p = List<Offset>(6);
+    final List<Offset?> p = List<Offset?>.filled(6, null, growable: false);
 
     // p0, p1, and p2 are the control points for segment A.
     p[0] = Offset(a - s1, b);
@@ -96,24 +95,24 @@ class CircularNotchedRectangle extends NotchedShape {
 
     // p3, p4, and p5 are the control points for segment B, which is a mirror
     // of segment A around the y axis.
-    p[3] = Offset(-1.0 * p[2].dx, p[2].dy);
-    p[4] = Offset(-1.0 * p[1].dx, p[1].dy);
-    p[5] = Offset(-1.0 * p[0].dx, p[0].dy);
+    p[3] = Offset(-1.0 * p[2]!.dx, p[2]!.dy);
+    p[4] = Offset(-1.0 * p[1]!.dx, p[1]!.dy);
+    p[5] = Offset(-1.0 * p[0]!.dx, p[0]!.dy);
 
     // translate all points back to the absolute coordinate system.
     for (int i = 0; i < p.length; i += 1)
-      p[i] += guest.center;
+      p[i] = p[i]! + guest.center;
 
     return Path()
       ..moveTo(host.left, host.top)
-      ..lineTo(p[0].dx, p[0].dy)
-      ..quadraticBezierTo(p[1].dx, p[1].dy, p[2].dx, p[2].dy)
+      ..lineTo(p[0]!.dx, p[0]!.dy)
+      ..quadraticBezierTo(p[1]!.dx, p[1]!.dy, p[2]!.dx, p[2]!.dy)
       ..arcToPoint(
-        p[3],
+        p[3]!,
         radius: Radius.circular(notchRadius),
         clockwise: false,
       )
-      ..quadraticBezierTo(p[4].dx, p[4].dy, p[5].dx, p[5].dy)
+      ..quadraticBezierTo(p[4]!.dx, p[4]!.dy, p[5]!.dx, p[5]!.dy)
       ..lineTo(host.right, host.top)
       ..lineTo(host.right, host.bottom)
       ..lineTo(host.left, host.bottom)
@@ -149,16 +148,16 @@ class AutomaticNotchedShape extends NotchedShape {
   /// is available to [NotchedShape]s.
   ///
   /// If this is null, [getOuterPath] ignores the guest rectangle.
-  final ShapeBorder guest;
+  final ShapeBorder? guest;
 
   @override
-  Path getOuterPath(Rect hostRect, Rect guestRect) { // ignore: avoid_renaming_method_parameters, the
+  Path getOuterPath(Rect hostRect, Rect? guestRect) { // ignore: avoid_renaming_method_parameters, the
     // parameters are renamed over the baseclass because they would clash
     // with properties of this object, and the use of all four of them in
     // the code below is really confusing if they have the same names.
     final Path hostPath = host.getOuterPath(hostRect);
     if (guest != null && guestRect != null) {
-      final Path guestPath = guest.getOuterPath(guestRect);
+      final Path guestPath = guest!.getOuterPath(guestRect);
       return Path.combine(PathOperation.difference, hostPath, guestPath);
     }
     return hostPath;

packages/flutter/lib/src/painting/paint_utilities.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/placeholder_span.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 PlaceholderAlignment;
 
@@ -39,7 +38,7 @@ abstract class PlaceholderSpan extends InlineSpan {
   const PlaceholderSpan({
     this.alignment = ui.PlaceholderAlignment.bottom,
     this.baseline,
-    TextStyle style,
+    TextStyle? style,
   }) : super(style: style,);
 
   /// How the placeholder aligns vertically with the text.
@@ -51,7 +50,7 @@ abstract class PlaceholderSpan extends InlineSpan {
   /// [ui.PlaceholderAlignment.aboveBaseline], and [ui.PlaceholderAlignment.belowBaseline].
   ///
   /// This is ignored when using other alignment modes.
-  final TextBaseline baseline;
+  final TextBaseline? baseline;
 
   /// [PlaceholderSpan]s are flattened to a `0xFFFC` object replacement character in the
   /// plain text representation when `includePlaceholders` is true.

packages/flutter/lib/src/painting/stadium_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:ui' as ui show lerpDouble;
 
@@ -41,7 +40,7 @@ class StadiumBorder extends OutlinedBorder {
   ShapeBorder scale(double t) => StadiumBorder(side: side.scale(t));
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     assert(t != null);
     if (a is StadiumBorder)
       return StadiumBorder(side: BorderSide.lerp(a.side, side, t));
@@ -62,7 +61,7 @@ class StadiumBorder extends OutlinedBorder {
   }
 
   @override
-  ShapeBorder lerpTo(ShapeBorder b, double t) {
+  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
     assert(t != null);
     if (b is StadiumBorder)
       return StadiumBorder(side: BorderSide.lerp(side, b.side, t));
@@ -83,26 +82,26 @@ class StadiumBorder extends OutlinedBorder {
   }
 
   @override
-  StadiumBorder copyWith({ BorderSide side }) {
+  StadiumBorder copyWith({ BorderSide? side }) {
     return StadiumBorder(side: side ?? this.side);
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     final Radius radius = Radius.circular(rect.shortestSide / 2.0);
     return Path()
       ..addRRect(RRect.fromRectAndRadius(rect, radius).deflate(side.width));
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     final Radius radius = Radius.circular(rect.shortestSide / 2.0);
     return Path()
       ..addRRect(RRect.fromRectAndRadius(rect, radius));
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     switch (side.style) {
       case BorderStyle.none:
         break;
@@ -157,7 +156,7 @@ class _StadiumToCircleBorder extends OutlinedBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     assert(t != null);
     if (a is StadiumBorder) {
       return _StadiumToCircleBorder(
@@ -174,14 +173,14 @@ class _StadiumToCircleBorder extends OutlinedBorder {
     if (a is _StadiumToCircleBorder) {
       return _StadiumToCircleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        circleness: ui.lerpDouble(a.circleness, circleness, t),
+        circleness: ui.lerpDouble(a.circleness, circleness, 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 StadiumBorder) {
       return _StadiumToCircleBorder(
@@ -198,7 +197,7 @@ class _StadiumToCircleBorder extends OutlinedBorder {
     if (b is _StadiumToCircleBorder) {
       return _StadiumToCircleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        circleness: ui.lerpDouble(circleness, b.circleness, t),
+        circleness: ui.lerpDouble(circleness, b.circleness, t)!,
       );
     }
     return super.lerpTo(b, t);
@@ -231,19 +230,19 @@ class _StadiumToCircleBorder extends OutlinedBorder {
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     return Path()
       ..addRRect(_adjustBorderRadius(rect).toRRect(_adjustRect(rect)).deflate(side.width));
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return Path()
       ..addRRect(_adjustBorderRadius(rect).toRRect(_adjustRect(rect)));
   }
 
   @override
-  _StadiumToCircleBorder copyWith({ BorderSide side, double circleness }) {
+  _StadiumToCircleBorder copyWith({ BorderSide? side, double? circleness }) {
     return _StadiumToCircleBorder(
       side: side ?? this.side,
       circleness: circleness ?? this.circleness,
@@ -251,7 +250,7 @@ class _StadiumToCircleBorder extends OutlinedBorder {
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     switch (side.style) {
       case BorderStyle.none:
         break;
@@ -318,7 +317,7 @@ class _StadiumToRoundedRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  ShapeBorder lerpFrom(ShapeBorder a, double t) {
+  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
     assert(t != null);
     if (a is StadiumBorder) {
       return _StadiumToRoundedRectangleBorder(
@@ -337,15 +336,15 @@ class _StadiumToRoundedRectangleBorder extends OutlinedBorder {
     if (a is _StadiumToRoundedRectangleBorder) {
       return _StadiumToRoundedRectangleBorder(
         side: BorderSide.lerp(a.side, side, t),
-        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
-        rectness: ui.lerpDouble(a.rectness, rectness, t),
+        borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t)!,
+        rectness: ui.lerpDouble(a.rectness, rectness, 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 StadiumBorder) {
       return _StadiumToRoundedRectangleBorder(
@@ -364,8 +363,8 @@ class _StadiumToRoundedRectangleBorder extends OutlinedBorder {
     if (b is _StadiumToRoundedRectangleBorder) {
       return _StadiumToRoundedRectangleBorder(
         side: BorderSide.lerp(side, b.side, t),
-        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
-        rectness: ui.lerpDouble(rectness, b.rectness, t),
+        borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t)!,
+        rectness: ui.lerpDouble(rectness, b.rectness, t)!,
       );
     }
     return super.lerpTo(b, t);
@@ -376,23 +375,23 @@ class _StadiumToRoundedRectangleBorder extends OutlinedBorder {
       borderRadius,
       BorderRadius.all(Radius.circular(rect.shortestSide / 2.0)),
       1.0 - rectness,
-    );
+    )!;
   }
 
   @override
-  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
+  Path getInnerPath(Rect rect, { TextDirection? textDirection }) {
     return Path()
       ..addRRect(_adjustBorderRadius(rect).toRRect(rect).deflate(side.width));
   }
 
   @override
-  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
+  Path getOuterPath(Rect rect, { TextDirection? textDirection }) {
     return Path()
       ..addRRect(_adjustBorderRadius(rect).toRRect(rect));
   }
 
   @override
-  _StadiumToRoundedRectangleBorder copyWith({ BorderSide side, BorderRadius borderRadius, double rectness }) {
+  _StadiumToRoundedRectangleBorder copyWith({ BorderSide? side, BorderRadius? borderRadius, double? rectness }) {
     return _StadiumToRoundedRectangleBorder(
       side: side ?? this.side,
       borderRadius: borderRadius ?? this.borderRadius,
@@ -401,7 +400,7 @@ class _StadiumToRoundedRectangleBorder extends OutlinedBorder {
   }
 
   @override
-  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
+  void paint(Canvas canvas, Rect rect, { TextDirection? textDirection }) {
     switch (side.style) {
       case BorderStyle.none:
         break;

packages/flutter/lib/src/painting/strut_style.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';
 
@@ -297,8 +296,8 @@ class StrutStyle with Diagnosticable {
   /// If provided, fontSize must be positive and non-zero, leading must be
   /// zero or positive.
   const StrutStyle({
-    String fontFamily,
-    List<String> fontFamilyFallback,
+    String? fontFamily,
+    List<String>? fontFamilyFallback,
     this.fontSize,
     this.height,
     this.leading,
@@ -306,13 +305,13 @@ class StrutStyle with Diagnosticable {
     this.fontStyle,
     this.forceStrutHeight,
     this.debugLabel,
-    String package,
+    String? package,
   }) : fontFamily = package == null ? fontFamily : 'packages/$package/$fontFamily',
        _fontFamilyFallback = fontFamilyFallback,
        _package = package,
        assert(fontSize == null || fontSize > 0),
        assert(leading == null || leading >= 0),
-       assert(package == null || (package != null && (fontFamily != null || fontFamilyFallback != null)));
+       assert(package == null || (fontFamily != null || fontFamilyFallback != null));
 
   /// Builds a StrutStyle that contains values of the equivalent properties in
   /// the provided [textStyle].
@@ -335,20 +334,20 @@ class StrutStyle with Diagnosticable {
   /// from being prepended twice.
   StrutStyle.fromTextStyle(
     TextStyle textStyle, {
-    String fontFamily,
-    List<String> fontFamilyFallback,
-    double fontSize,
-    double height,
+    String? fontFamily,
+    List<String>? fontFamilyFallback,
+    double? fontSize,
+    double? height,
     this.leading, // TextStyle does not have an equivalent (yet).
-    FontWeight fontWeight,
-    FontStyle fontStyle,
+    FontWeight? fontWeight,
+    FontStyle? fontStyle,
     this.forceStrutHeight,
-    String debugLabel,
-    String package,
+    String? debugLabel,
+    String? package,
   }) : assert(textStyle != null),
        assert(fontSize == null || fontSize > 0),
        assert(leading == null || leading >= 0),
-       assert(package == null || (package != null && (fontFamily != null || fontFamilyFallback != null))),
+       assert(package == null || fontFamily != null || fontFamilyFallback != null),
        fontFamily = fontFamily != null ? (package == null ? fontFamily : 'packages/$package/$fontFamily') : textStyle.fontFamily,
        _fontFamilyFallback = fontFamilyFallback ?? textStyle.fontFamilyFallback,
        height = height ?? textStyle.height,
@@ -380,7 +379,7 @@ class StrutStyle with Diagnosticable {
   /// was found, the default platform font family will be used instead. Unlike
   /// [TextStyle.fontFamilyFallback], the font does not need to contain the
   /// desired glyphs to match.
-  final String fontFamily;
+  final String? fontFamily;
 
   /// The ordered list of font families to fall back on when a higher priority
   /// font family cannot be found.
@@ -401,16 +400,16 @@ class StrutStyle with Diagnosticable {
   /// prefixed with 'packages/package_name/' (e.g. 'packages/cool_fonts/Roboto').
   /// The package name should be provided by the `package` argument in the
   /// constructor.
-  List<String> get fontFamilyFallback {
+  List<String>? get fontFamilyFallback {
     if (_package != null && _fontFamilyFallback != null)
-      return _fontFamilyFallback.map((String family) => 'packages/$_package/$family').toList();
+      return _fontFamilyFallback!.map((String family) => 'packages/$_package/$family').toList();
     return _fontFamilyFallback;
   }
-  final List<String> _fontFamilyFallback;
+  final List<String>? _fontFamilyFallback;
 
   // This is stored in order to prefix the fontFamilies in _fontFamilyFallback
   // in the [fontFamilyFallback] getter.
-  final String _package;
+  final String? _package;
 
   /// The size of text (in logical pixels) to use when obtaining metrics from the font.
   ///
@@ -419,7 +418,7 @@ class StrutStyle with Diagnosticable {
   /// [fontSize].
   ///
   /// The default fontSize is 14 logical pixels.
-  final double fontSize;
+  final double? fontSize;
 
   /// The multiple of [fontSize] to multiply the ascent and descent by where
   /// `ascent + descent = fontSize`.
@@ -447,17 +446,17 @@ class StrutStyle with Diagnosticable {
   /// See [TextStyle.height], which works in a similar manner.
   ///
   /// The default height is null.
-  final double height;
+  final double? height;
 
   /// The typeface thickness to use when calculating the strut (e.g., bold).
   ///
   /// The default fontWeight is [FontWeight.w400].
-  final FontWeight fontWeight;
+  final FontWeight? fontWeight;
 
   /// The typeface variant to use when calculating the strut (e.g., italics).
   ///
   /// The default fontStyle is [FontStyle.normal].
-  final FontStyle fontStyle;
+  final FontStyle? fontStyle;
 
   /// The custom leading to apply to the strut as a multiple of [fontSize].
   ///
@@ -467,7 +466,7 @@ class StrutStyle with Diagnosticable {
   /// baseline.
   ///
   /// The default leading is null, which will use the font-specified leading.
-  final double leading;
+  final double? leading;
 
   /// Whether the strut height should be forced.
   ///
@@ -486,7 +485,7 @@ class StrutStyle with Diagnosticable {
   /// of the strut.
   ///
   /// The default is false.
-  final bool forceStrutHeight;
+  final bool? forceStrutHeight;
 
   /// A human-readable description of this strut style.
   ///
@@ -494,7 +493,7 @@ class StrutStyle with Diagnosticable {
   ///
   /// This property is not considered when comparing strut styles using `==` or
   /// [compareTo], and it does not affect [hashCode].
-  final String debugLabel;
+  final String? debugLabel;
 
   /// Describe the difference between this style and another, in terms of how
   /// much damage it will make to the rendering.
@@ -525,7 +524,7 @@ class StrutStyle with Diagnosticable {
   /// [StrutStyle] shares many of the same basic properties as [TextStyle].
   ///
   /// If the given text style is null, returns this strut style.
-  StrutStyle inheritFromTextStyle(TextStyle other) {
+  StrutStyle inheritFromTextStyle(TextStyle? other) {
     if (other == null)
       return this;
 
@@ -580,15 +579,15 @@ class StrutStyle with Diagnosticable {
   void debugFillProperties(DiagnosticPropertiesBuilder properties, { String prefix = '' }) {
     super.debugFillProperties(properties);
     if (debugLabel != null)
-      properties.add(MessageProperty('${prefix}debugLabel', debugLabel));
+      properties.add(MessageProperty('${prefix}debugLabel', debugLabel!));
     final List<DiagnosticsNode> styles = <DiagnosticsNode>[
       StringProperty('${prefix}family', fontFamily, defaultValue: null, quoted: false),
       IterableProperty<String>('${prefix}familyFallback', fontFamilyFallback, defaultValue: null),
       DoubleProperty('${prefix}size', fontSize, defaultValue: null),
     ];
-    String weightDescription;
+    String? weightDescription;
     if (fontWeight != null) {
-      weightDescription = 'w${fontWeight.index + 1}00';
+      weightDescription = 'w${fontWeight!.index + 1}00';
     }
     // TODO(jacobr): switch this to use enumProperty which will either cause the
     // weight description to change to w600 from 600 or require existing

packages/flutter/lib/src/painting/text_span.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 ParagraphBuilder;
 
@@ -70,10 +69,10 @@ class TextSpan extends InlineSpan {
   const TextSpan({
     this.text,
     this.children,
-    TextStyle style,
+    TextStyle? style,
     this.recognizer,
     this.semanticsLabel,
-  }) : super(style: style,);
+  }) : super(style: style);
 
   /// The text contained in this span.
   ///
@@ -82,7 +81,7 @@ class TextSpan extends InlineSpan {
   ///
   /// This getter does not include the contents of its children.
   @override
-  final String text;
+  final String? text;
 
 
   /// Additional spans to include as children.
@@ -95,7 +94,7 @@ class TextSpan extends InlineSpan {
   ///
   /// The list must not contain any nulls.
   @override
-  final List<InlineSpan> children;
+  final List<InlineSpan>? children;
 
   /// A gesture recognizer that will receive events that hit this span.
   ///
@@ -173,7 +172,7 @@ class TextSpan extends InlineSpan {
   /// ```
   /// {@end-tool}
   @override
-  final GestureRecognizer recognizer;
+  final GestureRecognizer? recognizer;
 
   /// An alternative semantics label for this [TextSpan].
   ///
@@ -186,7 +185,7 @@ class TextSpan extends InlineSpan {
   /// ```dart
   /// TextSpan(text: r'$$', semanticsLabel: 'Double dollars')
   /// ```
-  final String semanticsLabel;
+  final String? semanticsLabel;
 
   /// Apply the [style], [text], and [children] of this object to the
   /// given [ParagraphBuilder], from which a [Paragraph] can be obtained.
@@ -199,16 +198,16 @@ class TextSpan extends InlineSpan {
   void build(
     ui.ParagraphBuilder builder, {
     double textScaleFactor = 1.0,
-    List<PlaceholderDimensions> dimensions,
+    List<PlaceholderDimensions>? dimensions,
   }) {
     assert(debugAssertIsValid());
     final bool hasStyle = style != null;
     if (hasStyle)
-      builder.pushStyle(style.getTextStyle(textScaleFactor: textScaleFactor));
+      builder.pushStyle(style!.getTextStyle(textScaleFactor: textScaleFactor));
     if (text != null)
-      builder.addText(text);
+      builder.addText(text!);
     if (children != null) {
-      for (final InlineSpan child in children) {
+      for (final InlineSpan child in children!) {
         assert(child != null);
         child.build(
           builder,
@@ -233,7 +232,7 @@ class TextSpan extends InlineSpan {
         return false;
     }
     if (children != null) {
-      for (final InlineSpan child in children) {
+      for (final InlineSpan child in children!) {
         if (!child.visitChildren(visitor))
           return false;
       }
@@ -258,7 +257,7 @@ class TextSpan extends InlineSpan {
         return false;
     }
     if (children != null) {
-      for (final InlineSpan child in children) {
+      for (final InlineSpan child in children!) {
         assert(
           child is TextSpan,
           'visitTextSpan is deprecated. Use visitChildren to support InlineSpans',
@@ -273,19 +272,19 @@ class TextSpan extends InlineSpan {
 
   /// Returns the text span that contains the given position in the text.
   @override
-  InlineSpan getSpanForPositionVisitor(TextPosition position, Accumulator offset) {
+  InlineSpan? getSpanForPositionVisitor(TextPosition position, Accumulator offset) {
     if (text == null) {
       return null;
     }
     final TextAffinity affinity = position.affinity;
     final int targetOffset = position.offset;
-    final int endOffset = offset.value + text.length;
+    final int endOffset = offset.value + text!.length;
     if (offset.value == targetOffset && affinity == TextAffinity.downstream ||
         offset.value < targetOffset && targetOffset < endOffset ||
         endOffset == targetOffset && affinity == TextAffinity.upstream) {
       return this;
     }
-    offset.increment(text.length);
+    offset.increment(text!.length);
     return null;
   }
 
@@ -302,7 +301,7 @@ class TextSpan extends InlineSpan {
       buffer.write(text);
     }
     if (children != null) {
-      for (final InlineSpan child in children) {
+      for (final InlineSpan child in children!) {
         child.computeToPlainText(buffer,
           includeSemanticsLabels: includeSemanticsLabels,
           includePlaceholders: includePlaceholders,
@@ -316,27 +315,27 @@ class TextSpan extends InlineSpan {
     assert(debugAssertIsValid());
     if (text != null || semanticsLabel != null) {
       collector.add(InlineSpanSemanticsInformation(
-        text,
+        text!,
         semanticsLabel: semanticsLabel,
         recognizer: recognizer,
       ));
     }
     if (children != null) {
-      for (final InlineSpan child in children) {
+      for (final InlineSpan child in children!) {
         child.computeSemanticsInformation(collector);
       }
     }
   }
 
   @override
-  int codeUnitAtVisitor(int index, Accumulator offset) {
+  int? codeUnitAtVisitor(int index, Accumulator offset) {
     if (text == null) {
       return null;
     }
-    if (index - offset.value < text.length) {
-      return text.codeUnitAt(index - offset.value);
+    if (index - offset.value < text!.length) {
+      return text!.codeUnitAt(index - offset.value);
     }
-    offset.increment(text.length);
+    offset.increment(text!.length);
     return null;
   }
 
@@ -346,12 +345,12 @@ class TextSpan extends InlineSpan {
       recognizer != null &&
       (recognizer is TapGestureRecognizer || recognizer is LongPressGestureRecognizer)
     ) {
-      final int length = semanticsLabel?.length ?? text.length;
+      final int length = semanticsLabel?.length ?? text!.length;
       semanticsOffsets.add(offset.value);
       semanticsOffsets.add(offset.value + length);
       semanticsElements.add(recognizer);
     }
-    offset.increment(text != null ? text.length : 0);
+    offset.increment(text != null ? text!.length : 0);
   }
 
   /// In checked mode, throws an exception if the object is not in a valid
@@ -366,7 +365,7 @@ class TextSpan extends InlineSpan {
   bool debugAssertIsValid() {
     assert(() {
       if (children != null) {
-        for (final InlineSpan child in children) {
+        for (final InlineSpan child in children!) {
           if (child == null) {
             throw FlutterError.fromParts(<DiagnosticsNode>[
               ErrorSummary('TextSpan contains a null child.'),
@@ -399,15 +398,15 @@ class TextSpan extends InlineSpan {
       RenderComparison.identical :
       RenderComparison.metadata;
     if (style != null) {
-      final RenderComparison candidate = style.compareTo(textSpan.style);
+      final RenderComparison candidate = style!.compareTo(textSpan.style!);
       if (candidate.index > result.index)
         result = candidate;
       if (result == RenderComparison.layout)
         return result;
     }
     if (children != null) {
-      for (int index = 0; index < children.length; index += 1) {
-        final RenderComparison candidate = children[index].compareTo(textSpan.children[index]);
+      for (int index = 0; index < children!.length; index += 1) {
+        final RenderComparison candidate = children![index].compareTo(textSpan.children![index]);
         if (candidate.index > result.index)
           result = candidate;
         if (result == RenderComparison.layout)
@@ -461,7 +460,7 @@ class TextSpan extends InlineSpan {
 
     properties.add(DiagnosticsProperty<GestureRecognizer>(
       'recognizer', recognizer,
-      description: recognizer?.runtimeType?.toString(),
+      description: recognizer?.runtimeType.toString(),
       defaultValue: null,
     ));
 
@@ -474,7 +473,7 @@ class TextSpan extends InlineSpan {
   List<DiagnosticsNode> debugDescribeChildren() {
     if (children == null)
       return const <DiagnosticsNode>[];
-    return children.map<DiagnosticsNode>((InlineSpan child) {
+    return children!.map<DiagnosticsNode>((InlineSpan child) {
       if (child != null) {
         return child.toDiagnosticsNode();
       } else {