migrate rendering to nullsafety (flutter#64621)

analysis_options.yaml

@@ -202,6 +202,7 @@ linter:
     - use_full_hex_values_for_flutter_colors
     # - use_function_type_syntax_for_parameters # not yet tested
     # - use_key_in_widget_constructors # not yet tested
+    - use_late_for_private_fields_and_variables
     - use_rethrow_when_possible
     # - use_setters_to_change_properties # not yet tested
     # - use_string_buffers # has false positives: https://github.com/dart-lang/sdk/issues/34182

packages/flutter/analysis_options.yaml

@@ -8,5 +8,6 @@ analyzer:
   errors:
     always_require_non_null_named_parameters: false # not needed with nnbd
     type_init_formals: false # https://github.com/dart-lang/linter/issues/2192
+    unrelated_type_equality_checks: false # https://github.com/dart-lang/linter/issues/2196
     void_checks: false # https://github.com/dart-lang/linter/issues/2185
     unnecessary_null_comparison: false # https://github.com/dart-lang/language/issues/1018 , turned off until https://github.com/flutter/flutter/issues/61042

packages/flutter/lib/rendering.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 rendering tree.
 ///
 /// To use, import `package:flutter/rendering.dart`.

packages/flutter/lib/src/animation/tween.dart

@@ -208,6 +208,20 @@ class _ChainedEvaluation<T> extends Animatable<T> {
 /// [Tween]s that use dedicated `lerp` methods instead of merely relying on the
 /// operators (in particular, this allows them to handle null values in a more
 /// useful manner).
+///
+/// ## Nullability
+///
+/// The [begin] and [end] fields are nullable; a [Tween] does not have to
+/// have non-null values specified when it is created.
+///
+/// If `T` is nullable, then [lerp] and [transform] may return null.
+/// This is typically seen in the case where [begin] is null and `t`
+/// is 0.0, or [end] is null and `t` is 1.0, or both are null (at any
+/// `t` value).
+///
+/// If `T` is not nullable, then [begin] and [end] must both be set to
+/// non-null values before using [lerp] or [transform], otherwise they
+/// will throw.
 class Tween<T extends dynamic> extends Animatable<T> {
   /// Creates a tween.
   ///
@@ -236,6 +250,9 @@ class Tween<T extends dynamic> extends Animatable<T> {
   /// The default implementation of this method uses the [+], [-], and [*]
   /// operators on `T`. The [begin] and [end] properties must therefore be
   /// non-null by the time this method is called.
+  ///
+  /// In general, however, it is possible for this to return null, especially
+  /// when `t`=0.0 and [begin] is null, or `t`=1.0 and [end] is null.
   @protected
   T lerp(double t) {
     assert(begin != null);
@@ -291,6 +308,9 @@ class ReverseTween<T> extends Tween<T> {
 /// This class specializes the interpolation of [Tween<Color>] to use
 /// [Color.lerp].
 ///
+/// The values can be null, representing no color (which is distinct to
+/// transparent black, as represented by [Colors.transparent]).
+///
 /// See [Tween] for a discussion on how to use interpolation objects.
 class ColorTween extends Tween<Color?> {
   /// Creates a [Color] tween.
@@ -314,6 +334,8 @@ class ColorTween extends Tween<Color?> {
 /// This class specializes the interpolation of [Tween<Size>] to use
 /// [Size.lerp].
 ///
+/// The values can be null, representing [Size.zero].
+///
 /// See [Tween] for a discussion on how to use interpolation objects.
 class SizeTween extends Tween<Size?> {
   /// Creates a [Size] tween.
@@ -332,6 +354,9 @@ class SizeTween extends Tween<Size?> {
 /// This class specializes the interpolation of [Tween<Rect>] to use
 /// [Rect.lerp].
 ///
+/// The values can be null, representing a zero-sized rectangle at the
+/// origin ([Rect.zero]).
+///
 /// See [Tween] for a discussion on how to use interpolation objects.
 class RectTween extends Tween<Rect?> {
   /// Creates a [Rect] tween.
@@ -355,6 +380,9 @@ class RectTween extends Tween<Rect?> {
 /// This is the closest approximation to a linear tween that is possible with an
 /// integer. Compare to [StepTween] and [Tween<double>].
 ///
+/// The [begin] and [end] values must be set to non-null values before
+/// calling [lerp] or [transform].
+///
 /// See [Tween] for a discussion on how to use interpolation objects.
 class IntTween extends Tween<int> {
   /// Creates an int tween.
@@ -380,6 +408,9 @@ class IntTween extends Tween<int> {
 /// This results in a value that is never greater than the equivalent
 /// value from a linear double interpolation. Compare to [IntTween].
 ///
+/// The [begin] and [end] values must be set to non-null values before
+/// calling [lerp] or [transform].
+///
 /// See [Tween] for a discussion on how to use interpolation objects.
 class StepTween extends Tween<int> {
   /// Creates an [int] tween that floors.

packages/flutter/lib/src/foundation/diagnostics.dart

@@ -3377,13 +3377,10 @@ abstract class DiagnosticableTree with Diagnosticable {
   ///
   ///  * [toString], for a brief description of the object.
   ///  * [toStringDeep], for a description of the subtree rooted at this object.
-  String? toStringShallow({
+  String toStringShallow({
     String joiner = ', ',
     DiagnosticLevel minLevel = DiagnosticLevel.debug,
   }) {
-    if (kReleaseMode) {
-      return toString();
-    }
     String? shallowString;
     assert(() {
       final StringBuffer result = StringBuffer();
@@ -3398,7 +3395,7 @@ abstract class DiagnosticableTree with Diagnosticable {
       shallowString = result.toString();
       return true;
     }());
-    return shallowString;
+    return shallowString ?? toString();
   }
 
   /// Returns a string representation of this node and its descendants.
@@ -3470,13 +3467,10 @@ mixin DiagnosticableTreeMixin implements DiagnosticableTree {
   }
 
   @override
-  String? toStringShallow({
+  String toStringShallow({
     String joiner = ', ',
     DiagnosticLevel minLevel = DiagnosticLevel.debug,
   }) {
-    if (kReleaseMode) {
-      return toString();
-    }
     String? shallowString;
     assert(() {
       final StringBuffer result = StringBuffer();
@@ -3491,7 +3485,7 @@ mixin DiagnosticableTreeMixin implements DiagnosticableTree {
       shallowString = result.toString();
       return true;
     }());
-    return shallowString;
+    return shallowString ?? toString();
   }
 
   @override

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

@@ -291,6 +291,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
         event is PointerHoverEvent ||
         event is PointerAddedEvent ||
         event is PointerRemovedEvent) {
+      assert(event.position != null);
       dispatchEvent(event, hitTestResult);
     }
   }

packages/flutter/lib/src/gestures/converter.dart

@@ -48,6 +48,7 @@ class PointerEventConverter {
   static Iterable<PointerEvent> expand(Iterable<ui.PointerData> data, double devicePixelRatio) sync* {
     for (final ui.PointerData datum in data) {
       final Offset position = Offset(datum.physicalX, datum.physicalY) / devicePixelRatio;
+      assert(position != null);
       final Offset delta = Offset(datum.physicalDeltaX, datum.physicalDeltaY) / devicePixelRatio;
       final double radiusMinor = _toLogicalPixels(datum.radiusMinor, devicePixelRatio);
       final double radiusMajor = _toLogicalPixels(datum.radiusMajor, devicePixelRatio);

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

@@ -44,6 +44,9 @@ class PlaceholderDimensions {
   }) : assert(size != null),
        assert(alignment != null);
 
+  /// A constant representing an empty placeholder.
+  static const PlaceholderDimensions empty = PlaceholderDimensions(size: Size.zero, alignment: ui.PlaceholderAlignment.bottom);
+
   /// Width and height dimensions of the placeholder.
   final Size size;
 

packages/flutter/lib/src/rendering/animated_size.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
-
 import 'package:flutter/animation.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
@@ -76,13 +74,13 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   /// The arguments [duration], [curve], [alignment], and [vsync] must
   /// not be null.
   RenderAnimatedSize({
-    @required TickerProvider vsync,
-    @required Duration duration,
-    Duration reverseDuration,
+    required TickerProvider vsync,
+    required Duration duration,
+    Duration? reverseDuration,
     Curve curve = Curves.linear,
     AlignmentGeometry alignment = Alignment.center,
-    TextDirection textDirection,
-    RenderBox child,
+    TextDirection? textDirection,
+    RenderBox? child,
   }) : assert(vsync != null),
        assert(duration != null),
        assert(curve != null),
@@ -102,11 +100,11 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     );
   }
 
-  AnimationController _controller;
-  CurvedAnimation _animation;
+  late final AnimationController _controller;
+  late final CurvedAnimation _animation;
   final SizeTween _sizeTween = SizeTween();
-  bool _hasVisualOverflow;
-  double _lastValue;
+  late bool _hasVisualOverflow;
+  double? _lastValue;
 
   /// The state this size animation is in.
   ///
@@ -116,7 +114,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   RenderAnimatedSizeState _state = RenderAnimatedSizeState.start;
 
   /// The duration of the animation.
-  Duration get duration => _controller.duration;
+  Duration get duration => _controller.duration!;
   set duration(Duration value) {
     assert(value != null);
     if (value == _controller.duration)
@@ -125,8 +123,8 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   }
 
   /// The duration of the animation when running in reverse.
-  Duration get reverseDuration => _controller.reverseDuration;
-  set reverseDuration(Duration value) {
+  Duration? get reverseDuration => _controller.reverseDuration;
+  set reverseDuration(Duration? value) {
     if (value == _controller.reverseDuration)
       return;
     _controller.reverseDuration = value;
@@ -164,7 +162,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     super.detach();
   }
 
-  Size get _animatedSize {
+  Size? get _animatedSize {
     return _sizeTween.evaluate(_animation);
   }
 
@@ -181,7 +179,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
       return;
     }
 
-    child.layout(constraints, parentUsesSize: true);
+    child!.layout(constraints, parentUsesSize: true);
 
     assert(_state != null);
     switch (_state) {
@@ -199,11 +197,11 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
         break;
     }
 
-    size = constraints.constrain(_animatedSize);
+    size = constraints.constrain(_animatedSize!);
     alignChild();
 
-    if (size.width < _sizeTween.end.width ||
-        size.height < _sizeTween.end.height)
+    if (size.width < _sizeTween.end!.width ||
+        size.height < _sizeTween.end!.height)
       _hasVisualOverflow = true;
   }
 
@@ -217,7 +215,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   /// We have the initial size to animate from, but we do not have the target
   /// size to animate to, so we set both ends to child's size.
   void _layoutStart() {
-    _sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
+    _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
     _state = RenderAnimatedSizeState.stable;
   }
 
@@ -227,14 +225,14 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   /// If during animation the size of the child changes we restart the
   /// animation.
   void _layoutStable() {
-    if (_sizeTween.end != child.size) {
+    if (_sizeTween.end != child!.size) {
       _sizeTween.begin = size;
-      _sizeTween.end = debugAdoptSize(child.size);
+      _sizeTween.end = debugAdoptSize(child!.size);
       _restartAnimation();
       _state = RenderAnimatedSizeState.changed;
     } else if (_controller.value == _controller.upperBound) {
       // Animation finished. Reset target sizes.
-      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
+      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
     } else if (!_controller.isAnimating) {
       _controller.forward(); // resume the animation after being detached
     }
@@ -247,9 +245,9 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   /// changes again, we match the child's size, restart animation and go to
   /// unstable state.
   void _layoutChanged() {
-    if (_sizeTween.end != child.size) {
+    if (_sizeTween.end != child!.size) {
       // Child size changed again. Match the child's size and restart animation.
-      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
+      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
       _restartAnimation();
       _state = RenderAnimatedSizeState.unstable;
     } else {
@@ -264,9 +262,9 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
   ///
   /// Continue tracking the child's size until is stabilizes.
   void _layoutUnstable() {
-    if (_sizeTween.end != child.size) {
+    if (_sizeTween.end != child!.size) {
       // Still unstable. Continue tracking the child.
-      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child.size);
+      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
       _restartAnimation();
     } else {
       // Child size stabilized.