Remove unnecessary null checks in `flutter/{animation,semantics,scheduler}` (#118922)

* Remove unnecessary null checks in flutter/animation

* Remove unnecessary null checks in flutter/semantics

* Remove unnecessary null checks in flutter/scheduler

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

@@ -269,7 +269,6 @@ abstract class Animation<T> extends Listenable implements ValueListenable<T> {
   /// * "&#x23ED;": [AnimationStatus.completed] ([value] == 1.0)
   /// * "&#x23EE;": [AnimationStatus.dismissed] ([value] == 0.0)
   String toStringDetails() {
-    assert(status != null);
     switch (status) {
       case AnimationStatus.forward:
         return '\u25B6'; // >

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

@@ -242,10 +242,7 @@ class AnimationController extends Animation<double>
     this.upperBound = 1.0,
     this.animationBehavior = AnimationBehavior.normal,
     required TickerProvider vsync,
-  }) : assert(lowerBound != null),
-       assert(upperBound != null),
-       assert(upperBound >= lowerBound),
-       assert(vsync != null),
+  }) : assert(upperBound >= lowerBound),
        _direction = _AnimationDirection.forward {
     _ticker = vsync.createTicker(_tick);
     _internalSetValue(value ?? lowerBound);
@@ -275,9 +272,7 @@ class AnimationController extends Animation<double>
     this.debugLabel,
     required TickerProvider vsync,
     this.animationBehavior = AnimationBehavior.preserve,
-  }) : assert(value != null),
-       assert(vsync != null),
-       lowerBound = double.negativeInfinity,
+  }) : lowerBound = double.negativeInfinity,
        upperBound = double.infinity,
        _direction = _AnimationDirection.forward {
     _ticker = vsync.createTicker(_tick);
@@ -363,7 +358,6 @@ class AnimationController extends Animation<double>
   ///  * [forward], [reverse], [animateTo], [animateWith], [fling], and [repeat],
   ///    which start the animation controller.
   set value(double newValue) {
-    assert(newValue != null);
     stop();
     _internalSetValue(newValue);
     notifyListeners();
@@ -657,7 +651,6 @@ class AnimationController extends Animation<double>
     }());
     assert(max >= min);
     assert(max <= upperBound && min >= lowerBound);
-    assert(reverse != null);
     stop();
     return _startSimulation(_RepeatingSimulation(_value, min, max, reverse, period!, _directionSetter));
   }
@@ -744,7 +737,6 @@ class AnimationController extends Animation<double>
   }
 
   TickerFuture _startSimulation(Simulation simulation) {
-    assert(simulation != null);
     assert(!isAnimating);
     _simulation = simulation;
     _lastElapsedDuration = Duration.zero;
@@ -856,9 +848,7 @@ class AnimationController extends Animation<double>
 
 class _InterpolationSimulation extends Simulation {
   _InterpolationSimulation(this._begin, this._end, Duration duration, this._curve, double scale)
-    : assert(_begin != null),
-      assert(_end != null),
-      assert(duration != null && duration.inMicroseconds > 0),
+    : assert(duration.inMicroseconds > 0),
       _durationInSeconds = (duration.inMicroseconds * scale) / Duration.microsecondsPerSecond;
 
   final double _durationInSeconds;

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

@@ -271,8 +271,7 @@ class ReverseAnimation extends Animation<double>
   /// Creates a reverse animation.
   ///
   /// The parent argument must not be null.
-  ReverseAnimation(this.parent)
-    : assert(parent != null);
+  ReverseAnimation(this.parent);
 
   /// The animation whose value and direction this animation is reversing.
   final Animation<double> parent;
@@ -310,7 +309,6 @@ class ReverseAnimation extends Animation<double>
   double get value => 1.0 - parent.value;
 
   AnimationStatus _reverseStatus(AnimationStatus status) {
-    assert(status != null);
     switch (status) {
       case AnimationStatus.forward: return AnimationStatus.reverse;
       case AnimationStatus.reverse: return AnimationStatus.forward;
@@ -384,8 +382,7 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
     required this.parent,
     required this.curve,
     this.reverseCurve,
-  }) : assert(parent != null),
-       assert(curve != null) {
+  }) {
     _updateCurveDirection(parent.status);
     parent.addStatusListener(_updateCurveDirection);
   }
@@ -518,7 +515,7 @@ class TrainHoppingAnimation extends Animation<double>
     Animation<double> this._currentTrain,
     this._nextTrain, {
     this.onSwitchedTrain,
-  }) : assert(_currentTrain != null) {
+  }) {
     if (_nextTrain != null) {
       if (_currentTrain!.value == _nextTrain!.value) {
         _currentTrain = _nextTrain;
@@ -644,8 +641,7 @@ abstract class CompoundAnimation<T> extends Animation<T>
   CompoundAnimation({
     required this.first,
     required this.next,
-  }) : assert(first != null),
-       assert(next != null);
+  });
 
   /// The first sub-animation. Its status takes precedence if neither are
   /// animating.

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

@@ -35,7 +35,6 @@ abstract class ParametricCurve<T> {
   /// implementation of [transform], which delegates the remaining logic to
   /// [transformInternal].
   T transform(double t) {
-    assert(t != null);
     assert(t >= 0.0 && t <= 1.0, 'parametric value $t is outside of [0, 1] range.');
     return transformInternal(t);
   }
@@ -129,7 +128,7 @@ class SawTooth extends Curve {
   /// Creates a sawtooth curve.
   ///
   /// The [count] argument must not be null.
-  const SawTooth(this.count) : assert(count != null);
+  const SawTooth(this.count);
 
   /// The number of repetitions of the sawtooth pattern in the unit interval.
   final int count;
@@ -159,10 +158,7 @@ class Interval extends Curve {
   /// Creates an interval curve.
   ///
   /// The arguments must not be null.
-  const Interval(this.begin, this.end, { this.curve = Curves.linear })
-    : assert(begin != null),
-      assert(end != null),
-      assert(curve != null);
+  const Interval(this.begin, this.end, { this.curve = Curves.linear });
 
   /// The largest value for which this interval is 0.0.
   ///
@@ -207,7 +203,7 @@ class Threshold extends Curve {
   /// Creates a threshold curve.
   ///
   /// The [threshold] argument must not be null.
-  const Threshold(this.threshold) : assert(threshold != null);
+  const Threshold(this.threshold);
 
   /// The value before which the curve is 0.0 and after which the curve is 1.0.
   ///
@@ -307,11 +303,7 @@ class Cubic extends Curve {
   /// cubic curves in [Curves].
   ///
   /// The [a] (x1), [b] (y1), [c] (x2) and [d] (y2) arguments must not be null.
-  const Cubic(this.a, this.b, this.c, this.d)
-    : assert(a != null),
-      assert(b != null),
-      assert(c != null),
-      assert(d != null);
+  const Cubic(this.a, this.b, this.c, this.d);
 
   /// The x coordinate of the first control point.
   ///
@@ -518,9 +510,6 @@ abstract class Curve2D extends ParametricCurve<Offset> {
     // 4. Recursively sample the two parts.
     //
     // This algorithm concentrates samples in areas of high curvature.
-    assert(tolerance != null);
-    assert(start != null);
-    assert(end != null);
     assert(end > start);
     // We want to pick a random seed that will keep the result stable if
     // evaluated again, so we use the first non-generated control point.
@@ -577,7 +566,6 @@ abstract class Curve2D extends ParametricCurve<Offset> {
   /// single-valued, it will return the parameter for only one of the values at
   /// the given `x` location.
   double findInverse(double x) {
-    assert(x != null);
     double start = 0.0;
     double end = 1.0;
     late double mid;
@@ -612,7 +600,7 @@ class Curve2DSample {
   /// Creates an object that holds a sample; used with [Curve2D] subclasses.
   ///
   /// All arguments must not be null.
-  const Curve2DSample(this.t, this.value) : assert(t != null), assert(value != null);
+  const Curve2DSample(this.t, this.value);
 
   /// The parametric location of this sample point along the curve.
   final double t;
@@ -682,9 +670,7 @@ class CatmullRomSpline extends Curve2D {
         double tension = 0.0,
         Offset? startHandle,
         Offset? endHandle,
-      }) : assert(controlPoints != null),
-           assert(tension != null),
-           assert(tension <= 1.0, 'tension $tension must not be greater than 1.0.'),
+      }) : assert(tension <= 1.0, 'tension $tension must not be greater than 1.0.'),
            assert(tension >= 0.0, 'tension $tension must not be negative.'),
            assert(controlPoints.length > 3, 'There must be at least four control points to create a CatmullRomSpline.'),
            _controlPoints = controlPoints,
@@ -702,9 +688,7 @@ class CatmullRomSpline extends Curve2D {
         double tension = 0.0,
         Offset? startHandle,
         Offset? endHandle,
-      }) : assert(controlPoints != null),
-           assert(tension != null),
-           assert(tension <= 1.0, 'tension $tension must not be greater than 1.0.'),
+      }) : assert(tension <= 1.0, 'tension $tension must not be greater than 1.0.'),
            assert(tension >= 0.0, 'tension $tension must not be negative.'),
            assert(controlPoints.length > 3, 'There must be at least four control points to create a CatmullRomSpline.'),
            _controlPoints = null,
@@ -860,8 +844,7 @@ class CatmullRomCurve extends Curve {
   ///
   ///  * This [paper on using Catmull-Rom splines](http://faculty.cs.tamu.edu/schaefer/research/cr_cad.pdf).
   CatmullRomCurve(this.controlPoints, {this.tension = 0.0})
-      : assert(tension != null),
-        assert(() {
+      : assert(() {
           return validateControlPoints(
             controlPoints,
             tension: tension,
@@ -877,8 +860,7 @@ class CatmullRomCurve extends Curve {
   /// Same as [CatmullRomCurve.new], but it precomputes the internal curve data
   /// structures for a more predictable computation load.
   CatmullRomCurve.precompute(this.controlPoints, {this.tension = 0.0})
-      : assert(tension != null),
-        assert(() {
+      : assert(() {
           return validateControlPoints(
             controlPoints,
             tension: tension,
@@ -963,7 +945,6 @@ class CatmullRomCurve extends Curve {
     double tension = 0.0,
     List<String>? reasons,
   }) {
-    assert(tension != null);
     if (controlPoints == null) {
       assert(() {
         reasons?.add('Supplied control points cannot be null');
@@ -1143,7 +1124,7 @@ class FlippedCurve extends Curve {
   /// Creates a flipped curve.
   ///
   /// The [curve] argument must not be null.
-  const FlippedCurve(this.curve) : assert(curve != null);
+  const FlippedCurve(this.curve);
 
   /// The curve that is being flipped.
   final Curve curve;

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

@@ -364,8 +364,7 @@ class Tween<T extends Object?> extends Animatable<T> {
 class ReverseTween<T extends Object?> extends Tween<T> {
   /// Construct a [Tween] that evaluates its [parent] in reverse.
   ReverseTween(this.parent)
-    : assert(parent != null),
-      super(begin: parent.end, end: parent.begin);
+    : super(begin: parent.end, end: parent.begin);
 
   /// This tween's value is the same as the parent's value evaluated in reverse.
   ///
@@ -544,8 +543,7 @@ class CurveTween extends Animatable<double> {
   /// Creates a curve tween.
   ///
   /// The [curve] argument must not be null.
-  CurveTween({ required this.curve })
-    : assert(curve != null);
+  CurveTween({ required this.curve });
 
   /// The curve to use when transforming the value of the animation.
   Curve curve;

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

@@ -51,8 +51,7 @@ class TweenSequence<T> extends Animatable<T> {
   /// best to reuse one, rather than rebuilding it on every frame, when that's
   /// possible.
   TweenSequence(List<TweenSequenceItem<T>> items)
-      : assert(items != null),
-        assert(items.isNotEmpty) {
+      : assert(items.isNotEmpty) {
     _items.addAll(items);
 
     double totalWeight = 0.0;
@@ -113,8 +112,7 @@ class FlippedTweenSequence extends TweenSequence<double> {
   /// There's a small cost associated with building a `TweenSequence` so it's
   /// best to reuse one, rather than rebuilding it on every frame, when that's
   /// possible.
-  FlippedTweenSequence(super.items)
-    : assert(items != null);
+  FlippedTweenSequence(super.items);
 
   @override
   double transform(double t) => 1 - super.transform(1 - t);
@@ -128,9 +126,7 @@ class TweenSequenceItem<T> {
   const TweenSequenceItem({
     required this.tween,
     required this.weight,
-  }) : assert(tween != null),
-       assert(weight != null),
-       assert(weight > 0.0);
+  }) : assert(weight > 0.0);
 
   /// Defines the value of the [TweenSequence] for the interval within the
   /// animation's duration indicated by [weight] and this item's position

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

@@ -385,7 +385,6 @@ mixin SchedulerBinding on BindingBase {
   @protected
   @mustCallSuper
   void handleAppLifecycleStateChanged(AppLifecycleState state) {
-    assert(state != null);
     _lifecycleState = state;
     switch (state) {
       case AppLifecycleState.resumed:
@@ -1026,7 +1025,6 @@ mixin SchedulerBinding on BindingBase {
   /// presentation time, and can be used to ensure that animations running in
   /// different processes are synchronized.
   Duration get currentSystemFrameTimeStamp {
-    assert(_lastRawTimeStamp != null);
     return _lastRawTimeStamp;
   }
 
@@ -1279,7 +1277,6 @@ mixin SchedulerBinding on BindingBase {
   // the error.
   @pragma('vm:notify-debugger-on-exception')
   void _invokeFrameCallback(FrameCallback callback, Duration timeStamp, [ StackTrace? callbackStack ]) {
-    assert(callback != null);
     assert(_FrameCallbackEntry.debugCurrentCallbackStack == null);
     assert(() {
       _FrameCallbackEntry.debugCurrentCallbackStack = callbackStack;

packages/flutter/lib/src/semantics/semantics_event.dart

@@ -87,9 +87,7 @@ class AnnounceSemanticsEvent extends SemanticsEvent {
 
   /// Constructs an event that triggers an announcement by the platform.
   const AnnounceSemanticsEvent(this.message, this.textDirection, {this.assertiveness = Assertiveness.polite})
-    : assert(message != null),
-      assert(textDirection != null),
-      super('announce');
+    : super('announce');
 
   /// The message to announce.
   ///