Change some dynamics to Object? and document slot better (#77026)

packages/flutter/lib/src/cupertino/text_selection_toolbar.dart

@@ -594,7 +594,7 @@ class _CupertinoTextSelectionToolbarItemsElement extends RenderObjectElement {
     assert(!_forgottenChildren.contains(child));
     // Handle forgetting a child in children or in a slot.
     if (slotToChild.containsKey(child.slot)) {
-      final _CupertinoTextSelectionToolbarItemsSlot slot = child.slot as _CupertinoTextSelectionToolbarItemsSlot;
+      final _CupertinoTextSelectionToolbarItemsSlot slot = child.slot! as _CupertinoTextSelectionToolbarItemsSlot;
       slotToChild.remove(slot);
     } else {
       _forgottenChildren.add(child);

packages/flutter/lib/src/widgets/framework.dart

@@ -1086,7 +1086,7 @@ abstract class State<T extends StatefulWidget> with Diagnosticable {
       }
       return true;
     }());
-    final dynamic result = fn() as dynamic;
+    final Object? result = fn() as dynamic;
     assert(() {
       if (result is Future) {
         throw FlutterError.fromParts(<DiagnosticsNode>[
@@ -3038,10 +3038,11 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// Information set by parent to define where this child fits in its parent's
   /// child list.
   ///
-  /// Subclasses of Element that only have one child should use null for
-  /// the slot for that child.
-  dynamic get slot => _slot;
-  dynamic _slot;
+  /// A child widget's slot is determined when the parent's [updateChild] method
+  /// is called to inflate the child widget. See [RenderObjectElement] for more
+  /// details on slots.
+  Object? get slot => _slot;
+  Object? _slot;
 
   /// An integer that is guaranteed to be greater than the parent's, if any.
   /// The element at the root of the tree must have a depth greater than 0.
@@ -3304,7 +3305,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   ///
   /// See the [RenderObjectElement] documentation for more information on slots.
   @protected
-  Element? updateChild(Element? child, Widget? newWidget, dynamic newSlot) {
+  Element? updateChild(Element? child, Widget? newWidget, Object? newSlot) {
     if (newWidget == null) {
       if (child != null)
         deactivateChild(child);
@@ -3389,7 +3390,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// Implementations of this method should start with a call to the inherited
   /// method, as in `super.mount(parent, newSlot)`.
   @mustCallSuper
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     assert(_lifecycleState == _ElementLifecycle.initial);
     assert(widget != null);
     assert(_parent == null);
@@ -3454,7 +3455,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// subclasses that have multiple children, when child moves from one position
   /// to another in this element's child list.
   @protected
-  void updateSlotForChild(Element child, dynamic newSlot) {
+  void updateSlotForChild(Element child, Object? newSlot) {
     assert(_lifecycleState == _ElementLifecycle.active);
     assert(child != null);
     assert(child._parent == this);
@@ -3466,7 +3467,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     visit(child);
   }
 
-  void _updateSlot(dynamic newSlot) {
+  void _updateSlot(Object? newSlot) {
     assert(_lifecycleState == _ElementLifecycle.active);
     assert(widget != null);
     assert(_parent != null);
@@ -3508,7 +3509,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// adding [renderObject] to the render tree.
   ///
   /// The `newSlot` argument specifies the new value for this element's [slot].
-  void attachRenderObject(dynamic newSlot) {
+  void attachRenderObject(Object? newSlot) {
     assert(_slot == null);
     visitChildren((Element child) {
       child.attachRenderObject(newSlot);
@@ -3577,7 +3578,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// The element returned by this function will already have been mounted and
   /// will be in the "active" lifecycle state.
   @protected
-  Element inflateWidget(Widget newWidget, dynamic newSlot) {
+  Element inflateWidget(Widget newWidget, Object? newSlot) {
     assert(newWidget != null);
     final Key? key = newWidget.key;
     if (key is GlobalKey) {
@@ -3678,7 +3679,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     }());
   }
 
-  void _activateWithParent(Element parent, dynamic newSlot) {
+  void _activateWithParent(Element parent, Object? newSlot) {
     assert(_lifecycleState == _ElementLifecycle.inactive);
     _parent = parent;
     assert(() {
@@ -4421,7 +4422,7 @@ class ErrorWidget extends LeafRenderObjectWidget {
     return ErrorWidget.withDetails(message: message, error: exception is FlutterError ? exception : null);
   }
 
-  static String _stringify(dynamic exception) {
+  static String _stringify(Object? exception) {
     try {
       return exception.toString();
     } catch (e) {
@@ -4533,7 +4534,7 @@ abstract class ComponentElement extends Element {
   bool get debugDoingBuild => _debugDoingBuild;
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     assert(_child == null);
     assert(_lifecycleState == _ElementLifecycle.active);
@@ -4700,7 +4701,7 @@ class StatefulElement extends ComponentElement {
     assert(state._debugLifecycleState == _StateLifecycle.created);
     try {
       _debugSetAllowIgnoredCallsToMarkNeedsBuild(true);
-      final dynamic debugCheckForReturnedFuture = state.initState() as dynamic;
+      final Object? debugCheckForReturnedFuture = state.initState() as dynamic;
       assert(() {
         if (debugCheckForReturnedFuture is Future) {
           throw FlutterError.fromParts(<DiagnosticsNode>[
@@ -4750,7 +4751,7 @@ class StatefulElement extends ComponentElement {
     state._widget = widget as StatefulWidget;
     try {
       _debugSetAllowIgnoredCallsToMarkNeedsBuild(true);
-      final dynamic debugCheckForReturnedFuture = state.didUpdateWidget(oldWidget) as dynamic;
+      final Object? debugCheckForReturnedFuture = state.didUpdateWidget(oldWidget) as dynamic;
       assert(() {
         if (debugCheckForReturnedFuture is Future) {
           throw FlutterError.fromParts(<DiagnosticsNode>[
@@ -5237,13 +5238,17 @@ class InheritedElement extends ProxyElement {
 /// corresponds to whatever [RenderObject] its child (the element returned by
 /// its [StatelessWidget.build] method) corresponds to.
 ///
-/// Each child is therefore assigned a _slot_ token. This is an identifier whose
+/// Each child is therefore assigned a _[slot]_ token. This is an identifier whose
 /// meaning is private to this [RenderObjectElement] node. When the descendant
 /// that finally produces the [RenderObject] is ready to attach it to this
 /// node's render object, it passes that slot token back to this node, and that
 /// allows this node to cheaply identify where to put the child render object
 /// relative to the others in the parent render object.
 ///
+/// A child's [slot] is determined when the parent calls [updateChild] to
+/// inflate the child (see the next section). It can be updated by calling
+/// [updateSlotForChild].
+///
 /// ### Updating children
 ///
 /// Early in the lifecycle of an element, the framework calls the [mount]
@@ -5409,7 +5414,7 @@ abstract class RenderObjectElement extends Element {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     assert(() {
       _debugDoingBuild = true;
@@ -5716,8 +5721,8 @@ abstract class RenderObjectElement extends Element {
   }
 
   @override
-  void _updateSlot(dynamic newSlot) {
-    final dynamic oldSlot = slot;
+  void _updateSlot(Object? newSlot) {
+    final Object? oldSlot = slot;
     assert(oldSlot != newSlot);
     super._updateSlot(newSlot);
     assert(slot == newSlot);
@@ -5725,7 +5730,7 @@ abstract class RenderObjectElement extends Element {
   }
 
   @override
-  void attachRenderObject(dynamic newSlot) {
+  void attachRenderObject(Object? newSlot) {
     assert(_ancestorRenderObjectElement == null);
     _slot = newSlot;
     _ancestorRenderObjectElement = _findAncestorRenderObjectElement();
@@ -5770,7 +5775,7 @@ abstract class RenderObjectElement extends Element {
     'Override insertRenderObjectChild instead. '
     'This feature was deprecated after v1.21.0-9.0.pre.'
   )
-  void insertChildRenderObject(covariant RenderObject child, covariant dynamic slot) {
+  void insertChildRenderObject(covariant RenderObject child, covariant Object? slot) {
     assert(() {
       throw FlutterError.fromParts(<DiagnosticsNode>[
         ErrorSummary('RenderObjectElement.insertChildRenderObject() is deprecated.'),
@@ -5800,7 +5805,7 @@ abstract class RenderObjectElement extends Element {
   /// [IndexedSlot] is a convenient value for the slot.
   /// {@endtemplate}
   @protected
-  void insertRenderObjectChild(covariant RenderObject child, covariant dynamic slot) {
+  void insertRenderObjectChild(covariant RenderObject child, covariant Object? slot) {
     insertChildRenderObject(child, slot);
   }
 
@@ -5843,7 +5848,7 @@ abstract class RenderObjectElement extends Element {
     'Override moveRenderObjectChild instead. '
     'This feature was deprecated after v1.21.0-9.0.pre.'
   )
-  void moveChildRenderObject(covariant RenderObject child, covariant dynamic slot) {
+  void moveChildRenderObject(covariant RenderObject child, covariant Object? slot) {
     assert(() {
       throw FlutterError.fromParts(<DiagnosticsNode>[
         ErrorSummary('RenderObjectElement.moveChildRenderObject() is deprecated.'),
@@ -5879,7 +5884,7 @@ abstract class RenderObjectElement extends Element {
   /// compared against each other for the purposes of updating one slot with the
   /// element from another slot) would never call this.
   @protected
-  void moveRenderObjectChild(covariant RenderObject child, covariant dynamic oldSlot, covariant dynamic newSlot) {
+  void moveRenderObjectChild(covariant RenderObject child, covariant Object? oldSlot, covariant Object? newSlot) {
     moveChildRenderObject(child, newSlot);
   }
 
@@ -5936,7 +5941,7 @@ abstract class RenderObjectElement extends Element {
   /// The given child is guaranteed to have been inserted at the given `slot`
   /// and have [renderObject] as its parent.
   @protected
-  void removeRenderObjectChild(covariant RenderObject child, covariant dynamic slot) {
+  void removeRenderObjectChild(covariant RenderObject child, covariant Object? slot) {
     removeChildRenderObject(child);
   }
 
@@ -5970,7 +5975,7 @@ abstract class RootRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     // Root elements should never have parents.
     assert(parent == null);
     assert(newSlot == null);
@@ -5990,17 +5995,17 @@ class LeafRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void insertRenderObjectChild(RenderObject child, dynamic slot) {
+  void insertRenderObjectChild(RenderObject child, Object? slot) {
     assert(false);
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false);
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     assert(false);
   }
 
@@ -6040,7 +6045,7 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     _child = updateChild(_child, widget.child, null);
   }
@@ -6053,7 +6058,7 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void insertRenderObjectChild(RenderObject child, dynamic slot) {
+  void insertRenderObjectChild(RenderObject child, Object? slot) {
     final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject as RenderObjectWithChildMixin<RenderObject>;
     assert(slot == null);
     assert(renderObject.debugValidateChild(child));
@@ -6062,12 +6067,12 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void moveRenderObjectChild(RenderObject child, dynamic oldSlot, dynamic newSlot) {
+  void moveRenderObjectChild(RenderObject child, Object? oldSlot, Object? newSlot) {
     assert(false);
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject as RenderObjectWithChildMixin<RenderObject>;
     assert(slot == null);
     assert(renderObject.child == child);
@@ -6133,7 +6138,7 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void removeRenderObjectChild(RenderObject child, dynamic slot) {
+  void removeRenderObjectChild(RenderObject child, Object? slot) {
     final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
     assert(child.parent == renderObject);
     renderObject.remove(child);
@@ -6157,7 +6162,7 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
   }
 
   @override
-  void mount(Element? parent, dynamic newSlot) {
+  void mount(Element? parent, Object? newSlot) {
     super.mount(parent, newSlot);
     final List<Element> children = List<Element>.filled(widget.children.length, _NullElement.instance, growable: false);
     Element? previousChild;