Follow up scroll semantics update with documentation fixes (#23444)

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

@@ -715,8 +715,10 @@ class ListView extends BoxScrollView {
   /// The `addAutomaticKeepAlives` argument corresponds to the
   /// [SliverChildListDelegate.addAutomaticKeepAlives] property. The
   /// `addRepaintBoundaries` argument corresponds to the
-  /// [SliverChildListDelegate.addRepaintBoundaries] property. Both must not be
-  /// null.
+  /// [SliverChildListDelegate.addRepaintBoundaries] property. The
+  /// `addSemanticIndexes` argument corresponds to the
+  /// [SliverChildListDelegate.addSemanticIndexes] property. None
+  /// may be null.
   ListView({
     Key key,
     Axis scrollDirection = Axis.vertical,
@@ -773,8 +775,10 @@ class ListView extends BoxScrollView {
   /// The `addAutomaticKeepAlives` argument corresponds to the
   /// [SliverChildBuilderDelegate.addAutomaticKeepAlives] property. The
   /// `addRepaintBoundaries` argument corresponds to the
-  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. Both must not
-  /// be null.
+  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. The
+  /// `addSemanticIndexes` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addSemanticIndexes] property. None may be
+  /// null.
   ListView.builder({
     Key key,
     Axis scrollDirection = Axis.vertical,
@@ -853,8 +857,10 @@ class ListView extends BoxScrollView {
   /// The `addAutomaticKeepAlives` argument corresponds to the
   /// [SliverChildBuilderDelegate.addAutomaticKeepAlives] property. The
   /// `addRepaintBoundaries` argument corresponds to the
-  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. Both must not
-  /// be null.
+  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. The
+  /// `addSemanticIndexes` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addSemanticIndexes] property. None may be
+  /// null.
   ListView.separated({
     Key key,
     Axis scrollDirection = Axis.vertical,

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

@@ -301,8 +301,9 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
   /// Creates a delegate that supplies children for slivers using the given
   /// builder callback.
   ///
-  /// The [builder], [addAutomaticKeepAlives], and [addRepaintBoundaries]
-  /// arguments must not be null.
+  /// The [builder], [addAutomaticKeepAlives], [addRepaintBoundaries],
+  /// [addSemanticIndexes], and [semanticIndexCallback] arguments must not be
+  /// null.
   const SliverChildBuilderDelegate(
     this.builder, {
     this.childCount,
@@ -313,7 +314,9 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
     this.semanticIndexOffset = 0,
   }) : assert(builder != null),
        assert(addAutomaticKeepAlives != null),
-       assert(addRepaintBoundaries != null);
+       assert(addRepaintBoundaries != null),
+       assert(addSemanticIndexes != null),
+       assert(semanticIndexCallback != null);
 
   /// Called to build children for the sliver.
   ///
@@ -363,10 +366,13 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
   /// Typically, children in a scrolling container must be annotated with a
   /// semantic index in order to generate the correct accessibility
   /// announcements. This should only be set to false if the indexes have
-  /// already been provided by wrapping the correct child widgets in an
-  /// indexed child semantics widget.
+  /// already been provided by an [IndexedChildSemantics] widget.
   ///
   /// Defaults to true.
+  ///
+  /// See also:
+  ///   * [IndexedChildSemantics], for an explanation of how to manually
+  ///     provide semantic indexes.
   final bool addSemanticIndexes;
 
   /// An initial offset to add to the semantic indexes generated by this widget.
@@ -461,8 +467,9 @@ class SliverChildListDelegate extends SliverChildDelegate {
   /// Creates a delegate that supplies children for slivers using the given
   /// list.
   ///
-  /// The [children], [addAutomaticKeepAlives], and [addRepaintBoundaries]
-  /// arguments must not be null.
+  /// The [children], [addAutomaticKeepAlives], [addRepaintBoundaries],
+  /// [addSemanticIndexes], and [semanticIndexCallback] arguments must not be
+  /// null.
   const SliverChildListDelegate(
     this.children, {
     this.addAutomaticKeepAlives = true,
@@ -472,7 +479,9 @@ class SliverChildListDelegate extends SliverChildDelegate {
     this.semanticIndexOffset = 0,
   }) : assert(children != null),
        assert(addAutomaticKeepAlives != null),
-       assert(addRepaintBoundaries != null);
+       assert(addRepaintBoundaries != null),
+       assert(addSemanticIndexes != null),
+       assert(semanticIndexCallback != null);
 
   /// Whether to wrap each child in an [AutomaticKeepAlive].
   ///
@@ -504,10 +513,13 @@ class SliverChildListDelegate extends SliverChildDelegate {
   /// Typically, children in a scrolling container must be annotated with a
   /// semantic index in order to generate the correct accessibility
   /// announcements. This should only be set to false if the indexes have
-  /// already been provided by wrapping the correct child widgets in an
-  /// indexed child semantics widget.
+  /// already been provided by an [IndexedChildSemantics] widget.
   ///
   /// Defaults to true.
+  ///
+  /// See also:
+  ///   * [IndexedChildSemantics], for an explanation of how to manually
+  ///     provide semantic indexes.
   final bool addSemanticIndexes;
 
   /// An initial offset to add to the semantic indexes generated by this widget.