Fix pointer scroll for nested NeverScrollables (#70953)

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

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:math' as math;
 import 'dart:ui';
 
 import 'package:flutter/gestures.dart';
@@ -628,25 +629,35 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
 
   // SCROLL WHEEL
 
+  // Returns the offset that should result from applying [event] to the current
+  // position, taking min/max scroll extent into account.
+  double _targetScrollOffsetForPointerScroll(PointerScrollEvent event) {
+    final double delta = _pointerSignalEventDelta(event);
+    return math.min(math.max(position.pixels + delta, position.minScrollExtent),
+      position.maxScrollExtent);
+  }
+
   // Returns the delta that should result from applying [event] with axis and
   // direction taken into account.
-  double _targetScrollDeltaForPointerScroll(PointerScrollEvent event) {
+  double _pointerSignalEventDelta(PointerScrollEvent event) {
     double delta = widget.axis == Axis.horizontal
-        ? event.scrollDelta.dx
-        : event.scrollDelta.dy;
+      ? event.scrollDelta.dx
+      : event.scrollDelta.dy;
 
     if (axisDirectionIsReversed(widget.axisDirection)) {
       delta *= -1;
     }
-
     return delta;
   }
 
   void _receivedPointerSignal(PointerSignalEvent event) {
     if (event is PointerScrollEvent && _position != null) {
-      final double targetScrollOffset = _targetScrollDeltaForPointerScroll(event);
+      if (_physics != null && !_physics!.shouldAcceptUserOffset(position)) {
+        return;
+      }
+      final double targetScrollOffset = _targetScrollOffsetForPointerScroll(event);
       // Only express interest in the event if it would actually result in a scroll.
-      if (targetScrollOffset != 0) {
+      if (targetScrollOffset != position.pixels) {
         GestureBinding.instance!.pointerSignalResolver.register(event, _handlePointerScroll);
       }
     }
@@ -654,12 +665,9 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
 
   void _handlePointerScroll(PointerEvent event) {
     assert(event is PointerScrollEvent);
-    if (_physics != null && !_physics!.shouldAcceptUserOffset(position)) {
-      return;
-    }
-    final double targetScrollOffset = _targetScrollDeltaForPointerScroll(event as PointerScrollEvent);
-    if (targetScrollOffset != 0) {
-      position.pointerScroll(targetScrollOffset);
+    final double targetScrollOffset = _targetScrollOffsetForPointerScroll(event as PointerScrollEvent);
+    if (targetScrollOffset != position.pixels) {
+      position.pointerScroll(_pointerSignalEventDelta(event));
     }
   }
 

packages/flutter/test/widgets/scrollable_test.dart

@@ -1148,6 +1148,64 @@ void main() {
     expect(targetMidRightPage1, findsOneWidget);
     expect(targetMidLeftPage1, findsOneWidget);
   });
+
+  testWidgets('PointerScroll on nested NeverScrollable ListView goes to outer Scrollable.', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/70948
+    final ScrollController outerController = ScrollController();
+    final ScrollController innerController = ScrollController();
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: SingleChildScrollView(
+          controller: outerController,
+          child: Container(
+            child: Row(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              mainAxisAlignment: MainAxisAlignment.start,
+              children: <Widget>[
+                Column(
+                  children: <Widget>[
+                    for (int i = 0; i < 100; i++)
+                      Text('SingleChildScrollView $i'),
+                  ]
+                ),
+                Container(
+                  height: 3000,
+                  width: 400,
+                  child: ListView.builder(
+                    controller: innerController,
+                    physics: const NeverScrollableScrollPhysics(),
+                    itemCount: 100,
+                    itemBuilder: (BuildContext context, int index) {
+                      return Text('Nested NeverScrollable ListView $index');
+                    },
+                  )
+                ),
+              ]
+            )
+          )
+        )
+      ),
+    ));
+    expect(outerController.position.pixels, 0.0);
+    expect(innerController.position.pixels, 0.0);
+    final Offset outerScrollable = tester.getCenter(find.text('SingleChildScrollView 3'));
+    final TestPointer testPointer = TestPointer(1, ui.PointerDeviceKind.mouse);
+    // Hover over the outer scroll view and create a pointer scroll.
+    testPointer.hover(outerScrollable);
+    await tester.sendEventToBinding(testPointer.scroll(const Offset(0.0, 20.0)));
+    await tester.pump(const Duration(milliseconds: 250));
+    expect(outerController.position.pixels, 20.0);
+    expect(innerController.position.pixels, 0.0);
+
+    final Offset innerScrollable = tester.getCenter(find.text('Nested NeverScrollable ListView 20'));
+    // Hover over the inner scroll view and create a pointer scroll.
+    // This inner scroll view is not scrollable, and so the outer should scroll.
+    testPointer.hover(innerScrollable);
+    await tester.sendEventToBinding(testPointer.scroll(const Offset(0.0, -20.0)));
+    await tester.pump(const Duration(milliseconds: 250));
+    expect(outerController.position.pixels, 0.0);
+    expect(innerController.position.pixels, 0.0);
+  });
 }
 
 // ignore: must_be_immutable