Stylus Gestures Not Recognized in PageListViewportGestures Widget

[Tsames]

The widget constructor for PageListViewportGestures accepts an argument called deviceKind. We expect that when stylus is added as a device, the user wil be able to use it to scroll. However, even after providing stylus as one of the device kinds the widget does not recognize gestures made with a stylus.

To confirm our findings, we created a test called operates as a panning device. In it, we fling with a stylus, expecting the velocity to update, but it never does.

    //Add stylus to PageListViewPortGestures
    final deviceKind = {
        PointerDeviceKind.mouse,
        PointerDeviceKind.trackpad,
        PointerDeviceKind.touch,
        PointerDeviceKind.stylus,
    };
    await _pumpPageListViewport(widgetTester, controller: controller, pointerDevices: deviceKind);

    Offset? latestVelocity;
    controller.addListener(() {
    latestVelocity = controller.velocity;
    });

    // Fling up with stylus
    await widgetTester.fling(find.byType(Scaffold), const Offset(0, -500), 4000,
        deviceKind: PointerDeviceKind.stylus);

    // The viewport is moving after fling
    await widgetTester.pump();
    expect(latestVelocity, isNotNull);

It looks like there is a slight issue with the control flow, intentionally preventing gestures with a stylus.

---

Despite stylus not being fully supported as a device, we observe that an already scrolling viewport can in practice be stopped with a stylus. Reproducing it in a test, we observe that on stylus down the viewport does not halt immediately (after a pump). Here is the full test. However, we notice that if we pump four times, the viewport action stops.

    // Fling up, to scroll down, and run a panning simulation.
    await widgetTester.fling(find.byType(Scaffold), const Offset(0, -500), 4000);
    // The viewport is moving
    await widgetTester.pump();
    expect(latestVelocity == Offset.zero, false);

    await widgetTester.startGesture(const Offset(0, 0), kind: PointerDeviceKind.stylus);
    // Pumping one frame does not suffice to propagate the stylus gesture
    // and stop the scrolling simulation, so we're using a pumping duration.
    await widgetTester.pump();

    expect(latestVelocity == Offset.zero, true); // Fails

It looks like stopMomentum() is not properly stopping the viewport controller.