[Webkit-unassigned] [Bug 257735] New: When mouse/trackpad click on WKWebView dismisses a UIKit menu, web gets touch down with no touch up, and no subsequent mouse events

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257735

            Bug ID: 257735
           Summary: When mouse/trackpad click on WKWebView dismisses a
                    UIKit menu, web gets touch down with no touch up, and
                    no subsequent mouse events
           Product: WebKit
           Version: Safari 16
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: UI Events
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: krevis at figma.com

Created attachment 466596

  --> https://bugs.webkit.org/attachment.cgi?id=466596&action=review

Xcode project for an iPad app to demonstrate the bug

We have a UIKit app containing a WKWebView, with buttons that show a UIKit menu above the web view. When we show a menu, then dismiss it by clicking with mouse/trackpad on the web view, the web view’s event handling is disrupted, making it unusable until the page is reloaded:
- A pointerdown event with pointerType “touch” is sent, with no corresponding pointerup or pointercancel.
- Subsequent clicks don’t send pointerdown or pointerup at all. Instead we get old-style mousedown and mouseup events.

Steps:
1. Run attached project on iPad with a mouse or trackpad attached, or in the simulator. 
2. Using any input method, press the “Menu” button to show a menu.
3. Using mouse or trackpad, click and release, outside the menu, on the web view.
4. Click again in the web view.

Expected:
- The web view prints “pointerdown mouse” and “pointerup mouse”, once for each click.

Actual:
- The first click makes the web view print “pointerdown touch”.  There is no subsequent “pointerup” or “pointer cancel”.
- The second click prints “Old-style mousedown! Should have seen a pointerdown instead” and “Old-style mouseup! Should have seen a pointerup instead”.
- It remains in this state until you press the Reload button to reload the page.

Notes:

The bug happens on iPadOS 15, 16, and 17 developer beta 1.  Both on device and in the simulator.

The sample app demonstrates two different bugs — see the explanatory text when you run the app. This is “Bug #2”.  

In the test app, there is a native gesture recognizer above the web view, that does nothing but observe touches and log them to the console. It sees touches with type `.indirectPointer` as expected.

When the bug is triggered, you’ll note that it gets a touch began, but *not* a touch ended or cancelled, and then reset. I’m guessing that WebKit’s `WKMouseGestureRecognizer` is not expecting that sequence, and somehow leaves the web content process in a weird state.

This bug makes it very difficult to use modern pointer events in our web content. We would really like to use them over the old-style mousedown/mouseup events, since they present a unified interface for touches, pointing devices, and Apple Pencil, but it’s very hard to deal with a bug where it just stops working and there’s no way to fix it afterwards. 

It’s also difficult to work around, because UIKit doesn’t always provide a simple way to find out when the menu is shown and dismissed. If the menu is the overflow menu in a navigation bar, for instance, it doesn’t provide a way to observe the menu, and there isn’t a way to make a custom subclass of UIBarButtonItem for it (which could).

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