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Immediate dismissal of a grabbing popup breaks input processing

Steps to reproduce

  1. Use Mutter, Weston, or Niri. (Other compositors I'm aware of don't validate popup grab serials and therefore don't dismiss the popup.)
  2. Open a program which opens a grabbing popup in response to a button press (tested with gtk4-demo-application).
  3. Hover the cursor over the element which opens the popup (e.g. a menu bar item).
  4. Press the right mouse button.
  5. Press the left mouse button. This should open the popup, but compositors listed expect the xdg_popup.grab serial to match that one of the right mouse button press event, so the popup is dismissed.
  6. Release both mouse buttons.

Current behavior

Despite the popup being dismissed, the program behaves as if the popup grab is active: keyboard focus is ignored and pointer button events aren't processed.

Expected outcome

Input events are processed correctly.

Version information

  • GTK version: commit f05eac61
  • Mutter version: 46.6
  • Weston version: commit 10ecf6084885acaf0b07ca69987f0110759677c5
  • Niri version: commit 1a0612cbfd0abee0796efa86470226686ae78f21

Additional information

Relevant parts of a Wayland client log:

$ WAYLAND_DISPLAY=wayland-0 WAYLAND_DEBUG=1 build/demos/gtk-demo/gtk4-demo-application 2>&1 | rg '(xdg_popup|button)'
[ 363021.874] {Default Queue} wl_pointer#25.button(5, 182185182, 273, 1)
[ 363268.463] {Default Queue} wl_pointer#25.button(6, 182185429, 272, 1)
[ 363276.785]  -> xdg_surface#134.get_popup(new id xdg_popup#135, xdg_surface#69, xdg_positioner#133)
[ 363276.808]  -> xdg_popup#135.grab(wl_seat#31, 6)
[ 363280.859] xdg_popup#135.popup_done()
[ 363284.067]  -> xdg_popup#135.destroy()
[ 363286.191]  -> xdg_surface#125.get_popup(new id xdg_popup#121, xdg_surface#69, xdg_positioner#129)
[ 363286.214]  -> xdg_popup#121.grab(wl_seat#31, 6)
[ 363289.335] xdg_popup#121.popup_done()
[ 363290.398]  -> xdg_popup#121.destroy()
[ 363392.306] {Default Queue} wl_pointer#25.button(7, 182185553, 272, 0)
[ 363848.344] {Default Queue} wl_pointer#25.button(8, 182186009, 273, 0)

For some reason, the program tries to open a popup twice.