bug#75120: 31.0.50; which-key crashes on xt if the scroll bar is activated.

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Sat, 28 Dec 2024 14:10:35 +0200, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Madhu <enometh@meer.net>
    >> Date: Thu, 26 Dec 2024 20:56:01 +0530
    >> 
    >> Hello, Having heard about which-key mode I decided to try it.
    >> 
    >> gdb --args ../build-xt-native/src/emacs  -Q  -eval '(which-key-mode 1)' -eval '(setq window-min-height 8)'
    >> 
    >> 1. type C-x, wait 5 seconds, type C-g.
    >> 2. type C-x, wait 2 seconds for the 8 line frame with scrollbar, click the "up
    >> arrow" on the top of the scrollbar.

    Eli> When I try this, Emacs signals an error, displaying "C-x
    Eli> <vertical-scroll-bar> <mouse-1> is undefined" in the echo area.  But
    Eli> I'm not on X.

    Eli> Can someone else reproduce the crash?

Yes. In xt_action_hook:

      x_send_scroll_bar_event (window_being_scrolled,
			       scroll_bar_end_scroll, 0, 0, false);
      w = XWINDOW (window_being_scrolled);
      bar = XSCROLL_BAR (w->vertical_scroll_bar); <-
			       w->vertical_scroll_bar == Qnil here

Although I have no clue what to do about it: I suspect the scrollbars
have been condemned by condemn_scroll_bars_hook, but then not
redeemed. Or maybe whatever is undoing or preventing the global
setting of "<vertical-scroll-bar> <mouse-1>" is responsible, but I
canʼt find where that is.

Robert
--