bug#47244: 28.0.50; SIGSEGV in long-runnning Emacs

[martin rudalics]

> Here is the state as I've been able to determine from the debugger:
>
> Vframe_list contains three entries: "build.ninja", "*Server*", and
> "F1".  This matches reality.  "F1" is the invisible frame created by
> --daemon.
>
> Frame "build.ninja" has a selected_window whose contents are the buffer
> "build.ninja".
>
> Frame "*Server*" has a selected_window whose contents are the buffer
> "*Server*".
>
> Frame "F1" has a selected_window whose contents are the buffer
> "*scratch*".
>
> Vwindow_list contains two entries: A window whose contents are
> "build.ninja", and a window whose contents are " *Minibuf-0*".
>
> Importantly, Vwindow_list does not contain the window whose contents are
> "*Server*".  Since the window_list_1() call uses the value of
> Vwindow_list to create its result, the loop in window_loop() will never
> compare EQ in the REPLACE_BUFFER_IN_WINDOWS_SAFELY case clause.

Impressive, thanks.  This means that if earlier everything worked as
intended someone did

(1) set Vwindow_list to nil (because otherwise the *Server* window would
    still figure in it), and

(2) window_list () recreated Vwindow_list but did _not_ include the
    *Server* window.

The mysterious aspect is (2): Why did window_list skip the *Server*
window?  What is the value of FRAME_ROOT_WINDOW (f) where f is the
*Server* frame?  What is the name of that window's buffer?  IIUC the
*Server* frame does not have a minibuffer window - correct?

martin