Subject: Re: bug#34317: 26.1.90; Wrong unbinding order in x_consider_frame_title

From: martin rudalics <[email-masked]>
Date: Sun, 24 Feb 2019 09:43:09 +0100

>> first of all I'd like to know whether your change was intentionally
 >> asymmetric (if so, why?), experimentally asymmetric (which
 >> experiments did you conduct?), or accidentally so (it's rather
 >> atypical of you to install asymmetric behavior and not document it).
 >
 > I didn't realize we were discussing my change.  Which change was that?

commit 821ea144bd446268fbe4a4a4775a06da52dea8cb

Display mini-window resized even when there are several frames

* src/xdisp.c (x_consider_frame_title): Bind inhibit-redisplay to
t to avoid resizing back the mini-window as result of considering
the title of other frames.  (Bug#24285)
(redisplay_window): No need to bind inhibit-redisplay here.

This means that in x_consider_frame_title we now do

       ptrdiff_t count = SPECPDL_INDEX ();

       ...

       record_unwind_protect (unwind_format_mode_line,
                              format_mode_line_unwind_data
                                (f, current_buffer, selected_window, false));
       ...

       specbind (Qinhibit_redisplay, Qt);

       Fselect_window (f->selected_window, Qt);

      ...

       unbind_to (count, Qnil);

where unwind_format_mode_line does

       Fselect_window (old_window, Qt);

The asymmetry I mentioned is that while binding Qinhibit_redisplay
covers the Fselect_window call in x_consider_frame_title, it does not
cover the Fselect_window in unwind_format_mode_line since that is
performed _after_ the special binding of Qinhibit_redisplay has been
abolished.  Which means that we call resize_mini_window for the first
call when the corresponding windows are on different frames but not
for the second.

martin