Subject: bug#18381: 24.3.93; Diary can wrongly be displayed in Calendar's window

From: martin rudalics <[email-masked]>
Date: Tue, 09 Sep 2014 08:58:47 +0200

> emacs -Q
 > M-x diary
 > M-x calendar
 > M-x diary    -> clobbered calendar window; not so in 24.3
 >
 > I see now that the cause is that the pixelwise change that I bisected to
 > earlier added display-buffer-in-previous-window to
 > display-buffer-fallback-action - it wasn't there before.
 >
 > So I can restore the 24.3 behaviour by using this horrible thing:
 >
 > (let ((display-buffer-fallback-action
 >         (list (delq 'display-buffer-in-previous-window
 >                  (copy-sequence (car display-buffer-fallback-action))))))
 >    ...)
 >
 > This is Not The Right Thing, but ought to restore 24.3-like behaviour.

That's what I meant earlier when I said that

 > > The window you're using to display `diary' here ...
 > > ... is the same window where you first show the calendar here.  As a
 > > consequence, `display-buffer-in-previous-window' will find a window
 > > where you have shown `diary' already and reuse that window.  I'm not
 > > sure what's the best thing to do here - maybe we should remove
 > > `display-buffer-in-previous-window' from
 > > `display-buffer-fallback-action' in `calendar-in-read-only-buffer'.

but obviously we should do something like

(let ((display-buffer-overriding-action
        (list (delq 'display-buffer-in-previous-window
                 (copy-sequence (car display-buffer-fallback-action))))))
   ...)

because (as you remarked earlier) `display-buffer-fallback-action' is a
constant and should not be changed by the user or an application.

 > I think what I really want is a way to say to display-buffer:
 > never use a window showing buffer X.
 >
 > Is that doable?

You can mark the calendar window as softly dedicated to its buffer,
ideally only as long as `diary' wants to use it.  Otherwise, we could
invent new alist entries à la `inhibit-same-window':

`inhibit-windows' (whose value would be a list of windows that should
not be used), and/or

`inhibit-windows-on' (whose value would be a list of buffers that should
remain displayed),

not for Emacs 24.4, in any case.

You still didn't tell me who actually is responsible for displaying the
calendar and then the diary.  Is it `calendar-in-read-only-buffer'?  If
we are sure that it's there, we can pass the necessary advice in that
mancro's `display-buffer' call's ACTION argument.

martin