bug#26513: 25.2; pop-up-frames and *Completions* buffer

[charles@aurox.ch (Charles A. Roelli)]

Hi Drew,

On Sun, Apr 16 2017 at 08:54:37 am, Drew Adams wrote:

>> 1) Does this still work without a standalone minibuffer frame?  I'm
>>    interested in using one, but I'd rather fix the *Completions* frame
>>    problem first before adding on a minibuffer-only frame to my setup.
>
> I can make it work without a standalone minibuffer frame
> in all Emacs versions before Emacs 25.  For some reason,
> redirecting the frame focus does not seem to work right
> for Emacs 25 when there is no standalone minibuffer frame.
> I hope I'm just missing something simple.
>
> The following code works, for example, except for Emacs 25.
> (I have Emacs 25.1-2.)  Maybe you or Martin can explain why.
> The debug `message' calls here don't tell me that anything
> is wrong, but clearly something is.
>
> I tried some variants also (no `w32-grab-focus-on-raise',
> explicitly select *Completions* frame (and even set focus
> to it temporarily), etc., to no avail.
>
> (defun foo ()
>   (interactive)
>   (add-to-list 'special-display-buffer-names
>                `("*Completions*" display-comp-fr))
>   (setq w32-grab-focus-on-raise  nil))
>
> (defun display-comp-fr (buf &optional args)
>   (let ((return-window
>          (select-window
>           (funcall special-display-function buf args))))
>     (raise-frame)
>     (message "BUF: %S, WIN: %S, FR: %S"
>              buf (get-buffer-window buf)
>              (window-frame (get-buffer-window buf)))
>     (let* ((mini-win  (active-minibuffer-window))
>            (redirect
>             (if mini-win
>                 (window-frame mini-win)
>               (and completion-reference-buffer
>                    (get-buffer-window
>                     completion-reference-buffer
>                     'visible)
>                    (not (eq (get-buffer "*Completions*")
>                             completion-reference-buffer))
>                    (window-frame
>                     (get-buffer-window
>                      completion-reference-buffer t))))))
>       (message "M: %S, REFB: %S, RFR: %S, SELFR: %S" ; @@@
>                mini-win completion-reference-buffer
>                redirect (selected-frame))
>       (redirect-frame-focus (selected-frame) redirect))
>     return-window))

Thanks for this minimal example.

It also doesn't work for me on Emacs 25 either.  Emacs 24.4 does work
fine, however.  I have no clue why... maybe redirect-frame-focus has
changed in Emacs 25?

Here is the recipe I used to check if it worked:

    emacs -Q
    load your two functions
    M-x foo
    M-x global- TAB auto

Typing "auto" resulted in a "Buffer is read-only: #<buffer
*Completions*>" error when the redirection wasn't working.  When the
redirection did work, the "auto" keyboard input was correctly sent to
the minibuffer.  I also tried Martin's suggestion of removing the
(select-window) call but that didn't get rid of the error for me.

>> 2) I don't understand why vanilla Emacs puts the *Completions*
>>    buffer in focus when it's popped into a new frame
>
> Martin answered this question, I think.  The window mgr does
> this, depending on your window mgr.  Once the frame exists,
> it does not do it.  But MS Windows, for example, gives the
> focus to a new frame that is displayed.

Yep, seems to be the case for most window managers.  I never noticed
this before.

>> > But frames remain the poor cousin to windows in
>> > Emacs.  Part of that is likely due to the fact that
>> > Emacs cannot completely control the behavior of
>> > frames for all window managers.  Window mgrs are
>> > different, and they have ultimate control.
>> 
>> Yes, this seems like it's the main issue here.  But 
>>still, sane frame behavior doesn't seem too far off.
>
> Hope springs eternal. ;-)

And that's what Emacs is built on. :D