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

[Drew Adams <drew.adams@oracle.com>]

> 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))

> 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.

> Standalone minibuffer frames are meant to work correctly
> almost out of the box, though, right?

They should be meant to do that, yes, IMO.

> > 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. ;-)