Re: Select completions from the minibuffer

[Ergus <spacibba@aol.com>]

On Fri, Mar 18, 2022 at 11:27:52AM +0200, Juri Linkov wrote:
>> Looking at the last line in `deactivate-mark` it seems like it is a
>> known issue and changing such optimization in the display engine may be
>> probably undesirable (Eli will confirm soon hopefully), so in your case
>> maybe is better to force the update on demand like in deactivate-mark:
>>
>> ```
>> (defmacro with-minibuffer-completions-window (&rest body)
>>    "Execute the forms in BODY from the minibuffer in its completions window.
>> When used in a minibuffer window, select the window with completions,
>> and execute the forms."
>>    (declare (indent 0) (debug t))
>>    `(let ((window (or (get-buffer-window "*Completions*" 0)
>>                       ;; Make sure we have a completions window.
>>                       (progn (minibuffer-completion-help)
>>                              (get-buffer-window "*Completions*" 0)))))
>>       (when window
>>         (with-selected-window window
>>           ,@body
>>           (redisplay--update-cursor-face-highlight window)))))
>> ```
>>
>> This seems to work.
>>
>> Is it enough?
>
>Thanks, I confirm such forcing the update fixes highlighting.
>
>But still when cursor-face-highlight-nonselected-window is nil by default,
>let-binding it to t has no effect:
>
>```
>(defun minibuffer-next-completion (&optional n)
>  "Run `next-completion' from the minibuffer in its completions window."
>  (interactive "p")
>  (with-minibuffer-completions-window
>    (let ((cursor-face-highlight-nonselected-window t))
>      (next-completion n))))
>```
>
Hi Juri:

This should be because when you force the
redisplay--update-cursor-face-highlight; then the display engine detects
that something more important than a point move changed (an overlay
moved) and it passes *Completions* to
redisplay--pre-redisplay-functions.

Then it calls redisplay--update-cursor-face-highlight once again (yes
now it calls redisplay--update-cursor-face-highlight 2 times instead of
none) but the second call is from outside of your function; so it gets
the buffer local value of cursor-face-highlight-nonselected-window.

In general (setq-local cursor-face-highlight-nonselected-window t)
should go into the completion-setup-function because you don't have a
full control for when the display engine calls
redisplay--pre-redisplay-functions for *Completions* window. For
example, in a resize the highlight may disappear too.

So you need:

(when completions-highlight-face
         (setq cursor-face-highlight-nonselected-window t)
         (cursor-face-highlight-mode 1))

in completion-setup-function OR add another function to
completion-setup-hook only to do the setq-local.

Eli:

If there is a way to force the display engine to detect a change in a
window and use it to pass *Completions* in the next call to
redisplay--pre-redisplay-functions? I mean to avoid the need to do a
redundant explicit call to redisplay--update-cursor-face-highlight which
doesn't really take effect?

Best,
Ergus