bug#67650: [PATCH] ; Hide completion preview when switching windows

[Eshel Yaron via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Dmitry Gutov <dmitry@gutov.dev> writes:

> On 05/12/2023 22:26, Eshel Yaron via Bug reports for GNU Emacs, the
> Swiss army knife of text editors wrote:
>> This patch ensures that we dismiss the completion preview when users
>> switch to another window.  Previously, the completion preview would
>> remain in a window after switching to another window showing another
>> buffer, since the `post-command-hook` that Completion Preview mode sets
>> up locally doesn't run after a command switches to another buffer.
>
> Another way to do this would look like this:
>
> diff --git a/lisp/completion-preview.el b/lisp/completion-preview.el
> index 1d5f1253702..f2560a98b23 100644
> --- a/lisp/completion-preview.el
> +++ b/lisp/completion-preview.el
> @@ -182,6 +182,7 @@ completion-preview--make-overlay
>                   (eq (get-text-property 0 'face previous)
>                       (get-text-property 0 'face string)))
>        (add-text-properties 0 1 '(cursor 1) string)
> +      (overlay-put completion-preview--overlay 'window (selected-window))
>        (overlay-put completion-preview--overlay 'after-string string))
>      completion-preview--overlay))
>

We actually have that already (a few lines above in this function),
but it doesn't do the trick.  This makes the overlay appear only in
the selected window when you're editing a buffer that's displayed
in multiple windows, but it doesn't make the overlay go away when
you switch to another window.

> You could also move some cleanup logic to pre-command-hook, which
> should be fine with the buffer-locality of the value.

Yes, I'm not sure if that's better than
`window-selection-change-functions` though in terms of performance,
and we'd need to put in some extra work to know if the command is
going to select another window.