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

[Dmitry Gutov <dmitry@gutov.dev>]

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))


Although it depends on whether the overlay itself staying around is a 
good thing for this feature.

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