bug#81630: 32.0.50; completions-format 'vertical scrolls the completion window on TAB tapping

On Sat, 15 Aug 2026 13:03:00 +0000 lucas jimenez <[email protected]> wrote:

> Hi.
>
> When setting completions-format to 'vertical
>
> and start TAB tapping the completions window starts scrolling up and
> down even though all the candidates can be seen in the window.
>
> To reproduce do:
> emacs -Q --eval "(setq completions-format 'vertical)"
> `M-x 5x5`  and start tapping TAB key or `M-x minibuffer-`
>
> Workaround: set (completion-auto-select 'second-tab) or
> (completion-auto-select t) or just don't tap TAB.
>
> This behaviour isn't noticed with 'horizontal or 'one-column

This happens because when `completions-format' is 'vertical the
*Completions* buffer ends in a newline, and that makes
`(pos-visible-in-window-p (point-max) window)' in the "normal tab" case
in `completion--in-region-1' return nil, resulting in the window being
scrolled.  The attached patch prevents this scrolling for me; can you
confirm?  But I cannot tell if such a change might have undesirable
consequences; maybe Stefan Monnier (added in CC:) can tell.

Steve Berman

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 4da651cc450..14840c21da3 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1765,7 +1765,11 @@ completion--in-region-1
             (with-selected-window window (scroll-down))))
          ;; Normal tab
          (t
-          (if (pos-visible-in-window-p (point-max) window)
+          (if (pos-visible-in-window-p
+               (if (eq completions-format 'vertical)
+                   (1- (point-max))     ; Vertical format has final newline.
+                 (point-max))
+               window)
               ;; If end is in view, scroll up to the end.
               (set-window-start window (point-min) nil)
             ;; Else scroll down one screen.