bug#74866: 29.4; fit-frame-to-window + no vertical scroll bar + changed face height = mess

[Eli Zaretskii <eliz@gnu.org>]

> From: toomas@rosin.ee
> Date: Sat, 14 Dec 2024 14:57:31 +0200
> 
> 
> ----------------8<----------------8<----------------8<----------------
> 
> In "emacs -Q" under X (I have XFCE), evaluate:
> 
> (defun fit (lin col)
>   "Fit some text (LIN lines and COL columns) into a newly created frame."
>   (interactive)
>   (let ((buf (get-buffer-create "*foo*"))
>         (frm (make-frame '((z-group . above)))))
>     (with-current-buffer buf
>       (erase-buffer)
>       (setq mode-line-format '(""))
>       (dotimes (_ lin) (insert (format "%s\n" (make-string col ?x))))
>       (goto-char (point-min)))
>     (with-selected-frame frm
>       (switch-to-buffer buf)
>       (fit-frame-to-buffer))))
> ;;; LIN and COL are arbitrary, make them sufficiently small.
> (fit 9 23)
> 
> So far, so good.  Now evaluate the following:
> 
> (setq-default vertical-scroll-bar nil)
> (set-face-attribute 'default nil :height 75)
> (fit 9 23)
> 
> On my system, the frame's width is now one character short and the lines
> do not fit in the new frame any more.
> 
> ---------------->8---------------->8---------------->8----------------
> 
> In GNU Emacs 29.4 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.41,
>  cairo version 1.18.2) of 2024-12-10 built on localhost
> Windowing system distributor 'The X.Org Foundation', version 11.0.12101014
> System Description: Gentoo Linux

FWIW, I cannot reproduce this, neither in Emacs 29.2 nor in the
current emacs-30 branch (which will soon become Emacs 30.1).

Martin, any comments?