bug#40124: Bad interaction between before-string and :box faces

[Eli Zaretskii]

> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Wed, 18 Mar 2020 15:26:38 -0400
> Cc: demisbalbach@googlemail.com
> 
> In the following sample, the word "test" should have its letters "e" and "s" 
> in a box; but instead they display with just a bar above and below.  Removing 
> the before-string property fixes the issue.
> 
> (with-current-buffer (get-buffer-create "box-test")
>   (erase-buffer)
>   (insert "test")
>   (let ((ov (make-overlay 2 4)))
>     (overlay-put ov 'face '(:box t))
>     (overlay-put ov 'before-string
>                  (propertize ">" 'display
>                              '(left-fringe right-arrow))))
>   (pop-to-buffer (current-buffer)))
> 
> This was reported by Artemios (cc'd) in 
> https://github.com/flycheck/flycheck/issues/1666.

Thanks, I think I fixed this now on the master branch.