Subject: bug#74536: 30.0.50; undocumented box behaviour in faces

From: Eli Zaretskii <[email-masked]>
Date: Mon, 25 Nov 2024 21:44:51 +0200

tags 74536 notabug
thanks

> From: Al Haji-Ali <[email-masked]>
> Date: Mon, 25 Nov 2024 19:34:41 +0000
> 
> 
> The output of the following code is
> 
> --8<---------------cut here---------------start------------->8---
> (progn
>   (fundamental-mode)
>   (insert (concat "\n"
>                   (propertize "hello" 'face '(:box (:line-width (3 . 0) :color "red")))
>                   (propertize " again" 'face '(:box (:line-width (3 . 0) :color "yellow")))
>                   (propertize " other" 'face '(:box (:line-width (3 . 0) :color "green"))))
>           "\n"))
> --8<---------------cut here---------------end--------------->8---
> 
> 
> |hello again other|
> 
> where the left border is red and the right one is green and the yellow border is completely hidden. Having negative line-width produces the same output.

As expected.

> It seems that one cannot have multiple adjacent borders unless one has some text in between without a border, like this
> --8<---------------cut here---------------start------------->8---
> (progn
>   (fundamental-mode)
>   (insert (concat "\n"
>                   (propertize "hello" 'face '(:box (:line-width (3 . 0) :color "red")))
>                   " "
>                   (propertize " again" 'face '(:box (:line-width (3 . 0) :color "yellow")))
>                   (propertize " othe " 'face '(:box (:line-width (3 . 0) :color "green"))))
>           "\n"))
> --8<---------------cut here---------------end--------------->8---
> 
> produces
> 
> |hello| | again other|
> 
> with (red, red, yellow, green) borders.

Yes.  Basically, Emacs doesn't examine box face changes unless it
changes from box to no-box or vice versa.

> I find this behaviour, if intended, sometimes helpful as it allows one to have a one-sided border. Though it would be helpful if the exact mechanism is documented.

What mechanism would you like to be documented?

> In any case, I was also originally expecting, and wanting, an output like this
> |hello| again | other|
> 
> with `(red, yellow, green, green)` and no text in between, but it seems there is no way to achieve such output? Is that correct?

Yes.