GNU bug report logs - #18441
whitespace-mode sometimes adds column to tab character

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Message #23 received at 18441 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Marcin Borkowski <mbork <at> mbork.pl>
Cc: 18441 <at> debbugs.gnu.org, Mario Valencia <mariovalspi <at> gmail.com>
Subject: Re: bug#18441: whitespace-mode sometimes adds column to tab character
Date: Sat, 04 Sep 2021 09:57:33 +0200

Marcin Borkowski <mbork <at> mbork.pl> writes:

>> well it appears to be a known problem, as commented in the source of
>> whitespace-mode.

I can confirm that this bug is still present in Emacs 28.

> To be more precise, the comment Mario meant is probably this part of
> definition of `whitespace-display-mappings':
>
>     ;; WARNING: the mapping below has a problem.
>     ;; When a TAB occupies exactly one column, it will display the
>     ;; character ?\xBB at that column followed by a TAB which goes to
>     ;; the next TAB column.
>     ;; If this is a problem for you, please, comment the line below.
>     (tab-mark     ?\t    [?» ?\t] [?\\ ?\t])	; tab - right guillemet
>
> Does anyone know why the workaround given there is not turned on by
> default?  Or maybe it should be made a user option?

If that mark is removed, then tabs won't be marked specially at all --
only with a background colour, which is presumably not what people want
here...

Looking at the whitespace code, I don't really see any easy way to fix
this -- the buffer display table and tab actions don't match?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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