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

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To reply to this bug, email your comments to 18441 AT debbugs.gnu.org.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mario Valencia <mariovalspi <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: tab bug
Date: Wed, 10 Sep 2014 01:55:42 -0500

[Message part 1 (text/plain, inline)]

In a buffer, set tab-width to 6. then insert 5 characters, then a literal
tab character (C-q TAB). Now you have a 7 column tab.

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Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mario Valencia <mariovalspi <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: tab bug
Date: Wed, 10 Sep 2014 02:12:47 -0500

[Message part 1 (text/plain, inline)]

sorry, this happens in a text-mode buffer with whitespace-mode on. without
whitespace mode it only occupies one column.

2014-09-10 1:55 GMT-05:00 Mario Valencia <mariovalspi <at> gmail.com>:

> In a buffer, set tab-width to 6. then insert 5 characters, then a literal
> tab character (C-q TAB). Now you have a 7 column tab.
>

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Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mario Valencia <mariovalspi <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: tab bug
Date: Wed, 10 Sep 2014 02:42:50 -0500

[Message part 1 (text/plain, inline)]

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

2014-09-10 2:12 GMT-05:00 Mario Valencia <mariovalspi <at> gmail.com>:

> sorry, this happens in a text-mode buffer with whitespace-mode on. without
> whitespace mode it only occupies one column.
>
> 2014-09-10 1:55 GMT-05:00 Mario Valencia <mariovalspi <at> gmail.com>:
>
>> In a buffer, set tab-width to 6. then insert 5 characters, then a literal
>> tab character (C-q TAB). Now you have a 7 column tab.
>>
>
>

[Message part 2 (text/html, inline)]

Message #14 received at 18441 <at> debbugs.gnu.org (full text, mbox):

From: Marcin Borkowski <mbork <at> mbork.pl>
To: Mario Valencia <mariovalspi <at> gmail.com>
Cc: 18441 <at> debbugs.gnu.org
Subject: Re: bug#18441: tab bug
Date: Thu, 18 Feb 2016 09:53:13 +0100

On 2014-09-10, at 03:42, Mario Valencia <mariovalspi <at> gmail.com> wrote:

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

To be more precise, the comment Mario meant is probably this part of
definition of `whitespace-display-mappings':

--8<---------------cut here---------------start------------->8---
    ;; 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
--8<---------------cut here---------------end--------------->8---

Does anyone know why the workaround given there is not turned on by
default?  Or maybe it should be made a user option?

Best,

--
mbork


> 2014-09-10 2:12 GMT-05:00 Mario Valencia <mariovalspi <at> gmail.com>:
>
>
>  sorry, this happens in a text-mode buffer with whitespace-mode on. without whitespace mode it only occupies one column.
>
>  2014-09-10 1:55 GMT-05:00 Mario Valencia <mariovalspi <at> gmail.com>:
>
>
>  In a buffer, set tab-width to 6. then insert 5 characters, then a literal tab character (C-q TAB). Now you have a 7 column tab.

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

Message #26 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: Mario Valencia <mariovalspi <at> gmail.com>, 18441 <at> debbugs.gnu.org
Subject: Re: bug#18441: whitespace-mode sometimes adds column to tab character
Date: Mon, 02 May 2022 11:48:46 +0200

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

>> To be more precise, the comment Mario meant is probably this part of
>> definition of `whitespace-display-mappings':

This looks like a duplicate of 18548, so I've now merged the two bug
reports.

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

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