bug#42811: 26.1; visual-line-mode wraps at no-break space

bug#42811: 26.1; visual-line-mode wraps at no-break space

[Marvin ‘quintus’ Gülker]

Dear maintainer,

the visual-line-mode minor mode wraps lines at non-breaking spaces
(U+000A0 No-Break Space, NBSP: ' '). It should not do that and instead
treat the sequence of characters before and after the NBSP as one
word. That is, if you have:

    Lorem ipsum dolor sit amet
                     ^
                   NBSP

Then visual-line-mode will consider the no-break space between 'dolor'
and 'sit' as a possible wrap point, which is contrary to what a no-break
space is meant to achieve.

To reproduce: enable visual-line-mode, write a document that contains a
NBSP, and shrink the window so that its edge hits the NBSP.
visual-line-mode will break the line at the NBSP, albeit it shouldn't.

  -quintus

In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-09-23, modified by Debian built on x86-grnet-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:	Debian GNU/Linux 10 (buster)

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For information about GNU Emacs and the GNU system, type C-h C-a.

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-- 
Dipl.-Jur. M. Gülker | https://mg.guelker.eu |    For security:
Unna, Germany        | kontakt@guelker.eu    | () Avoid HTML e-mail
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bug#42811: 26.1; visual-line-mode wraps at no-break space

[Eli Zaretskii]

> From: Marvin ‘quintus’ Gülker
>  <post+ebugs@guelker.eu>
> Date: Tue, 11 Aug 2020 16:03:44 +0200
> 
> To reproduce: enable visual-line-mode, write a document that contains a
> NBSP, and shrink the window so that its edge hits the NBSP.
> visual-line-mode will break the line at the NBSP, albeit it shouldn't.

If you set nobreak-char-display to nil, you get the behavior you want.

bug#42811: 26.1; visual-line-mode wraps at no-break space

[Marvin ‘quintus’ Gülker]

Am Dienstag, dem 11. August 2020 schrieb Eli Zaretskii:
> If you set nobreak-char-display to nil, you get the behavior you want.

Indeed, this works. But now the NBSP is not highlighted anymore as a
special character and I won't notice it is in there. Is there a way to
have both the highlighted display and the no-break behaviour?

  -quintus

-- 
Dipl.-Jur. M. Gülker | https://mg.guelker.eu |    For security:
Unna, Germany        | kontakt@guelker.eu    | () Avoid HTML e-mail
European Union       | PGP: see homepage     | /\ http://asciiribbon.org

bug#42811: 26.1; visual-line-mode wraps at no-break space

[Eli Zaretskii]

> From: Marvin ‘quintus’ Gülker
>  <post+ebugs@guelker.eu>
> Cc: 42811@debbugs.gnu.org
> Date: Wed, 12 Aug 2020 07:59:06 +0200
> 
> Am Dienstag, dem 11. August 2020 schrieb Eli Zaretskii:
> > If you set nobreak-char-display to nil, you get the behavior you want.
> 
> Indeed, this works. But now the NBSP is not highlighted anymore as a
> special character and I won't notice it is in there. Is there a way to
> have both the highlighted display and the no-break behaviour?

I made such a change (on the master branch), not without some
trepidation, as the current behavior is very old (15 years), so I
wonder whether some feature relies on that.  We shall see, I guess.

Note that when nobreak-char-display is non-nil and non-t, we still
produce an ASCII space after the backslash-escape, so the display
engine will still wrap at that spot.  But here, I cannot make the same
change, because the Emacs manual clearly documents this behavior.

Thanks.