bug#44236: [PATCH] xdisp: Apply nobreak-char-display also to NARROW NO-BREAK SPACE U+202F

[Neil Roberts via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

> But what is the purpose of showing this character like we do with
> NBSP?  We do that with NBSP because otherwise it will be easy to
> interpret NBSP as a SPC: they have the same width and appearance on
> display.  By contrast, U+202F NARROW NO-BREAK SPACE is much thinner,
> and cannot be mistaken to be SPC.

Most people use Emacs with a monospace font, as is the default if you
don’t change it, so in practice U+202F looks identical to NBSP and the
regular space. I would assume that most people using these characters
would be editing the source code for a document that would be displayed
in something else, such as editing an HTML document. In that case you
want to make sure that you got the right spaces in the source code and
without the visual indication it is really hard to do.

I guess ideally in my case it would be even better if U+202F had a
different face than NBSP so that I could also make sure I picked the
right non-breaking space when typing a document in French.

The other use case, which is probably more common for me, is that I am
editing some source code and I don’t want any non-breaking spaces at
all. With the bépo keyboard layout it’s kind of easy to accidentally
type them, so I just want to be able to recognise either of them. In
that case having the same face for both characters is still helpful.

> OTOH, if we make U+202F stand out, then why not others, for example
> U+2007? or U+2060? or U+2002? or U+2003? or U+2009 etc.

I think it would make sense to highlight all of the spaces that look
exactly the same as a regular space. That would exclude U+2060 because
that is zero-width. Maybe we could use all of the characters from the
“space separator” Unicode class except U+0020.

https://www.compart.com/en/unicode/category/Zs

- Neil