bug#20871: 25.0.50; fill-single-char-nobreak-p does not recognize a single-letter word when it is preceded by an open paren

[Eli Zaretskii]

> From: Marcin Borkowski <mbork@mbork.pl>
> Date: Sun, 17 Apr 2016 08:34:30 +0200
> 
> >> today I found that fill-single-char-nobreak-p is just a bit too
> >> simplistic.  When point is after e.g. the string " (a", it returns nil
> >> instead of t.  I am not sure which characters should be added to the
> >> regex, but at least the opening paren (and maybe bracket) should be
> >> there, so I'd change the regex into [[:space:]][[(]*[[:alpha:]].  (Two
> >> or more opening parens/brackets are unlikely, but when in doubt, I guess
> >> it's better to return t than nil than the other way round.)
> >>
> >> Best regards,
> >
> > Just noticed that there is a hardcoded (backward-char 2), so it
> > seems that adding a few characters to the regex is not enough.  Maybe
> > looking-back is the way to go (though it might slow filling down)?
> > I don't know.
> 
> Hi there,
> 
> so here's a patch for the bug I reported some time ago.

Could you please elaborate on the bug itself?

See, the function in question, fill-single-char-nobreak-p, is
documented as a possible value to use in the fill hook, for a very
specific purpose.  If you are saying that it doesn't fulfill that
purpose well enough, please show a use case where it fails to do that.
At least the situation you described, with " (a", doesn't seem to fit
the use cases which this function is supposed to cover, since the
parenthesis makes a 2-character sequence, whereas
fill-single-char-nobreak-p aims to support isolated one-character
words.

I also am not sure I understand what is so special about '(' that it
has to be hard-coded here.  What about '[' or '{' or '<' (or any other
punctuation character, for that matter)?

> Please review both the patch and the commit message (I'm still
> learning to write them...).

The commit message should begin with a capital letter.  Also, I think
this variant is more clear:

 Don't break after a single-character word that follows an opening
 parenthesis.

Thanks.