bug#63272: 29.0.90; xref fails on long lines

[Dmitry Gutov]

On 08/05/2023 18:41, Juri Linkov wrote:
> > > In the real case the prefix and suffix were unique, so I didn't expect
> > > that in a generated file there was a very long distance between prefix
> > > and suffix.  To limit the distance between prefix and suffix I tried:
> > >     C-x p g prefix.{0,100}suffix
> >
> > Try escaping { and }:
> >
> >    C-x p g prefix.\{0,100\}suffix
>
> Thanks, this works.
>
> > The regexp needs to use the syntax that Emacs can understand.
> >
> > Just the subset of it that can be translated to command like, so that Grep
> > and Ripgrep can work with it too.
> >
> > > but xref that uses ripgrep fails to find matches.
> > > So needed to fall back to ripgrep-based rgrep in this case:
> > >     M-x rgrep prefix.{0,100}suffix
> > > that works successfully.
> > > It seems the problem is because of different regexp syntax
> > > used by ripgrep and re-search-forward in xref--collect-matches-1.
> >
> > The conversion is performed by xref--regexp-to-extended.
>
> Shouldn't the conversion also escape { and } ?

It _un_escapes them in this case: { and } have to be escaped in Emacs 
regexps, but they don't need to be escaped in "extended regular extensions".

So the conversion toggles escaping.