bug#63272: 29.0.90; xref fails on long lines

[Dmitry Gutov <dmitry@gutov.dev>]

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.