bug#44983: Truncate long lines of grep output

[Juri Linkov <juri@linkov.net>]

> Alternatively, xref--collect-matches-1 could apply the limit itself, no
> matter whether grep or rg is used. And it could make sure to only do that
> after the last match. This might be the slower option, but hard to say in
> advance, some comparison benchmark could help here.

I think until a long string is inserted to the buffer, truncating the
string in the variable in xref--collect-matches-1 should be much faster.

>> But this also requires customizing grep-match-regexp to the value
>> "\033\\[[0-9]*m\033\\[[0-9]*1m\033\\[[0-9]*1m\\(.*?\\)\033\\[[0-9]*0m"
>> provided by Simon in bug#41766.
>
> It's odd your last suggestion in that bug was not applied (adding :type
> '(choice) to grep-match-regexp). Perhaps do that now?
>
> Although, personally, I've found a symbolic value to work better for a var
> like that (example: xref-search-program). This way we can ultimately
> consolidate info about a particular program in one place (some alist).
>
> That aside, could you explain the difference between the regexps? Do grep
> and rg use different colors or something like that? Ideally, of course,
> that would be just 1 regexp (if that's possible without loss in
> performance, or significant loss in clarify).

They should be merged into one regexp indeed.  Because after customizing it
to the rg regexp, grep output doesn't highlight matches anymore (I use both
grep and rg interchangeably by different commands).

Currently their separate regexps are:

grep:
"\033\\[0?1;31m
 \\(.*?\\)
 \033\\[[0-9]*m"

rg:
"\033\\[[0-9]*m
 \033\\[[0-9]*1m
 \033\\[[0-9]*1m
 \\(.*?\\)
 \033\\[[0-9]*0m"

That could be combined into one regexp:

"\033\\[[0-9?;]*m
 \\(?:\033\\[[0-9]*1m\\)\\{0,2\\}
 \\(.*?\\)
 \033\\[[0-9]*0?m"