bug#59888: [PATCH] Add 'grep-use-headings'

[Juri Linkov <juri@linkov.net>]

>>> +      (any ?: ?- ?=))
>>
>> I wonder what is the reason for this regexp to be different
>> from grep-regexp-alist?  Especially with such additional characters
>> as ?- and ?=.  This mismatch causes wrong handling of files when
>> file names contain these characters.
>
> This is because of context lines:
>
> $ git grep -nC 1 grep-use-headings
> lisp/progmodes/grep.el-459-
> lisp/progmodes/grep.el:460:(defcustom grep-use-headings nil
> lisp/progmodes/grep.el-461-  "If non-nil, subdivide grep output into sections, one per file."
> ...
> At least when using grep --null, I think there is no confusion possible.  I
> wrote a unit test that purports to prove that.

Thanks for mentioning --null, I completely forgot about it.
I've customized 'grep-find-template' to "rg --no-heading"
because ripgrep is fast, but since its headings are not
supported by grep.el, so also needed "--no-heading".
And now after adding "--null" to "rg --no-heading --null"
'grep-use-headings' correctly handles context lines
and file names with numbers separated by dashes.