>> > Could we provide an option to hide the barrage of ignored directories
>> > and files?  It might also be worth adding a text button or keybinding
>> > to toggle their visibility interactively.
>>
>> Yes, this is a real problem.  Even though I set truncate-lines to t,
>> often there is a need to see grep switches at the end of the
>> command line.  So there is a patch to hide uninteresting parts
>> under a button like is used to hide part of output by
>> elisp-last-sexp-toggle-display.  It supports rgrep, lgrep and zrgrep.
>
> Thanks, but where's the option to hide the long list?  It looks like
> this patch changes the behavior unconditionally, and makes it
> strikingly different from the previous behavior.

Like there is the option eval-expression-print-length to disable hiding
of long output from eval-last-sexp, we could add a similar option here
as well.

> In any case, this needs to be documented in NEWS and the manual, I
> think.

Changes to NEWS are added in this patch without “---” to not forget
to document it in the manual before the release of Emacs 27.1.