grep counting matches only with --color argument

[Tomas Hlavaty]

Hi,

why does this command shows the number of matches in the mode-line

   (grep "grep -r --color -nH -e TODO ~/git/emacs-pdf")

but this one (without --color argument) always shows 0?

   (grep "grep -r -nH -e TODO ~/git/emacs-pdf")

Is there a deeper reason that --color is required to see the number of
matches?  Could it simply count the number of matched lines if no
--color was specified?  Or is it not easy to detect?

I would like to see the number of matches with alternative programs like
ripgrep:

   (grep "rg -nH --no-heading --color=always -e TODO ~/git/emacs-pdf")
   (grep "rg -nH --no-heading --color=ansi -e TODO ~/git/emacs-pdf")

But the --color argument here does not seem to have an effect.

Thanks in advance,

Tomas