bug#30397: Random numbers in grep mode-line

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Date: Thu, 08 Feb 2018 23:32:51 +0200
> 
> What do these seemingly random numbers in the mode-line of the *grep*
> buffer mean?  I don't get any logic behind these colored numbers.
> They are neither the number of matches nor the number of matched lines.
> And why non-zero numbers are always highlighted in red as errors
> when there are no errors in the grep output?  What was the goal
> of this feature and where it is documented?

From NEWS:

  ** Compilation mode
  [...]
  *** The number of errors, warnings, and informational messages is now
  displayed in the mode line.  These are updated as compilation
  proceeds.

Also mentioned in the user manual, in "Compilation":

     While compilation proceeds, the mode line is updated to show the
  number of errors, warnings, and informational messages that have been
  seen so far.

I've now added a similar text in "Grep".

Maybe we should modify the display for Grep, e.g. show only one
number, and use a distinct face that doesn't display as red by
default.