bug#30397: Random numbers in grep mode-line

[Drew Adams]

> 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?

+1.

A mouseover tooltip says this:

1. Number of errors so far
2. Number of warnings so far
3. Number of informational messages so far

But `C-h m' says nothing about this (it should).

And clicking `compilation-mode' (the parent) in the `C-h m' output
shows that mode's doc, but it too says nothing about this.