bug#30397: Random numbers in grep mode-line

[Drew Adams <drew.adams@oracle.com>]

> > Is the total number of lines (in the search space) also
> > available?  If so, would that be useful?  Maybe something
> > like this?
> >
> > Grep finished at Thu Jul 21 15:02:15 - 42 matches in 5/113 lines
> >                                                       ^^^^
> 
> Unfortunately the total number of lines is not available.
> There is even problems with getting the right number of matches.
> When grep doesn't highlight matches, we can't count them.

In that case, the explanation/description should say that
it is the number of matches highlighted, not the number
of matches.

> Another problem is that grep matches to be printed at the end of the
> grep buffer can't be counted in grep-regexp-alist because it is
> based on font-lock which is invoked at unpredictable times
> when grep process is already finished.  This leaves only one way
> to count matches in grep-filter in this patch.
> 
> For the same reason, printing the number of compilation errors at
> the end of the compilation buffer can't be implemented for bug#13417.

If the numbers shown depend on font-lock and are not
necessarily accurate then the doc should make that
clear.