bug#13549: 24.3.50; FR: Improve grep output (show function names, when possible)

[Stefan Monnier]

> I used the following local modification to compile.el to sneak in the
> function names.
> The modification is in `compilation-parse-errors' which seems to be a
> font-lock handler.

It's not quite a font-lock handler: it's a function that can get called
to parse errors when needed.  It is triggered by font-lock, indeed, but
also by next-error (e.g. tho often font-lock will have done the work of
parsing already).

> I call `which-function' within this context.  Is it justified?

I'm not sure what you mean by "justified", but I see no particular
reason why it shouldn't work.

Your suggestion is interesting, and clearly since it is specific to
`grep' it should be moved to grep.el (maybe as a font-lock-keyword?).

It would need to be an option, since for some uses it doesn't make much
sense (especially considering the performance impact it can have, and
the amount of screen real-estate it requires).


        Stefan