bug#21824: 25.0.50; overlay modification-hooks called with wrong buffer

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 6 Nov 2015 21:24:50 -0500
> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Cc: 21824-done@debbugs.gnu.org
> 
> On Fri, Nov 6, 2015 at 10:23 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> >
> > Please see if the original bug is solved by the latest master.
> 
> Yes, it's fixed.

Thanks for testing.

> > Btw, any idea how come overlays wound up in *Messages* in the original
> > scenario?
> 
> global-highlight-parentheses-mode puts overlays in every buffer.

Does it really mean to do that in *Messages*?  If not, perhaps we
should suggest to the developers of highlight-parentheses to exempt
*Messages* from that, as that buffer is pretty specialized anyway.  In
particular, due to the way the message logging in *Messages* is
implemented, the overlay modification hooks will only ever be called
in that buffer with AFTER non-nil, and even that will only happen when
Emacs decides to delete some text from *Messages*; inserting a new
message there will never call the overlay modification hooks.

> > Actually, would you like converting your test case into a test, and
> > post a patch to the test suite to that effect?  TIA.
> 
> Something like this? I'm not sure where to put it.

Yes, this looks good to me.  How about creating a new file
buffer-tests.el (the offending code is in buffer.c)?

Thanks.