bug#17784: hilit-chg.el marks bigger change than necessary

[Lars Ingebrigtsen <larsi@gnus.org>]

Le Wang <l26wang@gmail.com> writes:

> Repro steps:
>
> 1 create file:
> <file>
> hi
> _
> </file>
>
> 2. insert "a" on line 2, before "_"
>
> 3. backspace
>
> 4. insert "a" on line 2, before "_", again
>
> 5. inspect text property of "_", and notice it has hilit-chg property
> even though it hasn't been changed.

This should now be fixed in Emacs 28.  The problem was that the code
tried to cater for the case where you have

hi
_

and then

hi
ab_

then deleting the "a" and then inserting something else.  That worked
for "b" (which was already highlighted), but not for "_", which was
not.  So I introduced a new text property to separate the two cases.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no