bug#30823: 25.3; modification-hooks of overlays are not run in some cases

[Noam Postavsky <npostavs@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Noam Postavsky <npostavs@gmail.com>
>> Cc: victorhge@gmail.com,  30823@debbugs.gnu.org,  monnier@iro.umontreal.ca
>> Date: Thu, 23 Aug 2018 08:13:59 -0400
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > Btw, I'm somewhat worried by the solution being proposed: it removes a
>> > general safety device and replaces it by a solution that targets only
>> > bug#21824, a much narrower class of problems.  Is that wise?
>> 
>> IMO, a safety device which causes new bugs is disqualified from its job.
>
> I'm not sure it caused a new bug.

It causes it in the sense that reverting the fix for #21284 stops this
new bug from happening.

> I'm hard pressed for free time lately, so I'd be grateful if you could
> see whether it would be possible to make the original change smarter,
> so that it avoids causing the current issue.  If not, I will try to
> look into it in a couple of weeks or so.
>
>> Furthermore, we're currently calling the after change hooks without
>> the before change hooks which is just asking for trouble (as
>> exemplified by Bug#21824 and this one).
>
> That's a separate issue, isn't it?  We could refrain from calling the
> after-change hooks as well.

It's not a separate issue.  The original reason for #21824 is that we
called the after-change hooks without doing the setup (i.e., passing
PREPARE=false to del_range_both).  With the addition of the "safety
device", #21824 is avoided, but this bug is caused instead.  Refraining
from calling after-change hooks is exactly what my patch does, this
fixes both cases.

This makes the "safety device" redundant, but with the after-change
suppression added it doesn't do any harm; so if you insist, we can leave
it in.  I don't think it's a good idea to have such things cluttering up
the source though.