bug#23276: 25.0.92; Crash in auto-revert when file no longer present

[Michael Albinus]

John Wiegley <jwiegley@gmail.com> writes:

>> And I still am not convinced that deleting a file under auto-revert
>> shouldn't erase its buffer. Otherwise, it sounds like just half-auto-revert
>> to me. Would we keep the buffer non-empty if the file existed but was empty?
>
> I would not want it to erase the buffer. Countless have been the times that
> I've been working on a project, and an unbridled rm took away code from the
> disk which I was very grateful to find was still in a buffer.

I have committed the patch as shown recently (plus a comment) to the
emacs-25 branch. This is the least invasive change I could imagine, not
endangering the release. Closing the bug.

Further changes should go to master. I've prepared already a test case
for this. And while testing I found another annoyance: autorevert did
not restart once a deleted file has reappeared. This I have fixed also
in master.

The changes in master will be pushed once the emacs-25 branch has been
merged next time.

Best regards, Michael.