bug#23871: 25.1.50; Undo unexpectedly leads to blank buffer

[Phillip Lord]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: phillip.lord@russet.org.uk (Phillip Lord)
>> Cc: triska@metalevel.at,  23871@debbugs.gnu.org
>> Date: Sat, 02 Jul 2016 21:21:28 +0100
>> 
>> > The problem, AFAIU, is in point movements _during_ eval-defun: they
>> > seem to not be recorded in buffer-undo-list.  The undo list I get
>> > after C-M-x is this:
>> >
>> >   (nil (117 . 122) (t 22391 27551 0 0))
>> >
>> 
>> So, I don't think this is a regression caused by my patch at all. It is
>> an bug that has been there since I altered undo.c last year.
>> 
>> The problem was caused because of undo only records point after a
>> boundary (or the first element). I'd changed things during slightly when
>> I update undo.c so that the timestamp list got added before checking
>> whether I was at a boundary, hence blocking addition of the point
>> restoration information.
>> 
>> This is why I found the problem so erratic to replicate; it only occurs
>> immediately the first change to a buffer.
>> 
>> I believe the following patch addresses the issue.
>
> Seems like this is still not the final patch, so I guess we will need
> to wait for the right one.

Yes. I will try and investigate 23871 as soon as I can.

> It should go to the emacs-25 branch, which probably means one more
> pretest, sigh.

Unfortunately, yes. It's a pity that I didn't 21722 when it came in.

Phil