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

[Phillip Lord]

Eli Zaretskii <eliz@gnu.org> writes:
>> I have tolerated the problems described in #1095 and #21722 for about a
>> decade and see no reason to delay Emacs 25: Neither Emacs 23 nor 24 were
>> delayed because of them although these issues were already reported!
>> #23871 was also present during this time but not yet reported.
>
> That may be so, but my problem, which _is_ a regression from 24.5, is
> that even this part of 1095:
>
>   In "emacs -Q", when I insert into *scratch* the form:
>
>      (progn (end-of-line) (insert "\nhi"))
>
>   then place point on the "g" and press C-M-x C-/, then the insertion is
>   undone, and point remains on the "g", as expected.
>
> doesn't work as expected in Emacs 25.  This is a regression I'd like
> to fix before 25.1 is released.

I think we have two bugs (one which covers the other). Handling of point
after an insertion. This was hiding another, which is handling of point
as the first change in a buffer. Although the last one was being hidden,
I think this would also affect deletes.


> And this part of 1095/21722 _is_ solved by Phillip's patch, so I think
> we should install it on the release branch.  However, I'd like Stefan
> to look over the patch before we install it.

Yeah, I'd really like Stefan to look over it also. Or, alternatively,
would could wait a week till I have had chance to finish reading the
"How to Program C" book I just bought.

Phil