bug#29118: 25.2.50; Undoing shell flush output results in weird state

[Noam Postavsky]

found 29118 26.0.90
tags 29118 + confirmed
quit

Allen Li <vianchielfaura@gmail.com> writes:

> Repro:
>
> 1. emacs -Q
> 2. M-x shell RET
> 3. echo hi RET
> 4. C-c C-o
> 5. C-/
> 6. echo bye RET
>
> The shell buffer ends up in a weird state that's hard to describe.

The process mark ends up in the wrong place.  That is,

    (process-mark (get-buffer-process (current-buffer)))

gives a different answer after step 3 vs after step 5.  Not really sure
why, debugging undo-list stuff is kind of a pain.