bug#35177: 27.0.50; Binding deactivate-mark to nil unexpectedly deactivates the mark

[Eli Zaretskii]

> From: Markus Triska <triska@metalevel.at>
> Cc: 35177@debbugs.gnu.org
> Date: Mon, 08 Apr 2019 17:50:10 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I cannot reproduce your result: the above does show an active mark
> > after the execution, both in Emacs 26.2 and Emacs 27.0.50.
> 
> Here is a more complete recipe, could you please try it:
> 
>   1. download deactivate_mark.el with
>      $ wget https://www.metalevel.at/ei/deactivate_mark.el
> 
>   2. start Emacs with
>      $ emacs -Q deactivate_mark.el
> 
>   3. move point at the end of the form and evaluate it with C-x C-e.
> 
> The result is that "hello" is displayed in buffer "t", and the mark is
> not active. The content of deactivate_mark.el is:
> 
> (let (deactivate-mark)
>   (switch-to-buffer (get-buffer-create "t"))
>   (insert "hello")
>   (set-mark-command nil)
>   (move-beginning-of-line nil))
> 
> It seems to play a role whether its buffer is modified or not, hence
> this receipe starting from a fresh file and an unmodified buffer.
> 
> Can you reproduce this up to here? If so, please proceed as follows:
> 
>   4. Kill the "t" buffer with C-x C-k RET
> 
>   5. Add a space to the end of deactivate_mark.el by pressing SPACE.
> 
>   6. Evaluate the form again with C-x C-e.
> 
> After these steps, "hello" is highlighted and the mark is active. Also,
> on all further iterations of (4) to (6), the region is again active.
> 
> Can you reproduce this?

Yes.

> If possible, could you please make it so that the mark is active
> also on the first run, i.e., after steps (1) to (3)?

Not sure.