bug#57434: 28.1.91; Terminal Emacs Mac OS flickering.

[Dmitrii Kuragin via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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On my remote linux machine `line_is_del_ok` should be false where
```
  tty->line_ins_del_ok
    = (((tty->TS_ins_line || tty->TS_ins_multi_lines)
        && (tty->TS_del_line || tty->TS_del_multi_lines))
       || (tty->scroll_region_ok
           && tty->TS_fwd_scroll && tty->TS_rev_scroll));
```
because `tput al` and `tput AL` are both false and `tput sr` and `tput sf`
are false ("unknown terminfo capability").

So, disabling `line_ins_del_ok` on mac os would lead to the same
configuration I have on the linux. On the linux machine scroll never caused
any troubles.

So, would it be ok to disable `line_ins_del_ok` for Mac OS? I would send a
patch if it's OK.

On Mon, Aug 29, 2022 at 1:25 PM Dmitrii Kuragin <kuragin@google.com> wrote:

> So far:
> ```
> :~/Desktop% tput al; echo $?
> 0
> :~/Desktop% tput AL; echo $?
> 1%dL0
> :~/Desktop% tput dl; echo $?
> 0
> :~/Desktop% tput DL; echo $?
> 1%dM0
> :~/Desktop% tput sf; echo $?
>
> 0
> 0~/Desktop% tput sr; echo $?
> :~/Desktop% tput wi; echo $?
> tput: unknown terminfo capability 'wi'
> 4
> :~/Desktop% tput cs; echo $?
> %p1%d;%p2%dr0
> :~/Desktop% tput cS; echo $?
> tput: unknown terminfo capability 'cS'
> 4
> ```
>
> Seems like Mac Os doesn't support "wi", but the condition is still going
> to be true.
>
> ```
> tty->line_ins_del_ok = 0;
> ```
>
> make the emacs really smooth w/o any flickering.
>
> On Mon, Aug 29, 2022 at 12:37 PM Eli Zaretskii <eliz@gnu.org> wrote:
>
>> > From: Dmitrii Kuragin <kuragin@google.com>
>> > Date: Mon, 29 Aug 2022 12:26:07 -0700
>> > Cc: Gerd Möllmann <gerd.moellmann@gmail.com>,
>> >       57434@debbugs.gnu.org
>> >
>> > I tried different terminal emulators, Alacritty, iTerm2, Terminal.app
>> (stock). All of them show the same issue.
>> > So, it is not a terminal emulator.
>>
>> If this happens with all terminal emulators on macOS, we should reset
>> the line_ins_del_ok flag for macOS.  Look in term.c, where it is
>> initialized by consulting various terminfo features supported by the
>> terminal.  If all the features it consults indeed work on macOS, then
>> simply say something like
>>
>>   #ifdef DARWIN_OS
>>     tty->line_ins_del_ok = 0;
>>   #else
>>   ... the current code...
>>   #endif
>>
>> and see if the problem goes away.
>>
>> Gerd, do you see the same on your system?
>>
>
>
> --
> *If you get an email from me outside of the 9-5 it is *not* because I'm
> always on or expect an immediate response from you; it is because of work
> flexibility
> <http://www.inc.com/john-boitnott/how-flexible-hours-can-create-a-better-work-life-balance.html>
> .  Evening and weekend emails are a sign I allocated some regular working
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> you to feel free to do the same.
>
>

-- 
*If you get an email from me outside of the 9-5 it is *not* because I'm
always on or expect an immediate response from you; it is because of work
flexibility
<http://www.inc.com/john-boitnott/how-flexible-hours-can-create-a-better-work-life-balance.html>
.  Evening and weekend emails are a sign I allocated some regular working
hours for other things (such as family, gym, friends,...).  And I encourage
you to feel free to do the same.

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