bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Cc: Stefan Kangas <stefan@marxist.se>,  matthew@mattleach.net,  
> 37564@debbugs.gnu.org
> Date: Mon, 20 Jan 2020 19:58:53 -0500
> 
> 
> No other terminal emulator exports LINES and COLUMNS as environment variables.

Maybe so, but that in itself doesn't yet mean Emacs cannot do that, if
we decide it's useful.

> Applications use ioctl to get the size.
>    -> Therefore setting LINES and COLUMNS is pointless.
> If LINES/COLUMNS are set, they override ioctl.

Is the last bit a generally accepted paradigm?  I could easily justify
the contrary preference.

And then there might be applications that don't use ioctl.

> You can't update the environment of an already running process.
> Therefore the presence of LINES/COLUMNS in the initial environment
> of a process spawned from Emacs means it will fail to react to resizing.
>  Therefore exporting LINES and COLUMNS is harmful.

Only if the application uses the variables in preference to ioctl.

> So don't export LINES and COLUMNS.

I agreed at the very beginning of the discussion to make the export
optional.  I don't think we can safely remove that unconditionally,
not yet.