why does git set X in LESS env var?

[Christoph Anton Mitterer <calestyo@scientia.org>]

Hey.


I recently stumbled over the problem that mouse wheel scrolling doesn't
work with (git-)delta[0], a problem[1][2], which apparently numerous
people had before me.

Numerous solutions were given in [1] and [2], for example using --mouse
as less option.
I noticed however, that this causes a somewhat different mouse
scrolling behaviour than my less usually gives me and dug a bit
further, noticing that the problem was that `X` was set in the `LESS`
env var for the less process, wrongly assuming[3] first that delta
would set it.

After delta's upstream noticed that this must be wrong, I looked
further and found that git set it since commit
0abc0260fa3419de649fcc1444e3d256a17ca6c7, which gives however no
indication why it was added.

A somewhat later commit, b3275838d969b7ecb91aae584226fccbeb046aca,
which removes `S` from being set, mentions:
> … The FRX flags actually make sense for Git (F and X because
> sometimes the output Git pipes to less is short, and R because Git
> pipes colored output).

But I still don't get from that why X would be needed?

My less manpage documents it as:
> -X or --no‐init
>     Disables sending the termcap initialization and deinitialization
>     strings to the terminal.  This is sometimes desirable if the
>     deinitialization string does something unnecessary, like clearing
>     the screen.

Is it to avoid clearing the screen?


Not sure whether git should really do something here... I mean it could
add --mouse per default, but then users who don't want that would need
to work around it (and there is no negative option for --mouse, it
seems).


Oh, I should add that scrolling without `X` and without `--mouse` sees
to only work on some terminals (e.g. VTE based ones, but not xterm).

Thanks,
Chris.


[0] https://github.com/dandavison/delta/
[1] https://github.com/dandavison/delta/issues/58
[2] https://github.com/dandavison/delta/issues/630
[3] https://github.com/dandavison/delta/issues/58#issuecomment-1756542986