[R-sig-Debian] Xenial repository for R 4.0.0

[J C Nash]

Over a week ago (on r-help, my bad!) I raised a question of why the
ubuntu install instructions

https://cran.r-project.org/bin/linux/ubuntu/README.html

instruct users with a xenial-based system to use

deb https://cloud.r-project.org/bin/linux/ubuntu xenial-cran40/

Looking at https://cloud.r-project.org/bin/linux/ubuntu/
there is no xenial-cran40 directory. However,
https://cran.r-project.org/bin/linux/ubuntu/
does have this directory, and I managed to update a machine
still running Linux Mint 18.3 by putting in
deb https://cran.r-project.org/bin/linux/ubuntu xenial-cran40/

I suspect novice users might not have found this work-around, and
it was only by chance I found it.

My query: Is it intended that xenial support will not be available
for R 4.0? Or is this this just an oversight? Or some quirk that affects
just my environment? I've tried to ensure caches are updated.

Side-bar: I would update the example machine, but it runs some software needed
for another use-case that is not working at all on more modern systems.
Where possible, I try to keep up to date, and am migrating the use-case over
time to a different software environment.

Best, JN