ggplot2 is a big library with a bunch of dependencies,
making our already slow R tests even slower. This PR
switches them to using the tinytest library, which has
no dependencies and is much smaller.
packagemanager.rstudio.com is a CRAN mirror provided
by rstudio, with *binary packages* prebuilt for many Linux
Distributions! https://www.rstudio.com/blog/announcing-public-package-manager/
has more excellent detail. It cuts down install times for R packages
by almost 90% in some cases!
Like MRAN (which we use now), they also provide a daily snapshot
of CRAN at that date
(https://docs.rstudio.com/rspm/news/#rstudio-package-manager-2021090).
The URL for CRAN for a particular date can be fetched via an API
call. We call that API, and if there is no snapshot for that date
(anything before Oct 2017), we fall back on to MRAN. Adds a test
to test this fallback.
One possible issue about changing existing binder repos to use binary
builds rather than source builds is that the binary builds sometimes
require you have an apt package installed, and will fail if it is
not. We had to install the zmq library apt package for example -
source installs compile zmq from source, which is where the speedup
comes from. But unlike python wheels or conda packages, these binary
builds are not self-contained - they are linked to apt packages from
the specific distros. So some repos that worked before might fail now.
We can choose a more recent cut-off date to prevent this from happening.
YuviPanda