How to make R package recommend a package hosted on GitHub?

Question

I'm developing an R package that works as a wrapper for functions from the parallel and Rhpc packages called ctools. I know that if I want my package to require these packages I need to include them in the Imports section of the DESCRIPTION file. When installing my package, these packages will be installed from CRAN. Similarly I can put them in the Suggests section if they aren't required, but useful. These won't be installed with my package.

But, I've forked the Rhpc package and added a function that I use in my ctools package. How do I get my package to Suggest/Import this package from my GitHub repo so of instead of installing the Rhpc package, it executes devtools::install_github("bamonroe/Rhpc")?

Answer 1

From the manual (and quoting source here):

@c DESCRIPTION field Additional_repositories

The @samp{Additional_repositories} field is a comma-separated list of repository URLs where the packages named in the other fields may be found. It is currently used by @command{R CMD check} to check that the packages can be found, at least as source packages (which can be installed on any platform).

You can add the package to Suggests: and point to additional repositories -- possibly created using drat. There used to a package doing that, and IIRC there is another one doing it now but its name escaped me now.

Edit: Found it! See here in the source DESCRIPTION file of RNeXML -- and note how the line disappears in the posted DESCRIPTION on CRAN. Better still, note how two of the packages in Suggests: are not listed a hyperlinks on CRAN. I thinks those come from the additional repos. And yes, rOpenSci uses drat to manage that.

Edit 2: And just to close the loop, you (easily) use drat to host such an additional repo on GitHub -- the prime use case for drat.

Edit 3: RNeXML has dropped the additional repository, but the github history still has it.

Edit 4: Currently (i.e. on 2020-03-13), the CRAN packages EMC, bcmaps, blkbox, broom.mixed, epikit, grattan, gtsummary, hurricaneexposure, memoise, multinomialeq, noaastormevents, pointblank, provSummarize, provViz, spData, swephR, tashu, taxadb, waveformbildar all list a field Additional_repositories containing a URL pointing to a drat repo.