Add a mechanism to retrieve package versions

[Enchufa2]

Use case: packages like renv could ask bspm what's available in the system repos to choose those preferentially if versions match.

[eddelbuettel]

For what it is worth, in r2u I just use available.packages(). (Some chin scratching ....) But I may misunderstand what you're after here.

[Enchufa2]

What renv does, basically, is:

• The lockfile says that pkgA vX.Y must be installed.
• renv downloads cran.r-project.org/src/contrib/Archive/pkgA/pkgA_X.Y.tar.gz
• installs it in the cache, and links it in the project repository.

And pak is basically the same with more bells and whistles. With this feature, this could be possible:

• The lockfile says that pkgA vX.Y must be installed.
• renv asks bspm what version is available for pkgA. This could be the latest one (it would normally be the latest one), but it could be an old one if r2u (or c2d4u4, or whatever) is not up-to-date for some reason. So available.packages is not 100% reliable here.
• If the version returned by bspm is X.Y, then renv just calls bspm::install_sys("pkgA")
• and links it in the project repository.

Of course, if the version returned by bspm is not X.Y, then renv can proceed as usual.

[eddelbuettel]

So available.packages is not 100% reliable here.

You are correct. I use that on the building side to find what I could inject into r2u. On the other side we could possibly use RcppAPT :) but it is probably simpler to just ask apt or dpkg from Python.

[jranke]

Use case: packages like renv could ask bspm what's available in the system repos to choose those preferentially if versions match.

Another use case for having the R package versions available in the binary repos that bspm accesses, would be to have install.packages() use the latest version. I was actually assuming this (eddelbuettel/r-ci#10)...