Disable X11, enable OpenBLAS and OpenMP

[rfriedman22]

I managed to install R without X11 support by removing the custom Cairo formula and instead requiring the default Cairo. I also made OpenBLAS and OpenMP defaults because they greatly speed up linear algebra computation and Homebrew 2 does not support optional arguments. I also added some other dependencies that are needed to install many R packages. Finally, I updated the README with some ways to check and make sure the install worked correctly. It works across multiple Macs but has not been tested on Linux.

[sethrfore]

@rfriedman22 Looks like you've done a lot of good work here, but I'm a bit unsure how to proceed. While the initial intent of this repo was to maintain R install options after Homebrew opted for precompiled binaries, the majority of important optional dependencies have since been incorporated into the base Homebrew R build. With the base Homebrew R build meeting most peoples requirements, the subset of people with continued interest in this formula were those reliant on X11.

In this sense, I'm hesitant to nix the X11 build since it is the primary reason people might be interested in installing from this repo rather than using the base R formula.

Personally, I do not use the master branch of this formula since I have no need for X11 (and as such haven't paid it much attention). The R formula specified in the r-standard branch of this repo is the one I generally use. This formula specifies a more current build configuration for non-X11 users.

So, the long and short is that while I appreciate all your work, I'm not sure how to incorporate it. On the one hand, I don't use an X11 build, I don't like maintaining one, and updating code to a non-X11 build would be simpler. On the other hand, there are very few repos for installing R using Homebrew with X11 capabilities. Dependency conflicts between non-X11 and X11 builds means they can't be integrated as options in the same formula... gotta go one direction or the other.

In the end, I'm not sure what route to take. I am certainly cool with you forking this repo or taking whatever code you want from it and creating a new R repo people can use!

[rfriedman22]

Thanks for this feedback @sethrfore. I took a look at the Homebrew core R formula and see what you mean. There are some things missing from that formula that we would like to have. I will spend some time experimenting between this formula and the one on Homebrew core to see what works best for us. Thanks for letting us fork the repo or take whatever code works!