R-devel macOS: Toolchain changes

[pat-s]

Two days ago Simon announced that R4.0 will use gfortran 8.2 and Apples native compiler along with the SDK 10.13.

There is a new alpha R4.0 branch that contains the latest R-devel changes: https://mac.r-project.org/.
There is a need to switch to the new gfortran version and change the URL for getting the R-devel tarball.

The R-devel el-capitan build is stuck at March-25 and might no longer be updated (not 100% sure about this though).

FYI: There are known issues with the 10.15 SDK (Rcpp issues you are most likely aware of, igraph issues). Therefore I am using a custom install of the 10.13 SDK. Maybe you also want to use that as the default SDK on Actions to mimic CRAN behavior?

wget https://github.com/phracker/MacOSX-SDKs/releases/download/10.15/MacOSX10.13.sdk.tar.xz
tar fxz MacOSX10.13.sdk.tar.xz
sudo mv MacOSX10.13.sdk /Library/Developer/CommandLineTools/SDKs/
rm -rf MacOSX10.13*

.R/Makevars

CFLAGS=-isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk
CCFLAGS=-isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk
CXXFLAGS=-isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk
CPPFLAGS=-isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.13.sdk

[jimhester]

Yes, I know about this.

There is some question in my mind whether we should try to mimic the CRAN toolchain, or the toolchains most often used by users on macOS. I tend to lean towards the latter. But maybe we could write a custom action to install the older sdk like you suggest, so people can opt-in to using it if/when needed.

[pat-s]

That would be great.

In addition CRAN uses gfortran 8.2 now: https://mac.r-project.org/

The homebrew cask only installs v6.3. Would be great if this could also be a simple config option in the R matrix:gfortran: 8.2

If https://github.com/fxcoudert/gfortran-for-macOS/releases would be used as the main download source and not brew, one could easily install/set gfortran 6.3 for R < 4.0

(The same would apply to the SDK versions).

[FelixErnst]

fyi: This might also affect other libraries as well. I am not sure whether this is related, but instead of opening a new issue I think it is good to add it here.

xml2 apparently cannot get installed on macOS using R-devel:

https://github.com/FelixErnst/tRNAdbImport/runs/576334378?check_suite_focus=true

[jimhester]

@FelixErnst that is xml2 specific and should be fixed by r-lib/xml2#297

[lrnv]

I do have a trouble with the instalation of the digest package, see there : eddelbuettel/digest#152

Do you think this is related ? Is it something known to be an issue ?

[pat-s]

Setting env var SDK_ROOT as in https://github.com/ropensci/tic/blob/8df939e3546a0a88449ab2c70f3663ff0a61869f/inst/templates/ghactions-env.yml#L19 should solve it.

[github-actions]

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