The nightly build started failing when R 3.6.2 came out. I’ve done some digging and debugging.
Here is the install log from the failure on 3.6.2: https://dl.bintray.com/ursalabs/arrow-r/logs/bin/macosx/el-capitan/contrib/3.6/20191216-00install.out
Here is the log from success on 3.6.0: https://dl.bintray.com/ursalabs/arrow-r/logs/bin/macosx/el-capitan/contrib/3.6/20191217-00install.out
On 3.6.2, there’s a longer temp dir path, with “working_dir” in it. I traced that to this change: https://github.com/wch/r-source/commit/956ea7f7d4db25ad6a2fb32f177e9ec5995d350d
When it fails, there’s a bunch of “Note: The post-install step did not complete successfully” messages, and then later “Error: too long unix socket path (123bytes given but 104bytes max)“. Which makes me think that the extra `/Rtmpyp98FZ/working_dir/` temp path is pushing us over some limit?