As of the April 4th CRAN update to devtools v2.0.2, Travis CI is encountering an error with devtools during its setup phrase when building R packages (the error occurs prior to Travis testing any of the user’s R code). I’ve encountered this issue with a R package today that previously passed Travis’ tests - neither package’s code was changed before running on Travis.
Error in match.arg(upgrade, c("ask", "always", "never")) : 'arg' must be of length 1
This is due to an inconsistency between devtools and the released version of the remotes package. I am planning on submitting a quick fix of remotes today to fix the issue. In the meantime you can install the development version of remotes to fix the issue in before_install.
before_install: R -e 'source("https://install-github.me/r-lib/remotes")'