remotes::install_github() assumes that the default branch is named "master", which is not always the case, e.g.

remotes::install_github("elizagrames/litsearchr")
#> Using github PAT from envvar GITHUB_PAT
#> Downloading GitHub repo elizagrames/litsearchr@master
#> Error in utils::download.file(url, path, method = method, quiet = quiet,  : 
#>   cannot open URL 'https://api.github.com/repos/elizagrames/litsearchr/tarball/master'

^{Created on 2020-06-13 by the reprex package (v0.3.0)}

The GitHub API notes a default_branch field that could provide this information, e.g.:

remotes:::github_GET("repos/elizagrames/litsearchr")$default_branch
#> [1] "main"

^{Created on 2020-06-13 by the reprex package (v0.3.0)}

So, I think this can be a drop-in for the default value for the ref argument in install_github. Some additional re-factoring might be needed if we wanted to bundle the GitHub API calls.

Note, to my knowledge, this issue was first reported by @elizagrames on twitter, and we chatted about a potential fix before writing up this issue. We're happy to work on a PR to this, and look into propagating the solution to other install_* functions, if so desired.