The [[Rcpp::depends(...)]]
functionality is for sourceCpp()
et al, for packages you should use Imports:
and Depends:
etc pp fields to set up a package.
I believe there is minor bug / nuisance with RStudio right now as you may need to swap fields in DESCRIPTION to get rid of the first warning. But it works otherwise.
Consider setting up a package with the function we provide: RcppArmadillo.package.skeleton()
and start from there.
Edit: And the other approach, of course, would be to load any of the sixty-five CRAN packages using RcppArmadillo and building it inside RStudio to then compare their setup (basically: Depends/Imports and LinkingTo, along with correct NAMESPACE file) to what you currently have and so see what you are lacking.