man-roxygen/details-license.R

In stan-dev/rstantools: Tools for Developing R Packages Interfacing with 'Stan'

#' @details In order to enable Stan functionality, \pkg{\link{rstantools}}
#'   copies some files to your package.  Since these files are licensed as 
#'   GPL >= 3, the same license applies to your package should you choose to
#'   distribute it.  Even if you don't use \pkg{\link{rstantools}} to create
#'   your package, it is likely that you will be linking to \pkg{\link{Rcpp}} to
#'   export the Stan C++ `stanmodel` objects to \R.  Since
#'   \pkg{\link{Rcpp}} is released under GPL >= 2, the same license would apply
#'   to your package upon distribution.