Include files in archive's root

Question

I want to archive two files stored in a temporary directory to the root of a tar.gz archive. I only found this ugly workaround (changing and resetting the working directory within the function). If I didn't do that, the files would be archived within their entire path to their temporary directory, which I don't want.

tar_files <- function(file, data) {
  
  # create tmp dir
  tmp <- tempdir()
  
  # write data file
  readr::write_csv(x = data,
                   file = file.path(tmp, "data.csv"),
                   na = "NA",
                   append = FALSE,
  )
  
  # write xml file
  readr::write_file(x = "test",
                    file = file.path(tmp, "meta.xml"),
                    append = FALSE
  )
  
  # working dirs
  where_i_was <- getwd()
  on.exit(setwd(where_i_was))
  setwd(tmp)
  
  # export as tar.gz
  tar(tarfile = file.path(where_i_was, file),
      files= c("data.csv",
               "meta.xml"),
      compression = "gzip",
      tar = "tar"
  )
  
  unlink(tmp)

}

Is there a more elegant way to achieve the same result?