My package “DESCRIPTION” includes several packages under “Suggests,” which are conditionally used in some functions. Previously, my code included a lot of statements like

fx <- function(...) {
  if !(requireNamespace("labelled", quietly = TRUE)) {
    stop('"labelled" must be installed to use `fx()`')
  }
  # ...
}

I decided to streamline this by writing an internal helper to check for suggested packages:

check_pkg <- function(pkg) {
  if (!all(sapply(pkg, requireNamespace, quietly = TRUE))) {
    pkg <- switch(
      min(length(pkg), 3),
      paste0('"', pkg, '" package'),
      paste0(paste0('"', pkg, '"', collapse = ' and '), ' packages'),
      paste0(
        paste0('"', pkg[-length(pkg)], '," ', collapse = ''),
        'and "', pkg[[length(pkg)]], '" packages'
      )
    )
    caller <- deparse(sys.call(-1)[[1]])
    stop(pkg, ' must be installed to use `', caller, '`.', call. = FALSE)
  }
}

Example usage:

#' @export
fx_needs_labelled <- function() {
  check_pkg("labelled")
  print("OK")
}
#' @export
fx_needs_fakepkg <- function() {
  check_pkg("fakepkg")
  print("OK")
}

fx_needs_labelled()
# "OK"
fx_needs_fakepkg()
# Error: "fakepkg" package must be installed to use `fx_needs_fakepkg`.

This all works fine, but I can no longer pass R CMD check (via devtools::check()).

❯ checking package dependencies ... ERROR
  Namespace dependency missing from DESCRIPTION Imports/Depends entries: 'labelled'

My guess is that R CMD check allows a namespace to appear in “Suggests” and not “Imports” if it’s used inside an if (requireNamespace(...)) { ... } block, but not if that check is offloaded to another function.

Is there any way around this, or do I need to ditch my helper and do all the checking inside functions that use suggested packages?