[R-pkg-devel] CRAN packages suggesting other packages but not using them conditionally

[Dirk Eddelbuettel]

On 12 December 2020 at 16:24, Michael L Friendly wrote:
| I got the email below concerning 3 of my packages but wonder if they are false alarms or
| if not, how to locate & fix the problem.
| 
|     This concerns packages: ...
| 
|     Suggested packages should be used conditionally: see �1.1.3.1 of 'Writing R Extensions'.  Some of these are hard to install on a platform without X11 such as M1 Macs: see the logs at https://www.stats.ox.ac.uk/pub/bdr/M1mac/.
| 
|     You can check all of the suggested packages by setting environment variable _R_CHECK_DEPENDS_ONLY_=true  -- see https://cran.r-project.org/doc/manuals/r-devel/R-ints.html#Tools .
| 
| Is this a false alarm?
| 
| In each case, the outfile contains:
| 
|     * checking package namespace information ... OK
|     * checking package dependencies ... NOTE
|     Package suggested but not available for checking: 'rgl'
| 
| indicating that rgl is not avaiable on the testing machine.  Then, when checking examples an error is triggered
| when an example calls something that requires rgl.
| 
|     >
|     > heplot3d(Adopted.mod, hypotheses=list("Reg"=c("AMED", "BMIQ")),
|     +         col = c("red", "blue", "black", "gray"), wire=FALSE)
|     Loading required namespace: rgl
|     Failed with error:  'there is no package called 'rgl''
|     Error in heplot3d.mlm(Adopted.mod, hypotheses = list(Reg = c("AMED", "BMIQ")),  :
|       rgl package is required.
|     Calls: heplot3d -> heplot3d.mlm
|     Execution halted
| 
| Yet, heplot3d seems to contain the required way to refer to the suggested rgl package:
| 
|                 if (!requireNamespace("rgl")) stop("rgl package is required.")
| 
| So, I'm mystified.  Can anyone help?

This is not conditional use in the sense of my reading of WRE.

What you have here is essentially an "assert()" and equivalent to
  stopifnot(requireNamespace("rgl"))
which, in turn, is equivalent to a strong Depends or Imports as your package
will experience a _critical error_ triggered by `stop()` if rgl is missing.

The idea of a conditional use is to, well, be conditional. Below I make use
of Rcpp if is present, but it is only a suggests:

  ## see the source files in the snippets/ directory of the package
  ## check for (optional, only in Suggests:) Rcpp, and also wrapped in a
  ## dontrun as it takes 10s at CRAN (yet only 3.5 here) yielding a NOTE
  if (requireNamespace("Rcpp", quietly=TRUE)) {
      Rcpp::sourceCpp(system.file("snippets", "convolveExample.cpp", package="tidyCpp"))
  }

If the _suggested_ package is present, it is used. If not we quietly move on. 
(It's not the full story as the compilation occassionally takes longer,
Windows complained so all this is now in a \dontrun{} block too. But the idea
is generic and there are many more examples to be found.)

Hope this helps,  Dirk

-- 
https://dirk.eddelbuettel.com | @eddelbuettel | edd using debian.org