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[R-pkg-devel] How to avoid R CMD check warning for documentation of non-package functions?

3 messages · Duncan Murdoch, Konrad Rudolph

#
My package provides infrastructure support for callback functions
defined in special environments in user code. They are conceptually
similar (in fact, almost identical) to the `.onLoad` etc. ?hooks for
namespace events? in base R [1]. Now I?m adding documentation for
these functions, via the following Rd code (or the equivalent roxygen2
code annotating a `NULL` value):

```
\name{topicname}
\alias{topicname}
\alias{onload}
\title{Hooks for environment events}
\usage{
onload(env)
}
\arguments{
\item{env}{the environment}
}
\description{
Short description
}
```

Unfortunately, this causes an `R CMD check` warning:
Right: this function does not exist in my package, and it *should not*
exist in the package. Yet I do need to document it for users. What is
the recommended way for doing so? In fact, from my reading of the R
source, the base R documentation of ?ns-hooks? doesn?t seem to do
anything special, and would presumably also cause this warning.

I?m open to doing this differently, but I?d strongly prefer if these
functions had their own help topic, with their own ?usage? section. I
don?t just want to add them as a custom section to the package
documentation topic if this is at all avoidable.

[1]: https://stat.ethz.ch/R-manual/R-devel/library/base/html/ns-hooks.html

PS: A note on API design, I considered doing this differently: rather
than define hooks via ?special names?, users would define them by
passing callbacks to a call to a package function; e.g.
`mypkg::define_onload(function (env) { ? })`. This would be
conceptually similar to R?s `setHook` [2]. However, from the user?s
point of view there?s no advantage to doing it this way, and it?s more
verbose. Defining callbacks via special names has ample precedence,
both in R and in other languages. And I don?t think `R CMD check`
warnings should dictate API design in this manner.

[2] https://stat.ethz.ch/R-manual/R-devel/library/base/html/userhooks.html
#
On 02/12/2020 12:57 p.m., Konrad Rudolph wrote:
I haven't tried this, but I believe if you define functions with the 
right name and header in your package but don't export them the warning 
will go away.

If that doesn't work (or defining those causes other issues), a more 
involved workaround would be to change the \docType{} declaration for 
the help page.  \docType{package} is the most free-form, but you might 
get warned if you have two of them.  \docType{data} might be flexible 
enough.  If you do this, you won't use \usage{} or \arguments{}, you'll 
put together your own sections using \section{Usage}{ ... } and 
\section{Arguments}{ ... } and try to get the formatting right.

Duncan Murdoch
#
On Wed, Dec 2, 2020 at 7:44 PM Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
Thanks, works like a charm.
I?ll keep this in mind! It might come handy.