[Rd] .onLoad, packageStartupMessage, and R CMD check

Michael Chirico ch|r|com @end|ng |rom goog|e@com
Fri Nov 5 06:08:51 CET 2021

Examining more closely, it's a NOTE produced by R CMD check --
originally I had thought it was a WARNING, which I think would have
been too strong for this case. A NOTE actually seems fine, on second

For a tiny bit of context, it's common for us to issue messaging
around some state initialization, which has to happen after some
(ex-ante unknown) set of packages are loaded. It's important to do so
whether or not the package is attached, so the proviso in .onLoad()
indeed makes the most sense.


On Thu, Nov 4, 2021 at 1:02 PM Gabriel Becker <gabembecker using gmail.com> wrote:
> Hi Michael,
> Indeed, just to elaborate further on what I believe Duncan's point is, can you give any examples, "dire" or not, that are appropriate when the package is loaded but not attached (ie none of its symbols are visible to the user without using :::)?
> The only things I can think of are a package that changes the behavior of other, attached package code, such as conflicted. Doing so is very much an anti-pattern imo generally, with something like conflicted being an (arguable) exception. And that's assuming conflicted even works/does anything when loaded but not attached (I have not confirmed whether thats the case or not). That or a package that is at end-of-life and is or soon will be unsupported entirely.
> The examples don't need to be yours, per se, if you know what those pushing back against your linter were using messages from .onLoad for...
> Best,
> ~G
> On Thu, Nov 4, 2021 at 12:37 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>> On 04/11/2021 2:50 p.m., Michael Chirico via R-devel wrote:
>> > I wrote a linter to stop users from using packageStartupMessage() in
>> > their .onLoad() hook because of the R CMD check warning it triggers:
>> >
>> > https://github.com/wch/r-source/blob/8b6625e39cd62424dc23399dade37f20fa8afa91/src/library/tools/R/QC.R#L5167
>> >
>> > However, this received some pushback which I ultimately agree with,
>> > and moreover ?.onLoad seems to agree as well:
>> >
>> >> Loading a namespace should where possible be silent, with startup
>> > messages given by \code{.onAttach}. These messages (**and any essential
>> > ones from \code{.onLoad}**) should use \code{\link{packageStartupMessage}}
>> > so they can be silenced where they would be a distraction.
>> >
>> > **emphasis** mine. That is, if we think some message is _essential_ to
>> > print during loadNamespace(), we are told to use
>> > packageStartupMessage().
>> >
>> > Should we remove this R CMD check warning?
>> The help page doesn't define what an "essential" message would be, but I
>> would assume it's a message about some dire condition, not just "Hi! I
>> just got loaded!".  So I think a note or warning would be appropriate,
>> but not an error.
>> Do you have an example of something that should routinely print, but
>> that triggers a warning when checked?
>> Duncan Murdoch
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