[Rd] Strange warnings when unloading packages with S4 classes

[Winston Chang]

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I've been seeing warnings when unloading packages. They can be seen
with the shiny and sp packages, among others (this is on R 3.0.2). For
example:
> library(sp)
> unloadNamespace('sp')
Warning messages:
1: In FUN(X[[2L]], ...) :
  Created a package name, ‘2013-12-19 12:14:24’, when none found
2: In FUN(X[[2L]], ...) :
  Created a package name, ‘2013-12-19 12:14:24’, when none found
3: In FUN(X[[2L]], ...) :
  Created a package name, ‘2013-12-19 12:14:24’, when none found
4: In FUN(X[[2L]], ...) :
  Created a package name, ‘2013-12-19 12:14:24’, when none found

It appears to be related to the methods:::.removeSuperclassBackRefs function.


I can get the warnings to appear when the following are both true:
* The package has an S4 class which inherits from a class outside of
the package.
* The NAMESPACE file contains import(methods)

I've created some very simple test packages here which illustrate the
problem, along with instructions on how to duplicate the warning.
https://github.com/wch/s4unload

The warnings only appear when unloading the package where both of the
conditions above are true. I'm not sure why import(methods) should
make a difference, but it does.

Is this a bug in the implementation of S4?

Best,
-Winston