[Rd] R CMD check and missing imports from base packages

[Martin Morgan]

On 04/28/2015 01:04 PM, Gábor Csárdi wrote:
> When a symbol in a package is resolved, R looks into the package's
> environment, and then into the package's imports environment. Then, if the
> symbol is still not resolved, it looks into the base package. So far so
> good.
>
> If still not found, it follows the 'search()' path, starting with the
> global environment and then all attached packages, finishing with base and
> recommended packages.
>
> This can be a problem if a package uses a function from a base package, but
> it does not formally import it via the NAMESPACE file. If another package
> on the search path also defines a function with the same name, then this
> second function will be called.
>
> E.g. if package 'ggplot2' uses 'stats::density()', and package 'igraph'
> also defines 'density()', and 'igraph' is on the search path, then
> 'ggplot2' will call 'igraph::density()' instead of 'stats::density()'.

stats::density() is an S3 generic, so igraph would define an S3 method, right? 
And in general a developer would avoid masking a function in a base package, so 
as not to require the user to distinguish between stats::density() and 
igraph::density(). Maybe the example is not meant literally.

Being able to easily flag non-imported, non-base symbols would definitely 
improve the robustness of package code, even if not helping the end user 
disambiguate duplicate symbols.

Martin Morgan

>
> I think that for a better solution, either
> 1) the search path should not be used at all to resolve symbols in
> packages, or
> 2) only base packages should be searched.
>
> I realize that this is something that is not easy to change, especially 1)
> would break a lot of packages. But maybe at least 'R CMD check' could
> report these cases. Currently it reports missing imports for non-base
> packages only. Is it reasonable to have a NOTE for missing imports from
> base packages as well?
>
> [As usual, please fix me if I am missing or misunderstood something.]
>
> Thank you, Best,
> Gabor
>
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>
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