Check imports when generating the NAMESPACE file

[gaborcsardi]

Ie. for an @importFrom pkg fun we could check if fun is an exported function of pkg.

Otherwise R will throw a warning when the package is loaded, and it is sometimes hard to deduct where the warning is coming from.

[MichaelChirico]

Not just a warning*, this prevents compilation (at least on R 4.1.3).

This happens too often in cases where I'm dumping all the imports into the top of a file (a la #include statements) and neglect to terminate the block with a NULL, e.g.

# in R/foo.R

#' @importFrom dplyr group_by
# <- should be a NULL here to terminate the block, but forgot it

#' Here is a function
#' @export
foo <- identity

roxygenize() makes this NAMESPACE:

# Generated by roxygen2: do not edit by hand

export(foo)
importFrom(dplyr,"function")
importFrom(dplyr,Here)
importFrom(dplyr,a)
importFrom(dplyr,group_by)
importFrom(dplyr,is)

And compilation fails:

R CMD INSTALL .

* installing to library ‘...’
* installing *source* package ‘tmpPkg’ ...
** using staged installation
** R
** byte-compile and prepare package for lazy loading
Error: object ‘function’ is not exported by 'namespace:dplyr'
Execution halted
ERROR: lazy loading failed for package ‘tmpPkg’

+💯 to difficulty dealing with this error without a trained eye.

* Oh, I see, roxygenize() throws a warning. But we don't always see the warning if other processes are calling roxygenize() or it gets buried.