[Rd] how to list external dependencies (i.e., non-R packages)?

[Greg Minshall]

hi.  i'm working on a package which only works if one (or both) of two
libraries (Imlib2 and MagickWand) exist on the machine on which the
package is compiled and executed.  as currently written, the program
purposely generates an error at *compile* time if neither library is
available (thinking the earlier the user is notified, the less
frustrating).

is there a way of specifying this dependency in, say, the DESCRIPTION
file?  (seems unlikely, as this is what the whole autotools/configure.ac
framework is supposed to deal with.)

or, should i take out the compile time error (maybe replace my #error
with a #warning), and just generate at error at run time?  (this will
require me to figure out what that means for build tests/, but obviously
some sort of hack is doable.)

cheers, Greg