build time dependency

Hello,

Is there such thing as a build time dependency between packages : 
package B needs package A so that it can build, but once built it lives 
without it.

Do you mean at a) "R CMD build" time or at b) "R CMD INSTALL" time?
For a), you probably do not need to declare it in DESCRIPTION at all 
(untested).
For b), you need to declare it. I feel uncomfortable to change the 
Depends field between source and binary version of a package. At least, 
it is not documented to work and if it works (have you tested that?), it 
might not work in some future release of R.
But since you gave at least 2 reasonable examples for a 
INSTALL-time-only dependency, you might want to contribute some patches 
to handle such a thing.

Best wishes,
Uwe

For example depending on the ant package to compile java code, or depend 
on roxygen to roxygenize the code, ...

Adding roxygen to Depends works, but then the installed package does not 
depend on it and therefore loads it for nothing. Maybe I can remove 
roxygen from the Depends as part of the ./configure[.win] ...

Romain