My 2 cents is that anything that can be derived from source should be
by default.
The extra cycles chewed during compilation aren't as important as
consistency and correctness. Using cvs checkin as a trigger might
introduce a disconnect between developer working directories and the
production repository.
I also think that rdoc should be run using the ruby and rdoc in the
working directory to close the development loop, i.e.
rdoc: ruby
./ruby -I lib bin/rdoc --all --op ./rdoc *.c
And then just installing from working dir ./rdoc to <sysdir> during
install phase. The reason for this is that you wouldn't want a process
which might fail running during install. Better that it die before
anything in production has been touched.
I guess my point is that by default you should be encouraged to update
and test your rdoc comments before either checkin or install.
-J