> The same as for make - shell out to the compiler, then parse the result. 
>  gcc -MM is what I'm familiar with, I presume other compilers have 
> similar switches.  Rant does have this built in, but I'm not familiar 
> with it (although having just researched it a little, I think I will 
> make the effort now :-) )
> 

I found

  require 'rake/loaders/makefile'

   file ".depends.mf" => [SRC_LIST] do |t|
     sh "makedepend -f- -- #{CFLAGS} -- #{t.prerequisites} > #{t.name}"
   end

   import ".depends.mf"

at

http://docs.rubyrake.org/read/chapter/4

Still a native Ruby solution would be nicer.

Brad