It looks to me like if you emerge rrdtool with the "ruby" USE flag, you get the Ruby bindings built. But if you emerge "ruby-rrd", you get the same thing. I haven't checked the sources yet to see if there are differences or which is more recent, but it seems to me that Portage should block this -- you get stuff over-written in /usr/lib/ruby if you emerge them both in a different order.
Then again, since the author of the ruby-rrd package hasn't documented it, maybe it should just be deleted from Portage and just keep the "ruby" USE flag on rrdtool. The main RRDTool web site points to this package anyhow, so that's the documentation as far as I'm concerned.
If you want portage to warn you about overwritting files, have a look at FEATURES="collision-protect".
It seems that the ruby USE flag is only present with rddtool-1.2.23-r1, so with older versions of of rddtool it still makes sense to have ruby-rdd around, especially since the stable version of rddtool is still 1.2.15-r3.
If the ruby bindings have now been folded into the main distribution then rddtool-1.2.23-r1 should probably block ruby-rdd-1.1 and vice versa. ruby-rdd can then be removed from the tree when there is a stable version of rddtool with the ruby USE flag.
netmon folks: can you confirm this scenario so that we can add the blockers, or am I overlooking something?
feel free to add whatever needed :)
I've added the blocker to rrdtool-1.2.23-r1 (only if the ruby USE flag is active). As far as I can tell that should be enough to start resolving this situation. Once rrdtool has been stable for some time and the old versions have been removed we should probably administer last rites to dev-ruby/ruby-rrd.