With the new split in Portage where system set packages are not 
considered in an "emerge -auDNv world" unless something in world 
RDEPENDs on it brings about a few issues.

i.e. Portage implicitly has a run time dependency on app-arch/tar, 
app-arch/bzip2, app-arch/gzip, app-arch/lzma due to the fact that 
Portage will use these utilities when "unpack" is called inside of an 
ebuild. As such these are run time depends of Portage and need to be in 
RDEPEND (the same would technically be true for pkgcore and paludis, 
unless they use tar's support for those formats and then its up to tar 
to depend properly).

This brings out the fun of circular depends. I don't really know how to 
address this but a lot of packages are going to have to be updated to 
contain proper depends. i.e. C based apps will need 
RDEPEND="virtual/libc". C++ packages will need a stdc++ depend.

If you're running Portage 2.2_rc1 on a system you can see if any 
packages have begun to slack behind on your system in the system set.

emerge -puv @system

You might notice packages in here that are used on a daily basis but are 
now no longer being updated.
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