[gentoo-portage-dev] Dynamic USE dependencies

[Rich Freeman]

Out of curiosity, what is keeping us from having USE flag dependencies
handled dynamically, in the same way that package dependencies are?
If portage can figure out that I need libxml2 installed even if I
don't put it in /var/lib/portage/world, why can't it figure out that I
need it built with USE=icu even if I don't put that in
/etc/portage/package.use?

I was concerned that it might be more work in calculating the
dependencies, but then I was thinking that portage probably already
does all this work just to validate that the current configuration is
still consistent.

I fully appreciate that there could be USE blocks, just as there can
be package blocks, and that resolving these could require hints such
as adding some USE settings to config files, or doing oneshot installs
(perhaps the dynamic configuration would be set up to preserve
whatever is installed unless it conflicts - just as is done with
virtuals today).

-- 
Rich