Looking to reports like:
Looks like the current output:
!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:
(media-libs/libvpx-1.3.0:0/0::gentoo, installed) pulled in by
=media-libs/libvpx-1.3.0* required by (www-client/firefox-31.7.0:0/0::gentoo, installed)
(media-libs/libvpx-1.4.0:0/2::gentoo, ebuild scheduled for merge) pulled in by
>=media-libs/libvpx-1.4.0:= required by (www-client/chromium-43.0.2357.65:0/0::gentoo, ebuild scheduled for merge)
Should point to the USE flag causing the blockers to allow people to guess they should switch it, in this case, the offending USE is "system-libvpx"
Thanks a lot :)
The slot_conflict_handler checks for solutions to USE deps, but apparently it doesn't check for USE conditional solutions like this.