root@spock ~ # emerge -uDp world --tree

These are the packages that I would merge, in reverse order:

Calculating world dependencies \
!!! All ebuilds that could satisfy ">=sys-apps/portage-2.0.51-r2" have been masked.
!!! One of the following masked packages is required to complete your request:
- sys-apps/portage-2.0.51.22-r1 (masked by: package.mask)
- sys-apps/portage-2.0.51.19 (masked by: package.mask)

For more information, see MASKED PACKAGES section in the emerge man page or
section 2.2 "Software Availability" in the Gentoo Handbook.
!!!    (dependency required by "sys-apps/shadow-4.0.7-r1" [ebuild])


!!! Problem with ebuild sys-apps/man-pages-2.02
!!! Possibly a DEPEND/*DEPEND problem.

!!! Depgraph creation failed.