These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! All ebuilds that could satisfy "=net-im/slack-4.50.143" have been masked.
!!! One of the following masked packages is required to complete your request:
- net-im/slack-4.50.143::gentoo (masked by: all-rights-reserved license(s))
A copy of the 'all-rights-reserved' license is located at '/Volumes/Disk 1/Repository/portage-git/licenses/all-rights-reserved'.


For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.