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

Calculating dependencies ... done!
Dependency resolution took 0.97 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/libsigc++-3.6.0:3::gentoo  USE="-gtk-doc -test" 969 KiB

Total: 1 package (1 new), Size of downloads: 969 KiB