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

Calculating dependencies ... done!
Dependency resolution took 0.98 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/libsigc++-2.12.1:2::gentoo  USE="-gtk-doc -test" 4924 KiB

Total: 1 package (1 new), Size of downloads: 4924 KiB