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

Calculating dependencies ... done!
Dependency resolution took 1.08 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/libgudev-238-r2::gentoo  USE="-introspection -test" 30 KiB
[ebuild  N     ] dev-libs/libevdev-1.13.7::gentoo  USE="-doc -test" 462 KiB
[ebuild  N     ] dev-libs/libusb-1.0.30:1::gentoo  USE="-debug -doc -examples -static-libs -test -udev -verify-sig" 641 KiB
[ebuild  N     ] virtual/libusb-1-r2:1::gentoo  USE="-udev" 0 KiB
[ebuild  N     ] dev-libs/hidapi-0.15.0::gentoo  USE="-doc" 356 KiB
[ebuild  N     ] dev-libs/libmanette-0.2.13::gentoo  USE="udev -doc -introspection -test -vala" 61 KiB

Total: 6 packages (6 new), Size of downloads: 1548 KiB