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

Calculating dependencies ... done!
Dependency resolution took 1.56 s (backtrack: 0/20).

[ebuild  N     ] dev-lang/luajit-2.1.1787165859:2/2.1.1787165859::gentoo  USE="-lua52compat -static-libs" 1078 KiB
[ebuild  N     ] dev-libs/libmpack-1.0.5-r5::gentoo  33 KiB
[ebuild  NS    ] dev-lang/lua-5.1.5-r200:5.1::gentoo [5.4.8:5.4::gentoo] USE="deprecated readline" 389 KiB
[ebuild  N     ] dev-lua/mpack-1.0.13::gentoo  USE="-test" LUA_TARGETS="lua5-1 luajit -lua5-3 -lua5-4" 17 KiB

Total: 4 packages (3 new, 1 in new slot), Size of downloads: 1514 KiB