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

Calculating dependencies ... done!
Dependency resolution took 1.51 s (backtrack: 0/20).

[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/luafilesystem-1.9.0::gentoo  USE="-test" LUA_TARGETS="lua5-1 -lua5-3 -lua5-4 -luajit" 29 KiB
[ebuild  N     ] dev-lua/penlight-1.15.0::gentoo  USE="-test" LUA_TARGETS="lua5-1 -lua5-3 -lua5-4 -luajit" 431 KiB

Total: 3 packages (2 new, 1 in new slot), Size of downloads: 848 KiB