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

Calculating dependencies ...

!!! Problem resolving dependencies for =net-im/prosody-13.0.5
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=net-im/prosody-13.0.5" has unmet requirements.
- net-im/prosody-13.0.5::gentoo USE="idn libevent sqlite ssl zlib -icu -ldap -mysql -postgres (-selinux) -test" LUA_SINGLE_TARGET="-lua5-3 -lua5-4"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( lua_single_target_lua5-3 lua_single_target_lua5-4 )

  The above constraints are a subset of the following complete expression:
    exactly-one-of ( icu idn ) exactly-one-of ( lua_single_target_lua5-3 lua_single_target_lua5-4 )