The kind of module source.
@type t() :: :LOCAL_SOURCE | :GIT_SOURCE | :DIR_SOURCE | :LOCAL | :GIT | :DIR
@spec dir() :: :DIR
@spec dir_source() :: :DIR_SOURCE
@spec git() :: :GIT
@spec git_source() :: :GIT_SOURCE
@spec local() :: :LOCAL
@spec local_source() :: :LOCAL_SOURCE