There has been a push - in the interests of compilation speed - to have jvm targets compile intransitively, which they should generally be able to do. Exports allow a scala_libray - for example - to say, the code in this library has a publically accessible API that uses a 3rdparty type - please export my dependency on that type to my consumers. Concretely, say you want to depend on a

src/scala/org/example/mappy

target that depends on a

3rdparty/com/google:guava

target which provides the

com.google.common.cache.Cache

symbol which is a return type in a public method of the library.