jbuild files declares the availability of a library like
bos below, every library that
bos depends on, like
astring, is also available: it is not necessary to declare
astring explicitly. This is dangerous because if
bos decides to drop this dependency, code that depends on
astring won’t compile any longer.
Dune warn about libraries that are used but are not declared explicitly?
(executable ((name main) (public_name hello) (libraries (cmdliner bos))))