I see this comment in the issue:

How to make sure, there is 1:1 correspondence between source_libraries and libraries?
This only affects publishing.
Is it pants which should not allow same sources to be part of different libs or the consumers to write good/clean  build files?

I think we (a) don’t want a 1:1 correspondence, eg for things like protobuf libraries it’s valid to use the same .proto sources for both Wire and Protobuf libraries, and potentially for different kinds of proto libraries (java vs python vs ruby etc). (b) This may not affect publishing exclusively, as use-case 2. mentions above