Github user StephanEwen commented on the issue:
https://github.com/apache/flink/pull/4801
Eclipse Public License is not impossible, but tricky.
I am not a lawyer, but this is what I picked up over the year: EPL is weak
copyleft, meaning linking is okay, but modifying not (from Apache License
compatibility) . Shading the code in the library (which we do when building the
flink dist jar) is a bit of an gray zone. It does not violate the spirit of the
license, but a court may see that differently.
Various Flink users that approached us to avoid weak copyleft as much as
possible because of that uncertainty, so avoiding this dependency would be
desirable.
Making it an optional dependency that users explicitly have to add is
possible, because then we do shade it into the Flink distribution jar.
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