FWIW, FB has a FAQ here on their intent: https://code.facebook.com/pages/850928938376556
We use a standard BSD license paired with an additional patent grant for most of our open source projects. For brevity, we call this combination the Facebook BSD+Patents license. We've compiled some answers to common questions about the additional patent grant:
Does the additional patent grant in the Facebook BSD+Patents license terminate if I create a competing product?
Does the additional patent grant in the Facebook BSD+Patents license terminate if I sue Facebook for something other than patent infringement?
Does the additional patent grant in the Facebook BSD+Patents license terminate if Facebook sues me for patent infringement first, and then I respond with a patent counterclaim against Facebook?
No, unless your patent counterclaim is related to Facebook's software licensed under the Facebook BSD+Patents license.
Does termination of the additional patent grant in the Facebook BSD+Patents license cause the copyright license to also terminate?
To Mark Thomas's point above:
My reading of that is if you use this code and Facebook infringes a completely unrelated patent that you own, you can't sue them for infringement without giving up this patent license. That is much broader than the language in the ALv2 which is limited to a single work.
I think FB's clarification is that this is not their intent - only claims involving the BSD+Patents licensed software cancels the patent grant, so it's not as broad as your fear.
Looks like we at least understand what options are - either plugin outside of the ASF repo, or ask FB to change the wording of the patent grant. Given statements here that the wording was intentionally incompatible with the Apache license, I'm not sure if that's likely to have much impact (though Dikang Gu , if you believe otherwise, that'd be good to know).
I'll leave the open question of Apache Flink and Apache Samza using RocksDB to legal.