v9.10 release of Java OR-Tools contains a binary-breaking upgrade to protobuf-java

[DavidGregory084]

Version: v9.10
Language: Java

The Java bindings for OR-Tools v9.9 depend upon protobuf-java 3.25.x.

The Java bindings for OR-Tools v9.10 depend upon protobuf-java 4.26.1, which isn't binary-compatible with 3.x.

It's not a big deal, as users can simply downgrade, but should this release be relabelled v10?

[lperron]

no, the use of protobuf is only internal. So even if its API change, it does not impact OR-Tools.

[DavidGregory084]

no, the use of protobuf is only internal. So even if its API change, it does not impact OR-Tools.

The public API of the Java bindings is full of proto classes, like MPSolver#solveWithProto, which returns an MPSolutionResponse that extends GeneratedMessage.

Unfortunately the protobuf 3.x runtime is still used in OpenTelemetry, grpc and many other open source projects.

Users trying to run OR-Tools Java v9.10 alongside any of those libraries will most likely run into ClassNotFoundException: com.google.protobuf.GeneratedMessageV3 after their build tool bumps protobuf-java up to 4.x.

I think that this is a manifestation of protocolbuffers/protobuf#16452.

[lperron]

for many reasons, we have no choice but to follow closely the releases of abseil, protobuf and re2.
Unfortunately, if other projects do not release updated versions, you are stuck with an older version.

[lperron]

Grpc has also been updated to use protobuf 26.1