Cross-version Runtime Guarantee

[pdecks]

Hey team, this isn't an issue so much as a request for clarification. Given the 2.x releases of your runtime library and code generators, do you have a stated cross-version runtime guarantee for utilizing a newer major version runtime with an older major version code generator similar to Google's cross-version runtime guarantee for protobuf as a whole?

Edit: I'm assuming that runtimes on a newer major version are not compatible with older code generators, given that protoc-gen-connect-es 1.x was incompatible with protobuf-es 2.x as discussed in #957 (comment).

[nicksnyder]

We do not have a documented guarantee, but the following things are true:

• We follow semantic versioning in both generators and runtimes, so breaking changes will result in a major version bump. When a breaking change happens, all bets are off. You should read the release notes to understand what the compatibility story is. In this case, protobuf-es was v2'd and was both (1) required to be used with protoc-gen-es v2 and (2) was not compatible with protoc-gen-connect-es v1.
• We aim to make breaking changes extremely rare. Aka, we would be happy if there was never a v3 of either protobuf-es or protoc-gen-es. As long as we are not bumping major versions, things should remain compatible.

Hope that helps.