java: ErrorProne generates warnings for codegen

[ejona86]

protoc 3.2.0 generates code that fails ErrorProne's MissingOverride, ReferenceEquality, and FunctionalInterfaceClash checks. It's not obvious that the protobuf project has any legitimate problems to fix based on those warnings, but their presence makes it hard to use ErrorProne to check non-generated code.

Maybe the best option is just to add @SuppressWarnings for each of those warnings at the top of the generated class.

[liujisi]

Protobuf code base should now pass the default ErrorProne settings. Do you have a list of patterns that you'd like to also cover? I guess maven only reports Error patterns, and didn't output anything for Warning patterns. I'd have to manually enable them.

[ejona86]

Oh, sweet! We use -Werror in our CI to prevent drowning in warnings, so resolving warnings would be good. We do use the default set of options though. The only ones I noticed failing were those I listed initially: MissingOverride, ReferenceEquality, and FunctionalInterfaceClash.

[liujisi]

It seems like SuppressWarnings doesn't work for those ErrorProne specific warnings -- I tested @SuppressWarnings("FunctionalInterfaceClash"). Could you blacklist those patterns in grpc instead?

[ejona86]

Huh. That's strange. Did you apply it to the class or the method? I think that one is necessary to suppress at the class level. I just tested and SuppressWarnings worked for me and it is documented.

We are using -Xep:FunctionalInterfaceClash:OFF now in order to build. But that also means the check is ignored for our own code, not just the generated code. I do agree that it doesn't seem quite protobuf's fault to fix. It's a combination of how generated code, errorprone, gradle, and the gradle-protobuf plugin interact. At this point I think I the individual decisions make sense, but overall we're left with an issue and nowhere obvious to fix it.

[jared2501]

Could you annotate the generated protobuf with the javax.annotation.Generated annotation? Then downstream projects that use protobuf just need to add -XepDisableWarningsInGeneratedCode, and can still add -Werror too!

[haberman]

The idea of adding generated annotations is covered in this issue: #42