Add class-retention @GrpcGenerated annotation to generated types

Is your feature request related to a problem?

Static analyzers (e.g. lint checks and proguard) would like to reliably detect that code has been generated by gRPC in order exclude it from some types of validation. Currently, gRPC-generated types are annotated with the @Generated annotation, but this only has SOURCE retention and is unavailable to these analyzers.

Describe the solution you’d like

Additionally add an @GrpcGenerated annotation with CLASS retention to generated types.

Describe alternatives you’ve considered

Currently we inspect generated code for anticipated naming schemes and structure (e.g. endsWith(“Grpc”) & contains X fields) in order to determine if it is grpc-generated. Obviously this is fragile and relies on implementation details that it shouldn’t.

Additional context

There is prior art for this kind of annotation in Dagger and AutoFactory (coming soon).

[ejona86]

I think @RpcService will be like @RpcMethod, nothing emphasizing generated code, or prohibiting non-generated usage.

@dapengzhang0, note that RpcMethod has this in its documentation:

This annotation is used by the gRPC stub compiler to annotate MethodDescriptor getters. Users should not annotate their own classes with this annotation.

[dapengzhang0]

This annotation is used by the gRPC stub compiler to annotate MethodDescriptor getters. Users should not annotate their own classes with this annotation.

Then inspecting for @RpcMethod is less fragile than I thought.