android-interop-testing spews lots of warnings

[ejona86]

For the generated code, we should probably disable the warning, like we do elsewhere:

grpc-java/protobuf-lite/build.gradle

Lines 29 to 32 in 9dec06c

	options.compilerArgs += [
	"-Xlint:-cast"
	]
	options.errorprone.excludedPaths = ".*/build/generated/source/proto/.*"

The rest look like they'll need changes, but I just too a cursory glance.

> Task :grpc-android-interop-testing:compileDebugJavaWithJavac
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/EmptyProtos.java:112: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:286: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:567: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:891: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:1715: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:2908: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:3584: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:4011: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:4411: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:4848: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:5548: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:6120: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:6415: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:6757: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:7141: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Messages.java:7621: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Metrics.java:354: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Metrics.java:774: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/build/generated/source/proto/debug/java/io/grpc/testing/integration/Metrics.java:1010: warning: [cast] redundant cast to Builder
      return (Builder) DEFAULT_INSTANCE.createBuilder(prototype);
             ^
grpc-java/android-interop-testing/src/main/java/io/grpc/android/integrationtest/InteropTask.java:72: warning: [Finally] If you return or throw from a finally, then values returned or thrown from the try-catch block will be ignored. Consider using try-with-resources instead.
        throw ex;
        ^
    (see https://errorprone.info/bugpattern/Finally)
grpc-java/android-interop-testing/src/main/java/io/grpc/android/integrationtest/InteropTask.java:74: warning: [Finally] If you return or throw from a finally, then values returned or thrown from the try-catch block will be ignored. Consider using try-with-resources instead.
        throw new RuntimeException(ex);
        ^
    (see https://errorprone.info/bugpattern/Finally)
grpc-java/interop-testing/src/main/java/io/grpc/testing/integration/AbstractInteropTest.java:294: warning: [UnnecessaryAnonymousClass] Implementing a functional interface is unnecessary; prefer to implement the functional interface method directly and use a method reference instead.
  private final ClientInterceptor tracerSetupInterceptor = new ClientInterceptor() {
                                  ^
    (see https://errorprone.info/bugpattern/UnnecessaryAnonymousClass)
  Did you mean 'private  <ReqT, RespT> ClientCall<ReqT, RespT> tracerSetupInterceptor('?
22 warnings

[voidzcy]

Yes, I realized that. I tried to let protobuf team know if they can fix this in javalite, but seems no one has replied me. I am going to disable the warning.

The couple of (there were more, fixed one or two easy ones in #6829) errorprone warnings in android-interop-testing do not have obvious solutions. I will try again to get rid of them.

[ejona86]

If we disagree with errorprone on a particular line we can always add a suppression, like @SuppressWarnings("Finally"). If we agree with errorprone but can't quite figure out what to do, we can suppress it and file a bug to track it (with a link to the issue at the suppression).

If an errorprone check just doesn't seem appropriate for us (like maybe Finally, given we haven't considered ourselves able to use try-with-resources), then we can disable that check completely with -Xep.

The important thing is to keep the build clean, because new warnings are really hard to spot in a sea of noise.