The plugin does not detect proto file was changed when running build for a second time

[dapengzhang0]

Use the gradle plugin to generate code, then change the proto file, then build again.
As reproduced in https://sponge.corp.google.com/target?id=ff244382-5595-48fd-b556-4b2694aaf5d4&target=grpc%2Fjava%2Fmaster%2Fpresubmit%2Fandroid&searchFor=

[ejona86]

This was for PR grpc/grpc-java#6099. It used pull/6099/merge:pull_branch ref to pull. Looks like the first build was f2ffd26d2d5500395a3c2bbdf28d92a7dd558ec6 and the second build was d507ea72a.

[voidzcy]

The issue is because proto files in the first build contains some proto messages that the proto files with the same filenames in the second build do not have. Since message types are generated in separate java files, when you switch to to the second build without a clean, generated java files for messages that only exist in the first build are not deleted, while they still have dependencies on other messages whose re-generated java files are modified, so compiling those "should-have-been-deleted" java files results in symbol not found error.

This only occurs for cases that the first build contains some messages that the second build does not have. Build systems only add/replace output files if necessary but do not delete things from previous build. This is normal. Gradle compiles all the source files in the SourceSet, this is also reasonable for how it works.

I believe it should be the application's responsibility to ensure output directory does not contain unwanted files before each build. grpc/grpc-java#6103 is doing the correct thing and it's not just a workaround.

[ejona86]

In general, Gradle notices when files have been deleted and recompiles. There's basically no change that is "the application's responsibility".

[voidzcy]

Filed #332, which should be done first before we can make changes to always wipe out generated file directories.

[devinrsmith]

I've ran across this just now (after a large update to our proto files). IMO, this should be the responsibility of the plugin.

Hopefully anybody else in this situation can use a workaround like this for now:

protobuf {
    protoc { artifact = "com.google.protobuf:protoc:${protocVersion}" }
    generateProtoTasks {
      all().each {
        generateProtoTask ->
          // The generateProto task does not seem to properly clean its previously generated outputs.
          // See https://github.com/google/protobuf-gradle-plugin/issues/332
          // See https://github.com/google/protobuf-gradle-plugin/issues/331
          generateProtoTask.doFirst {
            delete generateProtoTask.outputs
          }
      }
    }
  }

[clayburn]

Is this still an issue? I couldn't reproduce, although maybe I'm missing a step here.

[ejona86]

I suspect this still happens. Basically files can be left over from a previous compilation, so if you delete a message in the .proto you might get strange results.

[ejona86]

Duplicate of #33