Add transitive path arguments when compiling protobuf

rules/scala_proto/private/ScalaProtoWorker.scala

@@ -16,6 +16,13 @@ object ScalaProtoWorker extends WorkerMain[Unit] {
 
   private[this] val argParser: ArgumentParser = {
     val parser = ArgumentParsers.newFor("proto").addHelp(true).fromFilePrefix("@").build
+    parser
+      .addArgument("--proto_path")
+      .help("Proto path")
+      .metavar("proto_path")
+      .nargs("*")
+      .`type`(Arguments.fileType.verifyIsDirectory)
+      .setDefault_(Collections.emptyList)
     parser
       .addArgument("--output_dir")
       .help("Output dir")
@@ -36,11 +43,12 @@ object ScalaProtoWorker extends WorkerMain[Unit] {
   protected[this] def work(ctx: Unit, args: Array[String]): Unit = {
     val namespace = argParser.parseArgs(args)
     val sources = namespace.getList[File]("sources").asScala.toList
+    val path = namespace.getList[File]("proto_path").asScala.toList
 
     val scalaOut = namespace.get[File]("output_dir").toPath
     Files.createDirectories(scalaOut)
 
-    val params = s"--scala_out=$scalaOut" :: sources.map(_.getPath)
+    val params = s"--scala_out=$scalaOut" :: path.map("--proto_path " ++ _.getPath) ++ sources.map(_.getPath)
 
     ProtocBridge.runWithGenerators(
       protoc = a => com.github.os72.protocjar.Protoc.runProtoc(a.toArray),

rules/scala_proto/private/core.bzl

@@ -32,6 +32,7 @@ def scala_proto_library_implementation(ctx):
 
     args = ctx.actions.args()
     args.add("--output_dir", gendir.path)
+    args.add_all("--proto_path", transitive_proto_path)
     args.add_all("--", transitive_sources)
     args.set_param_file_format("multiline")
     args.use_param_file("@%s", use_always = True)