Based on my experiments, if a message contains a well-known type, http4s-grpc produces invalid code. For example, this protobuf:

syntax = "proto3";
package com.selvia.andrew.demo;
import "google/protobuf/empty.proto";
import "google/protobuf/wrappers.proto";
service Foo {
  rpc Bar (google.protobuf.Empty) returns (stream google.protobuf.Int64Value) {}
}

produces the following code:

trait Foo[F[_]] { 
  def bar(request: _root_.com.google.protobuf.empty.Empty, ctx: _root_.org.http4s.Headers): _root_.fs2.Stream[F, _root_._root_.scala.Long]
}

Notice how the return type has the invalid type prefix _root_._root_.

ScalaPB seems to handle these alright. Will some additional sbt configuration make this work or is this a bug?