Delete covariance from transformers

src/main/scala/io/moia/protos/teleproto/Reader.scala

@@ -31,7 +31,7 @@ import scala.util.Try
 /** Provides reading of a generated Protocol Buffers model into a business model.
   */
 @implicitNotFound("No Protocol Buffers mapper from type ${P} to ${M} was found. Try to implement an implicit Reader for this type.")
-trait Reader[-P, +M] {
+trait Reader[P, M] {
 
   /** Returns the read business model or an error message.
     */
@@ -150,6 +150,13 @@ object Reader extends LowPriorityReads {
       PbSuccess((Duration(protobuf.seconds, SECONDS) + Duration(protobuf.nanos.toLong, NANOSECONDS)).toCoarsest)
   }
 
+  /** Transforms a ScalaPB duration into a Scala concurrent duration.
+    */
+  implicit object DurationReader extends Reader[PBDuration, Duration] {
+    def read(protobuf: PBDuration): PbResult[FiniteDuration] =
+      PbSuccess((Duration(protobuf.seconds, SECONDS) + Duration(protobuf.nanos.toLong, NANOSECONDS)).toCoarsest)
+  }
+
   /** Transforms a string into a UUID.
     */
   implicit object UUIDReader extends Reader[String, UUID] {

src/main/scala/io/moia/protos/teleproto/VersionedModelWriter.scala

@@ -125,7 +125,7 @@ object VersionedModelWriter {
     def writer: Writer[DetachedModel, SpecificModel]
 
     final def versioned[V](version: V): (V, Writer[DetachedModel, GeneratedMessage]) =
-      version -> writer
+      version -> writer.map[GeneratedMessage](m => m)
   }
 
   object CompanionWriter {

src/main/scala/io/moia/protos/teleproto/Writer.scala

@@ -31,7 +31,7 @@ import scala.concurrent.duration.{Deadline, Duration}
 @implicitNotFound(
   "No mapper from business model type ${M} to Protocol Buffers type ${P} was found. Try to implement an implicit Writer for this type."
 )
-trait Writer[-M, +P] {
+trait Writer[M, P] {
 
   /** Returns the written Protocol Buffer object.
     */

src/main/scala/io/moia/protos/teleproto/WriterImpl.scala

@@ -69,7 +69,13 @@ class WriterImpl(val c: blackbox.Context) extends FormatImpl {
     // look for an implicit writer
     val writerType = appliedType(c.weakTypeTag[Writer[_, _]].tpe, modelType, protobufType)
 
-    val existingWriter = c.inferImplicitValue(writerType)
+    val existingWriter =
+      try {
+        c.inferImplicitValue(writerType)
+      } catch {
+        // Return EmptyTree in case of errors
+        case _: Throwable => EmptyTree
+      }
 
     // "ask" for the implicit writer or use the found one
     def ask: Compiled = (compileInner(q"implicitly[$writerType]"), Compatibility.full)