Try to make macro for Coder[P <: Product]

build.sbt

@@ -4,8 +4,16 @@ Global / onChangedBuildSource := ReloadOnSourceChanges
 inThisBuild(
   Seq(
     version := "0.1",
-    scalaVersion := "2.13.5",
-    scalacOptions ++= "-Ymacro-annotations" :: "-language:experimental.macros" :: Nil
+    scalaVersion := "2.13.6",
+    scalacOptions ++= Seq(
+      "-Ymacro-annotations",
+      "-language:experimental.macros",
+      //"-Xlog-implicits",
+      "-Ymacro-debug-lite",
+      // for nicer error messages
+      //"-Vimplicits",
+      "-Vtype-diffs"
+    )
   )
 )
 
@@ -16,12 +24,19 @@ lazy val `scala-macros` = (project in file("scala-macros"))
   .settings(
     libraryDependencies ++= Seq(
       scalaReflect % scalaVersion.value,
-      scalaPbRuntime
+      scalaPbRuntime,
+      beamSdksJavaCore,
+      beamRunnersDirectJava
     )
   )
 
 lazy val `scala-macros-usage` = (project in file("scala-macros-usage"))
   .dependsOn(`scala-macros`)
   .settings(
-    libraryDependencies ++= scalaPbRuntime :: Nil
+    libraryDependencies ++= Seq(
+      scalaPbRuntime,
+      beamSdksJavaCore,
+      beamRunnersDirectJava,
+      scalaTest
+    )
   )

project/Dependencies.scala

@@ -3,4 +3,10 @@ import sbt._
 object Dependencies {
   val scalaReflect = "org.scala-lang" % "scala-reflect"
   val scalaPbRuntime = "com.thesamet.scalapb" %% "scalapb-runtime" % scalapb.compiler.Version.scalapbVersion
+
+  val beamVersion = "2.28.0"
+  val beamSdksJavaCore = "org.apache.beam" % "beam-sdks-java-core" % beamVersion
+  val beamRunnersDirectJava = "org.apache.beam" % "beam-runners-direct-java" % beamVersion % Runtime
+
+  val scalaTest = "org.scalatest" %% "scalatest" % "3.2.7" % Test
 }

scala-macros-usage/src/test/scala/com/github/fpopic/scalamacros/beam/DefMacroCoderSpec.scala

@@ -0,0 +1,49 @@
+package com.github.fpopic.scalamacros.beam
+
+import org.apache.beam.sdk.coders.Coder
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+import java.io.{ByteArrayInputStream, ByteArrayOutputStream}
+
+case class Pojo(s: String, i: Int, l: List[Int], s2: String)
+case class ContainsNested(i: Int, pojo: Pojo)
+
+class DefMacroCoderSpec extends AnyFlatSpec with Matchers {
+
+  behavior of "DefMacroCoder"
+
+  it should "generate a coder and serialize/deserialize properly the value." in {
+    import DefMacroCoder.{intCoder, stringCoder, listCoder}
+    val coder: Coder[Pojo] = DefMacroCoder.productCoder[Pojo]
+
+    val pojo = Pojo(s = "4", i = 1, l = List(2, 3), s2 = "5")
+
+    val encoded: Array[Byte] = {
+      val os = new ByteArrayOutputStream()
+      coder.encode(pojo, os)
+      os.toByteArray
+    }
+    val decoded: Pojo = coder.decode(new ByteArrayInputStream(encoded))
+
+    pojo shouldBe decoded
+  }
+
+  it should "generate a coder for nested case class and serialize/deserialize properly the value." in {
+    import DefMacroCoder.{intCoder, stringCoder, listCoder}
+    implicit val pojoCoder: Coder[Pojo] = DefMacroCoder.productCoder[Pojo]
+    val coder: Coder[ContainsNested] = DefMacroCoder.productCoder[ContainsNested]
+
+    val pojo = ContainsNested(i = 7, pojo = Pojo(s = "4", i = 1, l = List(2, 3), s2 = "5"))
+
+    val encoded: Array[Byte] = {
+      val os = new ByteArrayOutputStream()
+      coder.encode(pojo, os)
+      os.toByteArray
+    }
+    val decoded: ContainsNested = coder.decode(new ByteArrayInputStream(encoded))
+
+    pojo shouldBe decoded
+  }
+
+}