sbt picks up Scala case classes generated by Java annotation processor

build.sbt

@@ -3101,6 +3101,11 @@ lazy val `runtime-parser` =
       frgaalJavaCompilerSetting,
       annotationProcSetting,
       commands += WithDebugCommand.withDebug,
+      // Java annotation processor in `runtime-parser-processor` generates scala
+      // case classes. This setting ensures that all the generated `*.scala` files
+      // are picked by the sbt for compilation.
+      Compile / managedSources ++=
+        Utils.listAllGeneratedScalaFiles.value,
       fork := true,
       libraryDependencies ++= Seq(
         "junit"            % "junit"                   % junitVersion       % Test,

project/Utils.scala

@@ -0,0 +1,36 @@
+import sbt.*
+import sbt.Keys.*
+
+import java.nio.file.attribute.BasicFileAttributes
+import java.nio.file.{FileVisitResult, Files, Path, SimpleFileVisitor}
+import scala.collection.mutable.ListBuffer
+
+object Utils {
+
+  /** Recursively lists all `*.scala` files in the `target/src_managed` directory.
+    * Should be put as a dependency of `Compile / managedSources` task to ensure
+    * that sbt picks up any scala sources generated by the Java annotation processor.
+    * @return
+    */
+  def listAllGeneratedScalaFiles(): Def.Initialize[Task[Seq[File]]] = Def.task {
+    val srcManagedDir = (Compile / sourceManaged).value
+    val scalaFiles    = ListBuffer[Path]()
+
+    Files.walkFileTree(
+      srcManagedDir.toPath,
+      new SimpleFileVisitor[Path]() {
+        override def visitFile(
+          file: Path,
+          attrs: BasicFileAttributes
+        ): FileVisitResult = {
+          if (file.toString.endsWith(".scala")) {
+            scalaFiles += file
+          }
+          FileVisitResult.CONTINUE
+        }
+      }
+    )
+
+    scalaFiles.map(_.toFile)
+  }
+}