Branch coverage for a simple case class is very low

[cuipengfei]

package cpf.branch.coverage

trait Result

case class OKResult[A](a: A) extends Result

case class FailureResult(msg: String) extends Result

the code is like the above. when I run jacoco:cover, the result says: all 16 branches missed for the FailureResult case class.

and the pattern match code that uses the case class is like this:

    ...... match {
      case OKResult(result) => result.toString
      case FailureResult(error) => error
    }

and the results says that 1 of 2 branches missed for the second case.

is this because scala compiler generates extra code that has more branches than I intended in the scala code? and how to work around this to make my branch coverage look normal?

the code above is here: https://github.com/cuipengfei/reproduce-weird-issues/tree/master/scala-jacoco-branch-coverage