Scalac test case: .../src/main/scala/not_found.scala:19: not found: value x$1

build.sbt

name := "Scala Test Case: not found"

not_found.scala

/*
 * [error] .../src/main/scala/not_found.scala:19: not found: value x$1
 * [error]   val name_conflict = c.map(f(_, name_conflict = true))
 */
object not_found {

  trait E
  trait C

  implicit class PimpedC(coll: C) extends Seq[E] {
    def iterator: Iterator[E] = ???
    def apply(idx: Int): E = ???
    def length: Int = ???
  }

  val c: C = ???

  // Compiles: val NOconflict = c.map(f(_, name_conflict = true))
  val name_conflict = c.map(f(_, name_conflict = true))

  def f(e: E, name_conflict: Boolean): Int = ???
}