Warn on unused given in class that only used for contructing the same class

[eejbyfeldt]

Compiler version

3.7.4

Minimized example

object test {
  trait TC[X] {
    def notTrivial: Int
  }

  class C[T: TC]() {
    def mod: C[T] = new C()
  }
}

Output

No warning.

Expectation

If one removes the mod method one gets a warning. It would be nice if it would still warn even when mod is defined. Since the TC[T] instances only get used for calling Cs constructor it is effectively unused.

[som-snytt]

As a review, marker interfaces don't warn. But you expect an Ordering to actually order something.

Evidence may also be passed down the stack.

Here, it's just a form of "self-dealing". There's a similar issue to make mutation x = x + 1 not count as a reading usage.