Incorrect "the type test for A cannot be checked at runtime because it's a local class" warning

[uosis]

Compiler version

Tested 3.4.2, 3.4.1, 3.4.0, 3.3.3, all with the same issue.

2.13.14 works fine and does not emit warning.

Minimized example

def f: Unit = {
  class A {
    override def equals(x: Any): Boolean = x match {
      case a: A => true
      case _ => false
    }
  }
}

Output Error/Warning message

1 warning found
def f: Unit
-- [E092] Pattern Match Unchecked Warning: -------------------------------------
4 |      case a: A => true
  |           ^
  |the type test for A cannot be checked at runtime because it's a local class
  |
  | longer explanation available when compiling with `-explain`

Why this Error/Warning was not helpful

The code seems correct and runs correctly, i.e. the type test executes correctly at runtime, contradictory to the warning.

Suggested improvement

No warning should be emitted.

[som-snytt]

The following with member A prints false twice

class B:
  class A {
    override def equals(x: Any): Boolean = x match {
      case a: A => true
      case _ => false
    }
  }
  def f(x: Any): Any = {
    val y = A()
    println(y == x)
    y
  }

@main def test() =
  val b0 = B()
  val f = b0.f(null)
  val b1 = B()
  b1.f(f)

but with local A, it is false (of course) then true. It's merely testing the implementation class.

Not sure if more words from the code comment would be elucidating:

8. if `P` is a local class which is not statically reachable from the scope where `X` is defined, "it's a local class"

[clavigne]

Can I try my hand at this one? Sounds interesting