i16018d.scala

// Additional negative coverage for the fix to `TypeComparer.compareCaptured`
// (#16018). The companion `pos/i16018d.scala` widens coverage to
// HKT-nested Function1, intersection, path-dependent, and acyclic dependent
// bound shapes. This file pins that recursive parameter bounds stay on the
// old conservative path: the surface widening would otherwise accept a
// relation that frozen Ycheck cannot justify.

object Test:

  // ---- A. F-bounded parameter: recursive bound guard -------------------
  //
  // The guard rejects this at compile time. Without it, the surface widening
  // `(M & FBounded[M]) <: M` succeeds but produces a typed tree that fails
  // frozen Ycheck:all with assertions like `M <:< xs.T`.

  class FBounded[+T <: FBounded[T]]
  def f_bounded_guard[M <: FBounded[M]](xs: FBounded[? <: M]): FBounded[M] = xs // error