Merge pull request #6022 from dotty-staging/close-5735

Close #5735: Add regression test

Author: smarter

tests/pos/i5735.scala

@@ -0,0 +1,12 @@
+object Test {
+  // The identity on types of the form N | P[a, P[b, ... P[z, N]]]
+  type Nested[X, P[_, _], N] = X match {
+    case N => N
+    case P[a, b] => P[a, Nested[b, P, N]]
+  }
+
+  class Foo[T] { def apply[Y >: T <: Nested[T, Tuple2, Unit]](t: T): T = t }
+  def foo[T] = new Foo[T]
+
+  foo.apply((21, ()))
+}