Add latest test case

Author: dwijnand

tests/neg/i15893.scala

@@ -0,0 +1,61 @@
+sealed trait NatT
+case class Zero() extends NatT
+case class Succ[+N <: NatT](n: N) extends NatT
+
+type Mod2[N <: NatT] <: NatT = N match
+  case Zero => Zero
+  case Succ[Zero] => Succ[Zero]
+  case Succ[Succ[predPredN]] => Mod2[predPredN]
+
+def mod2(n: NatT):  NatT = n match
+  case Zero() => Zero()
+  case Succ(Zero()) => Succ(Zero())
+  case Succ(Succ(predPredN)) => mod2(predPredN)
+
+inline def inlineMod2(inline n: NatT):  NatT = inline n match
+  case Zero() => Zero()
+  case Succ(Zero()) => Succ(Zero())
+  case Succ(Succ(predPredN)) => inlineMod2(predPredN)
+
+transparent inline def transparentInlineMod2(inline n: NatT):  NatT = inline n match
+  case Zero() => Zero()
+  case Succ(Zero()) => Succ(Zero())
+  case Succ(Succ(predPredN)) => transparentInlineMod2(predPredN)
+
+def dependentlyTypedMod2[N <: NatT](n: N): Mod2[N] = n match // exhaustivity warning; unexpected
+  case Zero(): Zero => Zero() // error
+  case Succ(Zero()): Succ[Zero] => Succ(Zero()) // error
+  case Succ(Succ(predPredN)): Succ[Succ[_]] => dependentlyTypedMod2(predPredN) // error
+
+inline def inlineDependentlyTypedMod2[N <: NatT](inline n: N): Mod2[N] = inline n match
+  case Zero(): Zero => Zero() // error
+  case Succ(Zero()): Succ[Zero] => Succ(Zero()) // error
+  case Succ(Succ(predPredN)): Succ[Succ[_]] => inlineDependentlyTypedMod2(predPredN) // error
+
+transparent inline def transparentInlineDependentlyTypedMod2[N <: NatT](inline n: N): Mod2[N] = inline n match
+  case Zero(): Zero => Zero() // error
+  case Succ(Zero()): Succ[Zero] => Succ(Zero()) // error
+  case Succ(Succ(predPredN)): Succ[Succ[_]] => transparentInlineDependentlyTypedMod2(predPredN) // error
+
+def foo(n: NatT): NatT = mod2(n) match
+  case Succ(Zero()) => Zero()
+  case _ => n
+
+inline def inlineFoo(inline n: NatT): NatT = inline inlineMod2(n) match
+  case Succ(Zero()) => Zero()
+  case _ => n
+
+inline def transparentInlineFoo(inline n: NatT): NatT = inline transparentInlineMod2(n) match
+  case Succ(Zero()) => Zero()
+  case _ => n
+
+@main def main(): Unit =
+  println(mod2(Succ(Succ(Succ(Zero()))))) // prints Succ(Zero()), as expected
+  println(foo(Succ(Succ(Succ(Zero()))))) // prints Zero(), as expected
+  println(inlineMod2(Succ(Succ(Succ(Zero()))))) // prints Succ(Zero()), as expected
+  println(inlineFoo(Succ(Succ(Succ(Zero()))))) // prints Succ(Succ(Succ(Zero()))); unexpected
+  println(transparentInlineMod2(Succ(Succ(Succ(Zero()))))) // prints Succ(Zero()), as expected
+  println(transparentInlineFoo(Succ(Succ(Succ(Zero()))))) // prints Zero(), as expected
+  println(dependentlyTypedMod2(Succ(Succ(Succ(Zero()))))) // runtime error; unexpected
+//  println(inlineDependentlyTypedMod2(Succ(Succ(Succ(Zero()))))) // doesn't compile; unexpected
+//  println(transparentInlineDependentlyTypedMod2(Succ(Succ(Succ(Zero()))))) // doesn't compile; unexpected