NCGenerics: add casting test

Author: kavon

test/Interpreter/moveonly_generics_casting.swift

@@ -0,0 +1,70 @@
+// RUN: %target-run-simple-swift(-Xfrontend -sil-verify-all -enable-experimental-feature NoncopyableGenerics) | %FileCheck %s
+// RUN: %target-run-simple-swift(-O -Xfrontend -sil-verify-all -enable-experimental-feature NoncopyableGenerics) | %FileCheck %s
+
+protocol P {
+  func speak()
+}
+
+extension P {
+  func speak() { print("hello") }
+}
+
+struct Noncopyable: ~Copyable {}
+struct Ordinary {}
+
+struct Dog<T: ~Copyable>: Copyable {}
+extension Dog: P where T: Copyable {}
+
+enum Cat<Left: ~Copyable, Right: ~Copyable>: Copyable {
+    case meows
+    init() { self = .meows }
+}
+extension Cat: P where Left: Copyable {}
+
+func attemptCall(_ a: Any) {
+  if let value = a as? P {
+    value.speak()
+    return
+  }
+  print("failed to cast (attemptCall)")
+}
+
+defer { main() }
+func main() {
+  // CHECK: hello
+  attemptCall(Dog<Ordinary>())
+
+  // FIXME: this is NOT suppose to succeed! (rdar://123466649)
+  // CHECK: hello
+  attemptCall(Dog<Noncopyable>())
+
+  // CHECK: hello
+  attemptCall(Cat<Ordinary, Noncopyable>())
+
+  // FIXME: this is NOT suppose to succeed! (rdar://123466649)
+  // CHECK: hello
+  attemptCall(Cat<Noncopyable, Ordinary>())
+
+  // FIXME: this should succeeed!!
+  // CHECK: failed to cast (test_radar124171788)
+  test_radar124171788(.nothing)
+}
+
+// coverage for rdar://124171788
+enum Maybe<Wrapped: ~Copyable>: ~Copyable {
+  case just(Wrapped)
+  case nothing
+}
+extension Maybe: Copyable {}
+extension Maybe: CustomStringConvertible {
+  var description: String {
+    "cast succeeded"
+  }
+}
+func test_radar124171788(_ v: Maybe<Int>) {
+  if let foo = v as? CustomDebugStringConvertible {
+    print("\(foo.debugDescription)")
+    return
+  }
+  print("failed to cast (test_radar124171788)")
+}