Merge pull request #37246 from xedin/test-case-for-valid-type-arg-of-subscript

[TypeChecker] NFC: Add a test-case for expression affected by rdar://61749633

Author: xedin

test/Constraints/subscript.swift

@@ -216,3 +216,15 @@ func rdar61084565() {
   let a = Foo()
   a[] // expected-error {{value of type 'Foo' has no subscripts}}
 }
+
+func test_subscript_accepts_type_name_argument() {
+  struct A {
+    subscript(a: A.Type) -> Int { get { 42 } }
+  }
+
+  func test(a: A?) {
+    let _ = a?[A] // expected-error {{expected member name or constructor call after type name}}
+    // expected-note@-1 {{add arguments after the type to construct a value of the type}} {{17-17=()}}
+    // expected-note@-2 {{use '.self' to reference the type object}} {{17-17=.self}}
+  }
+}