[test] coverage for key paths to effectful prop/subscript

Author: kavon

test/Misc/effectful_properties_keypath.swift

@@ -0,0 +1,43 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-concurrency
+
+// REQUIRES: concurrency
+// REQUIRES: objc_interop
+
+enum E : Error {
+  case DoesNotExist
+}
+
+class Vertex {
+  var marked : Bool = false
+
+  // FIXME: we should suppress this note about adding @objc, since that's not allowed!
+
+  // expected-note@+2 {{add '@objc' to expose this property to Objective-C}}
+  // expected-note@+1 5 {{property declared here}}
+  var parent : Vertex {
+    get throws { throw E.DoesNotExist }
+  }
+
+  // expected-note@+1 2 {{subscript declared here}}
+  subscript(_ i : Int) -> Vertex? {
+    get async throws {
+      if i == 0 {
+        return try? parent
+      }
+      return Vertex()
+    }
+  }
+}
+
+func asFunction(_ f : (Vertex) -> Bool) {}
+
+let _ = \Vertex.parent.parent.parent // expected-error 3 {{cannot form key path to property with 'throws' or 'async'}}
+let _ = \Vertex.[3]?.marked // expected-error {{cannot form key path to subscript with 'throws' or 'async'}}
+
+asFunction(\Vertex.[0]!.marked) // expected-error {{cannot form key path to subscript with 'throws' or 'async'}}
+asFunction(\Vertex.parent.marked) // expected-error {{cannot form key path to property with 'throws' or 'async'}}
+
+// expected-error@+2 {{argument of '#keyPath' refers to non-'@objc' property 'parent'}}
+// expected-error@+1 {{cannot form key path to property with 'throws' or 'async'}}
+let _ = #keyPath(Vertex.parent)
+