[test] update cast diagnostics for existing tests

Author: Suyash Srijan

test/Constraints/casts.swift

@@ -111,7 +111,7 @@ func protocol_concrete_casts(_ p1: P1, p2: P2, p12: P1 & P2) {
 
   _ = p1 as! P1 & P2
 
-  _ = p2 as! S1
+  _ = p2 as! S1 // expected-warning {{cast from 'P2' to unrelated type 'S1' always fails}}
 
   _ = p12 as! S1
   _ = p12 as! S2
@@ -126,7 +126,7 @@ func protocol_concrete_casts(_ p1: P1, p2: P2, p12: P1 & P2) {
 
   var _:Bool = p1 is P1 & P2
 
-  var _:Bool = p2 is S1
+  var _:Bool = p2 is S1 // expected-warning {{cast from 'P2' to unrelated type 'S1' always fails}}
 
   var _:Bool = p12 is S1
   var _:Bool = p12 is S2
@@ -153,9 +153,9 @@ func objc_protocol_casts(_ op1: ObjCProto1, opn: NonObjCProto) {
   _ = ObjCClass() as! ObjCProto1 & NonObjCProto
 
   _ = op1 as! ObjCProto1 & ObjCProto2
-  _ = op1 as! ObjCProto2
+  _ = op1 as! ObjCProto2 // expected-warning {{cast from 'ObjCProto1' to unrelated type 'ObjCProto2' always fails}}
   _ = op1 as! ObjCProto1 & NonObjCProto
-  _ = opn as! ObjCProto1
+  _ = opn as! ObjCProto1 // expected-warning {{cast from 'NonObjCProto' to unrelated type 'ObjCProto1' always fails}}
 
   _ = NonObjCClass() as! ObjCProto1
 }

test/Constraints/patterns.swift

@@ -55,7 +55,7 @@ case is B,
      is D,
      is S:
   ()
-case is E:
+case is E: // expected-warning {{cast from 'P' to unrelated type 'E' always fails}}
   ()
 default:
   ()
@@ -69,7 +69,7 @@ case let d as D:
   d.d()
 case let s as S:
   s.s()
-case let e as E:
+case let e as E: // expected-warning {{cast from 'P' to unrelated type 'E' always fails}}
   e.e()
 default:
   ()
@@ -120,7 +120,7 @@ case iPadHair<E>.HairForceOne:
   ()
 case iPadHair.HairForceOne: // expected-error{{generic enum type 'iPadHair' is ambiguous without explicit generic parameters when matching value of type 'HairType'}}
   ()
-case Watch.Edition: // TODO: should warn that cast can't succeed with currently known conformances
+case Watch.Edition: // expected-warning {{cast from 'HairType' to unrelated type 'Watch' always fails}}
   ()
 case .HairForceOne: // expected-error{{type 'HairType' has no member 'HairForceOne'}}
   ()