Diag: Fix inaccuracy in dynamic_self_invalid

Author: AnthonyLatsis

include/swift/AST/DiagnosticsSema.def

@@ -2931,8 +2931,8 @@ ERROR(dynamic_self_non_method,none,
       "%select{global|local}0 function cannot return 'Self'", (bool))
 
 ERROR(dynamic_self_invalid,none,
-      "covariant 'Self' can only appear as the type of a property, subscript or method result; "
-      "did you mean '%0'?", (StringRef))
+      "covariant 'Self' can only appear as the possibly optional type of a "
+      "property, subscript or method result; did you mean '%0'?", (StringRef))
 ERROR(dynamic_self_in_mutable_property,none,
       "mutable property cannot have covariant 'Self' type", ())
 ERROR(dynamic_self_in_stored_property,none,

test/decl/ext/generic.swift

@@ -149,7 +149,7 @@ extension Array where Element == String { }
 extension GenericClass : P3 where T : P3 { }
 
 extension GenericClass where Self : P3 { }
-// expected-error@-1{{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'GenericClass'?}} {{30-34=GenericClass}}
+// expected-error@-1{{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'GenericClass'?}} {{30-34=GenericClass}}
 // expected-error@-2{{'GenericClass<T>' in conformance requirement does not refer to a generic parameter or associated type}}
 
 protocol P4 {

test/decl/func/dynamic_self.swift

@@ -24,9 +24,9 @@ enum E0 {
 class C0 {
   func f() -> Self { } // okay
 
-  func g(_ ds: Self) { } // expected-error{{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'C0'?}}
+  func g(_ ds: Self) { } // expected-error{{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'C0'?}}
 
-  func h(_ ds: Self) -> Self { } // expected-error{{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'C0'?}}
+  func h(_ ds: Self) -> Self { } // expected-error{{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'C0'?}}
 }
 
 protocol P0 {

test/type/self.swift

@@ -5,7 +5,7 @@ struct S0<T> {
 }
 
 class C0<T> {
-  func foo(_ other: Self) { } // expected-error{{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'C0'?}}
+  func foo(_ other: Self) { } // expected-error{{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'C0'?}}
 }
 
 enum E0<T> {
@@ -47,15 +47,15 @@ final class FinalMario : Mario {
 
 class A<T> {
   typealias _Self = Self
-  // expected-error@-1 {{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'A'?}}
+  // expected-error@-1 {{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'A'?}}
   let b: Int
   required init(a: Int) {
     print("\(Self.self).\(#function)")
     Self.y()
     b = a
   }
   static func z(n: Self? = nil) {
-    // expected-error@-1 {{covariant 'Self' can only appear as the type of a property, subscript or method result; did you mean 'A'?}}
+    // expected-error@-1 {{covariant 'Self' can only appear as the possibly optional type of a property, subscript or method result; did you mean 'A'?}}
     print("\(Self.self).\(#function)")
   }
   class func y() {