Trait names are not Enforceable

Summary: Hack considered trait names as enforceable and allowed passing them explicitly to enforceable reified generics.  This diff makes trait names non-enforceable.

Reviewed By: madgen

Differential Revision: D57335063

fbshipit-source-id: ca988f4c53fb5e4b67207a61cb1dbd92c3d1c03b

hphp/hack/src/typing/typing_enforceable_hint.ml

@@ -70,50 +70,59 @@ let validator =
     method! on_class acc r cls tyl =
       match Env.get_class acc.Type_validator.env (snd cls) with
       | Decl_entry.Found tc ->
-        let tparams = Cls.tparams tc in
-        begin
-          match tyl with
-          | [] -> acc
-          (* this case should really be handled by the fold2,
-             but we still allow class hints without args in certain places *)
-          | targs ->
-            List.Or_unequal_lengths.(
-              begin
-                match
-                  List.fold2 ~init:acc targs tparams ~f:(fun acc targ tparam ->
-                      let inside_reified_class_generic_position =
-                        acc.Type_validator.inside_reified_class_generic_position
-                      in
-                      if this#is_wildcard targ then begin
-                        if inside_reified_class_generic_position then
-                          this#invalid
-                            acc
-                            r
-                            "a reified type containing a wildcard (`_`)"
-                        else
+        (match Cls.kind tc with
+        | Ast_defs.Ctrait -> this#invalid acc r "a trait name"
+        | _ ->
+          let tparams = Cls.tparams tc in
+          begin
+            match tyl with
+            | [] -> acc
+            (* this case should really be handled by the fold2,
+               but we still allow class hints without args in certain places *)
+            | targs ->
+              List.Or_unequal_lengths.(
+                begin
+                  match
+                    List.fold2
+                      ~init:acc
+                      targs
+                      tparams
+                      ~f:(fun acc targ tparam ->
+                        let inside_reified_class_generic_position =
                           acc
-                      end else if
-                            Aast.(equal_reify_kind tparam.tp_reified Reified)
-                          then
-                        this#on_type
-                          {
-                            acc with
-                            Type_validator.inside_reified_class_generic_position =
-                              true;
-                          }
-                          targ
-                      else if inside_reified_class_generic_position then
-                        this#on_type acc targ
-                      else
-                        let error_message =
-                          "a type with an erased generic type argument"
+                            .Type_validator
+                             .inside_reified_class_generic_position
                         in
-                        this#invalid acc r error_message)
-                with
-                | Ok new_acc -> new_acc
-                | Unequal_lengths -> acc (* arity error elsewhere *)
-              end)
-        end
+                        if this#is_wildcard targ then begin
+                          if inside_reified_class_generic_position then
+                            this#invalid
+                              acc
+                              r
+                              "a reified type containing a wildcard (`_`)"
+                          else
+                            acc
+                        end else if
+                              Aast.(equal_reify_kind tparam.tp_reified Reified)
+                            then
+                          this#on_type
+                            {
+                              acc with
+                              Type_validator
+                              .inside_reified_class_generic_position = true;
+                            }
+                            targ
+                        else if inside_reified_class_generic_position then
+                          this#on_type acc targ
+                        else
+                          let error_message =
+                            "a type with an erased generic type argument"
+                          in
+                          this#invalid acc r error_message)
+                  with
+                  | Ok new_acc -> new_acc
+                  | Unequal_lengths -> acc (* arity error elsewhere *)
+                end)
+          end)
       | Decl_entry.DoesNotExist
       | Decl_entry.NotYetAvailable ->
         acc

hphp/hack/test/typecheck/as_expression/trait.php.exp

@@ -2,3 +2,7 @@ ERROR: File "trait.php", line 6, characters 9-12:
 `TFoo` is uninstantiable (Typing[4002])
   File "trait.php", line 3, characters 7-10:
   Declaration is here
+ERROR: File "trait.php", line 6, characters 9-12:
+Invalid `as` expression hint (Typing[4195])
+  File "trait.php", line 6, characters 9-12:
+  The `as` operator cannot be used with a trait name

hphp/hack/test/typecheck/instanceof/trait_instanceof.php.exp

@@ -2,3 +2,7 @@ ERROR: File "trait_instanceof.php", line 10, characters 16-16:
 `X` is uninstantiable (Typing[4002])
   File "trait_instanceof.php", line 3, characters 7-7:
   Declaration is here
+ERROR: File "trait_instanceof.php", line 10, characters 16-16:
+Invalid `is` expression hint (Typing[4195])
+  File "trait_instanceof.php", line 10, characters 16-16:
+  The `is` operator cannot be used with a trait name

hphp/hack/test/typecheck/is_expression/trait.php.exp

@@ -2,3 +2,7 @@ ERROR: File "trait.php", line 6, characters 16-19:
 `TFoo` is uninstantiable (Typing[4002])
   File "trait.php", line 3, characters 7-10:
   Declaration is here
+ERROR: File "trait.php", line 6, characters 16-19:
+Invalid `is` expression hint (Typing[4195])
+  File "trait.php", line 6, characters 16-19:
+  The `is` operator cannot be used with a trait name

hphp/hack/test/typecheck/trait_not_enforceable.php

@@ -0,0 +1,14 @@
+<?hh
+
+trait FooTrait {}
+
+class C{}
+
+function foo<<<__Enforceable>> reify T>(mixed $in): void {
+  $in as T;
+}
+
+function test(): void {
+  foo<FooTrait>(42);
+  foo<C>(42);
+}

hphp/hack/test/typecheck/trait_not_enforceable.php.exp

@@ -0,0 +1,6 @@
+ERROR: File "trait_not_enforceable.php", line 12, characters 7-14:
+Invalid type (Typing[4302])
+  File "trait_not_enforceable.php", line 7, characters 38-38:
+  Type parameter `T` was declared `__Enforceable` here
+  File "trait_not_enforceable.php", line 12, characters 7-14:
+  This type is not enforceable because it has a trait name