Ban traits from implementing sealed interfaces

Summary: After speaking with dlreeves, we're gonna punt on allowing traits to implement sealed interfaces for now. HHVM should support it, because it models traits differently.

Reviewed By: jamesjwu

Differential Revision: D7863243

fbshipit-source-id: 671dc88120b10d2a75cdff3a632250caa045361f

hphp/hack/src/errors/errors.ml

@@ -2547,6 +2547,15 @@ let extend_sealed child_pos parent_pos parent_name parent_kind verb =
     parent_pos, "Declaration is here"
   ]
 
+let trait_implement_sealed child_pos parent_pos parent_name =
+  let name = (strip_ns parent_name) in
+  add_list (Typing.err_code Typing.ExtendSealed) [
+    child_pos, (
+      "A trait cannot implement sealed interface "^name^
+      ". Use `require implements` instead");
+    parent_pos, "Declaration is here"
+  ]
+
 let sealed_final pos name =
   let name = (strip_ns name) in
   add (Typing.err_code Typing.SealedFinal) pos ("Sealed class "^name^" cannot be marked final")

hphp/hack/src/errors/errors_sig.ml

@@ -217,6 +217,7 @@ module type S = sig
   val sketchy_null_check_primitive : Pos.t -> string option -> [< `Coalesce | `Eq | `Neq ] -> unit
   val extend_final : Pos.t -> Pos.t -> string -> unit
   val extend_sealed : Pos.t -> Pos.t -> string -> string -> string -> unit
+  val trait_implement_sealed : Pos.t -> Pos.t -> string -> unit
   val sealed_final : Pos.t -> string -> unit
   val read_before_write : Pos.t * string -> unit
   val interface_final : Pos.t -> unit

hphp/hack/src/typing/typing.ml

@@ -6138,19 +6138,28 @@ and check_parent class_def class_type parent_type =
 
 and check_parent_sealed child_type parent_type =
   match parent_type.dc_sealed_whitelist with
+    | None -> ()
     | Some whitelist ->
-      if not (SSet.mem child_type.tc_name whitelist)
-      then begin
-        let error = Errors.extend_sealed
-          child_type.tc_pos parent_type.dc_pos parent_type.dc_name in
-        match parent_type.dc_kind, child_type.tc_kind with
-          | Ast.Cabstract, _
-          | Ast.Cnormal, _ -> error "class" "extend"
-          | Ast.Cinterface, Ast.Cinterface -> error "interface" "extend"
-          | Ast.Cinterface, _ -> error "interface" "implement"
-          | _ -> ()
+      begin match child_type.tc_kind with
+        | Ast.Cabstract
+        | Ast.Cnormal
+        | Ast.Cinterface ->
+          if not (SSet.mem child_type.tc_name whitelist)
+          then begin
+            let error = Errors.extend_sealed
+              child_type.tc_pos parent_type.dc_pos parent_type.dc_name in
+            match parent_type.dc_kind, child_type.tc_kind with
+              | Ast.Cabstract, _
+              | Ast.Cnormal, _ -> error "class" "extend"
+              | Ast.Cinterface, Ast.Cinterface -> error "interface" "extend"
+              | Ast.Cinterface, _ -> error "interface" "implement"
+              | _ -> ()
+          end
+        | Ast.Ctrait ->
+          Errors.trait_implement_sealed
+            child_type.tc_pos parent_type.dc_pos parent_type.dc_name
+        | Ast.Cenum -> ()
       end
-    | None -> ()
 
 and check_parents_sealed env child_def child_type =
   List.iter (child_def.c_extends @ child_def.c_implements) begin function

hphp/hack/test/typecheck/sealed/trait.php

@@ -0,0 +1,14 @@
+<?hh // strict
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+<<__Sealed(B::class)>>
+interface A {}
+
+trait T implements A {}
+
+final class B {
+  use T;
+}
+final class C {
+  use T;
+}

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

@@ -0,0 +1,4 @@
+File "trait.php", line 7, characters 7-7:
+A trait cannot implement sealed interface A. Use `require implements` instead (Typing[4238])
+File "trait.php", line 5, characters 11-11:
+Declaration is here

hphp/hack/test/typecheck/sealed/trait2.php

@@ -0,0 +1,16 @@
+<?hh // strict
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+<<__Sealed(B::class)>>
+interface A {}
+
+trait T {
+  require implements A;
+}
+
+final class B implements A {
+  use T;
+}
+final class C implements A {
+  use T;
+}

hphp/hack/test/typecheck/sealed/trait2.php.exp

@@ -0,0 +1,4 @@
+File "trait2.php", line 14, characters 13-13:
+You cannot implement sealed interface A (Typing[4238])
+File "trait2.php", line 5, characters 11-11:
+Declaration is here