a class cannot be sealed with a trait

Summary:
The semantics of sealing a class with a trait, eg:

```
<<__Sealed(T::class)>>
class C { ... }

trait T { ... }
```

is unclear at best.  This diff bans sealing a class with a trait.

Reviewed By: geralt-encore

Differential Revision: D92393842

fbshipit-source-id: f8ba025f685702b4c4ff5497c52b1cb5d8d19c50

Author: Francesco Zappa Nardelli

hphp/hack/src/diagnostics/error_codes.ml

@@ -284,6 +284,7 @@ module NastCheck = struct
     (* | PackageExprInInvariantDEPRECATED [@value 3105] *)
     | NamedInTransformedPseudofunction [@value 3106]
     | RequirePackageStrictInclusion [@value 3107]
+    | ClassSealedWithTrait [@value 3108]
   (* Add new NastCheck codes here! Comment out when deprecating. *)
   [@@deriving enum, show { with_path = false }]
 

hphp/hack/src/hackc/compile/compile.rs

@@ -563,6 +563,7 @@ fn emit_fatal_nast_check_error(err: &NastCheckError) -> Result<Unit, Error> {
         NastCheckError::CloneReturnType(_) => todo!(),
         NastCheckError::AttributeImplementedByRestriction { .. } => todo!(),
         NastCheckError::RequirePackageStrictInclusion { .. } => todo!(),
+        NastCheckError::ClassSealedWithTrait { .. } => todo!(),
     }
 }
 

hphp/hack/src/oxidized/gen/error_codes.rs

@@ -3,7 +3,7 @@
 // This source code is licensed under the MIT license found in the
 // LICENSE file in the "hack" directory of this source tree.
 //
-// @generated SignedSource<<1979bd32cde8ff3069353e3a5093c26e>>
+// @generated SignedSource<<e8f3018ac482cee215fbdf70aca4ce8e>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -225,6 +225,7 @@ pub enum NastCheck {
     CloneReturnType = 3104,
     NamedInTransformedPseudofunction = 3106,
     RequirePackageStrictInclusion = 3107,
+    ClassSealedWithTrait = 3108,
 }
 impl TrivialDrop for NastCheck {}
 arena_deserializer::impl_deserialize_in_arena!(NastCheck);

hphp/hack/src/oxidized/gen/nast_check_error.rs

@@ -3,7 +3,7 @@
 // This source code is licensed under the MIT license found in the
 // LICENSE file in the "hack" directory of this source tree.
 //
-// @generated SignedSource<<c2c92aa563f43993231b16002ec3023c>>
+// @generated SignedSource<<88a1d0face0230950853fb28a36ecce6>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -313,6 +313,12 @@ pub enum NastCheckError {
     MissingAssign(pos::Pos),
     #[rust_to_ocaml(name = "Clone_return_type")]
     CloneReturnType(pos::Pos),
+    #[rust_to_ocaml(name = "Class_sealed_with_trait")]
+    ClassSealedWithTrait {
+        pos: pos::Pos,
+        class_name: String,
+        trait_name: String,
+    },
     #[rust_to_ocaml(name = "Require_package_strict_inclusion")]
     RequirePackageStrictInclusion {
         required_pos: pos::Pos,

hphp/hack/src/typing/nast_check/attribute_nast_checks.ml

@@ -206,6 +206,42 @@ let check_dynamically_referenced attrs =
           to_user_diagnostic
           @@ Attribute_too_many_arguments { pos; name; expected = 1 }))
 
+(* Check that a sealed attribute on a class does not refer to a trait. *)
+let check_no_class_sealed_with_trait env c =
+  (* Only check classes, not interfaces or traits *)
+  match c.c_kind with
+  | Ast_defs.Cclass _ -> begin
+    match find_attribute SN.UserAttributes.uaSealed c.c_user_attributes with
+    | None -> ()
+    | Some sealed_attr ->
+      let class_name = snd c.c_name in
+      let ctx = env.Nast_check_env.ctx in
+      List.iter
+        (fun (_, pos, expr_) ->
+          match expr_ with
+          | Class_const ((_, _, CI (_, name)), _) -> begin
+            (* Look up the referenced class to check if it's a trait *)
+            match Naming_provider.get_type_path ctx name with
+            | None -> ()
+            | Some path -> begin
+              match
+                Ast_provider.find_class_in_file ctx path name ~full:false
+              with
+              | None -> ()
+              | Some cls ->
+                if Ast_defs.is_c_trait cls.Aast.c_kind then
+                  Diagnostics.add_diagnostic
+                    Nast_check_error.(
+                      to_user_diagnostic
+                      @@ Class_sealed_with_trait
+                           { pos; class_name; trait_name = name })
+            end
+          end
+          | _ -> ())
+        sealed_attr.ua_params
+  end
+  | _ -> ()
+
 let check_no_sealed_on_constructors m =
   let (_, method_name) = m.m_name in
   if String.equal method_name SN.Members.__construct then begin
@@ -413,6 +449,7 @@ let handler =
       check_autocomplete_valid_text c.c_user_attributes;
       check_soft_internal_without_internal c.c_internal c.c_user_attributes;
       check_dynamically_referenced c.c_user_attributes;
+      check_no_class_sealed_with_trait env c;
       check_attribute_arity
         c.c_user_attributes
         SN.UserAttributes.uaDocs

hphp/hack/src/typing/nast_check/nast_check_error.ml

@@ -194,6 +194,11 @@ type t =
   | Lateinit_with_default of Pos.t
   | Missing_assign of Pos.t
   | Clone_return_type of Pos.t
+  | Class_sealed_with_trait of {
+      pos: Pos.t;
+      class_name: string;
+      trait_name: string;
+    }
   | Require_package_strict_inclusion of {
       required_pos: Pos.t;
       required: string;
@@ -856,6 +861,18 @@ let clone_return_type pos =
     )
     []
 
+let class_sealed_with_trait pos class_name trait_name =
+  let _ = class_name in
+  User_diagnostic.make_err
+    Error_code.(to_enum ClassSealedWithTrait)
+    (pos, "Traits cannot appear in sealed allowlists")
+    [
+      ( Pos_or_decl.of_raw_pos pos,
+        Printf.sprintf
+          "%s is a trait"
+          (Markdown_lite.md_codify @@ Render.strip_ns trait_name) );
+    ]
+
 let require_package_strict_inclusion
     required_pos
     required
@@ -995,6 +1012,8 @@ let to_user_diagnostic t =
     | Lateinit_with_default pos -> lateinit_with_default pos
     | Missing_assign pos -> missing_assign pos
     | Clone_return_type pos -> clone_return_type pos
+    | Class_sealed_with_trait { pos; class_name; trait_name } ->
+      class_sealed_with_trait pos class_name trait_name
     | Require_package_strict_inclusion
         {
           required_pos;

hphp/hack/src/typing/nast_check/nast_check_error.mli

@@ -193,6 +193,11 @@ type t =
   | Lateinit_with_default of Pos.t
   | Missing_assign of Pos.t
   | Clone_return_type of Pos.t
+  | Class_sealed_with_trait of {
+      pos: Pos.t;
+      class_name: string;
+      trait_name: string;
+    }
   | Require_package_strict_inclusion of {
       required_pos: Pos.t;
       required: string;

hphp/hack/src/typing/typing_class.ml

@@ -479,10 +479,19 @@ let sealed_subtype (c : Nast.class_) ~is_enum ~env =
             else
               Cls.has_ancestor decl parent_name
           in
-          if not includes_ancestor then
+          (* Skip the warning if this is a class with a trait in the sealed allowlist.
+             This case is now handled as a proper error in nast_check (NastCheck[3108])
+             since traits cannot extend classes. *)
+          let class_kind = Cls.kind decl in
+          let is_class_with_trait =
+            Ast_defs.(
+              match (parent_kind, class_kind) with
+              | (Cclass _, Ctrait) -> true
+              | _ -> false)
+          in
+          if (not includes_ancestor) && not is_class_with_trait then
             let parent_pos = pos in
             let child_name = Cls.name decl in
-            let class_kind = Cls.kind decl in
             let (child_kind, verb) =
               Ast_defs.(
                 match (parent_kind, class_kind) with

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

@@ -0,0 +1,6 @@
+<?hh
+
+trait MyTrait {}
+
+<<__Sealed(MyTrait::class)>>
+class MyClass {}

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

@@ -0,0 +1,4 @@
+ERROR: File "sealed_class_with_trait.php", line 5, characters 12-25:
+Traits cannot appear in sealed allowlists (NastCheck[3108])
+  File "sealed_class_with_trait.php", line 5, characters 12-25:
+  `MyTrait` is a trait