Warn against static property redeclaration

Summary:
Static property redeclaration is a footgun because it causes a separate static property be generated. In that sense it is not a (re)declaration but just a separate declaration.

```
<?hh

class C {
  public static vec<int> $p = vec[];
}

class D extends C {
  public static vec<int> $p = vec[];
}

<<__EntryPoint>>
function main(): void {
  C::$p[] = 1;
  D::$p[] = 2;
  var_dump(C::$p); // vec[1]
  var_dump(D::$p); // vec[2]
}
```

This diff warns against redeclaration.

We'd like this to be an error eventually.

Reviewed By: francesco-zappa-nardelli

Differential Revision: D77366104

fbshipit-source-id: ad28a6c1da574af4afd5e268bf17922e396b6aaa

Author: Mistral Contrastin

hphp/hack/src/errors/error_codes.ml

@@ -814,6 +814,7 @@ module Warning = struct
     | SafeAbstractConstAccess [@value 12018]
     | SwitchRedundancy [@value 12019]
     | StaticCallOnTrait [@value 12020]
+    | StaticPropertyOverride [@value 12021]
   [@@deriving enum, ord, show { with_path = false }]
 end
 

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<<d3b733ec198c93107656515825474fc5>>
+// @generated SignedSource<<b2809815fefe191e19d540522aeb0dd9>>
 //
 // To regenerate this file, run:
 //   hphp/hack/src/oxidized_regen.sh
@@ -652,6 +652,7 @@ pub enum Warning {
     SafeAbstractConstAccess = 12018,
     SwitchRedundancy = 12019,
     StaticCallOnTrait = 12020,
+    StaticPropertyOverride = 12021,
 }
 impl TrivialDrop for Warning {}
 arena_deserializer::impl_deserialize_in_arena!(Warning);

hphp/hack/src/typing/typing_class.ml

@@ -1786,6 +1786,7 @@ let class_wellformedness_checks env c tc (parents : class_parents) =
   - __Disposable attribute w.r.t. parents
   - individual member checks:
     - subtyping parent members
+    - not redeclaring class properties
     - __Override attribute check
     - enum inclusions
     - abstract members in concrete class

hphp/hack/src/typing/typing_extends.ml

@@ -492,6 +492,22 @@ let check_override_final_method env parent_class_elt class_elt on_error =
       Typing_error.(
         apply_reasons ~on_error @@ Secondary.Override_final { pos; parent_pos })
 
+(** Checks that we're not overriding a concrete static property. *)
+let check_override_concrete_static_prop
+    ~parent_pos env member_name parent_class_elt class_elt =
+  if
+    (not (get_ce_abstract parent_class_elt))
+    && not (get_ce_const parent_class_elt)
+  then
+    let child_prop_pos = Lazy.force class_elt.ce_pos in
+    Typing_warning_utils.add
+      env
+      Typing_warning.
+        ( parent_pos,
+          Static_property_override,
+          Static_property_override.{ prop_name = member_name; child_prop_pos }
+        )
+
 (** Checks that methods annotated with __DynamicallyCallable are only overridden with
     dynamically callable method. *)
 let check_dynamically_callable
@@ -981,6 +997,7 @@ let check_override
     ~class_
     ~parent_class
     ~(parent_type : decl_ty)
+    ~parent_pos
     ~(class_elt : class_elt)
     ~parent_class_elt
     on_error =
@@ -994,6 +1011,18 @@ let check_override
       on_error
   in
 
+  begin
+    match member_kind with
+    | MemberKind.Static_property ->
+      check_override_concrete_static_prop
+        ~parent_pos
+        env
+        member_name
+        parent_class_elt
+        class_elt
+    | _ -> ()
+  end;
+
   if MemberKind.is_method member_kind then begin
     (* We first verify that we aren't overriding a final method.  We only check
      * for final overrides on methods, not properties. Constructors have their
@@ -1548,6 +1577,7 @@ let check_class_against_parent_class_elt
           ~parent_class
           ~parent_class_elt
           ~parent_type
+          ~parent_pos
           ~class_elt
           (on_error (parent_pos, Cls.name parent_class)) )
   | None ->
@@ -1736,7 +1766,8 @@ let default_constructor_ce class_ =
   }
 
 (* When an interface defines a constructor, we check that they are compatible *)
-let check_constructors env (parent_class, parent_type) class_ psubst on_error =
+let check_constructors
+    ~parent_pos env (parent_class, parent_type) class_ psubst on_error =
   let parent_is_interface = Ast_defs.is_c_interface (Cls.kind parent_class) in
   let parent_is_consistent =
     constructor_is_consistent (snd (Cls.construct parent_class))
@@ -1772,6 +1803,7 @@ let check_constructors env (parent_class, parent_type) class_ psubst on_error =
             ~class_
             ~parent_class
             ~parent_type
+            ~parent_pos
             ~parent_class_elt:parent_cstr
             ~class_elt:cstr
             on_error
@@ -2127,14 +2159,21 @@ let check_typeconst_override
  * message pointing at the class being checked.
  *)
 let check_class_extends_parent_constructors
+    ~parent_pos
     env
     (parent_class : (Pos.t * string) * decl_ty * decl_ty list * Cls.t)
     class_
     on_error =
   let (_, parent_type, parent_tparaml, parent_class) = parent_class in
   let psubst = Inst.make_subst (Cls.tparams parent_class) parent_tparaml in
   let env =
-    check_constructors env (parent_class, parent_type) class_ psubst on_error
+    check_constructors
+      ~parent_pos
+      env
+      (parent_class, parent_type)
+      class_
+      psubst
+      on_error
   in
   env
 
@@ -2890,6 +2929,7 @@ let check_implements_extends_uses
       parents
       ~f:(fun env ((parent_name, _, _, _) as parent) ->
         check_class_extends_parent_constructors
+          ~parent_pos:(fst parent_name)
           env
           parent
           class_

hphp/hack/src/typing/typing_warning.ml

@@ -161,6 +161,13 @@ module Static_call_on_trait = struct
   }
 end
 
+module Static_property_override = struct
+  type t = {
+    prop_name: string;
+    child_prop_pos: Pos_or_decl.t;
+  }
+end
+
 type (_, _) kind =
   | Sketchy_equality : (Sketchy_equality.t, warn) kind
   | Safe_abstract : (Safe_abstract.t, warn) kind
@@ -175,5 +182,6 @@ type (_, _) kind =
   | No_disjoint_union_check : (No_disjoint_union_check.t, warn) kind
   | Switch_redundancy : (Switch_redundancy.t, warn) kind
   | Static_call_on_trait : (Static_call_on_trait.t, warn) kind
+  | Static_property_override : (Static_property_override.t, warn) kind
 
 type ('x, 'a) t = Pos.t * ('x, 'a) kind * 'x

hphp/hack/src/typing/typing_warning_utils.ml

@@ -587,6 +587,28 @@ module Static_call_on_trait = struct
   let quickfixes _ = []
 end
 
+module Static_property_override = struct
+  open Typing_warning.Static_property_override
+
+  type t = Typing_warning.Static_property_override.t
+
+  let code = Codes.StaticPropertyOverride
+
+  let codes = [code]
+
+  let code _ = code
+
+  let claim { prop_name; _ } =
+    Printf.sprintf
+      "Static property is overridden: %s"
+      (Markdown_lite.md_codify prop_name)
+
+  let reasons { child_prop_pos; _ } =
+    [(child_prop_pos, "Overriding static property is here")]
+
+  let quickfixes _ = []
+end
+
 let module_of (type a x) (kind : (x, a) Typing_warning.kind) :
     (module Warning with type t = x) =
   match kind with
@@ -603,6 +625,7 @@ let module_of (type a x) (kind : (x, a) Typing_warning.kind) :
   | Typing_warning.No_disjoint_union_check -> (module No_disjoint_union_check)
   | Typing_warning.Switch_redundancy -> (module Switch_redundancy)
   | Typing_warning.Static_call_on_trait -> (module Static_call_on_trait)
+  | Typing_warning.Static_property_override -> (module Static_property_override)
 
 let module_of_migrated
     (type x) (kind : (x, Typing_warning.migrated) Typing_warning.kind) :

hphp/hack/test/extracted_from_manual/07-traits-and-interfaces/03-using-a-trait-03.hack.exp

@@ -1,2 +1,6 @@
 WARN: File "03-using-a-trait-03.hack", line 20, characters 7-7:
 Duplicated property `x` in `C` (defined in `T1` and `T2`): all instances will be aliased at runtime (Warn[12008])
+WARN: File "03-using-a-trait-03.hack", line 21, characters 7-8:
+Static property is overridden: `$x` (Warn[12021])
+  File "03-using-a-trait-03.hack", line 13, characters 17-19:
+  Overriding static property is here

hphp/hack/test/typecheck/const_attribute/static/redeclare_to_const.php.exp

@@ -1,3 +1,7 @@
+WARN: File "redeclare_to_const.php", line 5, characters 17-17:
+Static property is overridden: `$p` (Warn[12021])
+  File "redeclare_to_const.php", line 5, characters 47-49:
+  Overriding static property is here
 ERROR: File "redeclare_to_const.php", line 5, characters 47-49:
 This property is `__Const` (Typing[4204])
   File "redeclare_to_const.php", line 4, characters 28-30:

hphp/hack/test/typecheck/inheritance/non_const_prop_override_static.php.exp

@@ -1,3 +1,7 @@
+WARN: File "non_const_prop_override_static.php", line 8, characters 17-17:
+Static property is overridden: `$p` (Warn[12021])
+  File "non_const_prop_override_static.php", line 9, characters 17-19:
+  Overriding static property is here
 ERROR: File "non_const_prop_override_static.php", line 9, characters 17-19:
 The property `$p` has the wrong type (Typing[4341])
   File "non_const_prop_override_static.php", line 9, characters 17-19:

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

@@ -1,3 +1,7 @@
+WARN: File "lsb_disallow_override_private.php", line 7, characters 17-17:
+Static property is overridden: `$x` (Warn[12021])
+  File "lsb_disallow_override_private.php", line 8, characters 18-20:
+  Overriding static property is here
 ERROR: File "lsb_disallow_override_private.php", line 8, characters 18-20:
 Member `$x` may not override `__LSB` member of parent (Typing[4284])
   File "lsb_disallow_override_private.php", line 4, characters 28-30: