Add an __ImplementedBy attribute for methods on primitives

Summary:
For methods on primitives, we want to give a class in an .hhi, and tie that to the top-level function that is the runtime implementation of the method. We also want to ensure that the types are compatible. We add an attribute (only allowed in .hhi files) that declares the name of the top-level function. We then fund  the function's decl and check that it is a subtype of the method's type. The methods type is instantiated as for `meth_caller` to take into account generics from the class. For example, in the .hhi for string, we might have:
```
class string {
  <<__ImplementedBy('\my_length')>>
  public method length(): int;
}

function my_length(string $s): int;
```

We use the `Fun_id.synth` and `Meth_caller.synth` functions from `typing.ml` to build the types of the functions. In particular, the Meth_caller one adds the "this" parameter for us, and moves class generics to function generics. It also tries to add `readonly` and `FunctionRef` wrappings, which we disable for this purpose.

Reviewed By: mheiber

Differential Revision: D88174803

fbshipit-source-id: 5308745bf57a91e71b94fa4eeaac54b7adc64fa1

Author: Scott Owens

hphp/hack/src/errors/error_codes.ml

@@ -169,6 +169,7 @@ module Naming = struct
     | ToplevelStatement [@value 2128]
     | InvalidTypeAccessInWhere [@value 2129]
     | AttributeOutsideAllowedFiles [@value 2130]
+    | HhiAttributeOutsideHhi [@value 2131]
   (* Add new Naming codes here! Comment out when deprecating. *)
   [@@deriving enum, show { with_path = false }]
 

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

@@ -568,6 +568,7 @@ fn emit_fatal_nast_check_error(err: &NastCheckError) -> Result<Unit, Error> {
         NastCheckError::MissingAssign(_) => todo!(),
         NastCheckError::CloneReturnType(_) => todo!(),
         NastCheckError::PackageExprInInvariant(_) => todo!(),
+        NastCheckError::AttributeImplementedByOnlyInHhi(_) => todo!(),
     }
 }
 

hphp/hack/src/naming/naming_special_names.ml

@@ -402,6 +402,8 @@ module UserAttributes = struct
 
   let uaAsioLowPri = "__AsioLowPri"
 
+  let uaImplementedBy = "__ImplementedBy"
+
   type attr_info = {
     contexts: string list;
     doc: string;
@@ -862,6 +864,13 @@ module UserAttributes = struct
               doc =
                 "Marks the function as low priority. Will suspend eager execution into a low priority awaitable.";
             } );
+          ( uaImplementedBy,
+            {
+              contexts = [mthd];
+              autocomplete = true;
+              doc =
+                "Specifies that this method is implemented by a specific top-level function. Only valid in .hhi files.";
+            } );
         ])
 
   (* These are names which are allowed in the systemlib but not in normal programs *)

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<<3f899c82f15b01a6cf584bae0dd43582>>
+// @generated SignedSource<<69f97f6775910fe2cb4cdcd55e935bbd>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -155,6 +155,7 @@ pub enum Naming {
     ToplevelStatement = 2128,
     InvalidTypeAccessInWhere = 2129,
     AttributeOutsideAllowedFiles = 2130,
+    HhiAttributeOutsideHhi = 2131,
 }
 impl TrivialDrop for Naming {}
 arena_deserializer::impl_deserialize_in_arena!(Naming);

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<<2564942d4c07d50efe5d36d05e246ed7>>
+// @generated SignedSource<<4073f83a7583567cc25e4fd4e5f52da3>>
 //
 // To regenerate this file, run:
 //   buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:oxidized_regen
@@ -276,6 +276,8 @@ pub enum NastCheckError {
     },
     #[rust_to_ocaml(name = "Attribute_no_auto_dynamic")]
     AttributeNoAutoDynamic(pos::Pos),
+    #[rust_to_ocaml(name = "Attribute_implemented_by_only_in_hhi")]
+    AttributeImplementedByOnlyInHhi(pos::Pos),
     #[rust_to_ocaml(name = "Generic_at_runtime")]
     GenericAtRuntime {
         pos: pos::Pos,

hphp/hack/src/typing/dune

@@ -212,6 +212,7 @@
  (modules
   nastInitCheck
   type_parameter_env_ops
+  typing
   typing_alias
   typing_ast_print
   typing_argument
@@ -225,6 +226,7 @@
   typing_exts
   typing_func_terminality
   typing_generic_rules
+  typing_implemented_by
   typing_lenv
   typing_local_ops
   typing_named_params
@@ -247,6 +249,7 @@
   typing_dynamic_utils
   typing_enforceability
   typing_enum
+  typing_extract_method
   typing_intersection
   typing_generic_constraint
   typing_helpers
@@ -266,6 +269,7 @@
   typing_structure
   typing_taccess
   typing_type_member
+  typing_type_wellformedness
   typing_union
   type_validator
   typing_const_reifiable
@@ -314,9 +318,7 @@
  (name typing_toplevel)
  (wrapped false)
  (modules
-  typing
   typing_class
-  typing_extract_method
   typing_memoize
   typing_toplevel
   typing_typedef
@@ -335,8 +337,7 @@
   trait_reuse_check
   typing_extends
   typing_requirements
-  typing_subtype_method
-  typing_type_wellformedness)
+  typing_subtype_method)
  (libraries
   typing
   typing_modules

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

@@ -139,6 +139,38 @@ let check_no_auto_dynamic env attrs =
         Nast_check_error.(to_user_error @@ Attribute_no_auto_dynamic pos)
     | _ -> ()
 
+let check_implemented_by attrs =
+  let attr = Naming_attributes.find SN.UserAttributes.uaImplementedBy attrs in
+  match attr with
+  | Some { ua_name = (pos, name); ua_params } ->
+    (* Check file extension *)
+    let filename = Pos.filename pos in
+    let path_str = Relative_path.suffix filename in
+    let is_hhi = Filename.check_suffix path_str ".hhi" in
+    if not is_hhi then
+      Errors.add_error
+        Nast_check_error.(
+          to_user_error @@ Attribute_implemented_by_only_in_hhi pos);
+    (* Check parameter count and type *)
+    (match ua_params with
+    | [] ->
+      Errors.add_error
+        Nast_check_error.(
+          to_user_error
+          @@ Attribute_too_few_arguments { pos; name; expected = 1 })
+    | [(_, _, String _)] -> () (* Valid: one string parameter *)
+    | [(_, p, _)] ->
+      Errors.add_error
+        Nast_check_error.(
+          to_user_error
+          @@ Attribute_param_type { pos = p; x = "a string literal" })
+    | _ ->
+      Errors.add_error
+        Nast_check_error.(
+          to_user_error
+          @@ Attribute_too_many_arguments { pos; name; expected = 1 }))
+  | _ -> ()
+
 let check_dynamically_referenced attrs =
   let attr =
     Naming_attributes.find SN.UserAttributes.uaDynamicallyReferenced attrs
@@ -342,6 +374,7 @@ let handler =
       check_autocomplete_valid_text m.m_user_attributes;
       check_duplicate_memoize m.m_user_attributes;
       check_no_auto_dynamic env m.m_user_attributes;
+      check_implemented_by m.m_user_attributes;
       check_no_sealed_on_constructors m;
       check_no_sealed_on_private_methods m;
       check_no_sealed_on_interface_methods env m;

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

@@ -167,6 +167,7 @@ type t =
       x: string;
     }
   | Attribute_no_auto_dynamic of Pos.t
+  | Attribute_implemented_by_only_in_hhi of Pos.t
   | Generic_at_runtime of {
       pos: Pos.t;
       prefix: string;
@@ -761,6 +762,12 @@ let attribute_no_auto_dynamic pos =
     (pos, "This attribute is not yet supported in user code")
     []
 
+let attribute_implemented_by_only_in_hhi pos =
+  User_error.make_err
+    Error_codes.Naming.(to_enum HhiAttributeOutsideHhi)
+    (pos, "This attribute can only be used in .hhi files")
+    []
+
 let generic_at_runtime p prefix =
   User_error.make_err
     Error_codes.Typing.(to_enum ErasedGenericAtRuntime)
@@ -926,6 +933,8 @@ let to_user_error t =
       attribute_not_exact_number_of_args pos name expected actual
     | Attribute_param_type { pos; x } -> attribute_param_type pos x
     | Attribute_no_auto_dynamic pos -> attribute_no_auto_dynamic pos
+    | Attribute_implemented_by_only_in_hhi pos ->
+      attribute_implemented_by_only_in_hhi pos
     | Generic_at_runtime { pos; prefix } -> generic_at_runtime pos prefix
     | Generics_not_allowed pos -> generics_not_allowed pos
     | Local_variable_modified_and_used { pos; pos_useds } ->

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

@@ -166,6 +166,7 @@ type t =
       x: string;
     }
   | Attribute_no_auto_dynamic of Pos.t
+  | Attribute_implemented_by_only_in_hhi of Pos.t
   | Generic_at_runtime of {
       pos: Pos.t;
       prefix: string;

hphp/hack/src/typing/typing.ml

@@ -8931,6 +8931,7 @@ end
 
 and Method_caller : sig
   val synth :
+    ?for_meth_caller:bool ->
     Pos.t ->
     Aast_defs.class_name * Ast_defs.pstring ->
     env ->
@@ -9047,7 +9048,7 @@ end = struct
                reason;
              }))
 
-  let synth pos (class_name, method_name) env =
+  let synth ?(for_meth_caller = true) pos (class_name, method_name) env =
     match Env.get_class env (snd class_name) with
     | Decl_entry.NotYetAvailable
     | Decl_entry.DoesNotExist ->
@@ -9156,8 +9157,18 @@ end = struct
                   (env, mk (get_reason ty, Tfun ft))
                 | _ -> (env, ty))
           in
-          let (env, ty) = set_capture_only_readonly env ty in
-          let ty = make_function_ref ~contains_generics:false env pos ty in
+          let (env, ty) =
+            if for_meth_caller then
+              set_capture_only_readonly env ty
+            else
+              (env, ty)
+          in
+          let ty =
+            if for_meth_caller then
+              make_function_ref ~contains_generics:false env pos ty
+            else
+              ty
+          in
           let expr = Method_caller (class_name, method_name) in
           make_result env pos expr ty
         | _ -> failwith "Expected a function type")