Check coeffects on __clone

[hiphop-php.git] / hphp / hack / src / typing / typing.ml

(*
 * Copyright (c) 2015, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the "hack" directory of this source tree.
 *
 *)

(* This module implements the typing.
 *
 * Given an Nast.program, it infers the type of all the local
 * variables, and checks that all the types are correct (aka
 * consistent) *)
open Hh_prelude
open Common
open Aast
open Tast
open Typing_defs
open Typing_env_types
open Utils
open Typing_helpers
module TFTerm = Typing_func_terminality
module TUtils = Typing_utils
module Reason = Typing_reason
module Type = Typing_ops
module Env = Typing_env
module Inf = Typing_inference_env
module LEnv = Typing_lenv
module Async = Typing_async
module SubType = Typing_subtype
module Union = Typing_union
module Inter = Typing_intersection
module SN = Naming_special_names
module TVis = Typing_visibility
module Phase = Typing_phase
module TOG = Typing_object_get
module Subst = Decl_subst
module ExprDepTy = Typing_dependent_type.ExprDepTy
module TCO = TypecheckerOptions
module EnvFromDef = Typing_env_from_def
module C = Typing_continuations
module CMap = C.Map
module Try = Typing_try
module TR = Typing_reactivity
module FL = FeatureLogging
module MakeType = Typing_make_type
module Cls = Decl_provider.Class
module Partial = Partial_provider
module Fake = Typing_fake_members
module ExpectedTy = Typing_helpers.ExpectedTy

type newable_class_info =
  env
  * Tast.targ list
  * Tast.class_id
  * [ `Class of sid * Cls.t * locl_ty | `Dynamic ] list

(*****************************************************************************)
(* Debugging *)
(*****************************************************************************)

(* A guess as to the last position we were typechecking, for use in debugging,
 * such as figuring out what a runaway hh_server thread is doing. Updated
 * only best-effort -- it's an approximation to point debugging in the right
 * direction, nothing more. *)
let debug_last_pos = ref Pos.none

let debug_print_last_pos _ =
  Hh_logger.info
    "Last typecheck pos: %s"
    (Pos.string (Pos.to_absolute !debug_last_pos))

(*****************************************************************************)
(* Helpers *)
(*****************************************************************************)

let err_witness env p = TUtils.terr env (Reason.Rwitness p)

(* Set all the types in an expression to the given type. *)
let with_type ty env (e : Nast.expr) : Tast.expr =
  let visitor =
    object
      inherit [_] Aast.map

      method on_'ex _ p = (p, ty)

      method on_'fb _ _ = ()

      method on_'en _ _ = env

      method on_'hi _ _ = ty
    end
  in
  visitor#on_expr () e

let expr_error env (r : Reason.t) (e : Nast.expr) =
  let ty = TUtils.terr env r in
  (env, with_type ty Tast.dummy_saved_env e, ty)

let expr_any env p e =
  let ty = Typing_utils.mk_tany env p in
  (env, with_type ty Tast.dummy_saved_env e, ty)

let unbound_name env (pos, name) e =
  let strictish = Partial.should_check_error (Env.get_mode env) 4107 in
  match Env.get_mode env with
  | FileInfo.Mstrict ->
    Errors.unbound_name_typing pos name;
    expr_error env (Reason.Rwitness pos) e
  | FileInfo.Mpartial when strictish ->
    Errors.unbound_name_typing pos name;
    expr_error env (Reason.Rwitness pos) e
  | FileInfo.Mdecl
  | FileInfo.Mpartial ->
    expr_any env pos e

(* Is this type Traversable<vty> or Container<vty> for some vty? *)
let get_value_collection_inst ty =
  match get_node ty with
  | Tclass ((_, c), _, [vty])
    when String.equal c SN.Collections.cTraversable
         || String.equal c SN.Collections.cContainer ->
    Some vty
  (* If we're expecting a mixed or a nonnull then we can just assume
   * that the element type is mixed *)
  | Tnonnull -> Some (MakeType.mixed Reason.Rnone)
  | Tany _ -> Some ty
  | _ -> None

(* Is this type KeyedTraversable<kty,vty>
 *           or KeyedContainer<kty,vty>
 * for some kty, vty?
 *)
let get_key_value_collection_inst p ty =
  match get_node ty with
  | Tclass ((_, c), _, [kty; vty])
    when String.equal c SN.Collections.cKeyedTraversable
         || String.equal c SN.Collections.cKeyedContainer ->
    Some (kty, vty)
  (* If we're expecting a mixed or a nonnull then we can just assume
   * that the key type is arraykey and the value type is mixed *)
  | Tnonnull ->
    let arraykey = MakeType.arraykey (Reason.Rkey_value_collection_key p) in
    let mixed = MakeType.mixed Reason.Rnone in
    Some (arraykey, mixed)
  | Tany _ -> Some (ty, ty)
  | _ -> None

(* Is this type varray<vty> or a supertype for some vty? *)
let get_varray_inst ty =
  match get_node ty with
  (* It's varray<vty> *)
  | Tvarray vty -> Some vty
  | _ -> get_value_collection_inst ty

(* Is this type one of the value collection types with element type vty? *)
let get_vc_inst vc_kind ty =
  match get_node ty with
  | Tclass ((_, c), _, [vty]) when String.equal c (Nast.vc_kind_to_name vc_kind)
    ->
    Some vty
  | _ -> get_value_collection_inst ty

(* Is this type one of the three key-value collection types
 * e.g. dict<kty,vty> or a supertype for some kty and vty? *)
let get_kvc_inst p kvc_kind ty =
  match get_node ty with
  | Tclass ((_, c), _, [kty; vty])
    when String.equal c (Nast.kvc_kind_to_name kvc_kind) ->
    Some (kty, vty)
  | _ -> get_key_value_collection_inst p ty

(* Is this type darray<kty, vty> or a supertype for some kty and vty? *)
let get_darray_inst p ty =
  match get_node ty with
  (* It's darray<kty, vty> *)
  | Tdarray (kty, vty) -> Some (kty, vty)
  | _ -> get_key_value_collection_inst p ty

(* Check whether this is a function type that (a) either returns a disposable
 * or (b) has the <<__ReturnDisposable>> attribute
 *)
let is_return_disposable_fun_type env ty =
  let (_env, ty) = Env.expand_type env ty in
  match get_node ty with
  | Tfun ft ->
    get_ft_return_disposable ft
    || Option.is_some
         (Typing_disposable.is_disposable_type env ft.ft_ret.et_type)
  | _ -> false

(* Turn an environment into a local_id_map suitable to be embedded
 * into an AssertEnv statement
 *)
let annot_map env =
  match Env.next_cont_opt env with
  | Some { Typing_per_cont_env.local_types; _ } ->
    Some (Local_id.Map.map (fun (ty, pos, _expr_id) -> (pos, ty)) local_types)
  | None -> None

(* Similar to annot_map above, but filters the map to only contain
 * information about locals in lset
 *)
let refinement_annot_map env lset =
  match annot_map env with
  | Some map ->
    let map =
      Local_id.Map.filter (fun lid _ -> Local_id.Set.mem lid lset) map
    in
    if Local_id.Map.is_empty map then
      None
    else
      Some map
  | None -> None

let assert_env_blk ~pos ~at annotation_kind env_map_opt blk =
  let mk_assert map = (pos, Aast.AssertEnv (annotation_kind, map)) in
  let annot_blk = Option.to_list (Option.map ~f:mk_assert env_map_opt) in
  match at with
  | `Start -> annot_blk @ blk
  | `End -> blk @ annot_blk

let assert_env_stmt ~pos ~at annotation_kind env_map_opt stmt =
  let mk_assert map = (pos, Aast.AssertEnv (annotation_kind, map)) in
  match env_map_opt with
  | Some env_map ->
    let blk =
      match at with
      | `Start -> [mk_assert env_map; (pos, stmt)]
      | `End -> [(pos, stmt); mk_assert env_map]
    in
    Aast.Block blk
  | None -> stmt

let set_tcopt_unstable_features env { fa_user_attributes; _ } =
  match
    Naming_attributes.find
      SN.UserAttributes.uaEnableUnstableFeatures
      fa_user_attributes
  with
  | None -> env
  | Some { ua_name = _; ua_params } ->
    let ( = ) = String.equal in
    List.fold ua_params ~init:env ~f:(fun env feature ->
        match snd feature with
        | Aast.String s when s = SN.UnstableFeatures.ifc ->
          Env.map_tcopt ~f:TypecheckerOptions.enable_ifc env
        | _ -> env)

(* Given a localized parameter type and parameter information, infer
 * a type for the parameter default expression (if present) and check that
 * it is a subtype of the parameter type (if present). If no parameter type
 * is specified, then union with Tany. (So it's as though we did a conditional
 * assignment of the default expression to the parameter).
 * Set the type of the parameter in the locals environment *)
let rec bind_param env (ty1, param) =
  let (env, param_te, ty1) =
    match param.param_expr with
    | None -> (env, None, ty1)
    | Some e ->
      let decl_hint =
        Option.map
          ~f:(Decl_hint.hint env.decl_env)
          (hint_of_type_hint param.param_type_hint)
      in
      let enforced =
        match decl_hint with
        | None -> false
        | Some ty -> Typing_enforceability.is_enforceable env ty
      in
      let ty1_enforced = { et_type = ty1; et_enforced = enforced } in
      let expected =
        ExpectedTy.make_and_allow_coercion
          param.param_pos
          Reason.URparam
          ty1_enforced
      in
      let (env, te, ty2) = expr ~expected env e in
      Typing_sequencing.sequence_check_expr e;
      let (env, ty1) =
        if
          Option.is_none (hint_of_type_hint param.param_type_hint)
          && (not @@ TCO.global_inference (Env.get_tcopt env))
          (* ty1 will be Tany iff we have no type hint and we are not in
           * 'infer missing mode'. When it ty1 is Tany we just union it with
           * the type of the default expression *)
        then
          Union.union env ty1 ty2
        (* Otherwise we have an explicit type, and the default expression type
         * must be a subtype *)
        else
          let env =
            Typing_coercion.coerce_type
              param.param_pos
              Reason.URhint
              env
              ty2
              ty1_enforced
              Errors.parameter_default_value_wrong_type
          in
          (env, ty1)
      in
      (env, Some te, ty1)
  in
  let (env, user_attributes) =
    List.map_env env param.param_user_attributes user_attribute
  in
  let tparam =
    {
      Aast.param_annotation = Tast.make_expr_annotation param.param_pos ty1;
      Aast.param_type_hint = (ty1, hint_of_type_hint param.param_type_hint);
      Aast.param_is_variadic = param.param_is_variadic;
      Aast.param_pos = param.param_pos;
      Aast.param_name = param.param_name;
      Aast.param_expr = param_te;
      Aast.param_callconv = param.param_callconv;
      Aast.param_user_attributes = user_attributes;
      Aast.param_visibility = param.param_visibility;
    }
  in
  let mode = get_param_mode param.param_callconv in
  let id = Local_id.make_unscoped param.param_name in
  let env = Env.set_local env id ty1 param.param_pos in
  let env = Env.set_param env id (ty1, param.param_pos, mode) in
  let env =
    if has_accept_disposable_attribute param then
      Env.set_using_var env id
    else
      env
  in
  let env =
    match get_param_mutability param with
    | Some Param_borrowed_mutable ->
      Env.add_mutable_var
        env
        id
        (param.param_pos, Typing_mutability_env.Borrowed)
    | Some Param_owned_mutable ->
      Env.add_mutable_var env id (param.param_pos, Typing_mutability_env.Mutable)
    | Some Param_maybe_mutable ->
      Env.add_mutable_var
        env
        id
        (param.param_pos, Typing_mutability_env.MaybeMutable)
    | None ->
      Env.add_mutable_var
        env
        id
        (param.param_pos, Typing_mutability_env.Immutable)
  in
  (env, tparam)

and check_inout_return ret_pos env =
  let params = Local_id.Map.elements (Env.get_params env) in
  List.fold params ~init:env ~f:(fun env (id, (ty, param_pos, mode)) ->
      match mode with
      | FPinout ->
        (* Whenever the function exits normally, we require that each local
         * corresponding to an inout parameter be compatible with the original
         * type for the parameter (under subtyping rules). *)
        let (local_ty, local_pos) = Env.get_local_pos env id in
        let (env, ety) = Env.expand_type env local_ty in
        let pos =
          if not (Pos.equal Pos.none local_pos) then
            local_pos
          else if not (Pos.equal Pos.none ret_pos) then
            ret_pos
          else
            param_pos
        in
        let param_ty = mk (Reason.Rinout_param (get_pos ty), get_node ty) in
        Type.sub_type
          pos
          Reason.URassign_inout
          env
          ety
          param_ty
          Errors.inout_return_type_mismatch
      | _ -> env)

(*****************************************************************************)
(* function used to type closures, functions and methods *)
(*****************************************************************************)
and fun_ ?(abstract = false) ?(disable = false) env return pos named_body f_kind
    =
  Env.with_env env (fun env ->
      debug_last_pos := pos;
      let env = Env.set_return env return in
      let (env, tb) =
        if disable then
          let () =
            Errors.internal_error
              pos
              ( "Type inference for this function has been disabled by the "
              ^ SN.UserAttributes.uaDisableTypecheckerInternal
              ^ " attribute" )
          in
          block env []
        else
          block env named_body.fb_ast
      in
      Typing_sequencing.sequence_check_block named_body.fb_ast;
      let { Typing_env_return_info.return_type = ret; _ } =
        Env.get_return env
      in
      let env =
        if
          (not @@ LEnv.has_next env)
          || abstract
          || Nast.named_body_is_unsafe named_body
        then
          env
        else
          fun_implicit_return env pos ret.et_type f_kind
      in
      debug_last_pos := Pos.none;
      (env, tb))

and fun_implicit_return env pos ret = function
  | Ast_defs.FGenerator
  | Ast_defs.FAsyncGenerator ->
    env
  | Ast_defs.FSync ->
    (* A function without a terminal block has an implicit return; the
     * "void" type *)
    let env = check_inout_return Pos.none env in
    let r = Reason.Rno_return pos in
    let rty = MakeType.void r in
    Typing_return.implicit_return env pos ~expected:ret ~actual:rty
  | Ast_defs.FAsync ->
    (* An async function without a terminal block has an implicit return;
     * the Awaitable<void> type *)
    let r = Reason.Rno_return_async pos in
    let rty = MakeType.awaitable r (MakeType.void r) in
    Typing_return.implicit_return env pos ~expected:ret ~actual:rty

and block env stl =
  Typing_env.with_origin env Decl_counters.Body @@ fun env ->
  List.map_env env stl ~f:stmt

(* Set a local; must not be already assigned if it is a using variable *)
and set_local ?(is_using_clause = false) env (pos, x) ty =
  if Env.is_using_var env x then
    if is_using_clause then
      Errors.duplicate_using_var pos
    else
      Errors.illegal_disposable pos "assigned";
  let env = Env.set_local env x ty pos in
  if is_using_clause then
    Env.set_using_var env x
  else
    env

(* Check an individual component in the expression `e` in the
 * `using (e) { ... }` statement.
 * This consists of either
 *   a simple assignment `$x = e`, in which `$x` is the using variable, or
 *   an arbitrary expression `e`, in which case a temporary is the using
 *      variable, inaccessible in the source.
 * Return the typed expression and its type, and any variables that must
 * be designated as "using variables" for avoiding escapes.
 *)
and check_using_expr has_await env ((pos, content) as using_clause) =
  match content with
  (* Simple assignment to local of form `$lvar = e` *)
  | Binop (Ast_defs.Eq None, (lvar_pos, Lvar lvar), e) ->
    let (env, te, ty) = expr ~is_using_clause:true env e in
    let env =
      Typing_disposable.enforce_is_disposable_type env has_await (fst e) ty
    in
    let env = set_local ~is_using_clause:true env lvar ty in
    (* We are assigning a new value to the local variable, so we need to
     * generate a new expression id
     *)
    let env = Env.set_local_expr_id env (snd lvar) (Ident.tmp ()) in
    ( env,
      ( Tast.make_typed_expr
          pos
          ty
          (Aast.Binop
             ( Ast_defs.Eq None,
               Tast.make_typed_expr lvar_pos ty (Aast.Lvar lvar),
               te )),
        [snd lvar] ) )
  (* Arbitrary expression. This will be assigned to a temporary *)
  | _ ->
    let (env, typed_using_clause, ty) =
      expr ~is_using_clause:true env using_clause
    in
    let env =
      Typing_disposable.enforce_is_disposable_type env has_await pos ty
    in
    (env, (typed_using_clause, []))

(* Check the using clause e in
 * `using (e) { ... }` statement (`has_await = false`) or
 * `await using (e) { ... }` statement (`has_await = true`).
 * `using_clauses` is a list of expressions.
 * Return the typed expression, and any variables that must
 * be designated as "using variables" for avoiding escapes.
 *)
and check_using_clause env has_await using_clauses =
  let (env, pairs) =
    List.map_env env using_clauses (check_using_expr has_await)
  in
  let (typed_using_clauses, vars) = List.unzip pairs in
  (env, typed_using_clauses, List.concat vars)

(* Require a new construct with disposable *)
and enforce_return_disposable _env e =
  match e with
  | (_, New _) -> ()
  | (_, Call _) -> ()
  | (_, Await (_, Call _)) -> ()
  | (p, _) -> Errors.invalid_return_disposable p

(* Wrappers around the function with the same name in Typing_lenv, which only
 * performs the move/save and merge operation if we are in a try block or in a
 * function with return type 'noreturn'.
 * This enables significant perf improvement, because this is called at every
 * function of method call, when most calls are outside of a try block. *)
and move_and_merge_next_in_catch env =
  if env.in_try || TFTerm.is_noreturn env then
    LEnv.move_and_merge_next_in_cont env C.Catch
  else
    LEnv.drop_cont env C.Next

and save_and_merge_next_in_catch env =
  if env.in_try || TFTerm.is_noreturn env then
    LEnv.save_and_merge_next_in_cont env C.Catch
  else
    env

and might_throw env = save_and_merge_next_in_catch env

and stmt env (pos, st) =
  let (env, st) = stmt_ env pos st in
  Typing_debug.log_env_if_too_big pos env;
  (env, (pos, st))

and stmt_ env pos st =
  (* Type check a loop. f env = (env, result) checks the body of the loop.
   * We iterate over the loop until the "next" continuation environment is
   * stable. alias_depth is supposed to be an upper bound on this; but in
   * certain cases this fails (e.g. a generic type grows unboundedly). TODO:
   * fix this.
   *)
  let infer_loop env f =
    let in_loop_outer = env.in_loop in
    let alias_depth =
      if in_loop_outer then
        1
      else
        Typing_alias.get_depth (pos, st)
    in
    let env = { env with in_loop = true } in
    let rec loop env n =
      (* Remember the old environment *)
      let old_next_entry = Env.next_cont_opt env in
      let (env, result) = f env in
      let new_next_entry = Env.next_cont_opt env in
      (* Finish if we reach the bound, or if the environments match *)
      if
        Int.equal n alias_depth
        || Typing_per_cont_ops.is_sub_opt_entry
             Typing_subtype.is_sub_type
             env
             new_next_entry
             old_next_entry
      then
        let env = { env with in_loop = in_loop_outer } in
        (env, result)
      else
        loop env (n + 1)
    in
    loop env 1
  in
  let env = Env.open_tyvars env pos in
  (fun (env, tb) ->
    (Typing_solver.close_tyvars_and_solve env Errors.unify_error, tb))
  @@
  match st with
  | Fallthrough ->
    let env =
      if env.in_case then
        LEnv.move_and_merge_next_in_cont env C.Fallthrough
      else
        env
    in
    (env, Aast.Fallthrough)
  | Noop -> (env, Aast.Noop)
  | AssertEnv _ -> (env, Aast.Noop)
  | Expr e ->
    let (env, te, _) = expr env e in
    let env =
      if TFTerm.typed_expression_exits te then
        LEnv.move_and_merge_next_in_cont env C.Exit
      else
        env
    in
    (env, Aast.Expr te)
  | If (e, b1, b2) ->
    let assert_refinement_env =
      assert_env_blk ~pos ~at:`Start Aast.Refinement
    in
    let (env, te, _) = expr env e in
    let (env, tb1, tb2) =
      branch
        env
        (fun env ->
          let (env, lset) = condition env true te in
          let refinement_map = refinement_annot_map env lset in
          let (env, b1) = block env b1 in
          let b1 = assert_refinement_env refinement_map b1 in
          (env, b1))
        (fun env ->
          let (env, lset) = condition env false te in
          let refinement_map = refinement_annot_map env lset in
          let (env, b2) = block env b2 in
          let b2 = assert_refinement_env refinement_map b2 in
          (env, b2))
    in
    (* TODO TAST: annotate with joined types *)
    (env, Aast.If (te, tb1, tb2))
  | Return None ->
    let env = check_inout_return pos env in
    let rty = MakeType.void (Reason.Rwitness pos) in
    let { Typing_env_return_info.return_type = expected_return; _ } =
      Env.get_return env
    in
    let expected_return =
      Typing_return.strip_awaitable (Env.get_fn_kind env) env expected_return
    in
    let env =
      match Env.get_fn_kind env with
      | Ast_defs.FGenerator
      | Ast_defs.FAsyncGenerator ->
        env
      | _ ->
        Typing_return.implicit_return
          env
          pos
          ~expected:expected_return.et_type
          ~actual:rty
    in
    let env = LEnv.move_and_merge_next_in_cont env C.Exit in
    (env, Aast.Return None)
  | Return (Some e) ->
    let env = check_inout_return pos env in
    let expr_pos = fst e in
    let Typing_env_return_info.
          {
            return_type;
            return_disposable;
            return_mutable;
            return_explicit;
            return_void_to_rx;
            return_dynamically_callable = _;
          } =
      Env.get_return env
    in
    let return_type =
      Typing_return.strip_awaitable (Env.get_fn_kind env) env return_type
    in
    let expected =
      if return_explicit then
        Some
          (ExpectedTy.make_and_allow_coercion
             expr_pos
             Reason.URreturn
             return_type)
      else
        None
    in
    if return_disposable then enforce_return_disposable env e;
    let (env, te, rty) =
      expr ~is_using_clause:return_disposable ?expected env e
    in
    let env =
      if not (equal_reactivity (env_reactivity env) Nonreactive) then
        Typing_mutability.handle_value_in_return
          ~function_returns_mutable:return_mutable
          ~function_returns_void_for_rx:return_void_to_rx
          env
          env.function_pos
          te
      else
        env
    in
    let return_type =
      {
        return_type with
        et_type = TR.strip_condition_type_in_return env return_type.et_type;
      }
    in
    (* This is a unify_error rather than a return_type_mismatch because the return
     * statement is the problem, not the return type itself. *)
    let env =
      Typing_coercion.coerce_type
        expr_pos
        Reason.URreturn
        env
        rty
        return_type
        Errors.unify_error
    in
    let env = LEnv.move_and_merge_next_in_cont env C.Exit in
    (env, Aast.Return (Some te))
  | Do (b, e) ->
    (* NOTE: leaks scope as currently implemented; this matches
       the behavior in naming (cf. `do_stmt` in naming/naming.ml).
     *)
    let (env, (tb, te)) =
      LEnv.stash_and_do env [C.Continue; C.Break; C.Do] (fun env ->
          let env = LEnv.save_and_merge_next_in_cont env C.Do in
          let (env, _) = block env b in
          (* saving the locals in continue here even if there is no continue
           * statement because they must be merged at the end of the loop, in
           * case there is no iteration *)
          let env = LEnv.save_and_merge_next_in_cont env C.Continue in
          let (env, tb) =
            infer_loop env (fun env ->
                let env =
                  LEnv.update_next_from_conts env [C.Continue; C.Next]
                in
                (* The following is necessary in case there is an assignment in the
                 * expression *)
                let (env, te, _) = expr env e in
                let (env, _lset) = condition env true te in
                let env = LEnv.update_next_from_conts env [C.Do; C.Next] in
                let (env, tb) = block env b in
                (env, tb))
          in
          let env = LEnv.update_next_from_conts env [C.Continue; C.Next] in
          let (env, te, _) = expr env e in
          let (env, _lset) = condition env false te in
          let env = LEnv.update_next_from_conts env [C.Break; C.Next] in
          (env, (tb, te)))
    in
    (env, Aast.Do (tb, te))
  | While (e, b) ->
    let (env, (te, tb, refinement_map)) =
      LEnv.stash_and_do env [C.Continue; C.Break] (fun env ->
          let env = LEnv.save_and_merge_next_in_cont env C.Continue in
          let (env, tb) =
            infer_loop env (fun env ->
                let env =
                  LEnv.update_next_from_conts env [C.Continue; C.Next]
                in
                let join_map = annot_map env in
                (* The following is necessary in case there is an assignment in the
                 * expression *)
                let (env, te, _) = expr env e in
                let (env, lset) = condition env true te in
                let refinement_map = refinement_annot_map env lset in
                (* TODO TAST: avoid repeated generation of block *)
                let (env, tb) = block env b in

                (* Annotate loop body with join and refined environments *)
                let assert_env_blk = assert_env_blk ~pos ~at:`Start in
                let tb = assert_env_blk Aast.Refinement refinement_map tb in
                let tb = assert_env_blk Aast.Join join_map tb in

                (env, tb))
          in
          let env = LEnv.update_next_from_conts env [C.Continue; C.Next] in
          let (env, te, _) = expr env e in
          let (env, lset) = condition env false te in
          let refinement_map_at_exit = refinement_annot_map env lset in
          let env = LEnv.update_next_from_conts env [C.Break; C.Next] in
          (env, (te, tb, refinement_map_at_exit)))
    in
    let while_st = Aast.While (te, tb) in
    (* Export the refined environment after the exit condition holds *)
    let while_st =
      assert_env_stmt ~pos ~at:`End Aast.Refinement refinement_map while_st
    in
    (env, while_st)
  | Using
      {
        us_has_await = has_await;
        us_exprs = (loc, using_clause);
        us_block = using_block;
        us_is_block_scoped;
      } ->
    let (env, typed_using_clause, using_vars) =
      check_using_clause env has_await using_clause
    in
    let (env, typed_using_block) = block env using_block in
    (* Remove any using variables from the environment, as they should not
     * be in scope outside the block *)
    let env = List.fold_left using_vars ~init:env ~f:Env.unset_local in
    ( env,
      Aast.Using
        Aast.
          {
            us_has_await = has_await;
            us_exprs = (loc, typed_using_clause);
            us_block = typed_using_block;
            us_is_block_scoped;
          } )
  | For (e1, e2, e3, b) ->
    let e2 =
      match e2 with
      | Some e2 -> e2
      | None -> (Pos.none, True)
    in
    let (env, (te1, te2, te3, tb, refinement_map)) =
      LEnv.stash_and_do env [C.Continue; C.Break] (fun env ->
          (* For loops leak their initalizer, but nothing that's defined in the
           body
         *)
          let (env, te1, _) = exprs env e1 in
          (* initializer *)
          let env = LEnv.save_and_merge_next_in_cont env C.Continue in
          let (env, (tb, te3)) =
            infer_loop env (fun env ->
                (* The following is necessary in case there is an assignment in the
                 * expression *)
                let (env, te2, _) = expr env e2 in
                let (env, lset) = condition env true te2 in
                let refinement_map = refinement_annot_map env lset in
                let (env, tb) = block env b in
                let env =
                  LEnv.update_next_from_conts env [C.Continue; C.Next]
                in
                let join_map = annot_map env in
                let (env, te3, _) = exprs env e3 in

                (* Export the join and refinement environments *)
                let assert_env_blk = assert_env_blk ~pos ~at:`Start in
                let tb = assert_env_blk Aast.Refinement refinement_map tb in
                let tb = assert_env_blk Aast.Join join_map tb in

                (env, (tb, te3)))
          in
          let env = LEnv.update_next_from_conts env [C.Continue; C.Next] in
          let (env, te2, _) = expr env e2 in
          let (env, lset) = condition env false te2 in
          let refinement_map_at_exit = refinement_annot_map env lset in
          let env = LEnv.update_next_from_conts env [C.Break; C.Next] in
          (env, (te1, te2, te3, tb, refinement_map_at_exit)))
    in
    let for_st = Aast.For (te1, Some te2, te3, tb) in
    let for_st =
      assert_env_stmt ~pos ~at:`End Aast.Refinement refinement_map for_st
    in
    (env, for_st)
  | Switch (((pos, _) as e), cl) ->
    let (env, te, ty) = expr env e in
    (* NB: A 'continue' inside a 'switch' block is equivalent to a 'break'.
     * See the note in
     * http://php.net/manual/en/control-structures.continue.php *)
    let (env, (te, tcl)) =
      LEnv.stash_and_do env [C.Continue; C.Break] (fun env ->
          let parent_locals = LEnv.get_all_locals env in
          let case_list env = case_list parent_locals ty env pos cl in
          let (env, tcl) = Env.in_case env case_list in
          let env =
            LEnv.update_next_from_conts env [C.Continue; C.Break; C.Next]
          in
          (env, (te, tcl)))
    in
    (env, Aast.Switch (te, tcl))
  | Foreach (e1, e2, b) ->
    (* It's safe to do foreach over a disposable, as no leaking is possible *)
    let (env, te1, ty1) = expr ~accept_using_var:true env e1 in
    let (env, (te1, te2, tb)) =
      LEnv.stash_and_do env [C.Continue; C.Break] (fun env ->
          let env = LEnv.save_and_merge_next_in_cont env C.Continue in
          let (env, tk, tv) = as_expr env ty1 (fst e1) e2 in
          let (env, (te2, tb)) =
            infer_loop env (fun env ->
                let env =
                  LEnv.update_next_from_conts env [C.Continue; C.Next]
                in
                let join_map = annot_map env in
                let (env, te2) = bind_as_expr env (fst e1) tk tv e2 in
                let (env, tb) = block env b in
                (* Export the join environment *)
                let tb = assert_env_blk ~pos ~at:`Start Aast.Join join_map tb in
                (env, (te2, tb)))
          in
          let env =
            LEnv.update_next_from_conts env [C.Continue; C.Break; C.Next]
          in
          (env, (te1, te2, tb)))
    in
    (env, Aast.Foreach (te1, te2, tb))
  | Try (tb, cl, fb) ->
    let (env, ttb, tcl, tfb) = try_catch env tb cl fb in
    (env, Aast.Try (ttb, tcl, tfb))
  | Awaitall (el, b) ->
    let env = might_throw env in
    let (env, el) =
      List.fold_left el ~init:(env, []) ~f:(fun (env, tel) (e1, e2) ->
          let (env, te2, ty2) = expr env e2 in
          let (env, ty2) =
            Async.overload_extract_from_awaitable env (fst e2) ty2
          in
          match e1 with
          | Some e1 ->
            let (env, _, _) = assign (fst e1) env (fst e1, Lvar e1) ty2 in
            (env, (Some e1, te2) :: tel)
          | None -> (env, (None, te2) :: tel))
    in
    let (env, b) = block env b in
    (env, Aast.Awaitall (el, b))
  | Throw e ->
    let p = fst e in
    let (env, te, ty) = expr env e in
    let env = coerce_to_throwable p env ty in
    let env = move_and_merge_next_in_catch env in
    (env, Aast.Throw te)
  | Continue ->
    let env = LEnv.move_and_merge_next_in_cont env C.Continue in
    (env, Aast.Continue)
  | Break ->
    let env = LEnv.move_and_merge_next_in_cont env C.Break in
    (env, Aast.Break)
  | Block _
  | Markup _ ->
    failwith
      "Unexpected nodes in AST. These nodes should have been removed in naming."

and branch :
    type res. env -> (env -> env * res) -> (env -> env * res) -> env * res * res
    =
 fun env branch1 branch2 ->
  let parent_lenv = env.lenv in
  let (env, tbr1) = branch1 env in
  let lenv1 = env.lenv in
  let env = { env with lenv = parent_lenv } in
  let (env, tbr2) = branch2 env in
  let lenv2 = env.lenv in
  let env = LEnv.union_lenvs env parent_lenv lenv1 lenv2 in
  (env, tbr1, tbr2)

and finally_cont fb env ctx =
  (* The only locals in scope are the ones from the current continuation *)
  let env = Env.env_with_locals env @@ CMap.singleton C.Next ctx in
  let (env, _tfb) = block env fb in
  (env, LEnv.get_all_locals env)

and finally env fb =
  match fb with
  | [] ->
    let env = LEnv.update_next_from_conts env [C.Next; C.Finally] in
    (env, [])
  | _ ->
    let parent_locals = LEnv.get_all_locals env in
    (* First typecheck the finally block against all continuations merged
    * together.
    * During this phase, record errors found in the finally block, but discard
    * the resulting environment. *)
    let all_conts = Env.all_continuations env in
    let env = LEnv.update_next_from_conts env all_conts in
    let (env, tfb) = block env fb in
    let env = LEnv.restore_conts_from env parent_locals all_conts in
    (* Second, typecheck the finally block once against each continuation. This
    * helps be more clever about what each continuation will be after the
    * finally block.
    * We don't want to record errors during this phase, because certain types
    * of errors will fire wrongly. For example, if $x is nullable in some
    * continuations but not in others, then we must use `?->` on $x, but an
    * error will fire when typechecking the finally block againts continuations
    * where $x is non-null.  *)
    let finally_cont env _key = finally_cont fb env in
    let (env, locals_map) =
      Errors.ignore_ (fun () -> CMap.map_env finally_cont env parent_locals)
    in
    let union env _key = LEnv.union_contextopts env in
    let (env, locals) = Try.finally_merge union env locals_map all_conts in
    (Env.env_with_locals env locals, tfb)

and try_catch env tb cl fb =
  let parent_locals = LEnv.get_all_locals env in
  let env =
    LEnv.drop_conts env [C.Break; C.Continue; C.Exit; C.Catch; C.Finally]
  in
  let (env, (ttb, tcb)) =
    Env.in_try env (fun env ->
        let (env, ttb) = block env tb in
        let env = LEnv.move_and_merge_next_in_cont env C.Finally in
        let catchctx = LEnv.get_cont_option env C.Catch in
        let (env, lenvtcblist) = List.map_env env ~f:(catch catchctx) cl in
        let (lenvl, tcb) = List.unzip lenvtcblist in
        let env = LEnv.union_lenv_list env env.lenv lenvl in
        let env = LEnv.move_and_merge_next_in_cont env C.Finally in
        (env, (ttb, tcb)))
  in
  let (env, tfb) = finally env fb in
  let env = LEnv.update_next_from_conts env [C.Finally] in
  let env = LEnv.drop_cont env C.Finally in
  let env =
    LEnv.restore_and_merge_conts_from
      env
      parent_locals
      [C.Break; C.Continue; C.Exit; C.Catch; C.Finally]
  in
  (env, ttb, tcb, tfb)

and case_list parent_locals ty env switch_pos cl =
  let initialize_next_cont env =
    let env = LEnv.restore_conts_from env parent_locals [C.Next] in
    let env = LEnv.update_next_from_conts env [C.Next; C.Fallthrough] in
    LEnv.drop_cont env C.Fallthrough
  in
  let check_fallthrough env switch_pos case_pos block rest_of_list ~is_default =
    if not @@ List.is_empty block then
      match rest_of_list with
      | []
      | [Default (_, [])] ->
        ()
      | _ ->
        begin
          match LEnv.get_cont_option env C.Next with
          | Some _ ->
            if is_default then
              Errors.default_fallthrough switch_pos
            else
              Errors.case_fallthrough switch_pos case_pos
          | None -> ()
        end
    (* match *)
    (* match *)
    else
      ()
  in
  let make_exhaustive_equivalent_case_list env cl =
    let has_default =
      List.exists cl ~f:(function
          | Default _ -> true
          | _ -> false)
    in
    let (env, ty) =
      (* If it hasn't got a default clause then we need to solve type variables
       * in order to check for an enum *)
      if has_default then
        Env.expand_type env ty
      else
        Typing_solver.expand_type_and_solve
          env
          ~description_of_expected:"a value"
          switch_pos
          ty
          Errors.unify_error
    in
    let is_enum =
      let top_type =
        MakeType.class_type
          Reason.Rnone
          SN.Classes.cHH_BuiltinEnum
          [MakeType.mixed Reason.Rnone]
      in
      Typing_subtype.is_sub_type_for_coercion env ty top_type
    in
    (* If there is no default case and this is not a switch on enum (since
     * exhaustiveness is garanteed elsewhere on enums),
     * then add a default case for control flow correctness
     *)
    if has_default || is_enum then
      (env, cl, false)
    else
      (env, cl @ [Default (Pos.none, [])], true)
  in
  let rec case_list env = function
    | [] -> (env, [])
    | Default (pos, b) :: rl ->
      let env = initialize_next_cont env in
      let (env, tb) = block env b in
      check_fallthrough env switch_pos pos b rl ~is_default:true;
      let (env, tcl) = case_list env rl in
      (env, Aast.Default (pos, tb) :: tcl)
    | Case (((pos, _) as e), b) :: rl ->
      let env = initialize_next_cont env in
      let (env, te, _) = expr env e in
      let (env, tb) = block env b in
      check_fallthrough env switch_pos pos b rl ~is_default:false;
      let (env, tcl) = case_list env rl in
      (env, Aast.Case (te, tb) :: tcl)
  in
  let (env, cl, added_empty_default) =
    make_exhaustive_equivalent_case_list env cl
  in
  let (env, tcl) = case_list env cl in
  let tcl =
    if added_empty_default then
      List.take tcl (List.length tcl - 1)
    else
      tcl
  in
  (env, tcl)

and catch catchctx env (sid, exn_lvar, b) =
  let env = LEnv.replace_cont env C.Next catchctx in
  let cid = CI sid in
  let ety_p = fst sid in
  let (env, _, _, _) = instantiable_cid ety_p env cid [] in
  let (env, _tal, _te, ety) =
    static_class_id ~check_constraints:false ety_p env [] cid
  in
  let env = coerce_to_throwable ety_p env ety in
  let env = set_local env exn_lvar ety in
  let (env, tb) = block env b in
  (env, (env.lenv, (sid, exn_lvar, tb)))

and as_expr env ty1 pe e =
  let env = Env.open_tyvars env pe in
  let (env, tv) = Env.fresh_type env pe in
  let (env, expected_ty, tk, tv) =
    match e with
    | As_v _ ->
      let tk = MakeType.mixed Reason.Rnone in
      (env, MakeType.traversable (Reason.Rforeach pe) tv, tk, tv)
    | As_kv _ ->
      let (env, tk) = Env.fresh_type env pe in
      (env, MakeType.keyed_traversable (Reason.Rforeach pe) tk tv, tk, tv)
    | Await_as_v _ ->
      let tk = MakeType.mixed Reason.Rnone in
      (env, MakeType.async_iterator (Reason.Rasyncforeach pe) tv, tk, tv)
    | Await_as_kv _ ->
      let (env, tk) = Env.fresh_type env pe in
      ( env,
        MakeType.async_keyed_iterator (Reason.Rasyncforeach pe) tk tv,
        tk,
        tv )
  in
  let rec distribute_union env ty =
    let (env, ty) = Env.expand_type env ty in
    match get_node ty with
    | Tunion tyl -> List.fold tyl ~init:env ~f:distribute_union
    | _ ->
      if SubType.is_sub_type_for_union env ty (MakeType.dynamic Reason.Rnone)
      then
        let env = SubType.sub_type env ty tk Errors.unify_error in
        let env = SubType.sub_type env ty tv Errors.unify_error in
        env
      else
        let ur = Reason.URforeach in
        Type.sub_type pe ur env ty expected_ty Errors.unify_error
  in
  let env = distribute_union env ty1 in
  let env = Env.set_tyvar_variance env expected_ty in
  (Typing_solver.close_tyvars_and_solve env Errors.unify_error, tk, tv)

and bind_as_expr env p ty1 ty2 aexpr =
  let check_reassigned_mutable env te =
    if Env.env_local_reactive env then
      Typing_mutability.handle_assignment_mutability env te None
    else
      env
  in
  match aexpr with
  | As_v ev ->
    let (env, te, _) = assign p env ev ty2 in
    let env = check_reassigned_mutable env te in
    (env, Aast.As_v te)
  | Await_as_v (p, ev) ->
    let (env, te, _) = assign p env ev ty2 in
    let env = check_reassigned_mutable env te in
    (env, Aast.Await_as_v (p, te))
  | As_kv ((p, Lvar ((_, k) as id)), ev) ->
    let env = set_valid_rvalue p env k ty1 in
    let (env, te, _) = assign p env ev ty2 in
    let tk = Tast.make_typed_expr p ty1 (Aast.Lvar id) in
    let env = check_reassigned_mutable env tk in
    let env = check_reassigned_mutable env te in
    (env, Aast.As_kv (tk, te))
  | Await_as_kv (p, (p1, Lvar ((_, k) as id)), ev) ->
    let env = set_valid_rvalue p env k ty1 in
    let (env, te, _) = assign p env ev ty2 in
    let tk = Tast.make_typed_expr p1 ty1 (Aast.Lvar id) in
    let env = check_reassigned_mutable env tk in
    let env = check_reassigned_mutable env te in
    (env, Aast.Await_as_kv (p, tk, te))
  | _ ->
    (* TODO Probably impossible, should check that *)
    assert false

and expr
    ?(expected : ExpectedTy.t option)
    ?(accept_using_var = false)
    ?(is_using_clause = false)
    ?(valkind = `other)
    ?(check_defined = true)
    ?in_await
    env
    ((p, _) as e) =
  try
    begin
      match expected with
      | None -> ()
      | Some ExpectedTy.{ reason = r; ty = { et_type = ty; _ }; _ } ->
        Typing_log.(
          log_with_level env "typing" 1 (fun () ->
              log_types
                p
                env
                [
                  Log_head
                    ( "Typing.expr " ^ Typing_reason.string_of_ureason r,
                      [Log_type ("expected_ty", ty)] );
                ]))
    end;
    raw_expr
      ~accept_using_var
      ~is_using_clause
      ~valkind
      ~check_defined
      ?in_await
      ?expected
      env
      e
  with Inf.InconsistentTypeVarState _ as e ->
    (* we don't want to catch unwanted exceptions here, eg Timeouts *)
    Errors.exception_occurred p (Exception.wrap e);
    make_result env p Aast.Any @@ err_witness env p

and raw_expr
    ?(accept_using_var = false)
    ?(is_using_clause = false)
    ?(expected : ExpectedTy.t option)
    ?lhs_of_null_coalesce
    ?(valkind = `other)
    ?(check_defined = true)
    ?in_await
    env
    e =
  debug_last_pos := fst e;
  expr_
    ~accept_using_var
    ~is_using_clause
    ?expected
    ?lhs_of_null_coalesce
    ?in_await
    ~valkind
    ~check_defined
    env
    e

and lvalue env e =
  let valkind = `lvalue in
  expr_ ~valkind ~check_defined:false env e

and lvalues env el =
  match el with
  | [] -> (env, [], [])
  | e :: el ->
    let (env, te, ty) = lvalue env e in
    let (env, tel, tyl) = lvalues env el in
    (env, te :: tel, ty :: tyl)

and is_pseudo_function s =
  String.equal s SN.PseudoFunctions.hh_show
  || String.equal s SN.PseudoFunctions.hh_show_env
  || String.equal s SN.PseudoFunctions.hh_log_level
  || String.equal s SN.PseudoFunctions.hh_force_solve
  || String.equal s SN.PseudoFunctions.hh_loop_forever

and loop_forever env =
  (* forever = up to 10 minutes, to avoid accidentally stuck processes *)
  for i = 1 to 600 do
    (* Look up things in shared memory occasionally to have a chance to be
     * interrupted *)
    match Env.get_class env "FOR_TEST_ONLY" with
    | None -> Unix.sleep 1
    | _ -> assert false
  done;
  Utils.assert_false_log_backtrace
    (Some "hh_loop_forever was looping for more than 10 minutes")

(* $x ?? 0 is handled similarly to $x ?: 0, except that the latter will also
 * look for sketchy null checks in the condition. *)
(* TODO TAST: type refinement should be made explicit in the typed AST *)
and eif env ~(expected : ExpectedTy.t option) ?in_await p c e1 e2 =
  let condition = condition ~lhs_of_null_coalesce:false in
  let (env, tc, tyc) = raw_expr ~lhs_of_null_coalesce:false env c in
  let parent_lenv = env.lenv in
  let (env, _lset) = condition env true tc in
  let (env, te1, ty1) =
    match e1 with
    | None ->
      let (env, ty) = Typing_solver.non_null env p tyc in
      (env, None, ty)
    | Some e1 ->
      let (env, te1, ty1) = expr ?expected ?in_await env e1 in
      (env, Some te1, ty1)
  in
  let lenv1 = env.lenv in
  let env = { env with lenv = parent_lenv } in
  let (env, _lset) = condition env false tc in
  let (env, te2, ty2) = expr ?expected ?in_await env e2 in
  let lenv2 = env.lenv in
  let env = LEnv.union_lenvs env parent_lenv lenv1 lenv2 in
  let (env, ty) = Union.union env ty1 ty2 in
  make_result env p (Aast.Eif (tc, te1, te2)) ty

and is_parameter env x = Local_id.Map.mem x (Env.get_params env)

and check_escaping_var env (pos, x) =
  if Env.is_using_var env x then
    if Local_id.equal x this then
      Errors.escaping_this pos
    else if is_parameter env x then
      Errors.escaping_disposable_parameter pos
    else
      Errors.escaping_disposable pos
  else
    ()

and exprs
    ?(accept_using_var = false)
    ?(expected : ExpectedTy.t option)
    ?(valkind = `other)
    ?(check_defined = true)
    env
    el =
  match el with
  | [] -> (env, [], [])
  | e :: el ->
    let (env, te, ty) =
      expr ~accept_using_var ?expected ~valkind ~check_defined env e
    in
    let (env, tel, tyl) =
      exprs ~accept_using_var ?expected ~valkind ~check_defined env el
    in
    (env, te :: tel, ty :: tyl)

and exprs_expected (pos, ur, expected_tyl) env el =
  match (el, expected_tyl) with
  | ([], _) -> (env, [], [])
  | (e :: el, expected_ty :: expected_tyl) ->
    let expected = ExpectedTy.make pos ur expected_ty in
    let (env, te, ty) = expr ~expected env e in
    let (env, tel, tyl) = exprs_expected (pos, ur, expected_tyl) env el in
    (env, te :: tel, ty :: tyl)
  | (el, []) -> exprs env el

and make_result env p te ty =
  (* Set the variance of any type variables that were generated according
   * to how they appear in the expression type *)
  let env = Env.set_tyvar_variance env ty in
  (env, Tast.make_typed_expr p ty te, ty)

and localize_targ env ta =
  let pos = fst ta in
  let (env, targ) = Phase.localize_targ ~check_well_kinded:true env ta in
  (env, targ, ExpectedTy.make pos Reason.URhint (fst targ))

and set_function_pointer ty =
  match get_node ty with
  | Tfun ft ->
    let ft = set_ft_is_function_pointer ft true in
    mk (get_reason ty, Tfun ft)
  | _ -> ty

and expr_
    ?(expected : ExpectedTy.t option)
    ?(accept_using_var = false)
    ?(is_using_clause = false)
    ?lhs_of_null_coalesce
    ?in_await
    ~(valkind : [> `lvalue | `lvalue_subexpr | `other ])
    ~check_defined
    env
    ((p, e) as outer) =
  let env = Env.open_tyvars env p in
  (fun (env, te, ty) ->
    let env = Typing_solver.close_tyvars_and_solve env Errors.unify_error in
    (env, te, ty))
  @@
  let expr = expr ~check_defined in
  let exprs = exprs ~check_defined in
  let raw_expr = raw_expr ~check_defined in
  (*
   * Given a list of types, computes their supertype. If any of the types are
   * unknown (e.g., comes from PHP), the supertype will be Typing_utils.tany env.
   *)
  let compute_supertype
      ~(expected : ExpectedTy.t option) ~reason ~use_pos r env tys =
    let (env, supertype) =
      match expected with
      | None -> Env.fresh_type_reason env r
      | Some ExpectedTy.{ ty = { et_type = ty; _ }; _ } -> (env, ty)
    in
    match get_node supertype with
    (* No need to check individual subtypes if expected type is mixed or any! *)
    | Tany _ -> (env, supertype)
    | _ ->
      let subtype_value env ty =
        Type.sub_type use_pos reason env ty supertype Errors.unify_error
      in
      let env = List.fold_left tys ~init:env ~f:subtype_value in
      if
        List.exists tys (fun ty ->
            equal_locl_ty_ (get_node ty) (Typing_utils.tany env))
      then
        (* If one of the values comes from PHP land, we have to be conservative
         * and consider that we don't know what the type of the values are. *)
        (env, Typing_utils.mk_tany env p)
      else
        (env, supertype)
  in
  (*
   * Given a 'a list and a method to extract an expr and its ty from a 'a, this
   * function extracts a list of exprs from the list, and computes the supertype
   * of all of the expressions' tys.
   *)
  let compute_exprs_and_supertype
      ~(expected : ExpectedTy.t option)
      ?(reason = Reason.URarray_value)
      ~use_pos
      r
      env
      l
      extract_expr_and_ty =
    let (env, exprs_and_tys) =
      List.map_env env l (extract_expr_and_ty ~expected)
    in
    let (exprs, tys) = List.unzip exprs_and_tys in
    let (env, supertype) =
      compute_supertype ~expected ~reason ~use_pos r env tys
    in
    (env, exprs, supertype)
  in
  let forget_fake_members env p callexpr =
    (* Some functions are well known to not change the types of members, e.g.
     * `is_null`.
     * There are a lot of usages like
     *   if (!is_null($x->a) && !is_null($x->a->b))
     * where the second is_null call invalidates the first condition.
     * This function is a bit best effort. Add stuff here when you want
     * To avoid adding too many undue HH_FIXMEs. *)
    match callexpr with
    | (_, Id (_, func))
      when String.equal func SN.StdlibFunctions.is_null
           || String.equal func SN.PseudoFunctions.isset ->
      env
    | _ -> Env.forget_members env Reason.(Blame (p, BScall))
  in
  let check_call
      ~is_using_clause
      ~(expected : ExpectedTy.t option)
      ?in_await
      env
      p
      e
      explicit_targs
      el
      unpacked_element =
    let (env, te, result) =
      dispatch_call
        ~is_using_clause
        ~expected
        ?in_await
        p
        env
        e
        explicit_targs
        el
        unpacked_element
    in
    let env = forget_fake_members env p e in
    (env, te, result)
  in
  match e with
  | Import _
  | Collection _ ->
    failwith "AST should not contain these nodes"
  | Omitted ->
    let ty = Typing_utils.mk_tany env p in
    make_result env p Aast.Omitted ty
  | Any -> expr_error env (Reason.Rwitness p) outer
  | Varray (th, el)
  | ValCollection (_, th, el) ->
    let (get_expected_kind, name, subtype_val, make_expr, make_ty) =
      match e with
      | ValCollection (kind, _, _) ->
        let class_name = Nast.vc_kind_to_name kind in
        let subtype_val =
          match kind with
          | Set
          | ImmSet
          | Keyset ->
            arraykey_value p class_name
          | Vector
          | ImmVector
          | Vec ->
            array_value
        in
        ( get_vc_inst kind,
          class_name,
          subtype_val,
          (fun th elements -> Aast.ValCollection (kind, th, elements)),
          fun value_ty ->
            MakeType.class_type (Reason.Rwitness p) class_name [value_ty] )
      | Varray _ ->
        ( get_varray_inst,
          "varray",
          array_value,
          (fun th elements -> Aast.Varray (th, elements)),
          (fun value_ty -> MakeType.varray (Reason.Rwitness p) value_ty) )
      | _ ->
        (* The parent match makes this case impossible *)
        failwith "impossible match case"
    in
    (* Use expected type to determine expected element type *)
    let (env, elem_expected, th) =
      match th with
      | Some (_, tv) ->
        let (env, tv, tv_expected) = localize_targ env tv in
        (env, Some tv_expected, Some tv)
      | _ ->
        begin
          match expand_expected_and_get_node env expected with
          | (env, Some (pos, ur, ety, _)) ->
            begin
              match get_expected_kind ety with
              | Some vty -> (env, Some (ExpectedTy.make pos ur vty), None)
              | None -> (env, None, None)
            end
          | _ -> (env, None, None)
        end
    in
    let (env, tel, elem_ty) =
      compute_exprs_and_supertype
        ~expected:elem_expected
        ~use_pos:p
        ~reason:Reason.URvector
        (Reason.Rtype_variable_generics (p, "T", strip_ns name))
        env
        el
        subtype_val
    in
    make_result env p (make_expr th tel) (make_ty elem_ty)
  | Darray (th, l)
  | KeyValCollection (_, th, l) ->
    let (get_expected_kind, name, make_expr, make_ty) =
      match e with
      | KeyValCollection (kind, _, _) ->
        let class_name = Nast.kvc_kind_to_name kind in
        ( get_kvc_inst p kind,
          class_name,
          (fun th pairs -> Aast.KeyValCollection (kind, th, pairs)),
          (fun k v -> MakeType.class_type (Reason.Rwitness p) class_name [k; v])
        )
      | Darray _ ->
        ( get_darray_inst p,
          "darray",
          (fun th pairs -> Aast.Darray (th, pairs)),
          (fun k v -> MakeType.darray (Reason.Rwitness p) k v) )
      | _ ->
        (* The parent match makes this case impossible *)
        failwith "impossible match case"
    in
    (* Use expected type to determine expected key and value types *)
    let (env, kexpected, vexpected, th) =
      match th with
      | Some ((_, tk), (_, tv)) ->
        let (env, tk, tk_expected) = localize_targ env tk in
        let (env, tv, tv_expected) = localize_targ env tv in
        (env, Some tk_expected, Some tv_expected, Some (tk, tv))
      | _ ->
        (* no explicit typehint, fallback to supplied expect *)
        begin
          match expand_expected_and_get_node env expected with
          | (env, Some (pos, reason, ety, _)) ->
            begin
              match get_expected_kind ety with
              | Some (kty, vty) ->
                let k_expected = ExpectedTy.make pos reason kty in
                let v_expected = ExpectedTy.make pos reason vty in
                (env, Some k_expected, Some v_expected, None)
              | None -> (env, None, None, None)
            end
          | _ -> (env, None, None, None)
        end
    in
    let (kl, vl) = List.unzip l in
    let (env, tkl, k) =
      compute_exprs_and_supertype
        ~expected:kexpected
        ~use_pos:p
        ~reason:Reason.URkey
        (Reason.Rtype_variable_generics (p, "Tk", strip_ns name))
        env
        kl
        (arraykey_value p name)
    in
    let (env, tvl, v) =
      compute_exprs_and_supertype
        ~expected:vexpected
        ~use_pos:p
        ~reason:Reason.URvalue
        (Reason.Rtype_variable_generics (p, "Tv", strip_ns name))
        env
        vl
        array_value
    in
    let pairs = List.zip_exn tkl tvl in
    make_result env p (make_expr th pairs) (make_ty k v)
  | Clone e ->
    let (env, te, ty) = expr env e in
    (* Clone only works on objects; anything else fatals at runtime.
     * Constructing a call `e`->__clone() checks that `e` is an object and
     * checks coeffects on __clone *)
    let clone_call =
      ( p,
        Call
          ( ( p,
              Obj_get (e, (p, Id (p, SN.Members.__clone)), OG_nullthrows, false)
            ),
            [],
            [],
            None ) )
    in
    let (env, _te, _ty) = expr env clone_call in
    make_result env p (Aast.Clone te) ty
  | This ->
    if Option.is_none (Env.get_self_ty env) then Errors.this_var_outside_class p;
    if not accept_using_var then check_escaping_var env (p, this);
    let ty = Env.get_local env this in
    let r = Reason.Rwitness p in
    let ty = mk (r, TUtils.this_of (mk (r, get_node ty))) in
    make_result env p Aast.This ty
  | True -> make_result env p Aast.True (MakeType.bool (Reason.Rwitness p))
  | False -> make_result env p Aast.False (MakeType.bool (Reason.Rwitness p))
  (* TODO TAST: consider checking that the integer is in range. Right now
   * it's possible for HHVM to fail on well-typed Hack code
   *)
  | Int s -> make_result env p (Aast.Int s) (MakeType.int (Reason.Rwitness p))
  | Float s ->
    make_result env p (Aast.Float s) (MakeType.float (Reason.Rwitness p))
  (* TODO TAST: consider introducing a "null" type, and defining ?t to
   * be null | t
   *)
  | Null -> make_result env p Aast.Null (MakeType.null (Reason.Rwitness p))
  | String s ->
    make_result env p (Aast.String s) (MakeType.string (Reason.Rwitness p))
  | String2 idl ->
    let (env, tel) = string2 env idl in
    make_result env p (Aast.String2 tel) (MakeType.string (Reason.Rwitness p))
  | PrefixedString (n, e) ->
    if String.( <> ) n "re" then (
      Errors.experimental_feature
        p
        "String prefixes other than `re` are not yet supported.";
      expr_error env Reason.Rnone outer
    ) else
      let (env, te, ty) = expr env e in
      let pe = fst e in
      let env = Typing_substring.sub_string pe env ty in
      (match snd e with
      | String _ ->
        begin
          try
            make_result
              env
              p
              (Aast.PrefixedString (n, te))
              (Typing_regex.type_pattern e)
          with
          | Pcre.Error (Pcre.BadPattern (s, i)) ->
            let s = s ^ " [" ^ string_of_int i ^ "]" in
            Errors.bad_regex_pattern pe s;
            expr_error env (Reason.Rregex pe) e
          | Typing_regex.Empty_regex_pattern ->
            Errors.bad_regex_pattern pe "This pattern is empty";
            expr_error env (Reason.Rregex pe) e
          | Typing_regex.Missing_delimiter ->
            Errors.bad_regex_pattern pe "Missing delimiter(s)";
            expr_error env (Reason.Rregex pe) e
          | Typing_regex.Invalid_global_option ->
            Errors.bad_regex_pattern pe "Invalid global option(s)";
            expr_error env (Reason.Rregex pe) e
        end
      | String2 _ ->
        Errors.re_prefixed_non_string pe "Strings with embedded expressions";
        expr_error env (Reason.Rregex pe) e
      | _ ->
        Errors.re_prefixed_non_string pe "Non-strings";
        expr_error env (Reason.Rregex pe) e)
  | Fun_id x ->
    let (env, fty, _tal) = fun_type_of_id env x [] [] in
    make_result env p (Aast.Fun_id x) fty
  | Id ((cst_pos, cst_name) as id) ->
    (match Env.get_gconst env cst_name with
    | None when Partial.should_check_error (Env.get_mode env) 4106 ->
      Errors.unbound_global cst_pos;
      let ty = err_witness env cst_pos in
      make_result env cst_pos (Aast.Id id) ty
    | None -> make_result env p (Aast.Id id) (Typing_utils.mk_tany env cst_pos)
    | Some ty ->
      let (env, ty) = Phase.localize_with_self ~pos:p env ty in
      make_result env p (Aast.Id id) ty)
  | Method_id (instance, meth) ->
    (* Method_id is used when creating a "method pointer" using the magic
     * inst_meth function.
     *
     * Typing this is pretty simple, we just need to check that instance->meth
     * is public+not static and then return its type.
     *)
    let (env, te, ty1) = expr env instance in
    let (env, (result, _tal)) =
      TOG.obj_get_
        ~inst_meth:true
        ~obj_pos:p
        ~is_method:true
        ~nullsafe:None
        ~coerce_from_ty:None
        ~is_nonnull:false
        ~explicit_targs:[]
        env
        ty1
        (CIexpr instance)
        meth
        (fun x -> x)
        Errors.unify_error
    in
    let (env, result) =
      Env.FakeMembers.check_instance_invalid env instance (snd meth) result
    in
    make_result env p (Aast.Method_id (te, meth)) result
  | Method_caller (((pos, class_name) as pos_cname), meth_name) ->
    (* meth_caller('X', 'foo') desugars to:
     * $x ==> $x->foo()
     *)
    let class_ = Env.get_class env class_name in
    (match class_ with
    | None -> unbound_name env pos_cname outer
    | Some class_ ->
      (* Create a class type for the given object instantiated with unresolved
       * types for its type parameters.
       *)
      let () =
        if Ast_defs.is_c_trait (Cls.kind class_) then
          Errors.meth_caller_trait pos class_name
      in
      let (env, tvarl) =
        List.map_env env (Cls.tparams class_) (fun env _ ->
            Env.fresh_type env p)
      in
      let params =
        List.map (Cls.tparams class_) (fun { tp_name = (p, n); _ } ->
            (* TODO(T69551141) handle type arguments for Tgeneric *)
            MakeType.generic (Reason.Rwitness p) n)
      in
      let obj_type = MakeType.apply (Reason.Rwitness p) pos_cname params in
      let ety_env =
        {
          (Phase.env_with_self env) with
          substs = TUtils.make_locl_subst_for_class_tparams class_ tvarl;
        }
      in
      let (env, local_obj_ty) = Phase.localize ~ety_env env obj_type in
      let (env, (fty, _tal)) =
        TOG.obj_get
          ~obj_pos:pos
          ~is_method:true
          ~nullsafe:None
          ~coerce_from_ty:None
          ~explicit_targs:[]
          env
          local_obj_ty
          (CI (pos, class_name))
          meth_name
          Errors.unify_error
      in
      let (env, fty) = Env.expand_type env fty in
      (match deref fty with
      | (reason, Tfun ftype) ->
        (* We are creating a fake closure:
         * function(Class $x, arg_types_of(Class::meth_name))
                 : return_type_of(Class::meth_name)
         *)
        let ety_env =
          {
            ety_env with
            substs = TUtils.make_locl_subst_for_class_tparams class_ tvarl;
          }
        in
        let env =
          Phase.check_tparams_constraints
            ~use_pos:p
            ~ety_env
            env
            (Cls.tparams class_)
        in
        let (env, local_obj_ty) = Phase.localize ~ety_env env obj_type in
        let local_obj_fp = TUtils.default_fun_param local_obj_ty in
        let fty = { ftype with ft_params = local_obj_fp :: ftype.ft_params } in
        let caller =
          {
            ft_arity = fty.ft_arity;
            ft_tparams = fty.ft_tparams;
            ft_where_constraints = fty.ft_where_constraints;
            ft_params = fty.ft_params;
            ft_implicit_params = fty.ft_implicit_params;
            ft_ret = fty.ft_ret;
            (* propagate 'is_coroutine' from the method being called*)
            ft_flags = fty.ft_flags;
            ft_reactive = fty.ft_reactive;
            ft_ifc_decl = fty.ft_ifc_decl;
          }
        in
        make_result
          env
          p
          (Aast.Method_caller (pos_cname, meth_name))
          (mk (reason, Tfun caller))
      | _ ->
        (* This can happen if the method lives in PHP *)
        make_result
          env
          p
          (Aast.Method_caller (pos_cname, meth_name))
          (Typing_utils.mk_tany env pos)))
  | FunctionPointer (FP_class_const ((cpos, cid), meth), targs) ->
    let (env, _, ce, cty) =
      static_class_id ~check_constraints:true cpos env [] cid
    in
    let (env, (fpty, tal)) =
      class_get
        ~is_method:true
        ~is_const:false
        ~incl_tc:false (* What is this? *)
        ~coerce_from_ty:None (* What is this? *)
        ~explicit_targs:targs
        ~function_pointer:true
        env
        cty
        meth
        cid
    in
    let env = Env.set_tyvar_variance env fpty in
    let fpty = set_function_pointer fpty in
    make_result
      env
      p
      (Aast.FunctionPointer (FP_class_const (ce, meth), tal))
      fpty
  | Smethod_id ((pc, cid), meth) ->
    (* Smethod_id is used when creating a "method pointer" using the magic
     * class_meth function.
     *
     * Typing this is pretty simple, we just need to check that c::meth is
     * public+static and then return its type.
     *)
    let (class_, classname) =
      match cid with
      | CIself
      | CIstatic ->
        (Env.get_self_class env, Env.get_self_id env)
      | CI (_, const) when String.equal const SN.PseudoConsts.g__CLASS__ ->
        (Env.get_self_class env, Env.get_self_id env)
      | CI (_, id) -> (Env.get_class env id, Some id)
      | _ -> (None, None)
    in
    let classname = Option.value classname ~default:"" in
    (match class_ with
    | None ->
      (* The class given as a static string was not found. *)
      unbound_name env (pc, classname) outer
    | Some class_ ->
      let smethod = Env.get_static_member true env class_ (snd meth) in
      (match smethod with
      | None ->
        (* The static method wasn't found. *)
        TOG.smember_not_found
          (fst meth)
          ~is_const:false
          ~is_method:true
          class_
          (snd meth)
          Errors.unify_error;
        expr_error env Reason.Rnone outer
      | Some ({ ce_type = (lazy ty); ce_pos = (lazy ce_pos); _ } as ce) ->
        let () =
          if get_ce_abstract ce then
            match cid with
            | CIstatic -> ()
            | _ -> Errors.class_meth_abstract_call classname (snd meth) p ce_pos
        in
        let ce_visibility = ce.ce_visibility in
        let ce_deprecated = ce.ce_deprecated in
        let (env, _tal, te, cid_ty) =
          static_class_id ~check_constraints:true pc env [] cid
        in
        let (env, cid_ty) = Env.expand_type env cid_ty in
        let tyargs =
          match get_node cid_ty with
          | Tclass (_, _, tyargs) -> tyargs
          | _ -> []
        in
        let ety_env =
          {
            type_expansions = [];
            substs = TUtils.make_locl_subst_for_class_tparams class_ tyargs;
            this_ty = cid_ty;
            from_class = Some cid;
            quiet = true;
            on_error = Errors.unify_error_at p;
          }
        in
        (match deref ty with
        | (r, Tfun ft) ->
          let ft =
            Typing_enforceability.compute_enforced_and_pessimize_fun_type env ft
          in
          let def_pos = ce_pos in
          let (env, tal) =
            Phase.localize_targs
              ~check_well_kinded:true
              ~is_method:true
              ~def_pos:ce_pos
              ~use_pos:p
              ~use_name:(strip_ns (snd meth))
              env
              ft.ft_tparams
              []
          in
          let (env, ft) =
            Phase.(
              localize_ft
                ~instantiation:
                  Phase.
                    {
                      use_name = strip_ns (snd meth);
                      use_pos = p;
                      explicit_targs = tal;
                    }
                ~ety_env
                ~def_pos:ce_pos
                env
                ft)
          in
          let ty = mk (r, Tfun ft) in
          let use_pos = fst meth in
          TVis.check_deprecated ~use_pos ~def_pos ce_deprecated;
          (match ce_visibility with
          | Vpublic -> make_result env p (Aast.Smethod_id (te, meth)) ty
          | Vprivate _ ->
            Errors.private_class_meth ~def_pos ~use_pos;
            expr_error env r outer
          | Vprotected _ ->
            Errors.protected_class_meth ~def_pos ~use_pos;
            expr_error env r outer)
        | (r, _) ->
          Errors.internal_error p "We have a method which isn't callable";
          expr_error env r outer)))
  | Lplaceholder p ->
    let r = Reason.Rplaceholder p in
    let ty = MakeType.void r in
    make_result env p (Aast.Lplaceholder p) ty
  | Dollardollar _ when phys_equal valkind `lvalue ->
    Errors.dollardollar_lvalue p;
    expr_error env (Reason.Rwitness p) outer
  | Dollardollar id ->
    let ty = Env.get_local_check_defined env id in
    let env = might_throw env in
    make_result env p (Aast.Dollardollar id) ty
  | Lvar ((_, x) as id) ->
    if not accept_using_var then check_escaping_var env id;
    let ty =
      if check_defined then
        Env.get_local_check_defined env id
      else
        Env.get_local env x
    in
    make_result env p (Aast.Lvar id) ty
  | List el ->
    let (env, tel, tyl) =
      match valkind with
      | `lvalue
      | `lvalue_subexpr ->
        lvalues env el
      | `other ->
        let (env, expected) = expand_expected_and_get_node env expected in
        (match expected with
        | Some (pos, ur, _, Ttuple expected_tyl) ->
          exprs_expected (pos, ur, expected_tyl) env el
        | _ -> exprs env el)
    in
    let ty = MakeType.tuple (Reason.Rwitness p) tyl in
    make_result env p (Aast.List tel) ty
  | Pair (th, e1, e2) ->
    let (env, expected1, expected2, th) =
      match th with
      | Some ((_, t1), (_, t2)) ->
        let (env, t1, t1_expected) = localize_targ env t1 in
        let (env, t2, t2_expected) = localize_targ env t2 in
        (env, Some t1_expected, Some t2_expected, Some (t1, t2))
      | None ->
        (* Use expected type to determine expected element types *)
        (match expand_expected_and_get_node env expected with
        | (env, Some (pos, reason, _ty, Tclass ((_, k), _, [ty1; ty2])))
          when String.equal k SN.Collections.cPair ->
          let ty1_expected = ExpectedTy.make pos reason ty1 in
          let ty2_expected = ExpectedTy.make pos reason ty2 in
          (env, Some ty1_expected, Some ty2_expected, None)
        | _ -> (env, None, None, None))
    in
    let (env, te1, ty1) = expr ?expected:expected1 env e1 in
    let (env, te2, ty2) = expr ?expected:expected2 env e2 in
    let p1 = fst e1 in
    let p2 = fst e2 in
    let (env, ty1) =
      compute_supertype
        ~expected:expected1
        ~reason:Reason.URpair_value
        ~use_pos:p1
        (Reason.Rtype_variable_generics (p1, "T1", "Pair"))
        env
        [ty1]
    in
    let (env, ty2) =
      compute_supertype
        ~expected:expected2
        ~reason:Reason.URpair_value
        ~use_pos:p2
        (Reason.Rtype_variable_generics (p2, "T2", "Pair"))
        env
        [ty2]
    in
    let ty = MakeType.pair (Reason.Rwitness p) ty1 ty2 in
    make_result env p (Aast.Pair (th, te1, te2)) ty
  | Array_get (e, None) ->
    let (env, te, _) = update_array_type p env e valkind in
    let env = might_throw env in
    (* NAST check reports an error if [] is used for reading in an
         lvalue context. *)
    let ty = err_witness env p in
    make_result env p (Aast.Array_get (te, None)) ty
  | Array_get (e1, Some e2) ->
    let (env, te1, ty1) =
      update_array_type ?lhs_of_null_coalesce p env e1 valkind
    in
    let (env, te2, ty2) = expr env e2 in
    let env = might_throw env in
    let is_lvalue = phys_equal valkind `lvalue in
    let (env, ty) =
      Typing_array_access.array_get
        ~array_pos:(fst e1)
        ~expr_pos:p
        ?lhs_of_null_coalesce
        is_lvalue
        env
        ty1
        e2
        ty2
    in
    make_result env p (Aast.Array_get (te1, Some te2)) ty
  | Call ((pos_id, Id ((_, s) as id)), [], el, None) when is_pseudo_function s
    ->
    let (env, tel, tys) = exprs ~accept_using_var:true env el in
    let env =
      if String.equal s SN.PseudoFunctions.hh_show then (
        List.iter tys (Typing_log.hh_show p env);
        env
      ) else if String.equal s SN.PseudoFunctions.hh_show_env then (
        Typing_log.hh_show_env p env;
        env
      ) else if String.equal s SN.PseudoFunctions.hh_log_level then
        match el with
        | [(_, String key_str); (_, Int level_str)] ->
          Env.set_log_level env key_str (int_of_string level_str)
        | _ -> env
      else if String.equal s SN.PseudoFunctions.hh_force_solve then
        Typing_solver.solve_all_unsolved_tyvars env Errors.unify_error
      else if String.equal s SN.PseudoFunctions.hh_loop_forever then (
        loop_forever env;
        env
      ) else
        env
    in
    let ty = MakeType.void (Reason.Rwitness p) in
    make_result
      env
      p
      (Aast.Call
         ( Tast.make_typed_expr pos_id (TUtils.mk_tany env pos_id) (Aast.Id id),
           [],
           tel,
           None ))
      ty
  | Call (e, explicit_targs, el, unpacked_element) ->
    let env =
      match snd e with
      | Id (pos, f) when String.equal f SN.SpecialFunctions.echo ->
        Typing_local_ops.enforce_output pos env
      | _ -> env
    in
    let env = might_throw env in
    check_call
      ~is_using_clause
      ~expected
      ?in_await
      env
      p
      e
      explicit_targs
      el
      unpacked_element
  | FunctionPointer (FP_id fid, targs) ->
    let (env, fty, targs) = fun_type_of_id env fid targs [] in
    let e = Aast.FunctionPointer (FP_id fid, targs) in
    let fty = set_function_pointer fty in
    make_result env p e fty
  | Binop (Ast_defs.QuestionQuestion, e1, e2) ->
    let (env, te1, ty1) = raw_expr ~lhs_of_null_coalesce:true env e1 in
    let (env, te2, ty2) = expr ?expected env e2 in
    let (env, ty1') = Env.fresh_type env (fst e1) in
    let env =
      SubType.sub_type
        env
        ty1
        (MakeType.nullable_locl Reason.Rnone ty1')
        Errors.unify_error
    in
    (* Essentially mimic a call to
     *   function coalesce<Tr, Ta as Tr, Tb as Tr>(?Ta, Tb): Tr
     * That way we let the constraint solver take care of the union logic.
     *)
    let (env, ty_result) = Env.fresh_type env (fst e2) in
    let env = SubType.sub_type env ty1' ty_result Errors.unify_error in
    let env = SubType.sub_type env ty2 ty_result Errors.unify_error in
    make_result
      env
      p
      (Aast.Binop (Ast_defs.QuestionQuestion, te1, te2))
      ty_result
  | Binop (Ast_defs.Eq op_opt, e1, e2) ->
    let make_result env p te ty =
      let (env, te, ty) = make_result env p te ty in
      let env = Typing_reactivity.check_assignment env te in
      (env, te, ty)
    in
    (match op_opt with
    (* For example, e1 += e2. This is typed and translated as if
     * written e1 = e1 + e2.
     * TODO TAST: is this right? e1 will get evaluated more than once
     *)
    | Some op ->
      begin
        match (op, snd e1) with
        | (Ast_defs.QuestionQuestion, Class_get _) ->
          Errors.experimental_feature
            p
            "null coalesce assignment operator with static properties";
          expr_error env Reason.Rnone outer
        | _ ->
          let e_fake =
            (p, Binop (Ast_defs.Eq None, e1, (p, Binop (op, e1, e2))))
          in
          let (env, te_fake, ty) = raw_expr env e_fake in
          begin
            match snd te_fake with
            | Aast.Binop (_, te1, (_, Aast.Binop (_, _, te2))) ->
              let te = Aast.Binop (Ast_defs.Eq (Some op), te1, te2) in
              make_result env p te ty
            | _ -> assert false
          end
      end
    | None ->
      let (env, te2, ty2) = raw_expr env e2 in
      let (env, te1, ty) = assign p env e1 ty2 in
      let env =
        if Env.env_local_reactive env then
          Typing_mutability.handle_assignment_mutability
            env
            te1
            (Some (snd te2))
        else
          env
      in
      make_result env p (Aast.Binop (Ast_defs.Eq None, te1, te2)) ty)
  | Binop (((Ast_defs.Ampamp | Ast_defs.Barbar) as bop), e1, e2) ->
    let c = Ast_defs.(equal_bop bop Ampamp) in
    let (env, te1, _) = expr env e1 in
    let lenv = env.lenv in
    let (env, _lset) = condition env c te1 in
    let (env, te2, _) = expr env e2 in
    let env = { env with lenv } in
    make_result
      env
      p
      (Aast.Binop (bop, te1, te2))
      (MakeType.bool (Reason.Rlogic_ret p))
  | Binop (bop, e1, e2) ->
    let (env, te1, ty1) = raw_expr env e1 in
    let (env, te2, ty2) = raw_expr env e2 in
    let env =
      match bop with
      (* TODO: This could be less conservative: we only need to account for
       * the possibility of exception if the operator is `/` or `/=`.
       *)
      | Ast_defs.Eqeqeq
      | Ast_defs.Diff2 ->
        env
      | _ -> might_throw env
    in
    let (env, te3, ty) =
      Typing_arithmetic.binop p env bop (fst e1) te1 ty1 (fst e2) te2 ty2
    in
    (env, te3, ty)
  | Pipe (e0, e1, e2) ->
    (* If it weren't for local variable assignment or refinement the pipe
     * expression e1 |> e2 could be typed using this rule (E is environment with
     * types for locals):
     *
     *    E |- e1 : ty1    E[$$:ty1] |- e2 : ty2
     *    --------------------------------------
     *                E |- e1|>e2 : ty2
     *
     * The possibility of e2 changing the types of locals in E means that E
     * can evolve, and so we need to restore $$ to its original state.
     *)
    let (env, te1, ty1) = expr env e1 in
    let dd_var = Local_id.make_unscoped SN.SpecialIdents.dollardollar in
    let dd_old_ty =
      if Env.is_local_defined env dd_var then
        Some (Env.get_local_pos env dd_var)
      else
        None
    in
    let env = Env.set_local env dd_var ty1 Pos.none in
    let (env, te2, ty2) = expr env e2 in
    let env =
      match dd_old_ty with
      | None -> Env.unset_local env dd_var
      | Some (ty, pos) -> Env.set_local env dd_var ty pos
    in
    make_result env p (Aast.Pipe (e0, te1, te2)) ty2
  | Unop (uop, e) ->
    let (env, te, ty) = raw_expr env e in
    let env = might_throw env in
    let (env, tuop, ty) = Typing_arithmetic.unop p env uop te ty in
    let env = Typing_reactivity.check_assignment env tuop in
    (env, tuop, ty)
  | Eif (c, e1, e2) -> eif env ~expected ?in_await p c e1 e2
  | Class_const ((p, CI sid), pstr)
    when String.equal (snd pstr) "class" && Env.is_typedef env (snd sid) ->
    begin
      match Env.get_typedef env (snd sid) with
      | Some { td_tparams = tparaml; _ } ->
        (* Typedef type parameters cannot have constraints *)
        let params =
          List.map
            ~f:
              begin
                fun { tp_name = (p, x); _ } ->
                (* TODO(T69551141) handle type arguments for Tgeneric *)
                MakeType.generic (Reason.Rwitness p) x
              end
            tparaml
        in
        let tdef = mk (Reason.Rwitness p, Tapply (sid, params)) in
        let typename =
          mk (Reason.Rwitness p, Tapply ((p, SN.Classes.cTypename), [tdef]))
        in
        let (env, tparams) =
          List.map_env env tparaml (fun env tp ->
              Env.fresh_type env (fst tp.tp_name))
        in
        let ety_env =
          {
            (Phase.env_with_self env) with
            substs = Subst.make_locl tparaml tparams;
          }
        in
        let env =
          Phase.check_tparams_constraints ~use_pos:p ~ety_env env tparaml
        in
        let (env, ty) = Phase.localize ~ety_env env typename in
        make_result env p (Class_const (((p, ty), CI sid), pstr)) ty
      | None ->
        (* Should not expect None as we've checked whether the sid is a typedef *)
        expr_error env (Reason.Rwitness p) outer
    end
  | Class_const (cid, mid) -> class_const env p (cid, mid)
  | Class_get ((cpos, cid), CGstring mid, in_parens)
    when Env.FakeMembers.is_valid_static env cid (snd mid) ->
    let (env, local) = Env.FakeMembers.make_static env cid (snd mid) p in
    let local = (p, Lvar (p, local)) in
    let (env, _, ty) = expr env local in
    let (env, _tal, te, _) =
      static_class_id ~check_constraints:false cpos env [] cid
    in
    make_result env p (Aast.Class_get (te, Aast.CGstring mid, in_parens)) ty
  | Class_get ((cpos, cid), CGstring ((ppos, _) as mid), in_parens) ->
    let (env, _tal, te, cty) =
      static_class_id ~check_constraints:false cpos env [] cid
    in
    let env = might_throw env in
    let (env, (ty, _tal)) =
      class_get
        ~is_method:false
        ~is_const:false
        ~coerce_from_ty:None
        env
        cty
        mid
        cid
    in
    let (env, ty) = Env.FakeMembers.check_static_invalid env cid (snd mid) ty in
    let env = Typing_local_ops.enforce_static_property_access ppos env in
    make_result env p (Aast.Class_get (te, Aast.CGstring mid, in_parens)) ty
  (* Fake member property access. For example:
   *   if ($x->f !== null) { ...$x->f... }
   *)
  | Class_get (_, CGexpr _, _) ->
    failwith "AST should not have any CGexprs after naming"
  | Obj_get (e, (pid, Id (py, y)), nf, in_parens)
    when Env.FakeMembers.is_valid env e y ->
    let env = might_throw env in
    let (env, local) = Env.FakeMembers.make env e y p in
    let local = (p, Lvar (p, local)) in
    let (env, _, ty) = expr env local in
    let (env, t_lhs, _) = expr ~accept_using_var:true env e in
    let t_rhs = Tast.make_typed_expr pid ty (Aast.Id (py, y)) in
    make_result env p (Aast.Obj_get (t_lhs, t_rhs, nf, in_parens)) ty
  (* Statically-known instance property access e.g. $x->f *)
  | Obj_get (e1, (pm, Id m), nullflavor, in_parens) ->
    let nullsafe =
      match nullflavor with
      | OG_nullthrows -> None
      | OG_nullsafe -> Some p
    in
    let (env, te1, ty1) = expr ~accept_using_var:true env e1 in
    let env = might_throw env in
    (* We typecheck Obj_get by checking whether it is a subtype of
    Thas_member(m, #1) where #1 is a fresh type variable. *)
    let (env, mem_ty) = Env.fresh_type env p in
    let r = Reason.Rwitness (fst e1) in
    let has_member_ty =
      MakeType.has_member
        r
        ~name:m
        ~ty:mem_ty
        ~class_id:(CIexpr e1)
        ~explicit_targs:None
    in
    let lty1 = LoclType ty1 in
    let (env, result_ty) =
      match nullsafe with
      | None ->
        let env =
          Type.sub_type_i
            (fst e1)
            Reason.URnone
            env
            lty1
            has_member_ty
            Errors.unify_error
        in
        (env, mem_ty)
      | Some _ ->
        (* In that case ty1 is a subtype of ?Thas_member(m, #1)
        and the result is ?#1 if ty1 is nullable. *)
        let r = Reason.Rnullsafe_op p in
        let null_ty = MakeType.null r in
        let (env, null_has_mem_ty) =
          Union.union_i env r has_member_ty null_ty
        in
        let env =
          Type.sub_type_i
            (fst e1)
            Reason.URnone
            env
            lty1
            null_has_mem_ty
            Errors.unify_error
        in
        let (env, null_or_nothing_ty) = Inter.intersect env ~r null_ty ty1 in
        let (env, result_ty) = Union.union env null_or_nothing_ty mem_ty in
        (env, result_ty)
    in
    let (env, result_ty) =
      Env.FakeMembers.check_instance_invalid env e1 (snd m) result_ty
    in
    make_result
      env
      p
      (Aast.Obj_get
         ( te1,
           Tast.make_typed_expr pm result_ty (Aast.Id m),
           nullflavor,
           in_parens ))
      result_ty
  (* Dynamic instance property access e.g. $x->$f *)
  | Obj_get (e1, e2, nullflavor, in_parens) ->
    let (env, te1, ty1) = expr ~accept_using_var:true env e1 in
    let (env, te2, _) = expr env e2 in
    let ty =
      if TUtils.is_dynamic env ty1 then
        MakeType.dynamic (Reason.Rwitness p)
      else
        Typing_utils.mk_tany env p
    in
    let ((pos, _), te2) = te2 in
    let env = might_throw env in
    let te2 = Tast.make_typed_expr pos ty te2 in
    make_result env p (Aast.Obj_get (te1, te2, nullflavor, in_parens)) ty
  | Yield_break ->
    make_result env p Aast.Yield_break (Typing_utils.mk_tany env p)
  | Yield af ->
    let (env, (taf, opt_key, value)) = array_field env af in
    let (env, send) = Env.fresh_type env p in
    let (env, key) =
      match (af, opt_key) with
      | (AFvalue (p, _), None) ->
        begin
          match Env.get_fn_kind env with
          | Ast_defs.FSync
          | Ast_defs.FAsync ->
            Errors.internal_error p "yield found in non-generator";
            (env, Typing_utils.mk_tany env p)
          | Ast_defs.FGenerator -> (env, MakeType.int (Reason.Rwitness p))
          | Ast_defs.FAsyncGenerator ->
            let (env, ty) = Env.fresh_type env p in
            (env, MakeType.nullable_locl (Reason.Ryield_asyncnull p) ty)
        end
      | (_, Some x) -> (env, x)
      | (_, _) -> assert false
    in
    let rty =
      match Env.get_fn_kind env with
      | Ast_defs.FGenerator ->
        MakeType.generator (Reason.Ryield_gen p) key value send
      | Ast_defs.FAsyncGenerator ->
        MakeType.async_generator (Reason.Ryield_asyncgen p) key value send
      | Ast_defs.FSync
      | Ast_defs.FAsync ->
        failwith "Parsing should never allow this"
    in
    let Typing_env_return_info.{ return_type = expected_return; _ } =
      Env.get_return env
    in
    let env =
      Typing_coercion.coerce_type
        p
        Reason.URyield
        env
        rty
        expected_return
        Errors.unify_error
    in
    let env = Env.forget_members env Reason.(Blame (p, BScall)) in
    let env = LEnv.save_and_merge_next_in_cont env C.Exit in
    make_result
      env
      p
      (Aast.Yield taf)
      (MakeType.nullable_locl (Reason.Ryield_send p) send)
  | Await e ->
    let env = might_throw env in
    (* Await is permitted in a using clause e.g. using (await make_handle()) *)
    let (env, te, rty) =
      expr ~is_using_clause ~in_await:(Reason.Rwitness p) env e
    in
    let (env, ty) = Async.overload_extract_from_awaitable env p rty in
    make_result env p (Aast.Await te) ty
  | New ((pos, c), explicit_targs, el, unpacked_element, p1) ->
    let env = might_throw env in
    let (env, tc, tal, tel, typed_unpack_element, ty, ctor_fty) =
      new_object
        ~expected
        ~is_using_clause
        ~check_parent:false
        ~check_not_abstract:true
        pos
        env
        c
        explicit_targs
        el
        unpacked_element
    in
    let env = Env.forget_members env Reason.(Blame (p, BScall)) in
    make_result
      env
      p
      (Aast.New (tc, tal, tel, typed_unpack_element, (p1, ctor_fty)))
      ty
  | Record ((pos, id), field_values) ->
    (match Decl_provider.get_record_def (Env.get_ctx env) id with
    | Some rd ->
      if rd.rdt_abstract then Errors.new_abstract_record (pos, id);

      let field_name (pos, expr_) =
        match expr_ with
        | Aast.String name -> Some (pos, name)
        | _ ->
          (* TODO T44306013: Ensure that other values for field names are banned. *)
          None
      in
      let fields_declared = Typing_helpers.all_record_fields env rd in
      let fields_present =
        List.map field_values ~f:(fun (name, _value) -> field_name name)
        |> List.filter_opt
      in
      (* Check for missing required fields. *)
      let fields_present_names =
        List.map ~f:snd fields_present |> SSet.of_list
      in
      SMap.iter
        (fun field_name info ->
          let ((field_pos, _), req) = info in
          match req with
          | Typing_defs.ValueRequired
            when not (SSet.mem field_name fields_present_names) ->
            Errors.missing_record_field_name
              ~field_name
              ~new_pos:pos
              ~record_name:id
              ~field_decl_pos:field_pos
          | _ -> ())
        fields_declared;

      (* Check for unknown fields.*)
      List.iter fields_present ~f:(fun (pos, field_name) ->
          if not (SMap.mem field_name fields_declared) then
            Errors.unexpected_record_field_name
              ~field_name
              ~field_pos:pos
              ~record_name:id
              ~decl_pos:(fst rd.rdt_name))
    | None -> Errors.type_not_record id pos);

    expr_error env (Reason.Rwitness p) outer
  | Cast (hint, e) ->
    let (env, te, ty2) = expr ?in_await env e in
    let env = might_throw env in
    let env =
      if
        TypecheckerOptions.experimental_feature_enabled
          (Env.get_tcopt env)
          TypecheckerOptions.experimental_forbid_nullable_cast
        && not (TUtils.is_mixed env ty2)
      then
        SubType.sub_type_or_fail
          env
          ty2
          (MakeType.nonnull (get_reason ty2))
          (fun () ->
            Errors.nullable_cast p (Typing_print.error env ty2) (get_pos ty2))
      else
        env
    in
    let (env, ty) = Phase.localize_hint_with_self env hint in
    make_result env p (Aast.Cast (hint, te)) ty
  | ExpressionTree et -> expression_tree { env with in_expr_tree = true } p et
  | Is (e, hint) ->
    Typing_kinding.Simple.check_well_kinded_hint env hint;
    let (env, te, _) = expr env e in
    make_result env p (Aast.Is (te, hint)) (MakeType.bool (Reason.Rwitness p))
  | As (e, hint, is_nullable) ->
    Typing_kinding.Simple.check_well_kinded_hint env hint;
    let refine_type env lpos lty rty =
      let reason = Reason.Ras lpos in
      let (env, rty) = Env.expand_type env rty in
      let (env, rty) = class_for_refinement env p reason lpos lty rty in
      Inter.intersect env reason lty rty
    in
    let (env, te, expr_ty) = expr env e in
    let env = might_throw env in
    let ety_env =
      { (Phase.env_with_self env) with from_class = Some CIstatic }
    in
    let (env, hint_ty) = Phase.localize_hint ~ety_env env hint in
    let enable_sound_dynamic =
      TypecheckerOptions.enable_sound_dynamic env.genv.tcopt
    in
    let is_dyn = Typing_utils.is_dynamic env hint_ty in
    ( if enable_sound_dynamic && is_dyn then
      let (_ : env * locl_ty) =
        ( SubType.sub_type
            ~allow_subtype_of_dynamic:true
            env
            expr_ty
            hint_ty
            Errors.unify_error,
          hint_ty )
      in
      () );
    let (env, hint_ty) =
      if is_dyn && not enable_sound_dynamic then
        let env =
          if is_instance_var e then
            let (env, ivar) = get_instance_var env e in
            set_local env ivar hint_ty
          else
            env
        in
        (env, hint_ty)
      else if is_nullable && not is_dyn then
        let (env, hint_ty) = refine_type env (fst e) expr_ty hint_ty in
        (env, MakeType.nullable_locl (Reason.Rwitness p) hint_ty)
      else if is_instance_var e then
        let (env, _, ivar_ty) = raw_expr env e in
        let (env, ((ivar_pos, _) as ivar)) = get_instance_var env e in
        let (env, hint_ty) = refine_type env ivar_pos ivar_ty hint_ty in
        let env = set_local env ivar hint_ty in
        (env, hint_ty)
      else
        refine_type env (fst e) expr_ty hint_ty
    in
    make_result env p (Aast.As (te, hint, is_nullable)) hint_ty
  | Efun (f, idl)
  | Lfun (f, idl) ->
    let is_anon =
      match e with
      | Efun _ -> true
      | Lfun _ -> false
      | _ -> assert false
    in
    (* Check type annotations on the lambda *)
    Typing_check_decls.fun_ env f;
    (* Check attributes on the lambda *)
    let env =
      attributes_check_def env SN.AttributeKinds.lambda f.f_user_attributes
    in
    (* This is the function type as declared on the lambda itself.
     * If type hints are absent then use Tany instead. *)
    let declared_fe =
      Decl_nast.fun_decl_in_env env.decl_env ~is_lambda:true f
    in
    let { fe_type; fe_pos; _ } = declared_fe in
    let (declared_pos, declared_ft) =
      match get_node fe_type with
      | Tfun ft -> (fe_pos, ft)
      | _ -> failwith "Not a function"
    in
    let declared_ft =
      Typing_enforceability.compute_enforced_and_pessimize_fun_type
        env
        declared_ft
    in
    (* When creating a closure, the 'this' type will mean the late bound type
     * of the current enclosing class
     *)
    let ety_env =
      { (Phase.env_with_self env) with from_class = Some CIstatic }
    in
    let (env, declared_ft) =
      Phase.(
        localize_ft
          ~instantiation:
            { use_name = "lambda"; use_pos = p; explicit_targs = [] }
          ~ety_env
          ~def_pos:declared_pos
          env
          declared_ft)
    in
    List.iter idl (check_escaping_var env);

    (* Ensure lambda arity is not ellipsis in strict mode *)
    begin
      match declared_ft.ft_arity with
      | Fvariadic { fp_name = None; _ }
        when Partial.should_check_error (Env.get_mode env) 4223 ->
        Errors.ellipsis_strict_mode ~require:`Param_name p
      | _ -> ()
    end;

    (* Is the return type declared? *)
    let is_explicit_ret = Option.is_some (hint_of_type_hint f.f_ret) in
    let reactivity =
      Decl_fun_utils.fun_reactivity_opt env.decl_env f.f_user_attributes
      |> Option.value
           ~default:(TR.strip_conditional_reactivity (env_reactivity env))
    in
    let check_body_under_known_params env ?ret_ty ft : env * _ * locl_ty =
      let old_reactivity = env_reactivity env in
      let env = Env.set_env_reactive env reactivity in
      let ft = { ft with ft_reactive = reactivity } in
      let (env, (tefun, ty, ft)) = anon_make ?ret_ty env p f ft idl is_anon in
      let env = Env.set_env_reactive env old_reactivity in
      let inferred_ty =
        mk
          ( Reason.Rwitness p,
            Tfun
              {
                ft with
                ft_ret =
                  ( if is_explicit_ret then
                    declared_ft.ft_ret
                  else
                    MakeType.unenforced ty );
              } )
      in
      (env, tefun, inferred_ty)
    in
    let (env, eexpected) = expand_expected_and_get_node env expected in
    (* TODO: move this into the expand_expected_and_get_node function and prune its callsites
     * Strip like type from function type hint *)
    let eexpected =
      match eexpected with
      | Some (pos, ur, _, Tunion [ty1; ty2]) when is_dynamic ty1 && is_fun ty2
        ->
        Some (pos, ur, ty2, get_node ty2)
      | _ -> eexpected
    in
    begin
      match eexpected with
      | Some (_pos, _ur, ty, Tfun expected_ft) ->
        (* First check that arities match up *)
        check_lambda_arity p (get_pos ty) declared_ft expected_ft;
        (* Use declared types for parameters in preference to those determined
         * by the context: they might be more general. *)
        let rec replace_non_declared_types
            params declared_ft_params expected_ft_params =
          match (params, declared_ft_params, expected_ft_params) with
          | ( param :: params,
              declared_ft_param :: declared_ft_params,
              expected_ft_param :: expected_ft_params ) ->
            let rest =
              replace_non_declared_types
                params
                declared_ft_params
                expected_ft_params
            in
            let resolved_ft_param =
              if Option.is_some (hint_of_type_hint param.param_type_hint) then
                declared_ft_param
              else
                { declared_ft_param with fp_type = expected_ft_param.fp_type }
            in
            resolved_ft_param :: rest
          | (_ :: params, declared_ft_param :: declared_ft_params, []) ->
            let rest =
              replace_non_declared_types
                params
                declared_ft_params
                expected_ft_params
            in
            declared_ft_param :: rest
          | (_, _, _) ->
            (* This means the expected_ft params list can have more parameters
             * than declared parameters in the lambda. For variadics, this is OK.
             *)
            expected_ft_params
        in
        let replace_non_declared_arity variadic declared_arity expected_arity =
          match variadic with
          | FVvariadicArg { param_type_hint = (_, Some _); _ } -> declared_arity
          | FVvariadicArg _ ->
            begin
              match (declared_arity, expected_arity) with
              | (Fvariadic declared, Fvariadic expected) ->
                Fvariadic { declared with fp_type = expected.fp_type }
              | (_, _) -> declared_arity
            end
          | _ -> declared_arity
        in
        let expected_ft =
          {
            expected_ft with
            ft_arity =
              replace_non_declared_arity
                f.f_variadic
                declared_ft.ft_arity
                expected_ft.ft_arity;
            ft_params =
              replace_non_declared_types
                f.f_params
                declared_ft.ft_params
                expected_ft.ft_params;
            ft_implicit_params = declared_ft.ft_implicit_params;
          }
        in
        (* Don't bother passing in `void` if there is no explicit return *)
        let ret_ty =
          match get_node expected_ft.ft_ret.et_type with
          | Tprim Tvoid when not is_explicit_ret -> None
          | _ -> Some expected_ft.ft_ret.et_type
        in
        Typing_log.increment_feature_count env FL.Lambda.contextual_params;
        check_body_under_known_params env ?ret_ty expected_ft
      | _ ->
        let explicit_variadic_param_or_non_variadic =
          match f.f_variadic with
          | FVvariadicArg { param_type_hint; _ } ->
            Option.is_some (hint_of_type_hint param_type_hint)
          | FVellipsis _ -> false
          | _ -> true
        in
        (* If all parameters are annotated with explicit types, then type-check
         * the body under those assumptions and pick up the result type *)
        let all_explicit_params =
          List.for_all f.f_params (fun param ->
              Option.is_some (hint_of_type_hint param.param_type_hint))
        in
        if all_explicit_params && explicit_variadic_param_or_non_variadic then (
          Typing_log.increment_feature_count
            env
            ( if List.is_empty f.f_params then
              FL.Lambda.no_params
            else
              FL.Lambda.explicit_params );
          check_body_under_known_params env declared_ft
        ) else (
          match expected with
          | Some ExpectedTy.{ ty = { et_type; _ }; _ } when is_any et_type ->
            (* If the expected type is Tany env then we're passing a lambda to
             * an untyped function and we just assume every parameter has type
             * Tany.
             * Note: we should be using 'nothing' to type the arguments. *)
            Typing_log.increment_feature_count env FL.Lambda.untyped_context;
            check_body_under_known_params env declared_ft
          | Some _ ->
            (* If the expected type is something concrete but not a function
             * then we should reject in strict mode. Check body anyway.
             * Note: we should be using 'nothing' to type the arguments. *)
            if Partial.should_check_error (Env.get_mode env) 4224 then
              Errors.untyped_lambda_strict_mode p;
            Typing_log.increment_feature_count
              env
              FL.Lambda.non_function_typed_context;
            check_body_under_known_params env declared_ft
          | None ->
            (* If we're in partial mode then type-check definition anyway,
             * so treating parameters without type hints as "untyped"
             *)
            if not (Env.is_strict env) then (
              Typing_log.increment_feature_count
                env
                FL.Lambda.non_strict_unknown_params;
              check_body_under_known_params env declared_ft
            ) else (
              Typing_log.increment_feature_count
                env
                FL.Lambda.fresh_tyvar_params;

              (* Replace uses of Tany that originated from "untyped" parameters or return type
               * with fresh type variables *)
              let freshen_ftype env ft =
                let freshen_ty env pos et =
                  match get_node et.et_type with
                  | Tany _ ->
                    let (env, ty) = Env.fresh_type env pos in
                    (env, { et with et_type = ty })
                  | Tclass (id, e, [ty])
                    when String.equal (snd id) SN.Classes.cAwaitable
                         && is_any ty ->
                    let (env, t) = Env.fresh_type env pos in
                    ( env,
                      {
                        et with
                        et_type = mk (get_reason et.et_type, Tclass (id, e, [t]));
                      } )
                  | _ -> (env, et)
                in
                let freshen_untyped_param env ft_param =
                  let (env, fp_type) =
                    freshen_ty env ft_param.fp_pos ft_param.fp_type
                  in
                  (env, { ft_param with fp_type })
                in
                let (env, ft_params) =
                  List.map_env env ft.ft_params freshen_untyped_param
                in
                let (env, ft_ret) = freshen_ty env declared_pos ft.ft_ret in
                (env, { ft with ft_params; ft_ret })
              in
              let (env, declared_ft) = freshen_ftype env declared_ft in
              let env =
                Env.set_tyvar_variance env (mk (Reason.Rnone, Tfun declared_ft))
              in
              (* TODO(jjwu): the declared_ft here is set to public,
                but is actually inferred from the surrounding context
                (don't think this matters in practice, since we check lambdas separately) *)
              check_body_under_known_params
                env
                ~ret_ty:declared_ft.ft_ret.et_type
                declared_ft
            )
        )
    end
  | Xml (sid, attrl, el) ->
    let cid = CI sid in
    let (env, _tal, _te, classes) =
      class_id_for_new ~exact:Nonexact p env cid []
    in
    (* OK to ignore rest of list; class_info only used for errors, and
    * cid = CI sid cannot produce a union of classes anyhow *)
    let class_info =
      List.find_map classes ~f:(function
          | `Dynamic -> None
          | `Class (_, class_info, _) -> Some class_info)
    in
    let (env, _te, obj) =
      expr env (fst sid, New ((fst sid, cid), [], [], None, fst sid))
    in
    let (env, typed_attrs, attr_types) =
      xhp_attribute_exprs env class_info attrl
    in
    let (env, tel) =
      List.map_env env el ~f:(fun env e ->
          let (env, te, _) = expr env e in
          (env, te))
    in
    let txml = Aast.Xml (sid, typed_attrs, List.rev tel) in
    (match class_info with
    | None -> make_result env p txml (mk (Reason.Runknown_class p, Tobject))
    | Some class_info ->
      let env =
        List.fold_left
          attr_types
          ~f:
            begin
              fun env attr ->
              let (namepstr, valpty) = attr in
              let (valp, valty) = valpty in
              let (env, (declty, _tal)) =
                TOG.obj_get
                  ~obj_pos:(fst sid)
                  ~is_method:false
                  ~nullsafe:None
                  ~coerce_from_ty:None
                  ~explicit_targs:[]
                  env
                  obj
                  cid
                  namepstr
                  Errors.unify_error
              in
              let ureason = Reason.URxhp (Cls.name class_info, snd namepstr) in
              Typing_coercion.coerce_type
                valp
                ureason
                env
                valty
                (MakeType.unenforced declty)
                Errors.xhp_attribute_does_not_match_hint
            end
          ~init:env
      in
      make_result env p txml obj)
  | Callconv (kind, e) ->
    let (env, te, ty) = expr env e in
    make_result env p (Aast.Callconv (kind, te)) ty
  | Shape fdm ->
    let (env, fdm_with_expected) =
      match expand_expected_and_get_node env expected with
      | (env, Some (pos, ur, _, Tshape (_, expected_fdm))) ->
        let fdme =
          List.map
            ~f:(fun (k, v) ->
              match ShapeMap.find_opt k expected_fdm with
              | None -> (k, (v, None))
              | Some sft -> (k, (v, Some (ExpectedTy.make pos ur sft.sft_ty))))
            fdm
        in
        (env, fdme)
      | _ -> (env, List.map ~f:(fun (k, v) -> (k, (v, None))) fdm)
    in
    (* allow_inter adds a type-variable *)
    let (env, tfdm) =
      List.map_env
        ~f:(fun env (key, (e, expected)) ->
          let (env, te, ty) = expr ?expected env e in
          (env, (key, (te, ty))))
        env
        fdm_with_expected
    in
    let (env, fdm) =
      let convert_expr_and_type_to_shape_field_type env (key, (_, ty)) =
        (* An expression evaluation always corresponds to a shape_field_type
             with sft_optional = false. *)
        (env, (key, { sft_optional = false; sft_ty = ty }))
      in
      List.map_env ~f:convert_expr_and_type_to_shape_field_type env tfdm
    in
    let fdm =
      List.fold_left
        ~f:(fun acc (k, v) -> ShapeMap.add k v acc)
        ~init:ShapeMap.empty
        fdm
    in
    let env = check_shape_keys_validity env p (ShapeMap.keys fdm) in
    (* Fields are fully known, because this shape is constructed
     * using shape keyword and we know exactly what fields are set. *)
    make_result
      env
      p
      (Aast.Shape (List.map ~f:(fun (k, (te, _)) -> (k, te)) tfdm))
      (mk (Reason.Rwitness p, Tshape (Closed_shape, fdm)))
  | ET_Splice e -> et_splice { env with in_expr_tree = true } p e
  | EnumAtom s ->
    Errors.atom_as_expr p;
    make_result env p (Aast.EnumAtom s) (mk (Reason.Rwitness p, Terr))

(* let ty = err_witness env cst_pos in *)
and class_const ?(incl_tc = false) env p ((cpos, cid), mid) =
  let (env, _tal, ce, cty) =
    static_class_id ~check_constraints:true cpos env [] cid
  in
  let (env, (const_ty, _tal)) =
    class_get
      ~is_method:false
      ~is_const:true
      ~incl_tc
      ~coerce_from_ty:None
      env
      cty
      mid
      cid
  in
  make_result env p (Aast.Class_const (ce, mid)) const_ty
  (*****************************************************************************)
  (* XHP attribute/body helpers. *)
  (*****************************************************************************)

(**
 * Process a spread operator by computing the intersection of XHP attributes
 * between the spread expression and the XHP constructor onto which we're
 * spreading.
 *)
and xhp_spread_attribute env c_onto valexpr =
  let (p, _) = valexpr in
  let (env, te, valty) = expr env valexpr in
  (* Build the typed attribute node *)
  let typed_attr = Aast.Xhp_spread te in
  let (env, attr_ptys) =
    match c_onto with
    | None -> (env, [])
    | Some class_info -> Typing_xhp.get_spread_attributes env p class_info valty
  in
  (env, typed_attr, attr_ptys)

(**
 * Simple XHP attributes (attr={expr} form) are simply interpreted as a member
 * variable prefixed with a colon, the types of which will be validated later
 *)
and xhp_simple_attribute env id valexpr =
  let (p, _) = valexpr in
  let (env, te, valty) = expr env valexpr in
  (* This converts the attribute name to a member name. *)
  let name = ":" ^ snd id in
  let attr_pty = ((fst id, name), (p, valty)) in
  let typed_attr = Aast.Xhp_simple (id, te) in
  (env, typed_attr, [attr_pty])

(**
 * Typecheck the attribute expressions - this just checks that the expressions are
 * valid, not that they match the declared type for the attribute and,
 * in case of spreads, makes sure they are XHP.
 *)
and xhp_attribute_exprs env cid attrl =
  let handle_attr (env, typed_attrl, attr_ptyl) attr =
    let (env, typed_attr, attr_ptys) =
      match attr with
      | Xhp_simple (id, valexpr) -> xhp_simple_attribute env id valexpr
      | Xhp_spread valexpr -> xhp_spread_attribute env cid valexpr
    in
    (env, typed_attr :: typed_attrl, attr_ptys @ attr_ptyl)
  in
  let (env, typed_attrl, attr_ptyl) =
    List.fold_left ~f:handle_attr ~init:(env, [], []) attrl
  in
  (env, List.rev typed_attrl, List.rev attr_ptyl)

(*****************************************************************************)
(* Anonymous functions. *)
(*****************************************************************************)
and anon_bind_param params (env, t_params) ty : env * Tast.fun_param list =
  match !params with
  | [] ->
    (* This code cannot be executed normally, because the arity is wrong
     * and it will error later. Bind as many parameters as we can and carry
     * on. *)
    (env, t_params)
  | param :: paraml ->
    params := paraml;
    (match hint_of_type_hint param.param_type_hint with
    | Some h ->
      let h = Decl_hint.hint env.decl_env h in
      (* When creating a closure, the 'this' type will mean the
       * late bound type of the current enclosing class
       *)
      let ety_env =
        { (Phase.env_with_self env) with from_class = Some CIstatic }
      in
      let (env, h) = Phase.localize ~ety_env env h in
      let pos = get_pos h in
      let env =
        Typing_coercion.coerce_type
          pos
          Reason.URparam
          env
          ty
          (MakeType.unenforced h)
          Errors.unify_error
      in
      (* Closures are allowed to have explicit type-hints. When
       * that is the case we should check that the argument passed
       * is compatible with the type-hint.
       * The body of the function should be type-checked with the
       * hint and not the type of the argument passed.
       * Otherwise it leads to strange results where
       * foo(?string $x = null) is called with a string and fails to
       * type-check. If $x is a string instead of ?string, null is not
       * subtype of string ...
       *)
      let (env, t_param) = bind_param env (h, param) in
      (env, t_params @ [t_param])
    | None ->
      let ty =
        mk (Reason.Rlambda_param (param.param_pos, get_reason ty), get_node ty)
      in
      let (env, t_param) = bind_param env (ty, param) in
      (env, t_params @ [t_param]))

and anon_bind_variadic env vparam variadic_ty =
  let (env, ty, pos) =
    match hint_of_type_hint vparam.param_type_hint with
    | None ->
      (* if the hint is missing, use the type we expect *)
      (env, variadic_ty, get_pos variadic_ty)
    | Some hint ->
      let h = Decl_hint.hint env.decl_env hint in
      let ety_env =
        { (Phase.env_with_self env) with from_class = Some CIstatic }
      in
      let (env, h) = Phase.localize ~ety_env env h in
      let pos = get_pos h in
      let env =
        Typing_coercion.coerce_type
          pos
          Reason.URparam
          env
          variadic_ty
          (MakeType.unenforced h)
          Errors.unify_error
      in
      (env, h, vparam.param_pos)
  in
  let r = Reason.Rvar_param pos in
  let arr_values = mk (r, get_node ty) in
  let ty = MakeType.varray r arr_values in
  let (env, t_variadic) = bind_param env (ty, vparam) in
  (env, t_variadic)

and anon_bind_opt_param env param : env =
  match param.param_expr with
  | None ->
    let ty = Typing_utils.mk_tany env param.param_pos in
    let (env, _) = bind_param env (ty, param) in
    env
  | Some default ->
    let (env, _te, ty) = expr env default in
    Typing_sequencing.sequence_check_expr default;
    let (env, _) = bind_param env (ty, param) in
    env

and anon_check_param env param =
  match hint_of_type_hint param.param_type_hint with
  | None -> env
  | Some hty ->
    let (env, hty) = Phase.localize_hint_with_self env hty in
    let paramty = Env.get_local env (Local_id.make_unscoped param.param_name) in
    let hint_pos = get_pos hty in
    let env =
      Typing_coercion.coerce_type
        hint_pos
        Reason.URhint
        env
        paramty
        (MakeType.unenforced hty)
        Errors.unify_error
    in
    env

and stash_conts_for_anon env p is_anon captured f =
  let captured =
    if is_anon && TypecheckerOptions.any_coeffects (Env.get_tcopt env) then
      Typing_coeffects.(
        (Pos.none, local_capability_id) :: (Pos.none, capability_id) :: captured)
    else
      captured
  in
  let captured =
    if Env.is_local_defined env this then
      (Pos.none, this) :: captured
    else
      captured
  in
  let init =
    Option.map (Env.next_cont_opt env) ~f:(fun next_cont ->
        let initial_locals =
          if is_anon then
            Env.get_locals env captured
          else
            next_cont.Typing_per_cont_env.local_types
        in
        let initial_fakes =
          Fake.forget (Env.get_fake_members env) Reason.(Blame (p, BSlambda))
        in
        let tpenv = Env.get_tpenv env in
        (initial_locals, initial_fakes, tpenv))
  in
  Typing_lenv.stash_and_do env (Env.all_continuations env) (fun env ->
      let env =
        match init with
        | None -> env
        | Some (initial_locals, initial_fakes, tpenv) ->
          let env = Env.reinitialize_locals env in
          let env = Env.set_locals env initial_locals in
          let env = Env.set_fake_members env initial_fakes in
          let env = Env.env_with_tpenv env tpenv in
          env
      in
      f env)

(* Make a type-checking function for an anonymous function. *)
(* Here ret_ty should include Awaitable wrapper *)
(* TODO: ?el is never set; so we need to fix variadic use of lambda *)
and anon_make ?el ?ret_ty env lambda_pos f ft idl is_anon =
  let nb = Nast.assert_named_body f.f_body in
  Env.anon env.lenv env (fun env ->
      (* Extract capabilities from AAST and add them to the environment *)
      let (env, capability) =
        match (f.f_ctxs, f.f_unsafe_ctxs) with
        | (None, None) ->
          (* if the closure has no explicit coeffect annotations,
            do _not_ insert (unsafe) capabilities into the environment;
            instead, rely on the fact that a capability from an enclosing
            scope can simply be captured, which has the same semantics
            as redeclaring and shadowing with another same-typed capability.
            This avoid unnecessary overhead in the most common case, i.e.,
            when a closure does not need a different (usually smaller)
            set of capabilities. *)
          (env, Env.get_local env Typing_coeffects.local_capability_id)
        | (_, _) ->
          let (env, cap_ty, unsafe_cap_ty) =
            type_capability env f.f_ctxs f.f_unsafe_ctxs (fst f.f_name)
          in
          Typing_coeffects.register_capabilities env cap_ty unsafe_cap_ty
      in
      let ft =
        { ft with ft_implicit_params = { capability = CapTy capability } }
      in
      stash_conts_for_anon env lambda_pos is_anon idl (fun env ->
          let env = Env.clear_params env in
          let make_variadic_arg env varg tyl =
            let remaining_types =
              (* It's possible the variadic arg will capture the variadic
               * parameter of the supplied arity (if arity is Fvariadic)
               * and additional supplied params.
               *
               * For example in cases such as:
               *  lambda1 = (int $a, string...$c) ==> {};
               *  lambda1(1, "hello", ...$y); (where $y is a variadic string)
               *  lambda1(1, "hello", "world");
               * then ...$c will contain "hello" and everything in $y in the first
               * example, and "hello" and "world" in the second example.
               *
               * To account for a mismatch in arity, we take the remaining supplied
               * parameters and return a list of all their types. We'll use this
               * to create a union type when creating the typed variadic arg.
               *)
              let remaining_params =
                List.drop ft.ft_params (List.length f.f_params)
              in
              List.map ~f:(fun param -> param.fp_type.et_type) remaining_params
            in
            let r = Reason.Rvar_param varg.param_pos in
            let union = Tunion (tyl @ remaining_types) in
            let (env, t_param) = anon_bind_variadic env varg (mk (r, union)) in
            (env, Aast.FVvariadicArg t_param)
          in
          let (env, t_variadic) =
            match (f.f_variadic, ft.ft_arity) with
            | (FVvariadicArg arg, Fvariadic variadic) ->
              make_variadic_arg env arg [variadic.fp_type.et_type]
            | (FVvariadicArg arg, Fstandard) -> make_variadic_arg env arg []
            | (FVellipsis pos, _) -> (env, Aast.FVellipsis pos)
            | (_, _) -> (env, Aast.FVnonVariadic)
          in
          let params = ref f.f_params in
          let (env, t_params) =
            List.fold_left
              ~f:(anon_bind_param params)
              ~init:(env, [])
              (List.map ft.ft_params (fun x -> x.fp_type.et_type))
          in
          let env = List.fold_left ~f:anon_bind_opt_param ~init:env !params in
          let env = List.fold_left ~f:anon_check_param ~init:env f.f_params in
          let env =
            match el with
            | None ->
              (*iter2_shortest
                      Unify.unify_param_modes
                      ft.ft_params
                      supplied_params; *)
              env
            | Some x ->
              let var_param =
                match f.f_variadic with
                | FVellipsis pos ->
                  let param =
                    TUtils.default_fun_param
                      ~pos
                      (mk (Reason.Rvar_param pos, Typing_defs.make_tany ()))
                  in
                  Some param
                | _ -> None
              in
              let rec iter l1 l2 =
                match (l1, l2, var_param) with
                | (_, [], _) -> ()
                | ([], _, None) -> ()
                | ([], x2 :: rl2, Some def1) ->
                  param_modes ~is_variadic:true def1 x2;
                  iter [] rl2
                | (x1 :: rl1, x2 :: rl2, _) ->
                  param_modes x1 x2;
                  iter rl1 rl2
              in
              iter ft.ft_params x;
              wfold_left2 inout_write_back env ft.ft_params x
          in
          let env = Env.set_fn_kind env f.f_fun_kind in
          let decl_ty =
            Option.map
              ~f:(Decl_hint.hint env.decl_env)
              (hint_of_type_hint f.f_ret)
          in
          let (env, hret) =
            match decl_ty with
            | None ->
              (* Do we have a contextual return type? *)
              begin
                match ret_ty with
                | None ->
                  let (env, ret_ty) = Env.fresh_type env lambda_pos in
                  (env, Typing_return.wrap_awaitable env lambda_pos ret_ty)
                | Some ret_ty ->
                  (* We might need to force it to be Awaitable if it is a type variable *)
                  Typing_return.force_awaitable env lambda_pos ret_ty
              end
            | Some ret ->
              (* If a 'this' type appears it needs to be compatible with the
               * late static type
               *)
              let ety_env =
                { (Phase.env_with_self env) with from_class = Some CIstatic }
              in
              Typing_return.make_return_type (Phase.localize ~ety_env) env ret
          in
          let env =
            Env.set_return
              env
              (Typing_return.make_info
                 f.f_fun_kind
                 []
                 env
                 ~is_explicit:(Option.is_some ret_ty)
                 hret
                 decl_ty)
          in
          let local_tpenv = Env.get_tpenv env in
          (* Outer pipe variables aren't available in closures. Note that
           * locals are restored by Env.anon after processing the closure
           *)
          let env =
            Env.unset_local
              env
              (Local_id.make_unscoped SN.SpecialIdents.dollardollar)
          in
          let (env, tb) = block env nb.fb_ast in
          let implicit_return = LEnv.has_next env in
          let env =
            if (not implicit_return) || Nast.named_body_is_unsafe nb then
              env
            else
              fun_implicit_return env lambda_pos hret f.f_fun_kind
          in
          let (env, tparams) = List.map_env env f.f_tparams type_param in
          let (env, user_attributes) =
            List.map_env env f.f_user_attributes user_attribute
          in
          let tfun_ =
            {
              Aast.f_annotation = Env.save local_tpenv env;
              Aast.f_span = f.f_span;
              Aast.f_mode = f.f_mode;
              Aast.f_ret = (hret, hint_of_type_hint f.f_ret);
              Aast.f_name = f.f_name;
              Aast.f_tparams = tparams;
              Aast.f_where_constraints = f.f_where_constraints;
              Aast.f_fun_kind = f.f_fun_kind;
              Aast.f_file_attributes = [];
              Aast.f_user_attributes = user_attributes;
              Aast.f_body = { Aast.fb_ast = tb; fb_annotation = () };
              Aast.f_ctxs = f.f_ctxs;
              Aast.f_unsafe_ctxs = f.f_unsafe_ctxs;
              Aast.f_params = t_params;
              Aast.f_variadic = t_variadic;
              (* TODO TAST: Variadic efuns *)
              Aast.f_external = f.f_external;
              Aast.f_namespace = f.f_namespace;
              Aast.f_doc_comment = f.f_doc_comment;
              Aast.f_static = f.f_static;
            }
          in
          let ty = mk (Reason.Rwitness lambda_pos, Tfun ft) in
          let te =
            Tast.make_typed_expr
              lambda_pos
              ty
              ( if is_anon then
                Aast.Efun (tfun_, idl)
              else
                Aast.Lfun (tfun_, idl) )
          in
          let env = Env.set_tyvar_variance env ty in
          (env, (te, hret, ft))
          (* stash_conts_for_anon *))
      (* Env.anon *))

(*****************************************************************************)
(* End of anonymous functions. *)
(*****************************************************************************)

(*****************************************************************************)
(* Expression trees *)
(*****************************************************************************)
and expression_tree env p et =
  let (_, t_src_expr, _) = expr_any env p et.et_src_expr in
  let (env, t_desugared_expr, ty_desugared) = expr env et.et_desugared_expr in
  make_result
    env
    p
    (Aast.ExpressionTree
       {
         et_hint = et.et_hint;
         et_src_expr = t_src_expr;
         et_desugared_expr = t_desugared_expr;
       })
    ty_desugared

and et_splice env p e =
  let (env, te, ty) = expr env e in
  let (env, ty_visitor) = Env.fresh_type env p in
  let (env, ty_res) = Env.fresh_type env p in
  let (env, ty_infer) = Env.fresh_type env p in
  let expr_tree_type =
    MakeType.expr_tree (Reason.Rsplice p) ty_visitor ty_res ty_infer
  in
  let env = SubType.sub_type env ty expr_tree_type Errors.unify_error in
  make_result env p (Aast.ET_Splice te) ty_infer

(*****************************************************************************)
(* End expression trees *)
(*****************************************************************************)
and type_capability env ctxs unsafe_ctxs default_pos =
  let cc = Decl_hint.aast_contexts_to_decl_capability in
  let (env, cap_ty) =
    match cc env.decl_env ctxs default_pos with
    | CapTy ty -> Phase.localize_with_self env ty
    | CapDefaults _p -> (env, MakeType.default_capability)
  in
  let (env, unsafe_cap_ty) =
    match cc env.decl_env unsafe_ctxs default_pos with
    | CapTy ty -> Phase.localize_with_self env ty
    | CapDefaults p ->
      (* default is no unsafe capabilities *)
      (env, MakeType.mixed (Reason.Rhint p))
  in
  (env, cap_ty, unsafe_cap_ty)

and requires_consistent_construct = function
  | CIstatic -> true
  | CIexpr _ -> true
  | CIparent -> false
  | CIself -> false
  | CI _ -> false

(* Caller will be looking for a particular form of expected type
 * e.g. a function type (when checking lambdas) or tuple type (when checking
 * tuples). First expand the expected type and elide single union; also
 * strip nullables, so ?t becomes t, as context will always accept a t if a ?t
 * is expected.
 *)
and expand_expected_and_get_node env (expected : ExpectedTy.t option) =
  match expected with
  | None -> (env, None)
  | Some ExpectedTy.{ pos = p; reason = ur; ty = { et_type = ty; _ }; _ } ->
    let (env, ty) = Env.expand_type env ty in
    (match get_node ty with
    | Tunion [ty] -> (env, Some (p, ur, ty, get_node ty))
    | Toption ty -> (env, Some (p, ur, ty, get_node ty))
    | _ -> (env, Some (p, ur, ty, get_node ty)))

(** Do a subtype check of inferred type against expected type *)
and check_expected_ty message env inferred_ty (expected : ExpectedTy.t option) =
  match expected with
  | None -> env
  | Some ExpectedTy.{ pos = p; reason = ur; ty } ->
    Typing_log.(
      log_with_level env "typing" 1 (fun () ->
          log_types
            p
            env
            [
              Log_head
                ( Printf.sprintf
                    "Typing.check_expected_ty %s enforced=%b"
                    message
                    ty.et_enforced,
                  [
                    Log_type ("inferred_ty", inferred_ty);
                    Log_type ("expected_ty", ty.et_type);
                  ] );
            ]));
    Typing_coercion.coerce_type p ur env inferred_ty ty Errors.unify_error

and new_object
    ~(expected : ExpectedTy.t option)
    ~check_parent
    ~check_not_abstract
    ~is_using_clause
    p
    env
    cid
    explicit_targs
    el
    unpacked_element =
  (* Obtain class info from the cid expression. We get multiple
   * results with a CIexpr that has a union type, e.g. in

      $classname = (mycond()? classname<A>: classname<B>);
      new $classname();
   *)
  let (env, tal, tcid, classes) =
    instantiable_cid ~exact:Exact p env cid explicit_targs
  in
  let allow_abstract_bound_generic =
    match tcid with
    | ((_, ty), Aast.CI (_, tn)) -> is_generic_equal_to tn ty
    | _ -> false
  in
  let gather (env, _tel, _typed_unpack_element) (cname, class_info, c_ty) =
    if
      check_not_abstract
      && Cls.abstract class_info
      && (not (requires_consistent_construct cid))
      && not allow_abstract_bound_generic
    then
      uninstantiable_error
        env
        p
        cid
        (Cls.pos class_info)
        (Cls.name class_info)
        p
        c_ty;
    let (env, obj_ty_, params) =
      let (env, c_ty) = Env.expand_type env c_ty in
      match (cid, tal, get_class_type c_ty) with
      (* Explicit type arguments *)
      | (CI _, _ :: _, Some (_, _, tyl)) -> (env, get_node c_ty, tyl)
      | (_, _, class_type_opt) ->
        let (env, params) =
          List.map_env env (Cls.tparams class_info) (fun env tparam ->
              let (env, tvar) =
                Env.fresh_type_reason
                  env
                  (Reason.Rtype_variable_generics
                     (p, snd tparam.tp_name, strip_ns (snd cname)))
              in
              Typing_log.log_new_tvar_for_new_object env p tvar cname tparam;
              (env, tvar))
        in
        begin
          match class_type_opt with
          | Some (_, Exact, _) -> (env, Tclass (cname, Exact, params), params)
          | _ -> (env, Tclass (cname, Nonexact, params), params)
        end
    in
    if
      (not check_parent)
      && (not is_using_clause)
      && Cls.is_disposable class_info
    then
      Errors.invalid_new_disposable p;
    let r_witness = Reason.Rwitness p in
    let obj_ty = mk (r_witness, obj_ty_) in
    let c_ty =
      match cid with
      | CIstatic
      | CIexpr _ ->
        mk (r_witness, get_node c_ty)
      | _ -> obj_ty
    in
    let (env, new_ty) =
      let ((_, cid_ty), _) = tcid in
      let (env, cid_ty) = Env.expand_type env cid_ty in
      if is_generic cid_ty then
        (env, cid_ty)
      else if check_parent then
        (env, c_ty)
      else
        ExprDepTy.make env cid c_ty
    in
    (* Set variance according to type of `new` expression now. Lambda arguments
     * to the constructor might depend on it, and `call_construct` only uses
     * `ctor_fty` to set the variance which has void return type *)
    let env = Env.set_tyvar_variance env new_ty in
    let (env, tel, typed_unpack_element, ctor_fty) =
      let env = check_expected_ty "New" env new_ty expected in
      call_construct p env class_info params el unpacked_element cid new_ty
    in
    ( if equal_consistent_kind (snd (Cls.construct class_info)) Inconsistent then
      match cid with
      | CIstatic -> Errors.new_inconsistent_construct p cname `static
      | CIexpr _ -> Errors.new_inconsistent_construct p cname `classname
      | _ -> () );
    match cid with
    | CIparent ->
      let (env, ctor_fty) =
        match fst (Cls.construct class_info) with
        | Some ({ ce_type = (lazy ty); _ } as ce) ->
          let ety_env =
            {
              type_expansions = [];
              substs =
                TUtils.make_locl_subst_for_class_tparams class_info params;
              this_ty = obj_ty;
              from_class = None;
              quiet = false;
              on_error = Errors.unify_error_at p;
            }
          in
          if get_ce_abstract ce then
            Errors.parent_abstract_call
              SN.Members.__construct
              p
              (get_pos ctor_fty);
          let (env, ctor_fty) = Phase.localize ~ety_env env ty in
          (env, ctor_fty)
        | None -> (env, ctor_fty)
      in
      ((env, tel, typed_unpack_element), (obj_ty, ctor_fty))
    | CIstatic
    | CI _
    | CIself ->
      ((env, tel, typed_unpack_element), (c_ty, ctor_fty))
    | CIexpr _ ->
      (* When constructing from a (classname) variable, the variable
       * dictates what the constructed object is going to be. This allows
       * for generic and dependent types to be correctly carried
       * through the 'new $foo()' iff the constructed obj_ty is a
       * supertype of the variable-dictated c_ty *)
      let env =
        Typing_ops.sub_type p Reason.URnone env c_ty obj_ty Errors.unify_error
      in
      ((env, tel, typed_unpack_element), (c_ty, ctor_fty))
  in
  let (had_dynamic, classes) =
    List.fold classes ~init:(false, []) ~f:(fun (seen_dynamic, classes) ->
      function
      | `Dynamic -> (true, classes)
      | `Class (cname, class_info, c_ty) ->
        (seen_dynamic, (cname, class_info, c_ty) :: classes))
  in
  let ((env, tel, typed_unpack_element), class_types_and_ctor_types) =
    List.fold_map classes ~init:(env, [], None) ~f:gather
  in
  let class_types_and_ctor_types =
    let r = Reason.Rdynamic_construct p in
    let dyn = (mk (r, Tdynamic), mk (r, Tdynamic)) in
    if had_dynamic then
      dyn :: class_types_and_ctor_types
    else
      class_types_and_ctor_types
  in
  let (env, tel, typed_unpack_element, ty, ctor_fty) =
    match class_types_and_ctor_types with
    | [] ->
      let (env, tel, _) = exprs env el in
      let (env, typed_unpack_element, _) =
        match unpacked_element with
        | None -> (env, None, MakeType.nothing Reason.Rnone)
        | Some unpacked_element ->
          let (env, e, ty) = expr env unpacked_element in
          (env, Some e, ty)
      in
      let r = Reason.Runknown_class p in
      (env, tel, typed_unpack_element, mk (r, Tobject), TUtils.terr env r)
    | [(ty, ctor_fty)] -> (env, tel, typed_unpack_element, ty, ctor_fty)
    | l ->
      let (tyl, ctyl) = List.unzip l in
      let r = Reason.Rwitness p in
      (env, tel, typed_unpack_element, mk (r, Tunion tyl), mk (r, Tunion ctyl))
  in
  let (env, new_ty) =
    let ((_, cid_ty), _) = tcid in
    let (env, cid_ty) = Env.expand_type env cid_ty in
    if is_generic cid_ty then
      (env, cid_ty)
    else if check_parent then
      (env, ty)
    else
      ExprDepTy.make env cid ty
  in
  (env, tcid, tal, tel, typed_unpack_element, new_ty, ctor_fty)

and attributes_check_def env kind attrs =
  (* TODO(coeffects) change to mixed after changing those constructors to pure *)
  let defaults = MakeType.default_capability in
  let (env, _) =
    Typing_lenv.stash_and_do env (Env.all_continuations env) (fun env ->
        let env =
          fst @@ Typing_coeffects.register_capabilities env defaults defaults
        in
        (Typing_attributes.check_def env new_object kind attrs, ()))
  in
  env

(** Get class infos for a class expression (e.g. `parent`, `self` or
    regular classnames) - which might resolve to a union or intersection
    of classes - and check they are instantiable.

    FIXME: we need to separate our instantiability into two parts. Currently,
    all this function is doing is checking if a given type is inhabited --
    that is, whether there are runtime values of type Aast. However,
    instantiability should be the stricter notion that T has a runtime
    constructor; that is, `new T()` should be valid. In particular, interfaces
    are inhabited, but not instantiable.
    To make this work with classname, we likely need to add something like
    concrete_classname<T>, where T cannot be an interface. *)
and instantiable_cid ?(exact = Nonexact) p env cid explicit_targs :
    newable_class_info =
  let (env, tal, te, classes) =
    class_id_for_new ~exact p env cid explicit_targs
  in
  List.iter classes (function
      | `Dynamic -> ()
      | `Class ((pos, name), class_info, c_ty) ->
        if
          Ast_defs.(equal_class_kind (Cls.kind class_info) Ctrait)
          || Ast_defs.(equal_class_kind (Cls.kind class_info) Cenum)
        then
          match cid with
          | CIexpr _
          | CI _ ->
            uninstantiable_error env p cid (Cls.pos class_info) name pos c_ty
          | CIstatic
          | CIparent
          | CIself ->
            ()
        else if
          Ast_defs.(equal_class_kind (Cls.kind class_info) Cabstract)
          && Cls.final class_info
        then
          uninstantiable_error env p cid (Cls.pos class_info) name pos c_ty
        else
          ());
  (env, tal, te, classes)

and uninstantiable_error env reason_pos cid c_tc_pos c_name c_usage_pos c_ty =
  let reason_msgl =
    match cid with
    | CIexpr _ ->
      let ty_str = "This would be " ^ Typing_print.error env c_ty in
      [(reason_pos, ty_str)]
    | _ -> []
  in
  Errors.uninstantiable_class c_usage_pos c_tc_pos c_name reason_msgl

and coerce_to_throwable pos env exn_ty =
  let throwable_ty = MakeType.throwable (Reason.Rthrow pos) in
  Typing_coercion.coerce_type
    pos
    Reason.URthrow
    env
    exn_ty
    { et_type = throwable_ty; et_enforced = false }
    Errors.unify_error

and shape_field_pos = function
  | Ast_defs.SFlit_int (p, _)
  | Ast_defs.SFlit_str (p, _) ->
    p
  | Ast_defs.SFclass_const ((cls_pos, _), (mem_pos, _)) ->
    Pos.btw cls_pos mem_pos

and check_shape_keys_validity env pos keys =
  (* If the key is a class constant, get its class name and type. *)
  let get_field_info env key =
    let key_pos = shape_field_pos key in
    (* Empty strings or literals that start with numbers are not
         permitted as shape field names. *)
    match key with
    | Ast_defs.SFlit_int _ -> (env, key_pos, None)
    | Ast_defs.SFlit_str (_, key_name) ->
      if Int.equal 0 (String.length key_name) then
        Errors.invalid_shape_field_name_empty key_pos;
      (env, key_pos, None)
    | Ast_defs.SFclass_const (((p, cls) as x), y) ->
      let (env, _te, ty) = class_const env pos ((p, CI x), y) in
      let r = Reason.Rwitness key_pos in
      let env =
        Type.sub_type
          key_pos
          Reason.URnone
          env
          ty
          (MakeType.arraykey r)
          (fun ?code:_ _ _ ->
            Errors.invalid_shape_field_type
              key_pos
              (get_pos ty)
              (Typing_print.error env ty)
              [])
      in
      (env, key_pos, Some (cls, ty))
  in
  let check_field witness_pos witness_info env key =
    let (env, key_pos, key_info) = get_field_info env key in
    match (witness_info, key_info) with
    | (Some _, None) ->
      Errors.invalid_shape_field_literal key_pos witness_pos;
      env
    | (None, Some _) ->
      Errors.invalid_shape_field_const key_pos witness_pos;
      env
    | (None, None) -> env
    | (Some (cls1, ty1), Some (cls2, ty2)) ->
      if String.( <> ) cls1 cls2 then
        Errors.shape_field_class_mismatch
          key_pos
          witness_pos
          (strip_ns cls2)
          (strip_ns cls1);
      if
        not
          ( Typing_solver.is_sub_type env ty1 ty2
          && Typing_solver.is_sub_type env ty2 ty1 )
      then
        Errors.shape_field_type_mismatch
          key_pos
          witness_pos
          (Typing_print.error env ty2)
          (Typing_print.error env ty1);
      env
  in
  (* Sort the keys by their positions since the error messages will make
   * more sense if we take the one that appears first as canonical and if
   * they are processed in source order. *)
  let cmp_keys x y = Pos.compare (shape_field_pos x) (shape_field_pos y) in
  let keys = List.sort ~compare:cmp_keys keys in
  match keys with
  | [] -> env
  | witness :: rest_keys ->
    let (env, pos, info) = get_field_info env witness in
    List.fold_left ~f:(check_field pos info) ~init:env rest_keys

and set_valid_rvalue p env x ty =
  let env = set_local env (p, x) ty in
  (* We are assigning a new value to the local variable, so we need to
   * generate a new expression id
   *)
  Env.set_local_expr_id env x (Ident.tmp ())

(* Produce an error if assignment is used in the scope of the |> operator, i.e.
 * if $$ is in scope *)
and error_if_assign_in_pipe p env =
  let dd_var = Local_id.make_unscoped SN.SpecialIdents.dollardollar in
  let dd_defined = Env.is_local_defined env dd_var in
  if dd_defined then
    Errors.unimplemented_feature p "Assignment within pipe expressions"

(* Deal with assignment of a value of type ty2 to lvalue e1 *)
and assign p env e1 ty2 : _ * Tast.expr * Tast.ty =
  error_if_assign_in_pipe p env;
  assign_ p Reason.URassign env e1 ty2

and is_hack_collection env ty =
  Typing_solver.is_sub_type
    env
    ty
    (MakeType.const_collection Reason.Rnone (MakeType.mixed Reason.Rnone))

and assign_ p ur env e1 ty2 =
  let env =
    match e1 with
    | (_, Lvar (_, x)) ->
      Env.forget_prefixed_members env x Reason.(Blame (p, BSassignment))
    (* If we ever extend fake members from $x->a to more complicated lvalues
      such as $x->a->b, we would need to call forget_prefixed_members on
      other lvalues as well. *)
    | (_, Obj_get (_, (_, Id (_, property)), _, _)) ->
      Env.forget_suffixed_members env property Reason.(Blame (p, BSassignment))
    | _ -> env
  in
  match e1 with
  | (_, Lvar ((_, x) as id)) ->
    let env = set_valid_rvalue p env x ty2 in
    make_result env (fst e1) (Aast.Lvar id) ty2
  | (_, Lplaceholder id) ->
    let placeholder_ty = MakeType.void (Reason.Rplaceholder p) in
    make_result env (fst e1) (Aast.Lplaceholder id) placeholder_ty
  | (_, List el) ->
    let (env, tyl) =
      List.map_env env el ~f:(fun env _ -> Env.fresh_type env (get_pos ty2))
    in
    let destructure_ty =
      MakeType.list_destructure (Reason.Rdestructure (fst e1)) tyl
    in
    let lty2 = LoclType ty2 in
    let env = Type.sub_type_i p ur env lty2 destructure_ty Errors.unify_error in
    let env = Env.set_tyvar_variance_i env destructure_ty in
    let (env, reversed_tel) =
      List.fold2_exn el tyl ~init:(env, []) ~f:(fun (env, tel) lvalue ty2 ->
          let (env, te, _) = assign p env lvalue ty2 in
          (env, te :: tel))
    in
    make_result env (fst e1) (Aast.List (List.rev reversed_tel)) ty2
  | ( pobj,
      Obj_get (obj, (pm, Id ((_, member_name) as m)), nullflavor, in_parens) )
    ->
    let lenv = env.lenv in
    let nullsafe =
      match nullflavor with
      | OG_nullthrows -> None
      | OG_nullsafe -> Some (Reason.Rnullsafe_op pobj)
    in
    let (env, tobj, obj_ty) = expr ~accept_using_var:true env obj in
    let env = might_throw env in
    let (env, (result, _tal)) =
      TOG.obj_get
        ~obj_pos:(fst obj)
        ~is_method:false
        ~nullsafe
        ~coerce_from_ty:(Some (p, ur, ty2))
        ~explicit_targs:[]
        env
        obj_ty
        (CIexpr e1)
        m
        Errors.unify_error
    in
    let te1 =
      Tast.make_typed_expr
        pobj
        result
        (Aast.Obj_get
           ( tobj,
             Tast.make_typed_expr pm result (Aast.Id m),
             nullflavor,
             in_parens ))
    in
    let env = { env with lenv } in
    begin
      match obj with
      | (_, This) ->
        let (env, local) = Env.FakeMembers.make env obj member_name p in
        let env = set_valid_rvalue p env local ty2 in
        (env, te1, ty2)
      | (_, Lvar _) ->
        let (env, local) = Env.FakeMembers.make env obj member_name p in
        let env = set_valid_rvalue p env local ty2 in
        (env, te1, ty2)
      | _ -> (env, te1, ty2)
    end
  | (_, Obj_get _) ->
    let lenv = env.lenv in
    let no_fakes = LEnv.env_with_empty_fakes env in
    let (env, te1, real_type) = lvalue no_fakes e1 in
    let (env, exp_real_type) = Env.expand_type env real_type in
    let env = { env with lenv } in
    let env =
      Typing_coercion.coerce_type
        p
        ur
        env
        ty2
        (MakeType.unenforced exp_real_type)
        Errors.unify_error
    in
    (env, te1, ty2)
  | (_, Class_get (_, CGexpr _, _)) ->
    failwith "AST should not have any CGexprs after naming"
  | (_, Class_get ((pos_classid, x), CGstring (pos_member, y), _)) ->
    let lenv = env.lenv in
    let no_fakes = LEnv.env_with_empty_fakes env in
    let (env, te1, _) = lvalue no_fakes e1 in
    let env = { env with lenv } in
    let (env, ety2) = Env.expand_type env ty2 in
    (* This defers the coercion check to class_get, which looks up the appropriate target type *)
    let (env, _tal, _, cty) =
      static_class_id ~check_constraints:false pos_classid env [] x
    in
    let env = might_throw env in
    let (env, _) =
      class_get
        ~is_method:false
        ~is_const:false
        ~coerce_from_ty:(Some (p, ur, ety2))
        env
        cty
        (pos_member, y)
        x
    in
    let (env, local) = Env.FakeMembers.make_static env x y p in
    let env = set_valid_rvalue p env local ty2 in
    (env, te1, ty2)
  | (pos, Array_get (e1, None)) ->
    let (env, te1, ty1) = update_array_type pos env e1 `lvalue in
    let (env, ty1') =
      Typing_array_access.assign_array_append
        ~array_pos:(fst e1)
        ~expr_pos:p
        ur
        env
        ty1
        ty2
    in
    let (env, te1) =
      if is_hack_collection env ty1 then
        (env, te1)
      else
        let (env, te1, _) = assign_ p ur env e1 ty1' in
        (env, te1)
    in
    make_result env pos (Aast.Array_get (te1, None)) ty2
  | (pos, Array_get (e1, Some e)) ->
    let (env, te1, ty1) = update_array_type pos env e1 `lvalue in
    let (env, te, ty) = expr env e in
    let (env, ty1') =
      Typing_array_access.assign_array_get
        ~array_pos:(fst e1)
        ~expr_pos:p
        ur
        env
        ty1
        e
        ty
        ty2
    in
    let (env, te1) =
      if is_hack_collection env ty1 then
        (env, te1)
      else
        let (env, te1, _) = assign_ p ur env e1 ty1' in
        (env, te1)
    in
    (env, ((pos, ty2), Aast.Array_get (te1, Some te)), ty2)
  | _ -> assign_simple p ur env e1 ty2

and assign_simple pos ur env e1 ty2 =
  let (env, te1, ty1) = lvalue env e1 in
  let env =
    Typing_coercion.coerce_type
      pos
      ur
      env
      ty2
      (MakeType.unenforced ty1)
      Errors.unify_error
  in
  (env, te1, ty2)

and array_field env = function
  | AFvalue ve ->
    let (env, tve, tv) = expr env ve in
    (env, (Aast.AFvalue tve, None, tv))
  | AFkvalue (ke, ve) ->
    let (env, tke, tk) = expr env ke in
    let (env, tve, tv) = expr env ve in
    (env, (Aast.AFkvalue (tke, tve), Some tk, tv))

and array_value ~(expected : ExpectedTy.t option) env x =
  let (env, te, ty) = expr ?expected env x in
  (env, (te, ty))

and arraykey_value
    p class_name ~(expected : ExpectedTy.t option) env ((pos, _) as x) =
  let (env, (te, ty)) = array_value ~expected env x in
  let ty_arraykey = MakeType.arraykey (Reason.Ridx_dict pos) in
  let env =
    Typing_coercion.coerce_type
      p
      (Reason.index_class class_name)
      env
      ty
      { et_type = ty_arraykey; et_enforced = true }
      Errors.unify_error
  in
  (env, (te, ty))

and check_parent_construct pos env el unpacked_element env_parent =
  let check_not_abstract = false in
  let (env, env_parent) = Phase.localize_with_self env env_parent in
  let (env, _tcid, _tal, tel, typed_unpack_element, parent, fty) =
    new_object
      ~expected:None
      ~check_parent:true
      ~check_not_abstract
      ~is_using_clause:false
      pos
      env
      CIparent
      []
      el
      unpacked_element
  in
  (* Not sure why we need to equate these types *)
  let env =
    Type.sub_type pos Reason.URnone env env_parent parent Errors.unify_error
  in
  let env =
    Type.sub_type pos Reason.URnone env parent env_parent Errors.unify_error
  in
  ( env,
    tel,
    typed_unpack_element,
    MakeType.void (Reason.Rwitness pos),
    parent,
    fty )

and check_class_get env p def_pos cid mid ce e function_pointer =
  match e with
  | CIself when get_ce_abstract ce ->
    begin
      match get_class_type (Env.get_self env) with
      | Some ((_, self), _, _) ->
        (* at runtime, self:: in a trait is a call to whatever
         * self:: is in the context of the non-trait "use"-ing
         * the trait's code *)
        begin
          match Env.get_class env self with
          | Some cls when Ast_defs.(equal_class_kind (Cls.kind cls) Ctrait) ->
            (* Ban self::some_abstract_method() in a trait, if the
             * method is also defined in a trait.
             *
             * Abstract methods from interfaces are fine: we'll check
             * in the child class that we actually have an
             * implementation. *)
            (match Decl_provider.get_class (Env.get_ctx env) ce.ce_origin with
            | Some meth_cls
              when Ast_defs.(equal_class_kind (Cls.kind meth_cls) Ctrait) ->
              Errors.self_abstract_call mid p def_pos
            | _ -> ())
          | _ ->
            (* Ban self::some_abstract_method() in a class. This will
             *  always error. *)
            Errors.self_abstract_call mid p def_pos
        end
      | None -> ()
    end
  | CIparent when get_ce_abstract ce ->
    Errors.parent_abstract_call mid p def_pos
  | CI _ when get_ce_abstract ce && function_pointer ->
    Errors.abstract_function_pointer cid mid p def_pos
  | CI _ when get_ce_abstract ce ->
    Errors.classname_abstract_call cid mid p def_pos
  | CI (_, classname) when get_ce_synthesized ce ->
    Errors.static_synthetic_method classname mid p def_pos
  | _ -> ()

and call_parent_construct pos env el unpacked_element =
  match Env.get_parent_ty env with
  | Some parent -> check_parent_construct pos env el unpacked_element parent
  | None ->
    (* continue here *)
    let ty = Typing_utils.mk_tany env pos in
    let default = (env, [], None, ty, ty, ty) in
    (match get_class_type (Env.get_self env) with
    | Some ((_, self), _, _) ->
      (match Env.get_class env self with
      | Some trait when Ast_defs.(equal_class_kind (Cls.kind trait) Ctrait) ->
        (match trait_most_concrete_req_class trait env with
        | None ->
          Errors.parent_in_trait pos;
          default
        | Some (_, parent_ty) ->
          check_parent_construct pos env el unpacked_element parent_ty)
      | Some self_tc ->
        if not (Cls.members_fully_known self_tc) then
          ()
        (* Don't know the hierarchy, assume it's correct *)
        else
          Errors.undefined_parent pos;
        default
      | None -> assert false)
    | None ->
      Errors.parent_outside_class pos;
      let ty = err_witness env pos in
      (env, [], None, ty, ty, ty))

(* Depending on the kind of expression we are dealing with
 * The typing of call is different.
 *)
and dispatch_call
    ~(expected : ExpectedTy.t option)
    ~is_using_clause
    ?in_await
    p
    env
    ((fpos, fun_expr) as e)
    explicit_targs
    el
    unpacked_element =
  let make_call env te tal tel typed_unpack_element ty =
    make_result env p (Aast.Call (te, tal, tel, typed_unpack_element)) ty
  in
  (* TODO: Avoid Tany annotations in TAST by eliminating `make_call_special` *)
  let make_call_special env id tel ty =
    make_call
      env
      (Tast.make_typed_expr fpos (TUtils.mk_tany env fpos) (Aast.Id id))
      []
      tel
      None
      ty
  in
  (* For special functions and pseudofunctions with a definition in hhi. *)
  let make_call_special_from_def env id tel ty_ =
    let (env, fty, tal) = fun_type_of_id env id explicit_targs el in
    let ty =
      match get_node fty with
      | Tfun ft -> ft.ft_ret.et_type
      | _ -> ty_ (Reason.Rwitness p)
    in
    make_call env (Tast.make_typed_expr fpos fty (Aast.Id id)) tal tel None ty
  in
  let overload_function = overload_function make_call fpos in
  let check_disposable_in_return env fty =
    if is_return_disposable_fun_type env fty && not is_using_clause then
      Errors.invalid_new_disposable p
  in
  match fun_expr with
  (* Special function `echo` *)
  | Id ((p, pseudo_func) as id)
    when String.equal pseudo_func SN.SpecialFunctions.echo ->
    let (env, tel, _) = exprs ~accept_using_var:true env el in
    make_call_special env id tel (MakeType.void (Reason.Rwitness p))
  (* Special function `isset` *)
  | Id ((_, pseudo_func) as id)
    when String.equal pseudo_func SN.PseudoFunctions.isset ->
    let (env, tel, _) =
      exprs ~accept_using_var:true ~check_defined:false env el
    in
    if Option.is_some unpacked_element then
      Errors.unpacking_disallowed_builtin_function p pseudo_func;
    make_call_special_from_def env id tel MakeType.bool
  (* Special function `unset` *)
  | Id ((_, pseudo_func) as id)
    when String.equal pseudo_func SN.PseudoFunctions.unset ->
    let (env, tel, _) = exprs env el in
    let env = Typing_reactivity.check_unset_target env tel in
    if Option.is_some unpacked_element then
      Errors.unpacking_disallowed_builtin_function p pseudo_func;
    let checked_unset_error =
      if Partial.should_check_error (Env.get_mode env) 4135 then
        Errors.unset_nonidx_in_strict
      else
        fun _ _ ->
      ()
    in
    let env =
      match (el, unpacked_element) with
      | ([(_, Array_get ((_, Class_const _), Some _))], None)
        when Partial.should_check_error (Env.get_mode env) 4011 ->
        Errors.const_mutation p Pos.none "";
        env
      | ([(_, Array_get (ea, Some _))], None) ->
        let (env, _te, ty) = expr env ea in
        let r = Reason.Rwitness p in
        let tmixed = MakeType.mixed r in
        let super =
          mk
            ( Reason.Rnone,
              Tunion
                [
                  MakeType.dynamic r;
                  MakeType.dict r tmixed tmixed;
                  MakeType.keyset r tmixed;
                  MakeType.darray r tmixed tmixed;
                ] )
        in
        SubType.sub_type_or_fail env ty super (fun () ->
            checked_unset_error
              p
              (Reason.to_string
                 ("This is " ^ Typing_print.error ~ignore_dynamic:true env ty)
                 (get_reason ty)))
      | _ ->
        checked_unset_error p [];
        env
    in
    (match el with
    | [(p, Obj_get (_, _, OG_nullsafe, _))] ->
      Errors.nullsafe_property_write_context p;
      make_call_special_from_def env id tel (TUtils.terr env)
    | _ -> make_call_special_from_def env id tel MakeType.void)
  (* Special function `array_filter` *)
  | Id ((_, array_filter) as id)
    when String.equal array_filter SN.StdlibFunctions.array_filter
         && (not (List.is_empty el))
         && Option.is_none unpacked_element ->
    (* dispatch the call to typecheck the arguments *)
    let (env, fty, tal) = fun_type_of_id env id explicit_targs el in
    let (env, (tel, typed_unpack_element, res)) =
      call ~expected p env fty el unpacked_element
    in
    (* but ignore the result and overwrite it with custom return type *)
    let x = List.hd_exn el in
    let (env, _tx, ty) = expr env x in
    let explain_array_filter ty =
      map_reason ty ~f:(fun r -> Reason.Rarray_filter (p, r))
    in
    let get_value_type env tv =
      let (env, tv) =
        if List.length el > 1 then
          (env, tv)
        else
          Typing_solver.non_null env p tv
      in
      (env, explain_array_filter tv)
    in
    let rec get_array_filter_return_type env ty =
      let (env, ety) = Env.expand_type env ty in
      match deref ety with
      | (r, Tvarray tv) ->
        let (env, tv) = get_value_type env tv in
        (env, MakeType.varray r tv)
      | (r, Tunion tyl) ->
        let (env, tyl) = List.map_env env tyl get_array_filter_return_type in
        Typing_union.union_list env r tyl
      | (r, Tintersection tyl) ->
        let (env, tyl) = List.map_env env tyl get_array_filter_return_type in
        Inter.intersect_list env r tyl
      | (r, Tany _) -> (env, mk (r, Typing_utils.tany env))
      | (r, Terr) -> (env, TUtils.terr env r)
      | (r, _) ->
        let (env, tk) = Env.fresh_type env p in
        let (env, tv) = Env.fresh_type env p in
        Errors.try_
          (fun () ->
            let keyed_container_type =
              MakeType.keyed_container Reason.Rnone tk tv
            in
            let env =
              SubType.sub_type env ety keyed_container_type Errors.unify_error
            in
            let (env, tv) = get_value_type env tv in
            (env, MakeType.darray r (explain_array_filter tk) tv))
          (fun _ ->
            Errors.try_
              (fun () ->
                let container_type = MakeType.container Reason.Rnone tv in
                let env =
                  SubType.sub_type env ety container_type Errors.unify_error
                in
                let (env, tv) = get_value_type env tv in
                ( env,
                  MakeType.darray
                    r
                    (explain_array_filter (MakeType.arraykey r))
                    tv ))
              (fun _ -> (env, res)))
    in
    let (env, rty) = get_array_filter_return_type env ty in
    let fty =
      map_ty fty ~f:(function
          | Tfun ft -> Tfun { ft with ft_ret = MakeType.unenforced rty }
          | ty -> ty)
    in
    make_call
      env
      (Tast.make_typed_expr fpos fty (Aast.Id id))
      tal
      tel
      typed_unpack_element
      rty
  (* Special function `type_structure` *)
  | Id (p, type_structure)
    when String.equal type_structure SN.StdlibFunctions.type_structure
         && Int.equal (List.length el) 2
         && Option.is_none unpacked_element ->
    (match el with
    | [e1; e2] ->
      (match e2 with
      | (p, String cst) ->
        (* find the class constant implicitly defined by the typeconst *)
        let cid =
          match e1 with
          | (_, Class_const (cid, (_, x)))
          | (_, Class_get (cid, CGstring (_, x), _))
            when String.equal x SN.Members.mClass ->
            cid
          | _ -> (fst e1, CIexpr e1)
        in
        class_const ~incl_tc:true env p (cid, (p, cst))
      | _ ->
        Errors.illegal_type_structure p "second argument is not a string";
        expr_error env (Reason.Rwitness p) e)
    | _ -> assert false)
  (* Special function `array_map` *)
  | Id ((_, array_map) as x)
    when String.equal array_map SN.StdlibFunctions.array_map
         && (not (List.is_empty el))
         && Option.is_none unpacked_element ->
    (* This uses the arity to determine a signature for array_map. But there
     * is more: for two-argument use of array_map, we specialize the return
     * type to the collection that's passed in, below. *)
    let (env, fty, tal) = fun_type_of_id env x explicit_targs el in
    let (env, fty) = Env.expand_type env fty in
    let r_fty = get_reason fty in
    (*
        Takes a Container type and returns a function that can "pack" a type
        into an array of appropriate shape, preserving the key type, i.e.:
        array                 -> f, where f R = array
        array<X>              -> f, where f R = array<R>
        array<X, Y>           -> f, where f R = array<X, R>
        Vector<X>             -> f  where f R = array<R>
        KeyedContainer<X, Y>  -> f, where f R = array<X, R>
        Container<X>          -> f, where f R = array<arraykey, R>
        X                     -> f, where f R = Y
      *)
    let rec build_output_container env (x : locl_ty) :
        env * (env -> locl_ty -> env * locl_ty) =
      let (env, x) = Env.expand_type env x in
      match deref x with
      | (r, Tvarray _) -> (env, (fun env tr -> (env, MakeType.varray r tr)))
      | (r, Tany _) -> (env, (fun env _ -> (env, mk (r, Typing_utils.tany env))))
      | (r, Terr) -> (env, (fun env _ -> (env, TUtils.terr env r)))
      | (r, Tunion tyl) ->
        let (env, builders) = List.map_env env tyl build_output_container in
        ( env,
          fun env tr ->
            let (env, tyl) =
              List.map_env env builders (fun env f -> f env tr)
            in
            Typing_union.union_list env r tyl )
      | (r, Tintersection tyl) ->
        let (env, builders) = List.map_env env tyl build_output_container in
        ( env,
          fun env tr ->
            let (env, tyl) =
              List.map_env env builders (fun env f -> f env tr)
            in
            Typing_intersection.intersect_list env r tyl )
      | (r, _) ->
        let (env, tk) = Env.fresh_type env p in
        let (env, tv) = Env.fresh_type env p in
        let try_vector env =
          let vector_type = MakeType.const_vector r_fty tv in
          let env = SubType.sub_type env x vector_type Errors.unify_error in
          (env, (fun env tr -> (env, MakeType.varray r tr)))
        in
        let try_keyed_container env =
          let keyed_container_type = MakeType.keyed_container r_fty tk tv in
          let env =
            SubType.sub_type env x keyed_container_type Errors.unify_error
          in
          (env, (fun env tr -> (env, MakeType.darray r tk tr)))
        in
        let try_container env =
          let container_type = MakeType.container r_fty tv in
          let env = SubType.sub_type env x container_type Errors.unify_error in
          ( env,
            (fun env tr -> (env, MakeType.darray r (MakeType.arraykey r) tr)) )
        in
        let (env, tr) =
          Errors.try_
            (fun () -> try_vector env)
            (fun _ ->
              Errors.try_
                (fun () -> try_keyed_container env)
                (fun _ ->
                  Errors.try_
                    (fun () -> try_container env)
                    (fun _ ->
                      (env, (fun env _ -> (env, Typing_utils.mk_tany env p))))))
        in
        (env, tr)
    in
    let (env, fty) =
      match (deref fty, el) with
      | ((_, Tfun funty), [_; x]) ->
        let (env, _tx, x) = expr env x in
        let (env, output_container) = build_output_container env x in
        begin
          match get_varray_inst funty.ft_ret.et_type with
          | None -> (env, fty)
          | Some elem_ty ->
            let (env, elem_ty) = output_container env elem_ty in
            let ft_ret = MakeType.unenforced elem_ty in
            (env, mk (r_fty, Tfun { funty with ft_ret }))
        end
      | _ -> (env, fty)
    in
    let (env, (tel, typed_unpack_element, ty)) =
      call ~expected p env fty el None
    in
    make_call
      env
      (Tast.make_typed_expr fpos fty (Aast.Id x))
      tal
      tel
      typed_unpack_element
      ty
  (* Special function `Shapes::idx` *)
  | Class_const (((_, CI (_, shapes)) as class_id), ((_, idx) as method_id))
    when String.equal shapes SN.Shapes.cShapes && String.equal idx SN.Shapes.idx
    ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env fty res el ->
        match el with
        | [shape; field] ->
          let (env, _ts, shape_ty) = expr env shape in
          Typing_shapes.idx
            env
            shape_ty
            field
            None
            ~expr_pos:p
            ~fun_pos:(get_reason fty)
            ~shape_pos:(fst shape)
        | [shape; field; default] ->
          let (env, _ts, shape_ty) = expr env shape in
          let (env, _td, default_ty) = expr env default in
          Typing_shapes.idx
            env
            shape_ty
            field
            (Some (fst default, default_ty))
            ~expr_pos:p
            ~fun_pos:(get_reason fty)
            ~shape_pos:(fst shape)
        | _ -> (env, res))
  (* Special function `Shapes::at` *)
  | Class_const (((_, CI (_, shapes)) as class_id), ((_, at) as method_id))
    when String.equal shapes SN.Shapes.cShapes && String.equal at SN.Shapes.at
    ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env _fty res el ->
        match el with
        | [shape; field] ->
          let (env, _te, shape_ty) = expr env shape in
          Typing_shapes.at env ~expr_pos:p ~shape_pos:(fst shape) shape_ty field
        | _ -> (env, res))
  (* Special function `Shapes::keyExists` *)
  | Class_const
      (((_, CI (_, shapes)) as class_id), ((_, key_exists) as method_id))
    when String.equal shapes SN.Shapes.cShapes
         && String.equal key_exists SN.Shapes.keyExists ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env fty res el ->
        match el with
        | [shape; field] ->
          let (env, _te, shape_ty) = expr env shape in
          (* try accessing the field, to verify existence, but ignore
           * the returned type and keep the one coming from function
           * return type hint *)
          let (env, _) =
            Typing_shapes.idx
              env
              shape_ty
              field
              None
              ~expr_pos:p
              ~fun_pos:(get_reason fty)
              ~shape_pos:(fst shape)
          in
          (env, res)
        | _ -> (env, res))
  (* Special function `Shapes::removeKey` *)
  | Class_const
      (((_, CI (_, shapes)) as class_id), ((_, remove_key) as method_id))
    when String.equal shapes SN.Shapes.cShapes
         && String.equal remove_key SN.Shapes.removeKey ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env _ res el ->
        match el with
        | [shape; field] ->
          begin
            match shape with
            | (_, Lvar (_, lvar))
            | (_, Callconv (Ast_defs.Pinout, (_, Lvar (_, lvar)))) ->
              let (env, _te, shape_ty) = expr env shape in
              let (env, shape_ty) =
                Typing_shapes.remove_key p env shape_ty field
              in
              let env = set_valid_rvalue p env lvar shape_ty in
              (env, res)
            | _ ->
              Errors.invalid_shape_remove_key (fst shape);
              (env, res)
          end
        | _ -> (env, res))
  (* Special function `Shapes::toArray` *)
  | Class_const (((_, CI (_, shapes)) as class_id), ((_, to_array) as method_id))
    when String.equal shapes SN.Shapes.cShapes
         && String.equal to_array SN.Shapes.toArray ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env _ res el ->
        match el with
        | [shape] ->
          let (env, _te, shape_ty) = expr env shape in
          Typing_shapes.to_array env p shape_ty res
        | _ -> (env, res))
  (* Special function `Shapes::toDict` *)
  | Class_const (((_, CI (_, shapes)) as class_id), ((_, to_array) as method_id))
    when String.equal shapes SN.Shapes.cShapes
         && String.equal to_array SN.Shapes.toDict ->
    overload_function
      p
      env
      class_id
      method_id
      el
      unpacked_element
      (fun env _ res el ->
        match el with
        | [shape] ->
          let (env, _te, shape_ty) = expr env shape in
          Typing_shapes.to_dict env p shape_ty res
        | _ -> (env, res))
  (* Special function `parent::__construct` *)
  | Class_const ((pos, CIparent), ((_, construct) as id))
    when String.equal construct SN.Members.__construct ->
    let (env, tel, typed_unpack_element, ty, pty, ctor_fty) =
      call_parent_construct p env el unpacked_element
    in
    make_call
      env
      (Tast.make_typed_expr
         fpos
         ctor_fty
         (Aast.Class_const (((pos, pty), Aast.CIparent), id)))
      [] (* tal: no type arguments to constructor *)
      tel
      typed_unpack_element
      ty
  (* Calling parent / class method *)
  | Class_const ((pos, e1), m) ->
    let (env, _tal, tcid, ty1) =
      static_class_id
        ~check_constraints:(not (Nast.equal_class_id_ e1 CIparent))
        pos
        env
        []
        e1
    in
    let this_ty =
      mk (Reason.Rwitness fpos, TUtils.this_of (Env.get_self env))
    in
    (* In static context, you can only call parent::foo() on static methods.
     * In instance context, you can call parent:foo() on static
     * methods as well as instance methods
     *)
    let is_static =
      (not (Nast.equal_class_id_ e1 CIparent))
      || Env.is_static env
      || class_contains_smethod env ty1 m
    in
    let (env, (fty, tal)) =
      if is_static then
        class_get
          ~coerce_from_ty:None
          ~is_method:true
          ~is_const:false
          ~explicit_targs
          env
          ty1
          m
          e1
      else
        (* parent::nonStaticFunc() is really weird. It's calling a method
         * defined on the parent class, but $this is still the child class.
         * We can deal with this by hijacking the continuation that
         * calculates the SN.Typehints.this type *)
        let k_lhs _ = this_ty in
        TOG.obj_get_
          ~inst_meth:false
          ~is_method:true
          ~nullsafe:None
          ~obj_pos:pos
          ~coerce_from_ty:None
          ~is_nonnull:false
          ~explicit_targs:[]
          env
          ty1
          e1
          m
          k_lhs
          Errors.unify_error
    in
    check_disposable_in_return env fty;
    let ty =
      if Nast.equal_class_id_ e1 CIparent then
        this_ty
      else
        ty1
    in
    let (env, (tel, typed_unpack_element, ty)) =
      call
        ~expected
        ~method_call_info:
          (TR.make_call_info
             ~receiver_is_self:(Nast.equal_class_id_ e1 CIself)
             ~is_static
             ty
             (snd m))
        p
        env
        fty
        el
        unpacked_element
    in
    make_call
      env
      (Tast.make_typed_expr fpos fty (Aast.Class_const (tcid, m)))
      tal
      tel
      typed_unpack_element
      ty
  (* Call instance method *)
  | Obj_get (e1, (pos_id, Id m), nullflavor, false)
    when not (TypecheckerOptions.method_call_inference (Env.get_tcopt env)) ->
    let (env, te1, ty1) = expr ~accept_using_var:true env e1 in
    let nullsafe =
      match nullflavor with
      | OG_nullthrows -> None
      | OG_nullsafe -> Some p
    in
    let (env, (tfty, tal)) =
      TOG.obj_get
        ~obj_pos:(fst e1)
        ~is_method:true
        ~nullsafe:(Option.map ~f:(fun p -> Reason.Rnullsafe_op p) nullsafe)
        ~coerce_from_ty:None
        ~explicit_targs
        env
        ty1
        (CIexpr e1)
        m
        Errors.unify_error
    in
    check_disposable_in_return env tfty;
    let (env, (tel, typed_unpack_element, ty)) =
      call
        ~nullsafe
        ~expected
        ~method_call_info:
          (TR.make_call_info
             ~receiver_is_self:false
             ~is_static:false
             ty1
             (snd m))
        p
        env
        tfty
        el
        unpacked_element
    in
    make_call
      env
      (Tast.make_typed_expr
         fpos
         tfty
         (Aast.Obj_get
            ( te1,
              Tast.make_typed_expr pos_id tfty (Aast.Id m),
              nullflavor,
              false )))
      tal
      tel
      typed_unpack_element
      ty
  (* Call instance method using new method call inference *)
  | Obj_get (receiver, (pos_id, Id meth), nullflavor, false) ->
    (*****
      Typecheck `Obj_get` by enforcing that:
      - `<instance_type>` <: `Thas_member(m, #1)`
      where #1 is a fresh type variable.
    *****)
    let (env, typed_receiver, receiver_ty) =
      expr ~accept_using_var:true env receiver
    in
    let env = might_throw env in
    let nullsafe =
      match nullflavor with
      | OG_nullthrows -> None
      | OG_nullsafe -> Some p
    in
    (* Generate a fresh type `method_ty` for the type of the
       instance method, i.e. #1 *)
    let (env, method_ty) = Env.fresh_type env p in
    (* Create `Thas_member` constraint type *)
    let reason = Reason.Rwitness (fst receiver) in
    let has_method_ty =
      MakeType.has_member
        reason
        ~name:meth
        ~ty:method_ty
        ~class_id:(CIexpr receiver)
        ~explicit_targs:(Some explicit_targs)
    in
    let env = Env.set_tyvar_variance env method_ty in
    let (env, has_method_super_ty) =
      if Option.is_none nullsafe then
        (env, has_method_ty)
      else
        (* If null-safe, then `receiver_ty` <: `?Thas_member(m, #1)`,
           but *unlike* property access typing in `expr_`, we still use `#1` as
           our "result" if `receiver_ty` is nullable  (as opposed to `?#1`),
           deferring null-safety handling to after `call` *)
        let r = Reason.Rnullsafe_op p in
        let null_ty = MakeType.null r in
        Union.union_i env r has_method_ty null_ty
    in
    let env =
      Type.sub_type_i
        (fst receiver)
        Reason.URnone
        env
        (LoclType receiver_ty)
        has_method_super_ty
        Errors.unify_error
    in
    (* Perhaps solve for `method_ty`. Opening and closing a scope is too coarse
       here - type parameters are localised to fresh type variables over the
       course of subtyping above, and we do not want to solve these until later.
       Once we typecheck all function calls with a subtyping of function types,
       we should not need to solve early at all - transitive closure of
       subtyping should give enough information. *)
    let env =
      match get_var method_ty with
      | Some var ->
        Typing_solver.solve_to_equal_bound_or_wrt_variance
          env
          Reason.Rnone
          var
          Errors.unify_error
      | None -> env
    in
    let localize_targ env (_, targ) = Phase.localize_targ env targ in
    let (env, typed_targs) =
      List.map_env env ~f:(localize_targ ~check_well_kinded:true) explicit_targs
    in
    check_disposable_in_return env method_ty;
    let (env, (typed_params, typed_unpack_element, ret_ty)) =
      call
        ~nullsafe
        ~expected
        ~method_call_info:
          (TR.make_call_info
             ~receiver_is_self:false
             ~is_static:false
             receiver_ty
             (snd meth))
        ?in_await
        p
        env
        method_ty
        el
        unpacked_element
    in
    (* If the call is nullsafe AND the receiver is nullable,
       make the return type nullable too *)
    let (env, ret_ty) =
      if Option.is_some nullsafe then
        let r = Reason.Rnullsafe_op p in
        let null_ty = MakeType.null r in
        let (env, null_or_nothing_ty) =
          Inter.intersect env ~r null_ty receiver_ty
        in
        let (env, ret_option_ty) = Union.union env null_or_nothing_ty ret_ty in
        (env, ret_option_ty)
      else
        (env, ret_ty)
    in
    make_call
      env
      (Tast.make_typed_expr
         fpos
         method_ty
         (Aast.Obj_get
            ( typed_receiver,
              Tast.make_typed_expr pos_id method_ty (Aast.Id meth),
              nullflavor,
              false )))
      typed_targs
      typed_params
      typed_unpack_element
      ret_ty
  (* Function invocation *)
  | Fun_id x ->
    let (env, fty, tal) = fun_type_of_id env x explicit_targs el in
    check_disposable_in_return env fty;
    let (env, (tel, typed_unpack_element, ty)) =
      call ~expected p env fty el unpacked_element
    in
    make_call
      env
      (Tast.make_typed_expr fpos fty (Aast.Fun_id x))
      tal
      tel
      typed_unpack_element
      ty
  | Id ((_, id) as x) ->
    let (env, fty, tal) = fun_type_of_id env x explicit_targs el in
    check_disposable_in_return env fty;
    let (env, (tel, typed_unpack_element, ty)) =
      call ~expected p env fty el unpacked_element
    in
    let is_mutable = String.equal id SN.Rx.mutable_ in
    let is_move = String.equal id SN.Rx.move in
    let is_freeze = String.equal id SN.Rx.freeze in
    (* error when rx builtins are used in non-reactive context *)
    if not (Env.env_local_reactive env) then
      if is_mutable then
        Errors.mutable_in_nonreactive_context p
      else if is_move then
        Errors.move_in_nonreactive_context p
      else if is_freeze then
        Errors.freeze_in_nonreactive_context p;

    (* ban unpacking when calling builtings *)
    if (is_mutable || is_move || is_freeze) && Option.is_some unpacked_element
    then
      Errors.unpacking_disallowed_builtin_function p id;

    (* adjust env for Rx\freeze or Rx\move calls *)
    let env =
      if is_freeze then
        Typing_mutability.freeze_local p env tel
      else if is_move then
        Typing_mutability.move_local p env tel
      else
        env
    in
    make_call
      env
      (Tast.make_typed_expr fpos fty (Aast.Id x))
      tal
      tel
      typed_unpack_element
      ty
  | _ ->
    let (env, te, fty) = expr env e in
    let (env, fty) =
      Typing_solver.expand_type_and_solve
        ~description_of_expected:"a function value"
        env
        fpos
        fty
        Errors.unify_error
    in
    check_disposable_in_return env fty;
    let (env, (tel, typed_unpack_element, ty)) =
      call ~expected p env fty el unpacked_element
    in
    make_call
      env
      te
      (* tal: no type arguments to function values, as they are non-generic *)
      []
      tel
      typed_unpack_element
      ty

and fun_type_of_id env x tal el =
  match Env.get_fun env (snd x) with
  | None ->
    let (env, _, ty) = unbound_name env x (Pos.none, Aast.Null) in
    (env, ty, [])
  | Some { fe_type; fe_pos; fe_deprecated; _ } ->
    (match get_node fe_type with
    | Tfun ft ->
      let ft =
        Typing_special_fun.transform_special_fun_ty ft x (List.length el)
      in
      let ety_env = Phase.env_with_self env in
      let (env, tal) =
        Phase.localize_targs
          ~check_well_kinded:true
          ~is_method:true
          ~def_pos:fe_pos
          ~use_pos:(fst x)
          ~use_name:(strip_ns (snd x))
          env
          ft.ft_tparams
          (List.map ~f:snd tal)
      in
      let ft =
        Typing_enforceability.compute_enforced_and_pessimize_fun_type env ft
      in
      let use_pos = fst x in
      let def_pos = fe_pos in
      let (env, ft) =
        Phase.(
          localize_ft
            ~instantiation:
              { use_name = strip_ns (snd x); use_pos; explicit_targs = tal }
            ~def_pos
            ~ety_env
            env
            ft)
      in
      let fty = mk (get_reason fe_type, Tfun ft) in
      TVis.check_deprecated ~use_pos ~def_pos fe_deprecated;
      (env, fty, tal)
    | _ -> failwith "Expected function type")

(**
 * Checks if a class (given by cty) contains a given static method.
 *
 * We could refactor this + class_get
 *)
and class_contains_smethod env cty (_pos, mid) =
  let lookup_member ty =
    match get_class_type ty with
    | Some ((_, c), _, _) ->
      (match Env.get_class env c with
      | None -> false
      | Some class_ ->
        Option.is_some @@ Env.get_static_member true env class_ mid)
    | None -> false
  in
  let (_env, tyl) = TUtils.get_concrete_supertypes env cty in
  List.exists tyl ~f:lookup_member

and class_get
    ~is_method
    ~is_const
    ~coerce_from_ty
    ?(explicit_targs = [])
    ?(incl_tc = false)
    ?(function_pointer = false)
    env
    cty
    (p, mid)
    cid =
  let (env, this_ty) =
    if is_method then
      this_for_method env cid cty
    else
      (env, cty)
  in
  class_get_
    ~is_method
    ~is_const
    ~this_ty
    ~explicit_targs
    ~incl_tc
    ~coerce_from_ty
    ~function_pointer
    env
    cid
    cty
    (p, mid)

and class_get_
    ~is_method
    ~is_const
    ~this_ty
    ~coerce_from_ty
    ?(explicit_targs = [])
    ?(incl_tc = false)
    ?(function_pointer = false)
    env
    cid
    cty
    (p, mid) =
  let (env, cty) = Env.expand_type env cty in
  match deref cty with
  | (r, Tany _) -> (env, (mk (r, Typing_utils.tany env), []))
  | (r, Terr) -> (env, (err_witness env (Reason.to_pos r), []))
  | (_, Tdynamic) -> (env, (cty, []))
  | (_, Tunion tyl) ->
    let (env, pairs) =
      List.map_env env tyl (fun env ty ->
          class_get
            ~is_method
            ~is_const
            ~explicit_targs
            ~incl_tc
            ~coerce_from_ty
            env
            ty
            (p, mid)
            cid)
    in
    let (env, ty) =
      Union.union_list env (get_reason cty) (List.map ~f:fst pairs)
    in
    (env, (ty, []))
  | (_, Tintersection tyl) ->
    let (env, pairs) =
      TUtils.run_on_intersection env tyl ~f:(fun env ty ->
          class_get
            ~is_method
            ~is_const
            ~explicit_targs
            ~incl_tc
            ~coerce_from_ty
            env
            ty
            (p, mid)
            cid)
    in
    let (env, ty) =
      Inter.intersect_list env (get_reason cty) (List.map ~f:fst pairs)
    in
    (env, (ty, []))
  | (_, Tnewtype (_, _, ty))
  | (_, Tdependent (_, ty)) ->
    class_get_
      ~is_method
      ~is_const
      ~this_ty
      ~explicit_targs
      ~incl_tc
      ~coerce_from_ty
      env
      cid
      ty
      (p, mid)
  | (r, Tgeneric _) ->
    let (env, tyl) = TUtils.get_concrete_supertypes env cty in
    if List.is_empty tyl then begin
      Errors.non_class_member
        ~is_method
        mid
        p
        (Typing_print.error env cty)
        (get_pos cty);
      (env, (err_witness env p, []))
    end else
      let (env, ty) = Typing_intersection.intersect_list env r tyl in
      class_get_
        ~is_method
        ~is_const
        ~this_ty
        ~explicit_targs
        ~incl_tc
        ~coerce_from_ty
        env
        cid
        ty
        (p, mid)
  | (_, Tclass ((_, c), _, paraml)) ->
    let class_ = Env.get_class env c in
    (match class_ with
    | None -> (env, (Typing_utils.mk_tany env p, []))
    | Some class_ ->
      (* We need to instantiate generic parameters in the method signature *)
      let ety_env =
        {
          type_expansions = [];
          this_ty;
          substs = TUtils.make_locl_subst_for_class_tparams class_ paraml;
          from_class = Some cid;
          quiet = true;
          on_error = Errors.unify_error_at p;
        }
      in
      let get_smember_from_constraints env class_info =
        let upper_bounds =
          Cls.upper_bounds_on_this_from_constraints class_info
        in
        let (env, upper_bounds) =
          List.map_env env upper_bounds ~f:(fun env up ->
              Phase.localize ~ety_env env up)
        in
        let (env, inter_ty) =
          Inter.intersect_list env (Reason.Rwitness p) upper_bounds
        in
        class_get_
          ~is_method
          ~is_const
          ~this_ty
          ~explicit_targs
          ~incl_tc
          ~coerce_from_ty
          env
          cid
          inter_ty
          (p, mid)
      in
      let try_get_smember_from_constraints env class_info =
        Errors.try_with_error
          (fun () -> get_smember_from_constraints env class_info)
          (fun () ->
            TOG.smember_not_found
              p
              ~is_const
              ~is_method
              class_info
              mid
              Errors.unify_error;
            (env, (TUtils.terr env Reason.Rnone, [])))
      in
      if is_const then (
        let const =
          if incl_tc then
            Env.get_const env class_ mid
          else
            match Env.get_typeconst env class_ mid with
            | Some _ ->
              Errors.illegal_typeconst_direct_access p;
              None
            | None -> Env.get_const env class_ mid
        in
        match const with
        | None when Cls.has_upper_bounds_on_this_from_constraints class_ ->
          try_get_smember_from_constraints env class_
        | None ->
          TOG.smember_not_found
            p
            ~is_const
            ~is_method
            class_
            mid
            Errors.unify_error;
          (env, (TUtils.terr env Reason.Rnone, []))
        | Some { cc_type; cc_abstract; cc_pos; _ } ->
          let (env, cc_locl_type) = Phase.localize ~ety_env env cc_type in
          ( if cc_abstract then
            match cid with
            | CIstatic
            | CIexpr _ ->
              ()
            | _ ->
              let cc_name = Cls.name class_ ^ "::" ^ mid in
              Errors.abstract_const_usage p cc_pos cc_name );
          (env, (cc_locl_type, []))
      ) else
        let static_member_opt =
          Env.get_static_member is_method env class_ mid
        in
        (match static_member_opt with
        | None when Cls.has_upper_bounds_on_this_from_constraints class_ ->
          try_get_smember_from_constraints env class_
        | None ->
          TOG.smember_not_found
            p
            ~is_const
            ~is_method
            class_
            mid
            Errors.unify_error;
          (env, (TUtils.terr env Reason.Rnone, []))
        | Some
            ( {
                ce_visibility = vis;
                ce_type = (lazy member_decl_ty);
                ce_deprecated;
                _;
              } as ce ) ->
          let def_pos = get_pos member_decl_ty in
          TVis.check_class_access
            ~use_pos:p
            ~def_pos
            env
            (vis, get_ce_lsb ce)
            cid
            class_;
          TVis.check_deprecated ~use_pos:p ~def_pos ce_deprecated;
          check_class_get env p def_pos c mid ce cid function_pointer;
          let (env, member_ty, et_enforced, tal) =
            match deref member_decl_ty with
            (* We special case Tfun here to allow passing in explicit tparams to localize_ft. *)
            | (r, Tfun ft) when is_method ->
              let (env, explicit_targs) =
                Phase.localize_targs
                  ~check_well_kinded:true
                  ~is_method:true
                  ~def_pos
                  ~use_pos:p
                  ~use_name:(strip_ns mid)
                  env
                  ft.ft_tparams
                  (List.map ~f:snd explicit_targs)
              in
              let ft =
                Typing_enforceability.compute_enforced_and_pessimize_fun_type
                  env
                  ft
              in
              let (env, ft) =
                Phase.(
                  localize_ft
                    ~instantiation:
                      { use_name = strip_ns mid; use_pos = p; explicit_targs }
                    ~ety_env
                    ~def_pos
                    env
                    ft)
              in
              (env, mk (r, Tfun ft), false, explicit_targs)
            (* unused *)
            | _ ->
              let { et_type; et_enforced } =
                Typing_enforceability.compute_enforced_and_pessimize_ty
                  env
                  member_decl_ty
              in
              let (env, member_ty) = Phase.localize ~ety_env env et_type in
              (* TODO(T52753871) make function just return possibly_enforced_ty
               * after considering intersection case *)
              (env, member_ty, et_enforced, [])
          in
          let (env, member_ty) =
            if Cls.has_upper_bounds_on_this_from_constraints class_ then
              let ((env, (member_ty', _)), succeed) =
                Errors.try_with_error
                  (fun () -> (get_smember_from_constraints env class_, true))
                  (fun () ->
                    (* No eligible functions found in constraints *)
                    ((env, (MakeType.mixed Reason.Rnone, [])), false))
              in
              if succeed then
                Inter.intersect env (Reason.Rwitness p) member_ty member_ty'
              else
                (env, member_ty)
            else
              (env, member_ty)
          in
          let env =
            match coerce_from_ty with
            | None -> env
            | Some (p, ur, ty) ->
              Typing_coercion.coerce_type
                p
                ur
                env
                ty
                { et_type = member_ty; et_enforced }
                Errors.unify_error
          in
          (env, (member_ty, tal))))
  | (_, Tunapplied_alias _) ->
    Typing_defs.error_Tunapplied_alias_in_illegal_context ()
  | ( _,
      ( Tvar _ | Tnonnull | Tvarray _ | Tdarray _ | Tvarray_or_darray _
      | Toption _ | Tprim _ | Tfun _ | Ttuple _ | Tobject | Tshape _ | Taccess _
        ) ) ->
    Errors.non_class_member
      ~is_method
      mid
      p
      (Typing_print.error env cty)
      (get_pos cty);
    (env, (err_witness env p, []))

and class_id_for_new
    ~exact p env (cid : Nast.class_id_) (explicit_targs : Nast.targ list) :
    newable_class_info =
  let (env, tal, te, cid_ty) =
    static_class_id
      ~check_targs_well_kinded:true
      ~check_explicit_targs:true
      ~exact
      ~check_constraints:false
      p
      env
      explicit_targs
      cid
  in
  (* Need to deal with union case *)
  let rec get_info res tyl =
    match tyl with
    | [] -> (env, tal, te, res)
    | ty :: tyl ->
      (match get_node ty with
      | Tunion tyl'
      | Tintersection tyl' ->
        get_info res (tyl' @ tyl)
      | _ ->
        (* Instantiation on an abstract class (e.g. from classname<T>) is
         * via the base type (to check constructor args), but the actual
         * type `ty` must be preserved. *)
        (match get_node (TUtils.get_base_type env ty) with
        | Tdynamic -> get_info (`Dynamic :: res) tyl
        | Tclass (sid, _, _) ->
          let class_ = Env.get_class env (snd sid) in
          (match class_ with
          | None -> get_info res tyl
          | Some class_info ->
            (match (te, cid_ty) with
            (* When computing the classes for a new T() where T is a generic,
             * the class must be consistent (final, final constructor, or
             * <<__ConsistentConstruct>>) for its constructor to be considered *)
            | ((_, Aast.CI (_, c)), ty) when is_generic_equal_to c ty ->
              (* Only have this choosing behavior for new T(), not all generic types
               * i.e. new classname<T>, TODO: T41190512 *)
              if Tast_utils.valid_newable_class class_info then
                get_info (`Class (sid, class_info, ty) :: res) tyl
              else
                get_info res tyl
            | _ -> get_info (`Class (sid, class_info, ty) :: res) tyl))
        | _ -> get_info res tyl))
  in
  get_info [] [cid_ty]

(* To be a valid trait declaration, all of its 'require extends' must
 * match; since there's no multiple inheritance, it follows that all of
 * the 'require extends' must belong to the same inheritance hierarchy
 * and one of them should be the child of all the others *)
and trait_most_concrete_req_class trait env =
  List.fold
    (Cls.all_ancestor_reqs trait)
    ~f:
      begin
        fun acc (_p, ty) ->
        let (_r, (_p, name), _paraml) = TUtils.unwrap_class_type ty in
        let keep =
          match acc with
          | Some (c, _ty) -> Cls.has_ancestor c name
          | None -> false
        in
        if keep then
          acc
        else
          let class_ = Env.get_class env name in
          match class_ with
          | None -> acc
          | Some c when Ast_defs.(equal_class_kind (Cls.kind c) Cinterface) ->
            acc
          | Some c when Ast_defs.(equal_class_kind (Cls.kind c) Ctrait) ->
            (* this is an error case for which Typing_check_decls spits out
             * an error, but does *not* currently remove the offending
             * 'require extends' or 'require implements' *)
            acc
          | Some c -> Some (c, ty)
      end
    ~init:None

(* When invoking a method the class_id is used to determine what class we
 * lookup the method in, but the type of 'this' will be the late bound type.
 * For example:
 *
 *  class C {
 *    public static function get(): this { return new static(); }
 *
 *    public static function alias(): this { return self::get(); }
 *  }
 *
 *  In C::alias, when we invoke self::get(), 'self' is resolved to the class
 *  in the lexical scope (C), so call C::get. However the method is executed in
 *  the current context, so static inside C::get will be resolved to the late
 *  bound type (get_called_class() within C::alias).
 *
 *  This means when determining the type of this, CIparent and CIself should be
 *  changed to CIstatic. For the other cases of C::get() or $c::get(), we only
 *  look at the left hand side of the '::' and use the type type associated
 *  with it.
 *
 *  Thus C::get() will return a type C, while $c::get() will return the same
 *  type as $c.
 *)
and this_for_method env cid default_ty =
  match cid with
  | CIparent
  | CIself
  | CIstatic ->
    let p = get_pos default_ty in
    let (env, _tal, _te, ty) =
      static_class_id ~check_constraints:false p env [] CIstatic
    in
    ExprDepTy.make env CIstatic ty
  | _ -> (env, default_ty)

(** Resolve class expressions like `parent`, `self`, `static`, classnames
    and others. *)
and static_class_id
    ?(check_targs_well_kinded = false)
    ?(exact = Nonexact)
    ?(check_explicit_targs = false)
    ~(check_constraints : bool)
    (p : pos)
    (env : env)
    (tal : Nast.targ list) :
    Nast.class_id_ -> env * Tast.targ list * Tast.class_id * locl_ty =
  let make_result env tal te ty = (env, tal, ((p, ty), te), ty) in
  function
  | CIparent ->
    (match get_class_type (Env.get_self env) with
    | Some ((_, self), _, _) ->
      (match Env.get_class env self with
      | Some trait when Ast_defs.(equal_class_kind (Cls.kind trait) Ctrait) ->
        (match trait_most_concrete_req_class trait env with
        | None ->
          Errors.parent_in_trait p;
          make_result env [] Aast.CIparent (err_witness env p)
        | Some (_, parent_ty) ->
          (* inside a trait, parent is SN.Typehints.this, but with the
           * type of the most concrete class that the trait has
           * "require extend"-ed *)
          let r = Reason.Rwitness p in
          let (env, parent_ty) = Phase.localize_with_self env parent_ty in
          make_result env [] Aast.CIparent (mk (r, TUtils.this_of parent_ty)))
      | _ ->
        let parent =
          match Env.get_parent_ty env with
          | None ->
            Errors.parent_undefined p;
            mk (Reason.none, Typing_defs.make_tany ())
          | Some parent -> parent
        in
        let r = Reason.Rwitness p in
        let (env, parent) = Phase.localize_with_self env parent in
        (* parent is still technically the same object. *)
        make_result
          env
          []
          Aast.CIparent
          (mk (r, TUtils.this_of (mk (r, get_node parent)))))
    | None ->
      let parent =
        match Env.get_parent_ty env with
        | None ->
          Errors.parent_undefined p;
          mk (Reason.none, Typing_defs.make_tany ())
        | Some parent -> parent
      in
      let r = Reason.Rwitness p in
      let (env, parent) = Phase.localize_with_self env parent in
      (* parent is still technically the same object. *)
      make_result
        env
        []
        Aast.CIparent
        (mk (r, TUtils.this_of (mk (r, get_node parent)))))
  | CIstatic ->
    let this = mk (Reason.Rwitness p, TUtils.this_of (Env.get_self env)) in
    make_result env [] Aast.CIstatic this
  | CIself ->
    let self =
      match get_node (Env.get_self env) with
      | Tclass (c, _, tyl) -> Tclass (c, exact, tyl)
      | self -> self
    in
    make_result env [] Aast.CIself (mk (Reason.Rwitness p, self))
  | CI ((p, id) as c) as e1 ->
    begin
      match Env.get_pos_and_kind_of_generic env id with
      | Some (def_pos, kind) ->
        let simple_kind = Typing_kinding_defs.Simple.from_full_kind kind in
        let param_nkinds =
          Typing_kinding_defs.Simple.get_named_parameter_kinds simple_kind
        in
        let (env, tal) =
          Phase.localize_targs_with_kinds
            ~check_well_kinded:check_targs_well_kinded
            ~is_method:true
            ~def_pos
            ~use_pos:p
            ~use_name:(strip_ns (snd c))
            ~check_explicit_targs
            env
            param_nkinds
            (List.map ~f:snd tal)
        in
        let r = Reason.Rhint p in
        let type_args = List.map tal fst in
        let tgeneric = MakeType.generic ~type_args r id in
        make_result env tal (Aast.CI c) tgeneric
      | None ->
        (* Not a type parameter *)
        let class_ = Env.get_class env id in
        (match class_ with
        | None -> make_result env [] (Aast.CI c) (Typing_utils.mk_tany env p)
        | Some class_ ->
          let (env, ty, tal) =
            List.map ~f:snd tal
            |> Phase.localize_targs_and_check_constraints
                 ~exact
                 ~check_well_kinded:check_targs_well_kinded
                 ~check_constraints
                 ~def_pos:(Cls.pos class_)
                 ~use_pos:p
                 ~check_explicit_targs
                 env
                 c
                 e1
                 (Cls.tparams class_)
          in
          make_result env tal (Aast.CI c) ty)
    end
  | CIexpr ((p, _) as e) ->
    let (env, te, ty) = expr env e in
    let rec resolve_ety env ty =
      let (env, ty) =
        Typing_solver.expand_type_and_solve
          ~description_of_expected:"an object"
          env
          p
          ty
          Errors.unify_error
      in
      let base_ty = TUtils.get_base_type env ty in
      match deref base_ty with
      | (_, Tnewtype (classname, [the_cls], _))
        when String.equal classname SN.Classes.cClassname ->
        resolve_ety env the_cls
      | (_, Tgeneric _)
      | (_, Tclass _) ->
        (env, ty)
      | (r, Tunion tyl) ->
        let (env, tyl) = List.map_env env tyl resolve_ety in
        (env, MakeType.union r tyl)
      | (r, Tintersection tyl) ->
        let (env, tyl) = TUtils.run_on_intersection env tyl ~f:resolve_ety in
        Inter.intersect_list env r tyl
      | (_, Tdynamic) -> (env, base_ty)
      | (_, (Tany _ | Tprim Tstring | Tobject)) when not (Env.is_strict env) ->
        (env, Typing_utils.mk_tany env p)
      | (_, Terr) -> (env, err_witness env p)
      | (r, Tvar _) ->
        Errors.unknown_type "an object" p (Reason.to_string "It is unknown" r);
        (env, err_witness env p)
      | (_, Tunapplied_alias _) ->
        Typing_defs.error_Tunapplied_alias_in_illegal_context ()
      | ( _,
          ( Tany _ | Tnonnull | Tvarray _ | Tdarray _ | Tvarray_or_darray _
          | Toption _ | Tprim _ | Tfun _ | Ttuple _ | Tnewtype _ | Tdependent _
          | Tobject | Tshape _ | Taccess _ ) ) ->
        Errors.expected_class
          ~suffix:(", but got " ^ Typing_print.error env base_ty)
          p;
        (env, err_witness env p)
    in
    let (env, result_ty) = resolve_ety env ty in
    make_result env [] (Aast.CIexpr te) result_ty

and call_construct p env class_ params el unpacked_element cid cid_ty =
  let (cid, cid_ty) =
    if Nast.equal_class_id_ cid CIparent then
      (CIstatic, mk (Reason.Rwitness p, TUtils.this_of (Env.get_self env)))
    else
      (cid, cid_ty)
  in
  let ety_env =
    {
      type_expansions = [];
      this_ty = cid_ty;
      substs = TUtils.make_locl_subst_for_class_tparams class_ params;
      from_class = Some cid;
      quiet = true;
      on_error = Errors.unify_error_at p;
    }
  in
  let env =
    Phase.check_tparams_constraints ~use_pos:p ~ety_env env (Cls.tparams class_)
  in
  let env =
    Phase.check_where_constraints
      ~in_class:true
      ~use_pos:p
      ~definition_pos:(Cls.pos class_)
      ~ety_env
      env
      (Cls.where_constraints class_)
  in
  if Cls.is_xhp class_ then
    (env, [], None, TUtils.mk_tany env p)
  else
    let cstr = Env.get_construct env class_ in
    let mode = Env.get_mode env in
    match fst cstr with
    | None ->
      if
        ((not (List.is_empty el)) || Option.is_some unpacked_element)
        && (FileInfo.is_strict mode || FileInfo.(equal_mode mode Mpartial))
        && Cls.members_fully_known class_
      then
        Errors.constructor_no_args p;
      let (env, tel, _tyl) = exprs env el in
      (env, tel, None, TUtils.terr env Reason.Rnone)
    | Some { ce_visibility = vis; ce_type = (lazy m); ce_deprecated; _ } ->
      let def_pos = get_pos m in
      TVis.check_obj_access ~use_pos:p ~def_pos env vis;
      TVis.check_deprecated ~use_pos:p ~def_pos ce_deprecated;
      (* Obtain the type of the constructor *)
      let (env, m) =
        match deref m with
        | (r, Tfun ft) ->
          let ft =
            Typing_enforceability.compute_enforced_and_pessimize_fun_type env ft
          in
          (* This creates type variables for non-denotable type parameters on constructors.
           * These are notably different from the tparams on the class, which are handled
           * at the top of this function. User-written type parameters on constructors
           * are still a parse error. This is a no-op if ft.ft_tparams is empty. *)
          let (env, implicit_constructor_targs) =
            Phase.localize_targs
              ~check_well_kinded:true
              ~is_method:true
              ~def_pos
              ~use_pos:p
              ~use_name:"constructor"
              env
              ft.ft_tparams
              []
          in
          let (env, ft) =
            Phase.(
              localize_ft
                ~instantiation:
                  {
                    use_name = "constructor";
                    use_pos = p;
                    explicit_targs = implicit_constructor_targs;
                  }
                ~ety_env
                ~def_pos
                env
                ft)
          in
          (env, mk (r, Tfun ft))
        | (r, _) ->
          Errors.internal_error p "Expected function type for constructor";
          let ty = TUtils.terr env r in
          (env, ty)
      in
      let (env, (tel, typed_unpack_element, _ty)) =
        call ~expected:None p env m el unpacked_element
      in
      (env, tel, typed_unpack_element, m)

and check_arity ?(did_unpack = false) pos pos_def ft (arity : int) =
  let exp_min = Typing_defs.arity_min ft in
  if arity < exp_min then
    Errors.typing_too_few_args exp_min arity pos pos_def None;
  match ft.ft_arity with
  | Fstandard ->
    let exp_max = List.length ft.ft_params in
    let arity =
      if did_unpack then
        arity + 1
      else
        arity
    in
    if arity > exp_max then
      Errors.typing_too_many_args exp_max arity pos pos_def None
  | Fvariadic _ -> ()

and check_lambda_arity lambda_pos def_pos lambda_ft expected_ft =
  match (lambda_ft.ft_arity, expected_ft.ft_arity) with
  | (Fstandard, Fstandard) ->
    let expected_min = Typing_defs.arity_min expected_ft in
    let lambda_min = Typing_defs.arity_min lambda_ft in
    if lambda_min < expected_min then
      Errors.typing_too_few_args expected_min lambda_min lambda_pos def_pos None;
    if lambda_min > expected_min then
      Errors.typing_too_many_args
        expected_min
        lambda_min
        lambda_pos
        def_pos
        None
  | (_, _) -> ()

(* The variadic capture argument is an array listing the passed
 * variable arguments for the purposes of the function body; callsites
 * should not unify with it *)
and variadic_param env ft =
  match ft.ft_arity with
  | Fvariadic param -> (env, Some param)
  | Fstandard -> (env, None)

and param_modes ?(is_variadic = false) ({ fp_pos; _ } as fp) (pos, e) =
  match (get_fp_mode fp, e) with
  | (FPnormal, Callconv _) ->
    Errors.inout_annotation_unexpected pos fp_pos is_variadic
  | (FPnormal, _) -> ()
  | (FPinout, Callconv (Ast_defs.Pinout, _)) -> ()
  | (FPinout, _) -> Errors.inout_annotation_missing pos fp_pos

and inout_write_back env { fp_type; _ } (_, e) =
  match e with
  | Callconv (Ast_defs.Pinout, e1) ->
    (* Translate the write-back semantics of inout parameters.
     *
     * This matters because we want to:
     * (1) make sure we can write to the original argument
     *     (modifiable lvalue check)
     * (2) allow for growing of locals / Tunions (type side effect)
     *     but otherwise unify the argument type with the parameter hint
     *)
    let (env, _te, _ty) =
      assign_ (fst e1) Reason.URparam_inout env e1 fp_type.et_type
    in
    env
  | _ -> env

(** Typechecks a call.
Returns in this order the typed expressions for the arguments, for the variadic arguments, and the return type. *)
and call
    ~(expected : ExpectedTy.t option)
    ?(method_call_info : TR.method_call_info option)
    ?(nullsafe : Pos.t option = None)
    ?in_await
    pos
    env
    fty
    (el : Nast.expr list)
    (unpacked_element : Nast.expr option) :
    env * (Tast.expr list * Tast.expr option * locl_ty) =
  let resl =
    TUtils.try_over_concrete_supertypes env fty (fun env fty ->
        let (env, efty) =
          if TypecheckerOptions.method_call_inference (Env.get_tcopt env) then
            Env.expand_type env fty
          else
            Typing_solver.expand_type_and_solve
              ~description_of_expected:"a function value"
              env
              pos
              fty
              Errors.unify_error
        in
        match deref efty with
        | (r, ((Tprim Tnull | Tdynamic | Terr | Tany _ | Tunion []) as ty))
          when match ty with
               | Tprim Tnull -> Option.is_some nullsafe
               | _ -> true ->
          let el =
            Option.value_map ~f:(fun u -> el @ [u]) ~default:el unpacked_element
          in
          let expected_arg_ty =
            (* Note: We ought to be using 'mixed' here *)
            ExpectedTy.make pos Reason.URparam (Typing_utils.mk_tany env pos)
          in
          let (env, tel) =
            List.map_env env el (fun env elt ->
                let (env, te, ty) = expr ~expected:expected_arg_ty env elt in
                let env =
                  if TCO.global_inference (Env.get_tcopt env) then
                    match get_node efty with
                    | Terr
                    | Tany _
                    | Tdynamic ->
                      Typing_coercion.coerce_type
                        pos
                        Reason.URparam
                        env
                        ty
                        (MakeType.unenforced efty)
                        Errors.unify_error
                    | _ -> env
                  else
                    env
                in
                let env =
                  match elt with
                  | (_, Callconv (Ast_defs.Pinout, e1)) ->
                    let (env, _te, _ty) =
                      assign_ (fst e1) Reason.URparam_inout env e1 efty
                    in
                    env
                  | _ -> env
                in
                (env, te))
          in
          let env =
            call_untyped_unpack env (Reason.to_pos r) unpacked_element
          in
          let ty =
            match ty with
            | Tprim Tnull -> mk (r, Tprim Tnull)
            | Tdynamic -> MakeType.dynamic (Reason.Rdynamic_call pos)
            | Terr
            | Tany _ ->
              Typing_utils.mk_tany env pos
            | Tunion []
            | _ (* _ should not happen! *) ->
              mk (r, Tunion [])
          in
          (env, (tel, None, ty))
        | (_, Tunion [ty]) ->
          call ~expected ~nullsafe ?in_await pos env ty el unpacked_element
        | (r, Tunion tyl) ->
          let (env, resl) =
            List.map_env env tyl (fun env ty ->
                call
                  ~expected
                  ~nullsafe
                  ?in_await
                  pos
                  env
                  ty
                  el
                  unpacked_element)
          in
          let retl = List.map resl ~f:(fun (_, _, x) -> x) in
          let (env, ty) = Union.union_list env r retl in
          (* We shouldn't be picking arbitrarily for the TAST here, as TAST checks
           * depend on the types inferred. Here's we're preserving legacy behaviour
           * by picking the last one.
           * TODO: don't do this, instead use subtyping to push unions
           * through function types
           *)
          let (tel, typed_unpack_element, _) = List.hd_exn (List.rev resl) in
          (env, (tel, typed_unpack_element, ty))
        | (r, Tintersection tyl) ->
          let (env, resl) =
            TUtils.run_on_intersection env tyl ~f:(fun env ty ->
                call
                  ~expected
                  ~nullsafe
                  ?in_await
                  pos
                  env
                  ty
                  el
                  unpacked_element)
          in
          let retl = List.map resl ~f:(fun (_, _, x) -> x) in
          let (env, ty) = Inter.intersect_list env r retl in
          (* We shouldn't be picking arbitrarily for the TAST here, as TAST checks
           * depend on the types inferred. Here we're preserving legacy behaviour
           * by picking the last one.
           * TODO: don't do this, instead use subtyping to push intersections
           * through function types
           *)
          let (tel, typed_unpack_element, _) = List.hd_exn (List.rev resl) in
          (env, (tel, typed_unpack_element, ty))
        | (r2, Tfun ft) ->
          (* Typing of format string functions. It is dependent on the arguments (el)
           * so it cannot be done earlier.
           *)
          let pos_def = Reason.to_pos r2 in
          let (env, ft) = Typing_exts.retype_magic_func env ft el in
          let (env, var_param) = variadic_param env ft in
          (* Force subtype with expected result *)
          let env =
            check_expected_ty "Call result" env ft.ft_ret.et_type expected
          in
          let env = Env.set_tyvar_variance env ft.ft_ret.et_type in
          let is_lambda e =
            match snd e with
            | Efun _
            | Lfun _ ->
              true
            | _ -> false
          in
          let get_next_param_info paraml =
            match paraml with
            | param :: paraml -> (false, Some param, paraml)
            | [] -> (true, var_param, paraml)
          in
          (* TODO: We're using plain String at the moment, until we
           * introduce actual atom notation (#A instead of "A")
           *)
          let expand_atom_in_enum env enum_name atom_name =
            let cls = Env.get_class env enum_name in
            match cls with
            | Some cls ->
              (match Env.get_const env cls atom_name with
              | Some const_def ->
                let dty = const_def.cc_type in
                let (env, lty) = Phase.localize_with_self env dty in
                let hi = (pos, lty) in
                let te = (hi, EnumAtom atom_name) in
                (env, Some (te, lty))
              | None ->
                Errors.atom_unknown pos atom_name enum_name;
                (env, None))
            | None -> (env, None)
          in
          let check_arg env ((pos, arg) as e) opt_param ~is_variadic =
            match opt_param with
            | Some param ->
              (* First check if __Atom is used *)
              let (env, atom_type) =
                let is_atom = get_fp_is_atom param in
                let ety = param.fp_type.et_type in
                match arg with
                | EnumAtom atom_name when is_atom ->
                  (match get_node ety with
                  | Tclass ((_, name), _, [ty_enum; _ty_interface])
                    when String.equal name SN.Classes.cEnumMember ->
                    (match get_node ty_enum with
                    | Tclass ((_, enum_name), _, _)
                      when Env.is_enum_class env enum_name ->
                      expand_atom_in_enum env enum_name atom_name
                    | Tgeneric (name, _) ->
                      let upper_bounds =
                        Typing_utils.collect_enum_class_upper_bounds env name
                      in
                      (* To avoid ambiguity, we only support the case where
                       * there is a single upper bound that is an EnumClass.
                       * We might want to relax that later (e.g. with  the
                       * support for intersections.
                       * See Typing_check_decls.check_atom_on_param.
                       *)
                      if SSet.cardinal upper_bounds = 1 then
                        let enum_name = SSet.choose upper_bounds in
                        expand_atom_in_enum env enum_name atom_name
                      else
                        (env, None)
                    | _ ->
                      (* Already reported, see Typing_check_decls *)
                      (env, None))
                  | _ ->
                    (* Already reported, see Typing_check_decls *)
                    (env, None))
                | Class_const _ when is_atom ->
                  Errors.atom_invalid_argument pos;
                  (env, None)
                | _ -> (env, None)
              in
              let (env, te, ty) =
                match atom_type with
                | Some (te, ty) -> (env, te, ty)
                | None ->
                  let expected =
                    ExpectedTy.make_and_allow_coercion
                      pos
                      Reason.URparam
                      param.fp_type
                  in
                  expr
                    ~accept_using_var:(get_fp_accept_disposable param)
                    ~expected
                    env
                    e
              in
              let env = call_param env param (e, ty) ~is_variadic in
              (env, Some (te, ty))
            | None ->
              let expected =
                ExpectedTy.make
                  pos
                  Reason.URparam
                  (Typing_utils.mk_tany env pos)
              in
              let (env, te, ty) = expr ~expected env e in
              (env, Some (te, ty))
          in
          let set_tyvar_variance_from_lambda_param env opt_param =
            match opt_param with
            | Some param ->
              let rec set_params_variance env ty =
                let (env, ty) = Env.expand_type env ty in
                match get_node ty with
                | Tunion [ty] -> set_params_variance env ty
                | Toption ty -> set_params_variance env ty
                | Tfun { ft_params; ft_ret; _ } ->
                  let env =
                    List.fold
                      ~init:env
                      ~f:(fun env param ->
                        Env.set_tyvar_variance env param.fp_type.et_type)
                      ft_params
                  in
                  Env.set_tyvar_variance env ft_ret.et_type ~flip:true
                | _ -> env
              in
              set_params_variance env param.fp_type.et_type
            | None -> env
          in
          (* Given an expected function type ft, check types for the non-unpacked
           * arguments. Don't check lambda expressions if check_lambdas=false *)
          let rec check_args check_lambdas env el paraml =
            match el with
            (* We've got an argument *)
            | (e, opt_result) :: el ->
              (* Pick up next parameter type info *)
              let (is_variadic, opt_param, paraml) =
                get_next_param_info paraml
              in
              let (env, one_result) =
                match (check_lambdas, is_lambda e) with
                | (false, false)
                | (true, true) ->
                  check_arg env e opt_param ~is_variadic
                | (false, true) ->
                  let env =
                    set_tyvar_variance_from_lambda_param env opt_param
                  in
                  (env, opt_result)
                | (true, false) -> (env, opt_result)
              in
              let (env, rl, paraml) = check_args check_lambdas env el paraml in
              (env, (e, one_result) :: rl, paraml)
            | [] -> (env, [], paraml)
          in
          (* Same as above, but checks the types of the implicit arguments, which are
           * read from the context *)
          let check_implicit_args env =
            let capability =
              Typing_coeffects.get_type ft.ft_implicit_params.capability
            in
            if not (TypecheckerOptions.call_coeffects (Env.get_tcopt env)) then
              env
            else
              let env_capability =
                Env.get_local_check_defined
                  env
                  (pos, Typing_coeffects.capability_id)
              in
              Type.sub_type
                pos
                Reason.URnone
                env
                env_capability
                capability
                (fun ?code:_c _ _ ->
                  Errors.call_coeffect_error
                    pos
                    ~available_incl_unsafe:
                      (Typing_print.coeffects env env_capability)
                    ~available_pos:(Typing_defs.get_pos env_capability)
                    ~required_pos:(Typing_defs.get_pos capability)
                    ~required:(Typing_print.coeffects env capability))
          in

          (* First check the non-lambda arguments. For generic functions, this
           * is likely to resolve type variables to concrete types *)
          let rl = List.map el (fun e -> (e, None)) in
          let (env, rl, _) = check_args false env rl ft.ft_params in
          (* Now check the lambda arguments, hopefully with type variables resolved *)
          let (env, rl, paraml) = check_args true env rl ft.ft_params in
          (* We expect to see results for all arguments after this second pass *)
          let get_param opt =
            match opt with
            | Some x -> x
            | None -> failwith "missing parameter in check_args"
          in
          let (tel, tys) =
            let l = List.map rl (fun (_, opt) -> get_param opt) in
            List.unzip l
          in
          let env = check_implicit_args env in
          let env = TR.check_call env method_call_info pos r2 ft tys in
          let (env, typed_unpack_element, arity, did_unpack) =
            match unpacked_element with
            | None -> (env, None, List.length el, false)
            | Some e ->
              (* Now that we're considering an splat (Some e) we need to construct a type that
               * represents the remainder of the function's parameters. `paraml` represents those
               * remaining parameters, and the variadic parameter is stored in `var_param`. For example, given
               *
               * function f(int $i, string $j, float $k = 3.14, mixed ...$m): void {}
               * function g((string, float, bool) $t): void {
               *   f(3, ...$t);
               * }
               *
               * the constraint type we want is splat([#1], [opt#2], #3).
               *)
              let (consumed, required_params, optional_params) =
                split_remaining_params_required_optional ft paraml
              in
              let (env, (d_required, d_optional, d_variadic)) =
                generate_splat_type_vars
                  env
                  (fst e)
                  required_params
                  optional_params
                  var_param
              in
              let destructure_ty =
                ConstraintType
                  (mk_constraint_type
                     ( Reason.Runpack_param (fst e, pos_def, consumed),
                       Tdestructure
                         {
                           d_required;
                           d_optional;
                           d_variadic;
                           d_kind = SplatUnpack;
                         } ))
              in
              let (env, te, ty) = expr env e in
              (* Populate the type variables from the expression in the splat *)
              let env =
                Type.sub_type_i
                  (fst e)
                  Reason.URparam
                  env
                  (LoclType ty)
                  destructure_ty
                  Errors.unify_error
              in
              (* Use the type variables for the remaining parameters *)
              let env =
                List.fold2_exn
                  ~init:env
                  d_required
                  required_params
                  ~f:(fun env elt param ->
                    call_param env param (e, elt) ~is_variadic:false)
              in
              let env =
                List.fold2_exn
                  ~init:env
                  d_optional
                  optional_params
                  ~f:(fun env elt param ->
                    call_param env param (e, elt) ~is_variadic:false)
              in
              let env =
                Option.map2 d_variadic var_param ~f:(fun v vp ->
                    call_param env vp (e, v) ~is_variadic:true)
                |> Option.value ~default:env
              in
              ( env,
                Some te,
                List.length el + List.length d_required,
                Option.is_some d_variadic )
          in
          (* If we unpacked an array, we don't check arity exactly. Since each
           * unpacked array consumes 1 or many parameters, it is nonsensical to say
           * that not enough args were passed in (so we don't do the min check).
           *)
          let () = check_arity ~did_unpack pos pos_def ft arity in
          (* Variadic params cannot be inout so we can stop early *)
          let env = wfold_left2 inout_write_back env ft.ft_params el in
          let (env, ret_ty) =
            TR.get_adjusted_return_type env method_call_info ft.ft_ret.et_type
          in
          (env, (tel, typed_unpack_element, ret_ty))
        | (r, Tvar _)
          when TypecheckerOptions.method_call_inference (Env.get_tcopt env) ->
          (*
            Typecheck calls with unresolved function type by constructing a
            suitable function type from the arguments and invoking subtyping.
          *)
          let (env, typed_el, type_of_el) =
            exprs ~accept_using_var:true env el
          in
          let (env, typed_unpacked_element, type_of_unpacked_element) =
            match unpacked_element with
            | Some unpacked ->
              let (env, typed_unpacked, type_of_unpacked) =
                expr ~accept_using_var:true env unpacked
              in
              (env, Some typed_unpacked, Some type_of_unpacked)
            | None -> (env, None, None)
          in
          let mk_function_supertype
              env pos (type_of_el, type_of_unpacked_element) =
            let mk_fun_param ty =
              let flags =
                (* Keep supertype as permissive as possible: *)
                make_fp_flags
                  ~mode:FPnormal (* TODO: deal with `inout` parameters *)
                  ~accept_disposable:false (* TODO: deal with disposables *)
                  ~mutability:(Some Param_maybe_mutable)
                  ~has_default:false
                  ~ifc_external:false
                  ~ifc_can_call:false
                  ~is_atom:false
              in
              {
                fp_pos = pos;
                fp_name = None;
                fp_type = MakeType.enforced ty;
                fp_rx_annotation = None;
                fp_flags = flags;
              }
            in
            let ft_arity =
              match type_of_unpacked_element with
              | Some type_of_unpacked ->
                let fun_param = mk_fun_param type_of_unpacked in
                Fvariadic fun_param
              | None -> Fstandard
            in
            (* TODO: ensure `ft_params`/`ft_where_constraints` don't affect subtyping *)
            let ft_tparams = [] in
            let ft_where_constraints = [] in
            let ft_params = List.map ~f:mk_fun_param type_of_el in
            let ft_implicit_params =
              {
                capability =
                  CapDefaults pos
                  (* TODO(coeffects) should this be a different type? *);
              }
            in
            let (env, return_ty) = Env.fresh_type env pos in
            let return_ty =
              match in_await with
              | None -> return_ty
              | Some r -> MakeType.awaitable r return_ty
            in
            let ft_ret = MakeType.enforced return_ty in
            (* A non-reactive supertype is most permissive: *)
            let ft_reactive = Nonreactive in
            let ft_flags =
              (* Keep supertype as permissive as possible: *)
              make_ft_flags
                Ast_defs.FSync (* `FSync` fun can still return `Awaitable<_>` *)
                (Some Param_maybe_mutable)
                ~return_disposable:false (* TODO: deal with disposable return *)
                ~returns_mutable:false
                ~returns_void_to_rx:false
            in
            let ft_ifc_decl = Typing_defs_core.default_ifc_fun_decl in
            let fun_locl_type =
              {
                ft_arity;
                ft_tparams;
                ft_where_constraints;
                ft_params;
                ft_implicit_params;
                ft_ret;
                ft_reactive;
                ft_flags;
                ft_ifc_decl;
              }
            in
            let fun_type = mk (r, Tfun fun_locl_type) in
            let env = Env.set_tyvar_variance env fun_type in
            (env, fun_type, return_ty)
          in
          let (env, fun_type, return_ty) =
            mk_function_supertype env pos (type_of_el, type_of_unpacked_element)
          in
          let env =
            Type.sub_type pos Reason.URnone env efty fun_type Errors.unify_error
          in
          (env, (typed_el, typed_unpacked_element, return_ty))
        | _ ->
          bad_call env pos efty;
          let env = call_untyped_unpack env (get_pos efty) unpacked_element in
          (env, ([], None, err_witness env pos)))
  in
  match resl with
  | [res] -> res
  | _ ->
    bad_call env pos fty;
    let env = call_untyped_unpack env (get_pos fty) unpacked_element in
    (env, ([], None, err_witness env pos))

and split_remaining_params_required_optional ft remaining_params =
  (* Same example as above
   *
   * function f(int $i, string $j, float $k = 3.14, mixed ...$m): void {}
   * function g((string, float, bool) $t): void {
   *   f(3, ...$t);
   * }
   *
   * `remaining_params` will contain [string, float] and there has been 1 parameter consumed. The min_arity
   * of this function is 2, so there is 1 required parameter remaining and 1 optional parameter.
   *)
  let min_arity =
    List.count
      ~f:(fun fp -> not (Typing_defs.get_fp_has_default fp))
      ft.ft_params
  in
  let original_params = ft.ft_params in
  let consumed = List.length original_params - List.length remaining_params in
  let required_remaining = Int.max (min_arity - consumed) 0 in
  let (required_params, optional_params) =
    List.split_n remaining_params required_remaining
  in
  (consumed, required_params, optional_params)

and generate_splat_type_vars
    env p required_params optional_params variadic_param =
  let (env, d_required) =
    List.map_env env required_params ~f:(fun env _ -> Env.fresh_type env p)
  in
  let (env, d_optional) =
    List.map_env env optional_params ~f:(fun env _ -> Env.fresh_type env p)
  in
  let (env, d_variadic) =
    match variadic_param with
    | None -> (env, None)
    | Some _ ->
      let (env, ty) = Env.fresh_type env p in
      (env, Some ty)
  in
  (env, (d_required, d_optional, d_variadic))

and call_param env param (((pos, _) as e), arg_ty) ~is_variadic =
  param_modes ~is_variadic param e;

  (* When checking params, the type 'x' may be expression dependent. Since
   * we store the expression id in the local env for Lvar, we want to apply
   * it in this case.
   *)
  let (env, dep_ty) =
    match snd e with
    | Lvar _ -> ExprDepTy.make env (CIexpr e) arg_ty
    | _ -> (env, arg_ty)
  in
  Typing_coercion.coerce_type
    pos
    Reason.URparam
    env
    dep_ty
    param.fp_type
    Errors.unify_error

and call_untyped_unpack env f_pos unpacked_element =
  match unpacked_element with
  (* In the event that we don't have a known function call type, we can still
   * verify that any unpacked arguments (`...$args`) are something that can
   * be actually unpacked. *)
  | None -> env
  | Some e ->
    let (env, _, ety) = expr env e in
    let (env, ty) = Env.fresh_type env (fst e) in
    let destructure_ty =
      MakeType.simple_variadic_splat (Reason.Runpack_param (fst e, f_pos, 0)) ty
    in
    Type.sub_type_i
      f_pos
      Reason.URnone
      env
      (LoclType ety)
      destructure_ty
      Errors.unify_error

and bad_call env p ty = Errors.bad_call p (Typing_print.error env ty)

and make_a_local_of env e =
  match e with
  | (p, Class_get ((_, cname), CGstring (_, member_name), _)) ->
    let (env, local) = Env.FakeMembers.make_static env cname member_name p in
    (env, Some (p, local))
  | ( p,
      Obj_get
        ((((_, This) | (_, Lvar _)) as obj), (_, Id (_, member_name)), _, _) )
    ->
    let (env, local) = Env.FakeMembers.make env obj member_name p in
    (env, Some (p, local))
  | (_, Lvar x)
  | (_, Dollardollar x) ->
    (env, Some x)
  | _ -> (env, None)

(* This function captures the common bits of logic behind refinement
 * of the type of a local variable or a class member variable as a
 * result of a dynamic check (e.g., nullity check, simple type check
 * using functions like is_int, is_string, is_array etc.).  The
 * argument refine is a function that takes the type of the variable
 * and returns a refined type (making necessary changes to the
 * environment, which is threaded through).
 *
 * All refinement functions return, in addition to the updated
 * environment, a (conservative) set of all the locals that got
 * refined. This set is used to construct AssertEnv statmements in
 * the typed AST.
 *)
and refine_lvalue_type env (((_p, ty), _) as te) ~refine =
  let (env, ty) = refine env ty in
  let e = Tast.to_nast_expr te in
  let (env, localopt) = make_a_local_of env e in
  (* TODO TAST: generate an assignment to the fake local in the TAST *)
  match localopt with
  | Some lid -> (set_local env lid ty, Local_id.Set.singleton (snd lid))
  | None -> (env, Local_id.Set.empty)

and condition_nullity ~nonnull (env : env) te =
  match te with
  (* assignment: both the rhs and lhs of the '=' must be made null/non-null *)
  | (_, Aast.Binop (Ast_defs.Eq None, var, te)) ->
    let (env, lset1) = condition_nullity ~nonnull env te in
    let (env, lset2) = condition_nullity ~nonnull env var in
    (env, Local_id.Set.union lset1 lset2)
  (* case where `Shapes::idx(...)` must be made null/non-null *)
  | ( _,
      Aast.Call
        ( (_, Aast.Class_const ((_, Aast.CI (_, shapes)), (_, idx))),
          _,
          [shape; field],
          _ ) )
    when String.equal shapes SN.Shapes.cShapes && String.equal idx SN.Shapes.idx
    ->
    let field = Tast.to_nast_expr field in
    let refine env shape_ty =
      if nonnull then
        Typing_shapes.shapes_idx_not_null env shape_ty field
      else
        (env, shape_ty)
    in
    refine_lvalue_type env shape ~refine
  | ((p, _), _) ->
    let refine env ty =
      if nonnull then
        Typing_solver.non_null env p ty
      else
        let r = Reason.Rwitness (get_pos ty) in
        Inter.intersect env r ty (MakeType.null r)
    in
    refine_lvalue_type env te ~refine

and condition_isset env = function
  | (_, Aast.Array_get (x, _)) -> condition_isset env x
  | v -> condition_nullity ~nonnull:true env v

(**
 * Build an environment for the true or false branch of
 * conditional statements.
 *)
and condition
    ?lhs_of_null_coalesce env tparamet ((((p, ty) as pty), e) as te : Tast.expr)
    =
  let condition = condition ?lhs_of_null_coalesce in
  match e with
  | Aast.True when not tparamet ->
    (LEnv.drop_cont env C.Next, Local_id.Set.empty)
  | Aast.False when tparamet -> (LEnv.drop_cont env C.Next, Local_id.Set.empty)
  | Aast.Call ((_, Aast.Id (_, func)), _, [param], None)
    when String.equal SN.PseudoFunctions.isset func
         && tparamet
         && not (Env.is_strict env) ->
    condition_isset env param
  | Aast.Call ((_, Aast.Id (_, func)), _, [te], None)
    when String.equal SN.StdlibFunctions.is_null func ->
    condition_nullity ~nonnull:(not tparamet) env te
  | Aast.Binop ((Ast_defs.Eqeq | Ast_defs.Eqeqeq), (_, Aast.Null), e)
  | Aast.Binop ((Ast_defs.Eqeq | Ast_defs.Eqeqeq), e, (_, Aast.Null)) ->
    condition_nullity ~nonnull:(not tparamet) env e
  | Aast.Lvar _
  | Aast.Obj_get _
  | Aast.Class_get _
  | Aast.Binop (Ast_defs.Eq None, _, _) ->
    let (env, ety) = Env.expand_type env ty in
    (match get_node ety with
    | Tprim Tbool -> (env, Local_id.Set.empty)
    | _ -> condition_nullity ~nonnull:tparamet env te)
  | Aast.Binop (((Ast_defs.Diff | Ast_defs.Diff2) as op), e1, e2) ->
    let op =
      if Ast_defs.(equal_bop op Diff) then
        Ast_defs.Eqeq
      else
        Ast_defs.Eqeqeq
    in
    condition env (not tparamet) (pty, Aast.Binop (op, e1, e2))
  | Aast.Id (_, s) when SN.Rx.is_enabled s ->
    (* when Rx\IS_ENABLED is false - switch env to non-reactive *)
    let env =
      if not tparamet then
        Env.set_env_reactive env Nonreactive
      else
        env
    in
    (env, Local_id.Set.empty)
  (* Conjunction of conditions. Matches the two following forms:
      if (cond1 && cond2)
      if (!(cond1 || cond2))
  *)
  | Aast.Binop (((Ast_defs.Ampamp | Ast_defs.Barbar) as bop), e1, e2)
    when Bool.equal tparamet Ast_defs.(equal_bop bop Ampamp) ->
    let (env, lset1) = condition env tparamet e1 in
    (* This is necessary in case there is an assignment in e2
     * We essentially redo what has been undone in the
     * `Binop (Ampamp|Barbar)` case of `expr` *)
    let (env, _, _) = expr env (Tast.to_nast_expr e2) in
    let (env, lset2) = condition env tparamet e2 in
    (env, Local_id.Set.union lset1 lset2)
  (* Disjunction of conditions. Matches the two following forms:
      if (cond1 || cond2)
      if (!(cond1 && cond2))
  *)
  | Aast.Binop (((Ast_defs.Ampamp | Ast_defs.Barbar) as bop), e1, e2)
    when Bool.equal tparamet Ast_defs.(equal_bop bop Barbar) ->
    let (env, lset1, lset2) =
      branch
        env
        (fun env ->
          (* Either cond1 is true and we don't know anything about cond2... *)
          condition env tparamet e1)
        (fun env ->
          (* ... Or cond1 is false and therefore cond2 must be true *)
          let (env, _lset) = condition env (not tparamet) e1 in
          (* Similarly to the conjunction case, there might be an assignment in
          cond2 which we must account for. Again we redo what has been undone in
          the `Binop (Ampamp|Barbar)` case of `expr` *)
          let (env, _, _) = expr env (Tast.to_nast_expr e2) in
          condition env tparamet e2)
    in
    (env, Local_id.Set.union lset1 lset2)
  | Aast.Call (((p, _), Aast.Id (_, f)), _, [lv], None)
    when tparamet && String.equal f SN.StdlibFunctions.is_dict_or_darray ->
    safely_refine_is_array env `HackDictOrDArray p f lv
  | Aast.Call (((p, _), Aast.Id (_, f)), _, [lv], None)
    when tparamet && String.equal f SN.StdlibFunctions.is_vec_or_varray ->
    safely_refine_is_array env `HackVecOrVArray p f lv
  | Aast.Call (((p, _), Aast.Id (_, f)), _, [lv], None)
    when tparamet && String.equal f SN.StdlibFunctions.is_any_array ->
    safely_refine_is_array env `AnyArray p f lv
  | Aast.Call (((p, _), Aast.Id (_, f)), _, [lv], None)
    when tparamet && String.equal f SN.StdlibFunctions.is_php_array ->
    safely_refine_is_array env `PHPArray p f lv
  | Aast.Call
      ( (_, Aast.Class_const ((_, Aast.CI (_, class_name)), (_, method_name))),
        _,
        [shape; field],
        None )
    when tparamet
         && String.equal class_name SN.Shapes.cShapes
         && String.equal method_name SN.Shapes.keyExists ->
    key_exists env p shape field
  | Aast.Unop (Ast_defs.Unot, e) -> condition env (not tparamet) e
  | Aast.Is (ivar, h) when is_instance_var (Tast.to_nast_expr ivar) ->
    let ety_env =
      { (Phase.env_with_self env) with from_class = Some CIstatic }
    in
    let (env, hint_ty) = Phase.localize_hint ~ety_env env h in
    let reason = Reason.Ris (fst h) in
    let refine_type env hint_ty =
      let (ivar_pos, ivar_ty) = fst ivar in
      let (env, ivar) = get_instance_var env (Tast.to_nast_expr ivar) in
      let (env, hint_ty) =
        class_for_refinement env p reason ivar_pos ivar_ty hint_ty
      in
      let (env, refined_ty) = Inter.intersect env reason ivar_ty hint_ty in
      (set_local env ivar refined_ty, Local_id.Set.singleton (snd ivar))
    in
    let (env, hint_ty) =
      if not tparamet then
        Inter.non env reason hint_ty ~approx:TUtils.ApproxUp
      else
        (env, hint_ty)
    in
    refine_type env hint_ty
  | _ -> (env, Local_id.Set.empty)

(** Transform a hint like `A<_>` to a localized type like `A<T#1>` for refinment of
an instance variable. ivar_ty is the previous type of that instance variable. *)
and class_for_refinement env p reason ivar_pos ivar_ty hint_ty =
  let (env, hint_ty) = Env.expand_type env hint_ty in
  match (get_node ivar_ty, get_node hint_ty) with
  | (_, Tclass (((_, cid) as _c), _, tyl)) ->
    begin
      match Env.get_class env cid with
      | Some class_info ->
        let (env, tparams_with_new_names, tyl_fresh) =
          generate_fresh_tparams env class_info reason tyl
        in
        safely_refine_class_type
          env
          p
          _c
          class_info
          ivar_ty
          hint_ty
          reason
          tparams_with_new_names
          tyl_fresh
      | None -> (env, mk (Reason.Rwitness ivar_pos, Tobject))
    end
  | (Ttuple ivar_tyl, Ttuple hint_tyl)
    when Int.equal (List.length ivar_tyl) (List.length hint_tyl) ->
    let (env, tyl) =
      List.map2_env env ivar_tyl hint_tyl (fun env ivar_ty hint_ty ->
          class_for_refinement env p reason ivar_pos ivar_ty hint_ty)
    in
    (env, MakeType.tuple reason tyl)
  | _ -> (env, hint_ty)

(** If we are dealing with a refinement like
      $x is MyClass<A, B>
    then class_info is the class info of MyClass and hint_tyl corresponds
    to A, B. *)
and generate_fresh_tparams env class_info reason hint_tyl =
  let tparams_len = List.length (Cls.tparams class_info) in
  let hint_tyl = List.take hint_tyl tparams_len in
  let pad_len = tparams_len - List.length hint_tyl in
  let hint_tyl =
    List.map hint_tyl (fun x -> Some x) @ List.init pad_len (fun _ -> None)
  in
  let replace_wildcard env hint_ty tp =
    let {
      tp_name = (_, tparam_name);
      tp_reified = reified;
      tp_user_attributes;
      _;
    } =
      tp
    in
    let enforceable =
      Attributes.mem SN.UserAttributes.uaEnforceable tp_user_attributes
    in
    let newable =
      Attributes.mem SN.UserAttributes.uaNewable tp_user_attributes
    in
    match hint_ty with
    | Some ty ->
      begin
        match get_node ty with
        | Tgeneric (name, _targs) when Env.is_fresh_generic_parameter name ->
          (* TODO(T69551141) handle type arguments above and below *)
          (env, (Some (tp, name), MakeType.generic reason name))
        | _ -> (env, (None, ty))
      end
    | None ->
      let (env, new_name) =
        Env.add_fresh_generic_parameter
          env
          tparam_name
          ~reified
          ~enforceable
          ~newable
      in
      (* TODO(T69551141) handle type arguments for Tgeneric *)
      (env, (Some (tp, new_name), MakeType.generic reason new_name))
  in
  let (env, tparams_and_tyl) =
    List.map2_env env hint_tyl (Cls.tparams class_info) ~f:replace_wildcard
  in
  let (tparams_with_new_names, tyl_fresh) = List.unzip tparams_and_tyl in
  (env, tparams_with_new_names, tyl_fresh)

and safely_refine_class_type
    env
    p
    class_name
    class_info
    ivar_ty
    obj_ty
    reason
    (tparams_with_new_names : (decl_tparam * string) option list)
    tyl_fresh =
  (* Type of variable in block will be class name
   * with fresh type parameters *)
  let obj_ty =
    mk (get_reason obj_ty, Tclass (class_name, Nonexact, tyl_fresh))
  in
  let tparams = Cls.tparams class_info in
  (* Add in constraints as assumptions on those type parameters *)
  let ety_env =
    {
      type_expansions = [];
      substs = Subst.make_locl tparams tyl_fresh;
      this_ty = obj_ty;
      (* In case `this` appears in constraints *)
      from_class = None;
      quiet = true;
      on_error = Errors.unify_error_at p;
    }
  in
  let add_bounds env (t, ty_fresh) =
    List.fold_left t.tp_constraints ~init:env ~f:(fun env (ck, ty) ->
        (* Substitute fresh type parameters for
         * original formals in constraint *)
        let (env, ty) = Phase.localize ~ety_env env ty in
        SubType.add_constraint p env ck ty_fresh ty)
  in
  let env =
    List.fold_left (List.zip_exn tparams tyl_fresh) ~f:add_bounds ~init:env
  in
  (* Finally, if we have a class-test on something with static classish type,
   * then we can chase the hierarchy and decompose the types to deduce
   * further assumptions on type parameters. For example, we might have
   *   class B<Tb> { ... }
   *   class C extends B<int>
   * and have obj_ty = C and x_ty = B<T> for a generic parameter Aast.
   * Then SubType.add_constraint will deduce that T=int and add int as
   * both lower and upper bound on T in env.lenv.tpenv
   *)
  let (env, supertypes) = TUtils.get_concrete_supertypes env ivar_ty in
  let env =
    List.fold_left supertypes ~init:env ~f:(fun env ty ->
        SubType.add_constraint p env Ast_defs.Constraint_as obj_ty ty)
  in
  (* It's often the case that the fresh name isn't necessary. For
   * example, if C<T> extends B<T>, and we have $x:B<t> for some type t
   * then $x is C should refine to $x:C<t>.
   * We take a simple approach:
   *    For a fresh type parameter T#1, if
   *      - There is an eqality constraint T#1 = t,
   *      - T#1 is covariant, and T#1 has upper bound t (or mixed if absent)
   *      - T#1 is contravariant, and T#1 has lower bound t (or nothing if absent)
   *    then replace T#1 with t.
   * This is done in Type_parameter_env_ops.simplify_tpenv
   *)
  let (env, tparam_substs) =
    Type_parameter_env_ops.simplify_tpenv
      env
      (List.zip_exn tparams_with_new_names tyl_fresh)
      reason
  in
  let tyl_fresh =
    List.map2_exn tyl_fresh tparams_with_new_names ~f:(fun orig_ty tparam_opt ->
        match tparam_opt with
        | None -> orig_ty
        | Some (_tp, name) -> SMap.find name tparam_substs)
  in
  let obj_ty_simplified =
    mk (get_reason obj_ty, Tclass (class_name, Nonexact, tyl_fresh))
  in
  (env, obj_ty_simplified)

and is_instance_var = function
  | (_, (Lvar _ | This | Dollardollar _)) -> true
  | (_, Obj_get ((_, This), (_, Id _), _, _)) -> true
  | (_, Obj_get ((_, Lvar _), (_, Id _), _, _)) -> true
  | (_, Class_get (_, _, _)) -> true
  | _ -> false

and get_instance_var env = function
  | (p, Class_get ((_, cname), CGstring (_, member_name), _)) ->
    let (env, local) = Env.FakeMembers.make_static env cname member_name p in
    (env, (p, local))
  | ( p,
      Obj_get
        ((((_, This) | (_, Lvar _)) as obj), (_, Id (_, member_name)), _, _) )
    ->
    let (env, local) = Env.FakeMembers.make env obj member_name p in
    (env, (p, local))
  | (_, Dollardollar (p, x))
  | (_, Lvar (p, x)) ->
    (env, (p, x))
  | (p, This) -> (env, (p, this))
  | _ -> failwith "Should only be called when is_instance_var is true"

(* Refine type for is_array, is_vec, is_keyset and is_dict tests
 * `pred_name` is the function name itself (e.g. 'is_vec')
 * `p` is position of the function name in the source
 * `arg_expr` is the argument to the function
 *)
and safely_refine_is_array env ty p pred_name arg_expr =
  refine_lvalue_type env arg_expr ~refine:(fun env arg_ty ->
      let r = Reason.Rpredicated (p, pred_name) in
      let (env, tarrkey_name) =
        Env.add_fresh_generic_parameter
          env
          "Tk"
          ~reified:Erased
          ~enforceable:false
          ~newable:false
      in
      (* TODO(T69551141) handle type arguments for Tgeneric *)
      let tarrkey = MakeType.generic r tarrkey_name in
      let env =
        SubType.add_constraint
          p
          env
          Ast_defs.Constraint_as
          tarrkey
          (MakeType.arraykey r)
      in
      let (env, tfresh_name) =
        Env.add_fresh_generic_parameter
          env
          "T"
          ~reified:Erased
          ~enforceable:false
          ~newable:false
      in
      (* TODO(T69551141) handle type arguments for Tgeneric *)
      let tfresh = MakeType.generic r tfresh_name in
      (* If we're refining the type for `is_array` we have a slightly more
       * involved process. Let's separate out that logic so we can re-use it.
       *)
      let array_ty =
        let safe_isarray_enabled =
          TypecheckerOptions.experimental_feature_enabled
            (Env.get_tcopt env)
            TypecheckerOptions.experimental_isarray
        in
        let tk = MakeType.arraykey Reason.(Rvarray_or_darray_key (to_pos r)) in
        let tv =
          if safe_isarray_enabled then
            tfresh
          else
            mk (r, TUtils.tany env)
        in
        MakeType.varray_or_darray r tk tv
      in
      (* This is the refined type of e inside the branch *)
      let hint_ty =
        match ty with
        | `HackDict -> MakeType.dict r tarrkey tfresh
        | `HackVec -> MakeType.vec r tfresh
        | `HackKeyset -> MakeType.keyset r tarrkey
        | `PHPArray -> array_ty
        | `AnyArray -> MakeType.any_array r tarrkey tfresh
        | `HackDictOrDArray ->
          MakeType.union
            r
            [MakeType.dict r tarrkey tfresh; MakeType.darray r tarrkey tfresh]
        | `HackVecOrVArray ->
          MakeType.union r [MakeType.vec r tfresh; MakeType.varray r tfresh]
      in
      let ((arg_pos, _), _) = arg_expr in
      let (env, hint_ty) =
        class_for_refinement env p r arg_pos arg_ty hint_ty
      in
      (* Add constraints on generic parameters that must
       * hold for refined_ty <:arg_ty. For example, if arg_ty is Traversable<T>
       * and refined_ty is keyset<T#1> then we know T#1 <: T.
       * See analogous code in safely_refine_class_type.
       *)
      let (env, supertypes) = TUtils.get_concrete_supertypes env arg_ty in
      let env =
        List.fold_left supertypes ~init:env ~f:(fun env ty ->
            SubType.add_constraint p env Ast_defs.Constraint_as hint_ty ty)
      in
      Inter.intersect ~r env hint_ty arg_ty)

and key_exists env pos shape field =
  let field = Tast.to_nast_expr field in
  refine_lvalue_type env shape ~refine:(fun env shape_ty ->
      match TUtils.shape_field_name env field with
      | None -> (env, shape_ty)
      | Some field_name ->
        Typing_shapes.refine_shape field_name pos env shape_ty)

and string2 env idl =
  let (env, tel) =
    List.fold_left idl ~init:(env, []) ~f:(fun (env, tel) x ->
        let (env, te, ty) = expr env x in
        let p = fst x in
        let env = Typing_substring.sub_string p env ty in
        (env, te :: tel))
  in
  (env, List.rev tel)

and user_attribute env ua =
  let (env, typed_ua_params) =
    List.map_env env ua.ua_params (fun env e ->
        let (env, te, _) = expr env e in
        (env, te))
  in
  (env, { Aast.ua_name = ua.ua_name; Aast.ua_params = typed_ua_params })

and file_attributes env file_attrs =
  (* Disable checking of error positions, as file attributes have spans that
   * aren't subspans of the class or function into which they are copied *)
  Errors.run_with_span Pos.none @@ fun () ->
  let uas = List.concat_map ~f:(fun fa -> fa.fa_user_attributes) file_attrs in
  let env = attributes_check_def env SN.AttributeKinds.file uas in
  List.map_env env file_attrs (fun env fa ->
      let (env, user_attributes) =
        List.map_env env fa.fa_user_attributes user_attribute
      in
      let env = set_tcopt_unstable_features env fa in
      ( env,
        {
          Aast.fa_user_attributes = user_attributes;
          Aast.fa_namespace = fa.fa_namespace;
        } ))

and type_param env t =
  let env =
    attributes_check_def env SN.AttributeKinds.typeparam t.tp_user_attributes
  in
  let (env, user_attributes) =
    List.map_env env t.tp_user_attributes user_attribute
  in
  let (env, tp_parameters) = List.map_env env t.tp_parameters type_param in
  ( env,
    {
      Aast.tp_variance = t.tp_variance;
      Aast.tp_name = t.tp_name;
      Aast.tp_parameters;
      Aast.tp_constraints = t.tp_constraints;
      Aast.tp_reified = reify_kind t.tp_reified;
      Aast.tp_user_attributes = user_attributes;
    } )

and typedef_def ctx typedef =
  let env = EnvFromDef.typedef_env ~origin:Decl_counters.TopLevel ctx typedef in
  let env =
    Phase.localize_and_add_ast_generic_parameters_and_where_constraints
      (fst typedef.t_name)
      env
      typedef.t_tparams
      []
  in
  Typing_check_decls.typedef env typedef;
  Typing_variance.typedef env (snd typedef.t_name);
  let {
    t_annotation = ();
    t_name = (t_pos, t_name);
    t_tparams = _;
    t_constraint = tcstr;
    t_kind = hint;
    t_user_attributes = _;
    t_vis = _;
    t_mode = _;
    t_namespace = _;
    t_span = _;
    t_emit_id = _;
  } =
    typedef
  in
  let ty = Decl_hint.hint env.decl_env hint in
  (* We want to report cycles through the definition *)
  let (env, ty) =
    Phase.localize_with_self env ~pos:t_pos ~report_cycle:(t_pos, t_name) ty
  in
  let env =
    match tcstr with
    | Some tcstr ->
      let cstr = Decl_hint.hint env.decl_env tcstr in
      let (env, cstr) = Phase.localize_with_self ~pos:t_pos env cstr in
      Typing_ops.sub_type
        t_pos
        Reason.URnewtype_cstr
        env
        ty
        cstr
        Errors.newtype_alias_must_satisfy_constraint
    | _ -> env
  in
  let env =
    match hint with
    | (pos, Hshape { nsi_allows_unknown_fields = _; nsi_field_map }) ->
      let get_name sfi = sfi.sfi_name in
      check_shape_keys_validity env pos (List.map ~f:get_name nsi_field_map)
    | _ -> env
  in
  let env =
    attributes_check_def
      env
      SN.AttributeKinds.typealias
      typedef.t_user_attributes
  in
  let (env, tparams) = List.map_env env typedef.t_tparams type_param in
  let (env, user_attributes) =
    List.map_env env typedef.t_user_attributes user_attribute
  in
  {
    Aast.t_annotation = Env.save (Env.get_tpenv env) env;
    Aast.t_name = typedef.t_name;
    Aast.t_mode = typedef.t_mode;
    Aast.t_vis = typedef.t_vis;
    Aast.t_user_attributes = user_attributes;
    Aast.t_constraint = typedef.t_constraint;
    Aast.t_kind = typedef.t_kind;
    Aast.t_tparams = tparams;
    Aast.t_namespace = typedef.t_namespace;
    Aast.t_span = typedef.t_span;
    Aast.t_emit_id = typedef.t_emit_id;
  }

(* Calls the method of a class, but allows the f callback to override the
 * return value type *)
and overload_function
    make_call fpos p env (cpos, class_id) method_id el unpacked_element f =
  let (env, _tal, tcid, ty) =
    static_class_id ~check_constraints:false cpos env [] class_id
  in
  let (env, _tel, _) = exprs env el in
  let (env, (fty, tal)) =
    class_get
      ~is_method:true
      ~is_const:false
      ~coerce_from_ty:None
      env
      ty
      method_id
      class_id
  in
  let (env, (tel, typed_unpack_element, res)) =
    call ~expected:None p env fty el unpacked_element
  in
  let (env, ty) = f env fty res el in
  let (env, fty) = Env.expand_type env fty in
  let fty =
    map_ty fty ~f:(function
        | Tfun ft -> Tfun { ft with ft_ret = MakeType.unenforced ty }
        | ty -> ty)
  in
  let te = Tast.make_typed_expr fpos fty (Aast.Class_const (tcid, method_id)) in
  make_call env te tal tel typed_unpack_element ty

and update_array_type ?lhs_of_null_coalesce p env e1 valkind =
  match valkind with
  | `lvalue
  | `lvalue_subexpr ->
    let (env, te1, ty1) =
      raw_expr ~valkind:`lvalue_subexpr ~check_defined:true env e1
    in
    begin
      match e1 with
      | (_, Lvar (_, x)) ->
        (* type_mapper has updated the type in ty1 typevars, but we
             need to update the local variable type too *)
        let env = set_valid_rvalue p env x ty1 in
        (env, te1, ty1)
      | _ -> (env, te1, ty1)
    end
  | _ -> raw_expr ?lhs_of_null_coalesce env e1

(* External API *)
let expr ?expected env e =
  Typing_env.with_origin2 env Decl_counters.Body (fun env ->
      expr ?expected env e)

let stmt env st =
  Typing_env.with_origin env Decl_counters.Body (fun env -> stmt env st)