object_parser.ml

(*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *)

module Ast = Flow_ast
open Token
open Parser_env
open Flow_ast
module SMap = Map.Make (String)
open Parser_common
open Comment_attachment

(* A module for parsing various object related things, like object literals
 * and classes *)

module type OBJECT = sig
  val key : ?class_body:bool -> env -> Loc.t * (Loc.t, Loc.t) Ast.Expression.Object.Property.key
  val _initializer : env -> Loc.t * (Loc.t, Loc.t) Ast.Expression.Object.t * pattern_errors

  val class_declaration :
    env -> (Loc.t, Loc.t) Ast.Class.Decorator.t list -> (Loc.t, Loc.t) Ast.Statement.t

  val class_expression : env -> (Loc.t, Loc.t) Ast.Expression.t
  val class_implements : env -> attach_leading:bool -> (Loc.t, Loc.t) Ast.Class.Implements.t
  val decorator_list : env -> (Loc.t, Loc.t) Ast.Class.Decorator.t list
end

module Object
    (Parse : Parser_common.PARSER)
    (Type : Type_parser.TYPE)
    (Declaration : Declaration_parser.DECLARATION)
    (Expression : Expression_parser.EXPRESSION)
    (Pattern_cover : Pattern_cover.COVER) : OBJECT = struct
  let decorator_list =
    let expression env =
      let expression = Expression.left_hand_side env in
      let { remove_trailing; _ } =
        if Peek.is_line_terminator env then
          trailing_and_remover_after_last_line env
        else
          trailing_and_remover_after_last_loc env
      in
      remove_trailing expression (fun remover expression -> remover#expression expression)
    in
    let decorator env =
      let leading = Peek.comments env in
      Eat.token env;
      {
        Ast.Class.Decorator.expression = expression env;
        comments = Flow_ast_utils.mk_comments_opt ~leading ();
      }
    in
    let rec decorator_list_helper env decorators =
      match Peek.token env with
      | T_AT -> decorator_list_helper env (with_loc decorator env :: decorators)
      | _ -> decorators
    in
    fun env ->
      if (parse_options env).esproposal_decorators then
        List.rev (decorator_list_helper env [])
      else
        []

  let key ?(class_body = false) env =
    let open Ast.Expression.Object.Property in
    let leading = Peek.comments env in
    let tkn = Peek.token env in
    match tkn with
    | T_STRING (loc, value, raw, octal) ->
      if octal then strict_error env Parse_error.StrictOctalLiteral;
      Expect.token env (T_STRING (loc, value, raw, octal));
      let value = Literal.String value in
      let trailing = Eat.trailing_comments env in
      ( loc,
        Literal
          ( loc,
            { Literal.value; raw; comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing () }
          )
      )
    | T_NUMBER { kind; raw } ->
      let loc = Peek.loc env in
      let value = Expression.number env kind raw in
      let value = Literal.Number value in
      let trailing = Eat.trailing_comments env in
      ( loc,
        Literal
          ( loc,
            { Literal.value; raw; comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing () }
          )
      )
    | T_LBRACKET ->
      let (loc, key) =
        with_loc
          (fun env ->
            let leading = Peek.comments env in
            Expect.token env T_LBRACKET;
            let expr = Parse.assignment (env |> with_no_in false) in
            Expect.token env T_RBRACKET;
            let trailing = Eat.trailing_comments env in
            {
              ComputedKey.expression = expr;
              comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing ();
            })
          env
      in
      (loc, Ast.Expression.Object.Property.Computed (loc, key))
    | T_POUND when class_body ->
      let ((loc, { PrivateName.name; _ }) as id) = private_identifier env in
      add_declared_private env name;
      (loc, PrivateName id)
    | T_POUND ->
      let (loc, id) =
        with_loc
          (fun env ->
            Eat.token env;
            Identifier (identifier_name env))
          env
      in
      error_at env (loc, Parse_error.PrivateNotInClass);
      (loc, id)
    | _ ->
      let ((loc, _) as id) = identifier_name env in
      (loc, Identifier id)

  let getter_or_setter env ~in_class_body is_getter =
    (* this is a getter or setter, it cannot be async *)
    let async = false in
    let (generator, leading) = Declaration.generator env in
    let (key_loc, key) = key ~class_body:in_class_body env in
    let key = object_key_remove_trailing env key in
    let value =
      with_loc
        (fun env ->
          (* #sec-function-definitions-static-semantics-early-errors *)
          let env = env |> with_allow_super Super_prop in
          let (sig_loc, (tparams, params, return)) =
            with_loc
              (fun env ->
                (* It's not clear how type params on getters & setters would make sense
                 * in Flow's type system. Since this is a Flow syntax extension, we might
                 * as well disallow it until we need it *)
                let tparams = None in
                let params =
                  let params = Declaration.function_params ~await:false ~yield:false env in
                  if Peek.token env = T_COLON then
                    params
                  else
                    function_params_remove_trailing env params
                in
                begin
                  match (is_getter, params) with
                  | (true, (_, { Ast.Function.Params.this_ = Some _; _ })) ->
                    error_at env (key_loc, Parse_error.GetterMayNotHaveThisParam)
                  | (false, (_, { Ast.Function.Params.this_ = Some _; _ })) ->
                    error_at env (key_loc, Parse_error.SetterMayNotHaveThisParam)
                  | ( true,
                      ( _,
                        { Ast.Function.Params.params = []; rest = None; this_ = None; comments = _ }
                      )
                    ) ->
                    ()
                  | (false, (_, { Ast.Function.Params.rest = Some _; _ })) ->
                    (* rest params don't make sense on a setter *)
                    error_at env (key_loc, Parse_error.SetterArity)
                  | ( false,
                      ( _,
                        {
                          Ast.Function.Params.params = [_];
                          rest = None;
                          this_ = None;
                          comments = _;
                        }
                      )
                    ) ->
                    ()
                  | (true, _) -> error_at env (key_loc, Parse_error.GetterArity)
                  | (false, _) -> error_at env (key_loc, Parse_error.SetterArity)
                end;
                let return = type_annotation_hint_remove_trailing env (Type.annotation_opt env) in
                (tparams, params, return))
              env
          in
          let simple_params = is_simple_parameter_list params in
          let (body, contains_use_strict) =
            Declaration.function_body env ~async ~generator ~expression:false ~simple_params
          in
          Declaration.strict_post_check env ~contains_use_strict None params;
          {
            Function.id = None;
            params;
            body;
            generator;
            async;
            predicate = None;
            (* setters/getter are not predicates *)
            return;
            tparams;
            sig_loc;
            comments = Flow_ast_utils.mk_comments_opt ~leading ();
          })
        env
    in
    (key, value)

  let _initializer =
    let parse_assignment_cover env =
      match Expression.assignment_cover env with
      | Cover_expr expr -> (expr, Pattern_cover.empty_errors)
      | Cover_patt (expr, errs) -> (expr, errs)
    in
    let get env start_loc leading =
      let (loc, (key, value)) =
        with_loc ~start_loc (fun env -> getter_or_setter env ~in_class_body:false true) env
      in
      let open Ast.Expression.Object in
      Property
        (loc, Property.Get { key; value; comments = Flow_ast_utils.mk_comments_opt ~leading () })
    in
    let set env start_loc leading =
      let (loc, (key, value)) =
        with_loc ~start_loc (fun env -> getter_or_setter env ~in_class_body:false false) env
      in
      let open Ast.Expression.Object in
      Property
        (loc, Property.Set { key; value; comments = Flow_ast_utils.mk_comments_opt ~leading () })
    in
    (* #prod-PropertyDefinition *)
    let init =
      let open Ast.Expression.Object.Property in
      (* #prod-IdentifierReference *)
      let parse_shorthand env key =
        match key with
        | Literal (loc, lit) ->
          error_at env (loc, Parse_error.LiteralShorthandProperty);
          (loc, Ast.Expression.Literal lit)
        | Identifier ((loc, { Identifier.name; comments = _ }) as id) ->
          (* #sec-identifiers-static-semantics-early-errors *)
          if is_reserved name && name <> "yield" && name <> "await" then
            (* it is a syntax error if `name` is a reserved word other than await or yield *)
            error_at env (loc, Parse_error.UnexpectedReserved)
          else if is_strict_reserved name then
            (* it is a syntax error if `name` is a strict reserved word, in strict mode *)
            strict_error_at env (loc, Parse_error.StrictReservedWord);
          (loc, Ast.Expression.Identifier id)
        | PrivateName _ -> failwith "Internal Error: private name found in object props"
        | Computed (_, { ComputedKey.expression = expr; comments = _ }) ->
          error_at env (fst expr, Parse_error.ComputedShorthandProperty);
          expr
      in
      (* #prod-MethodDefinition *)
      let parse_method ~async ~generator ~leading =
        with_loc (fun env ->
            (* #sec-function-definitions-static-semantics-early-errors *)
            let env = env |> with_allow_super Super_prop in
            let (sig_loc, (tparams, params, return)) =
              with_loc
                (fun env ->
                  let tparams = type_params_remove_trailing env (Type.type_params env) in
                  let params =
                    let (yield, await) =
                      match (async, generator) with
                      | (true, true) ->
                        (true, true) (* proposal-async-iteration/#prod-AsyncGeneratorMethod *)
                      | (true, false) -> (false, allow_await env) (* #prod-AsyncMethod *)
                      | (false, true) -> (true, false) (* #prod-GeneratorMethod *)
                      | (false, false) -> (false, false)
                      (* #prod-MethodDefinition *)
                    in
                    let params = Declaration.function_params ~await ~yield env in
                    if Peek.token env = T_COLON then
                      params
                    else
                      function_params_remove_trailing env params
                  in
                  let return = type_annotation_hint_remove_trailing env (Type.annotation_opt env) in
                  (tparams, params, return))
                env
            in
            let simple_params = is_simple_parameter_list params in
            let (body, contains_use_strict) =
              Declaration.function_body env ~async ~generator ~expression:false ~simple_params
            in
            Declaration.strict_post_check env ~contains_use_strict None params;
            {
              Function.id = None;
              params;
              body;
              generator;
              async;
              (* TODO: add support for object method predicates *)
              predicate = None;
              return;
              tparams;
              sig_loc;
              comments = Flow_ast_utils.mk_comments_opt ~leading ();
            }
        )
      in
      (* PropertyName `:` AssignmentExpression *)
      let parse_value env =
        Expect.token env T_COLON;
        parse_assignment_cover env
      in
      (* #prod-CoverInitializedName *)
      let parse_assignment_pattern ~key env =
        let open Ast.Expression.Object in
        match key with
        | Property.Identifier id ->
          let assignment_loc = Peek.loc env in
          let ast =
            with_loc
              ~start_loc:(fst id)
              (fun env ->
                let leading = Peek.comments env in
                Expect.token env T_ASSIGN;
                let trailing = Eat.trailing_comments env in
                let left = Parse.pattern_from_expr env (fst id, Ast.Expression.Identifier id) in
                let right = Parse.assignment env in
                let comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing () in
                Ast.Expression.Assignment
                  { Ast.Expression.Assignment.operator = None; left; right; comments })
              env
          in
          let errs =
            {
              if_expr = [(assignment_loc, Parse_error.Unexpected (Token.quote_token_value "="))];
              if_patt = [];
            }
          in
          (ast, errs)
        | Property.Literal _
        | Property.PrivateName _
        | Property.Computed _ ->
          parse_value env
      in
      let parse_init ~key ~async ~generator ~leading env =
        if async || generator then
          let key = object_key_remove_trailing env key in
          (* the `async` and `*` modifiers are only valid on methods *)
          let value = parse_method env ~async ~generator ~leading in
          let prop = Method { key; value } in
          (prop, Pattern_cover.empty_errors)
        else
          match Peek.token env with
          | T_RCURLY
          | T_COMMA ->
            let value = parse_shorthand env key in
            let prop = Init { key; value; shorthand = true } in
            (prop, Pattern_cover.empty_errors)
          | T_LESS_THAN
          | T_LPAREN ->
            let key = object_key_remove_trailing env key in
            let value = parse_method env ~async ~generator ~leading in
            let prop = Method { key; value } in
            (prop, Pattern_cover.empty_errors)
          | T_ASSIGN ->
            let (value, errs) = parse_assignment_pattern ~key env in
            let prop = Init { key; value; shorthand = true } in
            (prop, errs)
          | T_COLON ->
            let (value, errs) = parse_value env in
            let prop = Init { key; value; shorthand = false } in
            (prop, errs)
          | _ ->
            (* error. we recover by treating it as a shorthand property so as to not
               consume any more tokens and make the error worse. we don't error here
               because we'll expect a comma before the next token. *)
            let value = parse_shorthand env key in
            let prop = Init { key; value; shorthand = true } in
            (prop, Pattern_cover.empty_errors)
      in
      fun env start_loc key async generator leading ->
        let (loc, (prop, errs)) =
          with_loc ~start_loc (parse_init ~key ~async ~generator ~leading) env
        in
        (Ast.Expression.Object.Property (loc, prop), errs)
    in
    let property env =
      let open Ast.Expression.Object in
      if Peek.token env = T_ELLIPSIS then
        (* Spread property *)
        let leading = Peek.comments env in
        let (loc, (argument, errs)) =
          with_loc
            (fun env ->
              Expect.token env T_ELLIPSIS;
              parse_assignment_cover env)
            env
        in
        ( SpreadProperty
            (loc, { SpreadProperty.argument; comments = Flow_ast_utils.mk_comments_opt ~leading () }),
          errs
        )
      else
        let start_loc = Peek.loc env in
        let (async, leading_async) =
          match Peek.ith_token ~i:1 env with
          | T_ASSIGN
          (* { async = true } (destructuring) *)
          | T_COLON
          (* { async: true } *)
          | T_LESS_THAN
          (* { async<T>() {} } *)
          | T_LPAREN
          (* { async() {} } *)
          | T_COMMA
          (* { async, other, shorthand } *)
          | T_RCURLY (* { async } *) ->
            (false, [])
          | _ -> Declaration.async env
        in
        let (generator, leading_generator) = Declaration.generator env in
        let leading = leading_async @ leading_generator in
        match (async, generator, Peek.token env) with
        | (false, false, T_IDENTIFIER { raw = "get"; _ }) ->
          let leading = Peek.comments env in
          let (_, key) = key env in
          begin
            match Peek.token env with
            | T_ASSIGN
            | T_COLON
            | T_LESS_THAN
            | T_LPAREN
            | T_COMMA
            | T_RCURLY ->
              init env start_loc key false false []
            | _ ->
              ignore (Comment_attachment.object_key_remove_trailing env key);
              (get env start_loc leading, Pattern_cover.empty_errors)
          end
        | (false, false, T_IDENTIFIER { raw = "set"; _ }) ->
          let leading = Peek.comments env in
          let (_, key) = key env in
          begin
            match Peek.token env with
            | T_ASSIGN
            | T_COLON
            | T_LESS_THAN
            | T_LPAREN
            | T_COMMA
            | T_RCURLY ->
              init env start_loc key false false []
            | _ ->
              ignore (Comment_attachment.object_key_remove_trailing env key);
              (set env start_loc leading, Pattern_cover.empty_errors)
          end
        | (async, generator, _) ->
          let (_, key) = key env in
          init env start_loc key async generator leading
    in
    let rec properties env ~rest_trailing_comma (props, errs) =
      match Peek.token env with
      | T_EOF
      | T_RCURLY ->
        let errs =
          match rest_trailing_comma with
          | Some loc ->
            { errs with if_patt = (loc, Parse_error.TrailingCommaAfterRestElement) :: errs.if_patt }
          | None -> errs
        in
        (List.rev props, Pattern_cover.rev_errors errs)
      | _ ->
        let (prop, new_errs) = property env in
        let rest_trailing_comma =
          match prop with
          | Ast.Expression.Object.SpreadProperty _ when Peek.token env = T_COMMA ->
            Some (Peek.loc env)
          | _ -> None
        in
        let errs = Pattern_cover.rev_append_errors new_errs errs in
        let errs =
          match Peek.token env with
          | T_RCURLY
          | T_EOF ->
            errs
          | T_COMMA ->
            Eat.token env;
            errs
          | _ ->
            (* we could use [Expect.error env T_COMMA], but we're in a weird
               cover grammar situation where we're storing errors in
               [Pattern_cover]. if we used [Expect.error], the errors would
               end up out of order. *)
            let err = Expect.get_error env T_COMMA in
            (* if the unexpected token is a semicolon, consume it to aid
               recovery. using a semicolon instead of a comma is a common
               mistake. *)
            let _ = Eat.maybe env T_SEMICOLON in
            Pattern_cover.cons_error err errs
        in
        properties env ~rest_trailing_comma (prop :: props, errs)
    in
    fun env ->
      let (loc, (expr, errs)) =
        with_loc
          (fun env ->
            let leading = Peek.comments env in
            Expect.token env T_LCURLY;
            let (props, errs) =
              properties env ~rest_trailing_comma:None ([], Pattern_cover.empty_errors)
            in
            let internal = Peek.comments env in
            Expect.token env T_RCURLY;
            let trailing = Eat.trailing_comments env in
            ( {
                Ast.Expression.Object.properties = props;
                comments =
                  Flow_ast_utils.mk_comments_with_internal_opt ~leading ~trailing ~internal ();
              },
              errs
            ))
          env
      in
      (loc, expr, errs)

  let check_property_name env loc name static =
    if String.equal name "constructor" || (String.equal name "prototype" && static) then
      error_at
        env
        (loc, Parse_error.InvalidClassMemberName { name; static; method_ = false; private_ = false })

  let check_private_names
      env seen_names private_name (kind : [ `Method | `Field | `Getter | `Setter ]) =
    let (loc, { PrivateName.name; comments = _ }) = private_name in
    if String.equal name "constructor" then
      let () =
        error_at
          env
          ( loc,
            Parse_error.InvalidClassMemberName
              { name; static = false; method_ = kind = `Method; private_ = true }
          )
      in
      seen_names
    else
      match SMap.find_opt name seen_names with
      | Some seen ->
        begin
          match (kind, seen) with
          | (`Getter, `Setter)
          | (`Setter, `Getter) ->
            (* one getter and one setter are allowed as long as it's not used as a field *)
            ()
          | _ -> error_at env (loc, Parse_error.DuplicatePrivateFields name)
        end;
        SMap.add name `Field seen_names
      | None -> SMap.add name kind seen_names

  let class_implements env ~attach_leading =
    let rec interfaces env acc =
      let interface =
        with_loc
          (fun env ->
            let id =
              let id = Type.type_identifier env in
              if Peek.token env <> T_LESS_THAN then
                id
              else
                let { remove_trailing; _ } = trailing_and_remover env in
                remove_trailing id (fun remover id -> remover#identifier id)
            in
            let targs = Type.type_args env in
            { Ast.Class.Implements.Interface.id; targs })
          env
      in
      let acc = interface :: acc in
      match Peek.token env with
      | T_COMMA ->
        Expect.token env T_COMMA;
        interfaces env acc
      | _ -> List.rev acc
    in
    with_loc
      (fun env ->
        let leading =
          if attach_leading then
            Peek.comments env
          else
            []
        in
        Expect.token env T_IMPLEMENTS;
        let interfaces = interfaces env [] in
        { Ast.Class.Implements.interfaces; comments = Flow_ast_utils.mk_comments_opt ~leading () })
      env

  let class_extends ~leading =
    with_loc (fun env ->
        let expr =
          let expr = Expression.left_hand_side (env |> with_allow_yield false) in
          if Peek.token env <> T_LESS_THAN then
            expr
          else
            let { remove_trailing; _ } = trailing_and_remover env in
            remove_trailing expr (fun remover expr -> remover#expression expr)
        in
        let targs = Type.type_args env in
        { Class.Extends.expr; targs; comments = Flow_ast_utils.mk_comments_opt ~leading () }
    )

  (* https://tc39.es/ecma262/#prod-ClassHeritage *)
  let class_heritage env =
    let extends =
      let leading = Peek.comments env in
      if Eat.maybe env T_EXTENDS then
        let (loc, extends) = class_extends ~leading env in
        let { remove_trailing; _ } = trailing_and_remover env in
        Some
          (loc, remove_trailing extends (fun remover extends -> remover#class_extends loc extends))
      else
        None
    in
    let implements =
      if Peek.token env = T_IMPLEMENTS then (
        if not (should_parse_types env) then error env Parse_error.UnexpectedTypeInterface;
        Some (class_implements_remove_trailing env (class_implements env ~attach_leading:true))
      ) else
        None
    in
    (extends, implements)

  (* In the ES6 draft, all elements are methods. No properties (though there
   * are getter and setters allowed *)
  let class_element =
    let get env start_loc decorators static leading =
      let (loc, (key, value)) =
        with_loc ~start_loc (fun env -> getter_or_setter env ~in_class_body:true true) env
      in
      let open Ast.Class in
      Body.Method
        ( loc,
          {
            Method.key;
            value;
            kind = Method.Get;
            static;
            decorators;
            comments = Flow_ast_utils.mk_comments_opt ~leading ();
          }
        )
    in
    let set env start_loc decorators static leading =
      let (loc, (key, value)) =
        with_loc ~start_loc (fun env -> getter_or_setter env ~in_class_body:true false) env
      in
      let open Ast.Class in
      Body.Method
        ( loc,
          {
            Method.key;
            value;
            kind = Method.Set;
            static;
            decorators;
            comments = Flow_ast_utils.mk_comments_opt ~leading ();
          }
        )
    in
    let error_unsupported_variance env = function
      | Some (loc, _) -> error_at env (loc, Parse_error.UnexpectedVariance)
      | None -> ()
      (* Class property with annotation *)
    in
    let error_unsupported_declare env = function
      | Some loc -> error_at env (loc, Parse_error.DeclareClassElement)
      | None -> ()
    in
    let property_end_and_semicolon env key annot value =
      match Peek.token env with
      | T_LBRACKET
      | T_LPAREN ->
        error_unexpected env;
        (key, annot, value, [])
      | T_SEMICOLON ->
        Eat.token env;
        let trailing =
          match Peek.token env with
          | T_EOF
          | T_RCURLY ->
            Eat.trailing_comments env
          | _ when Peek.is_line_terminator env -> Eat.comments_until_next_line env
          | _ -> []
        in
        (key, annot, value, trailing)
      | _ ->
        let remover =
          match Peek.token env with
          | T_EOF
          | T_RCURLY ->
            { trailing = []; remove_trailing = (fun x _ -> x) }
          | _ when Peek.is_line_terminator env ->
            Comment_attachment.trailing_and_remover_after_last_line env
          | _ -> Comment_attachment.trailing_and_remover_after_last_loc env
        in
        (* Remove trailing comments from the last node in this property *)
        let (key, annot, value) =
          match (annot, value) with
          (* prop = init *)
          | (_, Class.Property.Initialized expr) ->
            ( key,
              annot,
              Class.Property.Initialized
                (remover.remove_trailing expr (fun remover expr -> remover#expression expr))
            )
          (* prop: annot *)
          | (Ast.Type.Available annot, _) ->
            ( key,
              Ast.Type.Available
                (remover.remove_trailing annot (fun remover annot -> remover#type_annotation annot)),
              value
            )
          (* prop *)
          | _ ->
            (remover.remove_trailing key (fun remover key -> remover#object_key key), annot, value)
        in
        (key, annot, value, [])
    in
    let property env start_loc key static declare variance leading =
      let (loc, (key, annot, value, comments)) =
        with_loc
          ~start_loc
          (fun env ->
            let annot = Type.annotation_opt env in
            let value =
              match (declare, Peek.token env) with
              | (None, T_ASSIGN) ->
                Eat.token env;
                Ast.Class.Property.Initialized
                  (Parse.expression (env |> with_allow_super Super_prop))
              | (Some _, T_ASSIGN) ->
                error env Parse_error.DeclareClassFieldInitializer;
                Eat.token env;
                Ast.Class.Property.Declared
              | (None, _) -> Ast.Class.Property.Uninitialized
              | (Some _, _) -> Ast.Class.Property.Declared
            in
            let (key, annot, value, trailing) = property_end_and_semicolon env key annot value in
            (key, annot, value, Flow_ast_utils.mk_comments_opt ~leading ~trailing ()))
          env
      in
      match key with
      | Ast.Expression.Object.Property.PrivateName private_name ->
        let open Ast.Class in
        Body.PrivateField
          (loc, { PrivateField.key = private_name; value; annot; static; variance; comments })
      | _ ->
        Ast.Class.(Body.Property (loc, { Property.key; value; annot; static; variance; comments }))
    in
    let is_asi env =
      match Peek.token env with
      | T_LESS_THAN -> false
      | T_LPAREN -> false
      | _ when Peek.is_implicit_semicolon env -> true
      | _ -> false
    in
    let rec init env start_loc decorators key ~async ~generator ~static ~declare variance leading =
      match Peek.token env with
      | T_COLON
      | T_ASSIGN
      | T_SEMICOLON
      | T_RCURLY
        when (not async) && not generator ->
        property env start_loc key static declare variance leading
      | T_PLING ->
        (* TODO: add support for optional class properties *)
        error_unexpected env;
        Eat.token env;
        init env start_loc decorators key ~async ~generator ~static ~declare variance leading
      | _ when is_asi env ->
        (* an uninitialized, unannotated property *)
        property env start_loc key static declare variance leading
      | _ ->
        error_unsupported_declare env declare;
        error_unsupported_variance env variance;
        let (kind, env) =
          match (static, key) with
          | ( false,
              Ast.Expression.Object.Property.Identifier
                (_, { Identifier.name = "constructor"; comments = _ })
            )
          | ( false,
              Ast.Expression.Object.Property.Literal
                (_, { Literal.value = Literal.String "constructor"; _ })
            ) ->
            (Ast.Class.Method.Constructor, env |> with_allow_super Super_prop_or_call)
          | _ -> (Ast.Class.Method.Method, env |> with_allow_super Super_prop)
        in
        let key = object_key_remove_trailing env key in
        let value =
          with_loc
            (fun env ->
              let (sig_loc, (tparams, params, return)) =
                with_loc
                  (fun env ->
                    let tparams = type_params_remove_trailing env (Type.type_params env) in
                    let params =
                      let (yield, await) =
                        match (async, generator) with
                        | (true, true) ->
                          (true, true) (* proposal-async-iteration/#prod-AsyncGeneratorMethod *)
                        | (true, false) -> (false, allow_await env) (* #prod-AsyncMethod *)
                        | (false, true) -> (true, false) (* #prod-GeneratorMethod *)
                        | (false, false) -> (false, false)
                        (* #prod-MethodDefinition *)
                      in
                      let params = Declaration.function_params ~await ~yield env in
                      let params =
                        if Peek.token env = T_COLON then
                          params
                        else
                          function_params_remove_trailing env params
                      in
                      Ast.Function.Params.(
                        match params with
                        | (loc, ({ this_ = Some (this_loc, _); _ } as params))
                          when kind = Ast.Class.Method.Constructor ->
                          (* Disallow this param annotations for constructors *)
                          error_at env (this_loc, Parse_error.ThisParamBannedInConstructor);
                          (loc, { params with this_ = None })
                        | params -> params
                      )
                    in
                    let return =
                      type_annotation_hint_remove_trailing env (Type.annotation_opt env)
                    in
                    (tparams, params, return))
                  env
              in
              let simple_params = is_simple_parameter_list params in
              let (body, contains_use_strict) =
                Declaration.function_body env ~async ~generator ~expression:false ~simple_params
              in
              Declaration.strict_post_check env ~contains_use_strict None params;
              {
                Function.id = None;
                params;
                body;
                generator;
                async;
                (* TODO: add support for method predicates *)
                predicate = None;
                return;
                tparams;
                sig_loc;
                comments = None;
              })
            env
        in
        let open Ast.Class in
        Body.Method
          ( Loc.btwn start_loc (fst value),
            {
              Method.key;
              value;
              kind;
              static;
              decorators;
              comments = Flow_ast_utils.mk_comments_opt ~leading ();
            }
          )
    in
    let ith_implies_identifier ~i env =
      match Peek.ith_token ~i env with
      | T_LESS_THAN
      | T_COLON
      | T_ASSIGN
      | T_SEMICOLON
      | T_LPAREN
      | T_RCURLY ->
        true
      | _ -> false
    in
    let implies_identifier = ith_implies_identifier ~i:0 in
    fun env ->
      let start_loc = Peek.loc env in
      let decorators = decorator_list env in
      let (declare, leading_declare) =
        match Peek.token env with
        | T_DECLARE when not (ith_implies_identifier ~i:1 env) ->
          let ret = Some (Peek.loc env) in
          let leading = Peek.comments env in
          Eat.token env;
          (ret, leading)
        | _ -> (None, [])
      in
      let static =
        Peek.ith_token ~i:1 env <> T_LPAREN
        && Peek.ith_token ~i:1 env <> T_LESS_THAN
        && Peek.token env = T_STATIC
      in
      let leading_static =
        if static then (
          let leading = Peek.comments env in
          Eat.token env;
          leading
        ) else
          []
      in
      let async =
        Peek.token env = T_ASYNC
        && (not (ith_implies_identifier ~i:1 env))
        && not (Peek.ith_is_line_terminator ~i:1 env)
      in
      (* consume `async` *)
      let leading_async =
        if async then (
          let leading = Peek.comments env in
          Eat.token env;
          leading
        ) else
          []
      in
      let (generator, leading_generator) = Declaration.generator env in
      let variance = Declaration.variance env async generator in
      let (generator, leading_generator) =
        match (generator, variance) with
        | (false, Some _) -> Declaration.generator env
        | _ -> (generator, leading_generator)
      in
      let leading =
        List.concat [leading_declare; leading_static; leading_async; leading_generator]
      in
      match (async, generator, Peek.token env) with
      | (false, false, T_IDENTIFIER { raw = "get"; _ }) ->
        let leading_get = Peek.comments env in
        let (_, key) = key ~class_body:true env in
        if implies_identifier env then
          init env start_loc decorators key ~async ~generator ~static ~declare variance leading
        else (
          error_unsupported_declare env declare;
          error_unsupported_variance env variance;
          ignore (object_key_remove_trailing env key);
          get env start_loc decorators static (leading @ leading_get)
        )
      | (false, false, T_IDENTIFIER { raw = "set"; _ }) ->
        let leading_set = Peek.comments env in
        let (_, key) = key ~class_body:true env in
        if implies_identifier env then
          init env start_loc decorators key ~async ~generator ~static ~declare variance leading
        else (
          error_unsupported_declare env declare;
          error_unsupported_variance env variance;
          ignore (object_key_remove_trailing env key);
          set env start_loc decorators static (leading @ leading_set)
        )
      | (_, _, _) ->
        let (_, key) = key ~class_body:true env in
        init env start_loc decorators key ~async ~generator ~static ~declare variance leading

  let class_body =
    let rec elements env seen_constructor private_names acc =
      match Peek.token env with
      | T_EOF
      | T_RCURLY ->
        List.rev acc
      | T_SEMICOLON ->
        (* Skip empty elements *)
        Expect.token env T_SEMICOLON;
        elements env seen_constructor private_names acc
      | _ ->
        let element = class_element env in
        let (seen_constructor', private_names') =
          match element with
          | Ast.Class.Body.Method (loc, m) ->
            let open Ast.Class.Method in
            (match m.kind with
            | Constructor ->
              if m.static then
                (seen_constructor, private_names)
              else (
                if seen_constructor then error_at env (loc, Parse_error.DuplicateConstructor);
                (true, private_names)
              )
            | Method ->
              let private_names =
                match m.key with
                | Ast.Expression.Object.Property.PrivateName name ->
                  check_private_names env private_names name `Method
                | _ -> private_names
              in
              (seen_constructor, private_names)
            | Get ->
              let open Ast.Expression.Object.Property in
              let private_names =
                match m.key with
                | PrivateName name -> check_private_names env private_names name `Getter
                | _ -> private_names
              in
              (seen_constructor, private_names)
            | Set ->
              let open Ast.Expression.Object.Property in
              let private_names =
                match m.key with
                | PrivateName name -> check_private_names env private_names name `Setter
                | _ -> private_names
              in
              (seen_constructor, private_names))
          | Ast.Class.Body.Property (_, { Ast.Class.Property.key; static; _ }) ->
            let open Ast.Expression.Object.Property in
            begin
              match key with
              | Identifier (loc, { Identifier.name; comments = _ })
              | Literal (loc, { Literal.value = Literal.String name; _ }) ->
                check_property_name env loc name static
              | Literal _
              | Computed _ ->
                ()
              | PrivateName _ ->
                failwith "unexpected PrivateName in Property, expected a PrivateField"
            end;
            (seen_constructor, private_names)
          | Ast.Class.Body.PrivateField (_, { Ast.Class.PrivateField.key; _ }) ->
            let private_names = check_private_names env private_names key `Field in
            (seen_constructor, private_names)
        in
        elements env seen_constructor' private_names' (element :: acc)
    in
    fun ~expression env ->
      with_loc
        (fun env ->
          let leading = Peek.comments env in
          if Eat.maybe env T_LCURLY then (
            enter_class env;
            let body = elements env false SMap.empty [] in
            exit_class env;
            Expect.token env T_RCURLY;
            let trailing =
              match (expression, Peek.token env) with
              | (true, _)
              | (_, (T_RCURLY | T_EOF)) ->
                Eat.trailing_comments env
              | _ when Peek.is_line_terminator env -> Eat.comments_until_next_line env
              | _ -> []
            in
            { Ast.Class.Body.body; comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing () }
          ) else (
            Expect.error env T_LCURLY;
            { Ast.Class.Body.body = []; comments = None }
          ))
        env

  let _class ?(decorators = []) env ~optional_id ~expression =
    (* 10.2.1 says all parts of a class definition are strict *)
    let env = env |> with_strict true in
    let decorators = decorators @ decorator_list env in
    let leading = Peek.comments env in
    Expect.token env T_CLASS;
    let id =
      let tmp_env = env |> with_no_let true in
      match (optional_id, Peek.token tmp_env) with
      | (true, (T_EXTENDS | T_IMPLEMENTS | T_LESS_THAN | T_LCURLY)) -> None
      | _ when Peek.is_identifier env ->
        let id = Parse.identifier tmp_env in
        let { remove_trailing; _ } = trailing_and_remover env in
        let id = remove_trailing id (fun remover id -> remover#identifier id) in
        Some id
      | _ ->
        (* error, but don't consume a token like Parse.identifier does. this helps
           with recovery, and the parser won't get stuck because we consumed the
           `class` token above. *)
        error_nameless_declaration env "class";
        Some (Peek.loc env, { Identifier.name = ""; comments = None })
    in
    let tparams =
      match Type.type_params env with
      | None -> None
      | Some tparams ->
        let { remove_trailing; _ } = trailing_and_remover env in
        Some (remove_trailing tparams (fun remover tparams -> remover#type_params tparams))
    in
    let (extends, implements) = class_heritage env in
    let body = class_body env ~expression in
    let comments = Flow_ast_utils.mk_comments_opt ~leading () in
    { Class.id; body; tparams; extends; implements; class_decorators = decorators; comments }

  let class_declaration env decorators =
    with_loc
      (fun env ->
        let optional_id = in_export_default env in
        Ast.Statement.ClassDeclaration (_class env ~decorators ~optional_id ~expression:false))
      env

  let class_expression =
    with_loc (fun env -> Ast.Expression.Class (_class env ~optional_id:true ~expression:true))
end