Source file printtyp.ml

(**************************************************************************)
(*                                                                        *)
(*                                 OCaml                                  *)
(*                                                                        *)
(*  Xavier Leroy and Jerome Vouillon, projet Cristal, INRIA Rocquencourt  *)
(*                                                                        *)
(*   Copyright 1996 Institut National de Recherche en Informatique et     *)
(*     en Automatique.                                                    *)
(*                                                                        *)
(*   All rights reserved.  This file is distributed under the terms of    *)
(*   the GNU Lesser General Public License version 2.1, with the          *)
(*   special exception on linking described in the file LICENSE.          *)
(*                                                                        *)
(**************************************************************************)

(* Printing functions *)

module M = Misc.String.Map
module S = Misc.String.Set

open Misc
open Ctype
open Format
open Longident
open Path
open Asttypes
open Types
open Btype
open Outcometree

(* Print a long identifier *)

let rec longident ppf = function
  | Lident s -> pp_print_string ppf s
  | Ldot(p, s) -> fprintf ppf "%a.%s" longident p s
  | Lapply(p1, p2) -> fprintf ppf "%a(%a)" longident p1 longident p2

let () = Env.print_longident := longident

(* Print an identifier avoiding name collisions *)

module Out_name = struct
  let create x = { printed_name = x }
  let print x = x.printed_name
end

(** Some identifiers may require hiding when printing *)
type bound_ident = { hide:bool; ident:Ident.t }

(* printing environment for path shortening and naming *)
let printing_env = ref Env.empty

(* When printing, it is important to only observe the
   current printing environment, without reading any new
   cmi present on the file system *)
let in_printing_env f = Env.without_cmis f !printing_env

 type namespace = Shape.Sig_component_kind.t =
    | Value
    | Type
    | Module
    | Module_type
    | Extension_constructor
    | Class
    | Class_type


module Namespace = struct

  let id = function
    | Type -> 0
    | Module -> 1
    | Module_type -> 2
    | Class -> 3
    | Class_type -> 4
    | Extension_constructor | Value -> 5
     (* we do not handle those component *)

  let size = 1 + id Value


  let pp ppf x =
    Format.pp_print_string ppf (Shape.Sig_component_kind.to_string x)

  let lookup =
    let to_lookup f lid = fst @@ in_printing_env (f (Lident lid)) in
    function
    | Some Type -> to_lookup Env.find_type_by_name
    | Some Module -> to_lookup Env.find_module_by_name
    | Some Module_type -> to_lookup Env.find_modtype_by_name
    | Some Class -> to_lookup Env.find_class_by_name
    | Some Class_type -> to_lookup Env.find_cltype_by_name
    | None | Some(Value|Extension_constructor) -> fun _ -> raise Not_found

  let location namespace id =
    let path = Path.Pident id in
    try Some (
        match namespace with
        | Some Type -> (in_printing_env @@ Env.find_type path).type_loc
        | Some Module -> (in_printing_env @@ Env.find_module path).md_loc
        | Some Module_type -> (in_printing_env @@ Env.find_modtype path).mtd_loc
        | Some Class -> (in_printing_env @@ Env.find_class path).cty_loc
        | Some Class_type -> (in_printing_env @@ Env.find_cltype path).clty_loc
        | Some (Extension_constructor|Value) | None -> Location.none
      ) with Not_found -> None

  let best_class_namespace = function
    | Papply _ | Pdot _ -> Some Module
    | Pextra_ty _ -> assert false (* Only in type path *)
    | Pident c ->
        match location (Some Class) c with
        | Some _ -> Some Class
        | None -> Some Class_type

end

(** {2 Conflicts printing}
    Conflicts arise when multiple items are attributed the same name,
    the following module stores the global conflict references and
    provides the printing functions for explaining the source of
    the conflicts.
*)
module Conflicts = struct
  type explanation =
    { kind: namespace; name:string; root_name:string; location:Location.t}
  let explanations = ref M.empty

  let add namespace name id =
    match Namespace.location (Some namespace) id with
    | None -> ()
    | Some location ->
        let explanation =
          { kind = namespace; location; name; root_name=Ident.name id}
        in
        explanations := M.add name explanation !explanations

  let collect_explanation namespace id ~name =
    let root_name = Ident.name id in
    (* if [name] is of the form "root_name/%d", we register both
      [id] and the identifier in scope for [root_name].
     *)
    if root_name <> name && not (M.mem name !explanations) then
      begin
        add namespace name id;
        if not (M.mem root_name !explanations) then
          (* lookup the identifier in scope with name [root_name] and
             add it too
           *)
          match Namespace.lookup (Some namespace) root_name with
          | Pident root_id -> add namespace root_name root_id
          | exception Not_found | _ -> ()
      end

  let pp_explanation ppf r=
    Format.fprintf ppf "@[<v 2>%a:@,Definition of %s %s@]"
      Location.print_loc r.location
        (Shape.Sig_component_kind.to_string r.kind) r.name

  let print_located_explanations ppf l =
    Format.fprintf ppf "@[<v>%a@]" (Format.pp_print_list pp_explanation) l

  let reset () = explanations := M.empty
  let list_explanations () =
    let c = !explanations in
    reset ();
    c |> M.bindings |> List.map snd |> List.sort Stdlib.compare


  let print_toplevel_hint ppf l =
    let conj ppf () = Format.fprintf ppf " and@ " in
    let pp_namespace_plural ppf n = Format.fprintf ppf "%as" Namespace.pp n in
    let root_names = List.map (fun r -> r.kind, r.root_name) l in
    let unique_root_names = List.sort_uniq Stdlib.compare root_names in
    let submsgs = Array.make Namespace.size [] in
    let () = List.iter (fun (n,_ as x) ->
        submsgs.(Namespace.id n) <- x :: submsgs.(Namespace.id n)
      )  unique_root_names in
    let pp_submsg ppf names =
      match names with
      | [] -> ()
      | [namespace, a] ->
          Format.fprintf ppf
        "@ \
         @[<2>@{<hint>Hint@}: The %a %s has been defined multiple times@ \
         in@ this@ toplevel@ session.@ \
         Some toplevel values still refer to@ old@ versions@ of@ this@ %a.\
         @ Did you try to redefine them?@]"
        Namespace.pp namespace a Namespace.pp namespace
      | (namespace, _) :: _ :: _ ->
      Format.fprintf ppf
        "@ \
         @[<2>@{<hint>Hint@}: The %a %a have been defined multiple times@ \
         in@ this@ toplevel@ session.@ \
         Some toplevel values still refer to@ old@ versions@ of@ those@ %a.\
         @ Did you try to redefine them?@]"
        pp_namespace_plural namespace
        Format.(pp_print_list ~pp_sep:conj pp_print_string) (List.map snd names)
        pp_namespace_plural namespace in
    Array.iter (pp_submsg ppf) submsgs

  let print_explanations ppf =
    let ltop, l =
      (* isolate toplevel locations, since they are too imprecise *)
      let from_toplevel a =
        a.location.Location.loc_start.Lexing.pos_fname = "//toplevel//" in
      List.partition from_toplevel (list_explanations ())
    in
    begin match l with
    | [] -> ()
    | l -> Format.fprintf ppf "@,%a" print_located_explanations l
    end;
    (* if there are name collisions in a toplevel session,
       display at least one generic hint by namespace *)
    print_toplevel_hint ppf ltop

  let exists () = M.cardinal !explanations >0
end

module Naming_context = struct

let enabled = ref true
let enable b = enabled := b

(* Names bound in recursive definitions should be considered as bound
   in the environment when printing identifiers but not when trying
   to find shortest path.
   For instance, if we define
   [{
   module Avoid__me = struct
     type t = A
   end
   type t = X
   type u = [` A of t * t ]
   module M = struct
     type t = A of [ u | `B ]
     type r = Avoid__me.t
   end
  }]
  It is is important that in the definition of [t] that the outer type [t] is
  printed as [t/2] reserving the name [t] to the type being defined in the
  current recursive definition.
     Contrarily, in the definition of [r], one should not shorten the
  path [Avoid__me.t] to [r] until the end of the definition of [r].
  The [bound_in_recursion] bridges the gap between those two slightly different
  notions of printing environment.
*)
let bound_in_recursion = ref M.empty

(* When dealing with functor arguments, identity becomes fuzzy because the same
   syntactic argument may be represented by different identifiers during the
   error processing, we are thus disabling disambiguation on the argument name
*)
let fuzzy = ref S.empty
let with_arg id f =
  protect_refs [ R(fuzzy, S.add (Ident.name id) !fuzzy) ] f
let fuzzy_id namespace id = namespace = Module && S.mem (Ident.name id) !fuzzy

let with_hidden ids f =
  let update m id = M.add (Ident.name id.ident) id.ident m in
  let updated = List.fold_left update !bound_in_recursion ids in
  protect_refs [ R(bound_in_recursion, updated )] f

let human_id id index =
  (* The identifier with index [k] is the (k+1)-th most recent identifier in
     the printing environment. We print them as [name/(k+1)] except for [k=0]
     which is printed as [name] rather than [name/1].
  *)
  if index = 0 then
    Ident.name id
  else
    let ordinal = index + 1 in
    String.concat "/" [Ident.name id; string_of_int ordinal]

let indexed_name namespace id =
  let find namespace id env = match namespace with
    | Type -> Env.find_type_index id env
    | Module -> Env.find_module_index id env
    | Module_type -> Env.find_modtype_index id env
    | Class -> Env.find_class_index id env
    | Class_type-> Env.find_cltype_index id env
    | Value | Extension_constructor -> None
  in
  let index =
    match M.find_opt (Ident.name id) !bound_in_recursion with
    | Some rec_bound_id ->
        (* the identifier name appears in the current group of recursive
           definition *)
        if Ident.same rec_bound_id id then
          Some 0
        else
          (* the current recursive definition shadows one more time the
            previously existing identifier with the same name *)
          Option.map succ (in_printing_env (find namespace id))
    | None ->
        in_printing_env (find namespace id)
  in
  let index =
    (* If [index] is [None] at this point, it might indicate that
       the identifier id is not defined in the environment, while there
       are other identifiers in scope that share the same name.
       Currently, this kind of partially incoherent environment happens
       within functor error messages where the left and right hand side
       have a different views of the environment at the source level.
       Printing the source-level by using a default index of `0`
       seems like a reasonable compromise in this situation however.*)
    Option.value index ~default:0
  in
  human_id id index

let ident_name namespace id =
  match namespace, !enabled with
  | None, _ | _, false -> Out_name.create (Ident.name id)
  | Some namespace, true ->
      if fuzzy_id namespace id then Out_name.create (Ident.name id)
      else
        let name = indexed_name namespace id in
        Conflicts.collect_explanation namespace id ~name;
        Out_name.create name
end
let ident_name = Naming_context.ident_name

let ident ppf id = pp_print_string ppf
    (Out_name.print (Naming_context.ident_name None id))

let namespaced_ident namespace  id =
  Out_name.print (Naming_context.ident_name (Some namespace) id)


(* Print a path *)

let ident_stdlib = Ident.create_persistent "Stdlib"

let non_shadowed_stdlib namespace = function
  | Pdot(Pident id, s) as path ->
      Ident.same id ident_stdlib &&
      (match Namespace.lookup namespace s with
       | path' -> Path.same path path'
       | exception Not_found -> true)
  | _ -> false

let find_double_underscore s =
  let len = String.length s in
  let rec loop i =
    if i + 1 >= len then
      None
    else if s.[i] = '_' && s.[i + 1] = '_' then
      Some i
    else
      loop (i + 1)
  in
  loop 0

let rec module_path_is_an_alias_of env path ~alias_of =
  match Env.find_module path env with
  | { md_type = Mty_alias path'; _ } ->
    Path.same path' alias_of ||
    module_path_is_an_alias_of env path' ~alias_of
  | _ -> false
  | exception Not_found -> false

(* Simple heuristic to print Foo__bar.* as Foo.Bar.* when Foo.Bar is an alias
   for Foo__bar. This pattern is used by the stdlib. *)
let rec rewrite_double_underscore_paths env p =
  match p with
  | Pdot (p, s) ->
    Pdot (rewrite_double_underscore_paths env p, s)
  | Papply (a, b) ->
    Papply (rewrite_double_underscore_paths env a,
            rewrite_double_underscore_paths env b)
  | Pextra_ty (p, extra) ->
    Pextra_ty (rewrite_double_underscore_paths env p, extra)
  | Pident id ->
    let name = Ident.name id in
    match find_double_underscore name with
    | None -> p
    | Some i ->
      let better_lid =
        Ldot
          (Lident (String.sub name 0 i),
           String.capitalize_ascii
             (String.sub name (i + 2) (String.length name - i - 2)))
      in
      match Env.find_module_by_name better_lid env with
      | exception Not_found -> p
      | p', _ ->
          if module_path_is_an_alias_of env p' ~alias_of:p then
            p'
          else
          p

let rewrite_double_underscore_paths env p =
  if env == Env.empty then
    p
  else
    rewrite_double_underscore_paths env p

let rec tree_of_path ?(disambiguation=true) namespace p =
  let tree_of_path namespace p = tree_of_path ~disambiguation namespace p in
  let namespace = if disambiguation then namespace else None in
  match p with
  | Pident id ->
      Oide_ident (ident_name namespace id)
  | Pdot(_, s) as path when non_shadowed_stdlib namespace path ->
      Oide_ident (Out_name.create s)
  | Pdot(p, s) ->
      Oide_dot (tree_of_path (Some Module) p, s)
  | Papply(p1, p2) ->
      let t1 = tree_of_path (Some Module) p1 in
      let t2 = tree_of_path (Some Module) p2 in
      Oide_apply (t1, t2)
  | Pextra_ty (p, extra) -> begin
      (* inline record types are syntactically prevented from escaping their
         binding scope, and are never shown to users. *)
      match extra with
        Pcstr_ty s ->
          Oide_dot (tree_of_path (Some Type) p, s)
      | Pext_ty ->
          tree_of_path None p
    end

let tree_of_path ?disambiguation namespace p =
  tree_of_path ?disambiguation namespace
    (rewrite_double_underscore_paths !printing_env p)

let path ppf p =
  !Oprint.out_ident ppf (tree_of_path None p)

let string_of_path p =
  Format.asprintf "%a" path p

let strings_of_paths namespace p =
  let trees = List.map (tree_of_path namespace) p in
  List.map (Format.asprintf "%a" !Oprint.out_ident) trees

let () = Env.print_path := path

(* Print a recursive annotation *)

let tree_of_rec = function
  | Trec_not -> Orec_not
  | Trec_first -> Orec_first
  | Trec_next -> Orec_next

(* Print a raw type expression, with sharing *)

let raw_list pr ppf = function
    [] -> fprintf ppf "[]"
  | a :: l ->
      fprintf ppf "@[<1>[%a%t]@]" pr a
        (fun ppf -> List.iter (fun x -> fprintf ppf ";@,%a" pr x) l)

let kind_vars = ref []
let kind_count = ref 0

let string_of_field_kind v =
  match field_kind_repr v with
  | Fpublic -> "Fpublic"
  | Fabsent -> "Fabsent"
  | Fprivate -> "Fprivate"

let rec safe_repr v t =
  match Transient_expr.coerce t with
    {desc = Tlink t} when not (List.memq t v) ->
      safe_repr (t::v) t
  | t' -> t'

let rec list_of_memo = function
    Mnil -> []
  | Mcons (_priv, p, _t1, _t2, rem) -> p :: list_of_memo rem
  | Mlink rem -> list_of_memo !rem

let print_name ppf = function
    None -> fprintf ppf "None"
  | Some name -> fprintf ppf "\"%s\"" name

let string_of_label = function
    Nolabel -> ""
  | Labelled s -> s
  | Optional s -> "?"^s

let visited = ref []
let rec raw_type ppf ty =
  let ty = safe_repr [] ty in
  if List.memq ty !visited then fprintf ppf "{id=%d}" ty.id else begin
    visited := ty :: !visited;
    fprintf ppf "@[<1>{id=%d;level=%d;scope=%d;desc=@,%a}@]" ty.id ty.level
      ty.scope raw_type_desc ty.desc
  end
and raw_type_list tl = raw_list raw_type tl
and raw_type_desc ppf = function
    Tvar name -> fprintf ppf "Tvar %a" print_name name
  | Tarrow(l,t1,t2,c) ->
      fprintf ppf "@[<hov1>Tarrow(\"%s\",@,%a,@,%a,@,%s)@]"
        (string_of_label l) raw_type t1 raw_type t2
        (if is_commu_ok c then "Cok" else "Cunknown")
  | Ttuple tl ->
      fprintf ppf "@[<1>Ttuple@,%a@]" raw_type_list tl
  | Tconstr (p, tl, abbrev) ->
      fprintf ppf "@[<hov1>Tconstr(@,%a,@,%a,@,%a)@]" path p
        raw_type_list tl
        (raw_list path) (list_of_memo !abbrev)
  | Tobject (t, nm) ->
      fprintf ppf "@[<hov1>Tobject(@,%a,@,@[<1>ref%t@])@]" raw_type t
        (fun ppf ->
          match !nm with None -> fprintf ppf " None"
          | Some(p,tl) ->
              fprintf ppf "(Some(@,%a,@,%a))" path p raw_type_list tl)
  | Tfield (f, k, t1, t2) ->
      fprintf ppf "@[<hov1>Tfield(@,%s,@,%s,@,%a,@;<0 -1>%a)@]" f
        (string_of_field_kind k)
        raw_type t1 raw_type t2
  | Tnil -> fprintf ppf "Tnil"
  | Tlink t -> fprintf ppf "@[<1>Tlink@,%a@]" raw_type t
  | Tsubst (t, None) -> fprintf ppf "@[<1>Tsubst@,(%a,None)@]" raw_type t
  | Tsubst (t, Some t') ->
      fprintf ppf "@[<1>Tsubst@,(%a,@ Some%a)@]" raw_type t raw_type t'
  | Tunivar name -> fprintf ppf "Tunivar %a" print_name name
  | Tpoly (t, tl) ->
      fprintf ppf "@[<hov1>Tpoly(@,%a,@,%a)@]"
        raw_type t
        raw_type_list tl
  | Tvariant row ->
      let Row {fields; more; name; fixed; closed} = row_repr row in
      fprintf ppf
        "@[<hov1>{@[%s@,%a;@]@ @[%s@,%a;@]@ %s%B;@ %s%a;@ @[<1>%s%t@]}@]"
        "row_fields="
        (raw_list (fun ppf (l, f) ->
          fprintf ppf "@[%s,@ %a@]" l raw_field f))
        fields
        "row_more=" raw_type more
        "row_closed=" closed
        "row_fixed=" raw_row_fixed fixed
        "row_name="
        (fun ppf ->
          match name with None -> fprintf ppf "None"
          | Some(p,tl) ->
              fprintf ppf "Some(@,%a,@,%a)" path p raw_type_list tl)
  | Tpackage (p, fl) ->
      fprintf ppf "@[<hov1>Tpackage(@,%a@,%a)@]" path p
        raw_type_list (List.map snd fl)
and raw_row_fixed ppf = function
| None -> fprintf ppf "None"
| Some Types.Fixed_private -> fprintf ppf "Some Fixed_private"
| Some Types.Rigid -> fprintf ppf "Some Rigid"
| Some Types.Univar t -> fprintf ppf "Some(Univar(%a))" raw_type t
| Some Types.Reified p -> fprintf ppf "Some(Reified(%a))" path p

and raw_field ppf rf =
  match_row_field
    ~absent:(fun _ -> fprintf ppf "RFabsent")
    ~present:(function
      | None ->
          fprintf ppf "RFpresent None"
      | Some t ->
          fprintf ppf  "@[<1>RFpresent(Some@,%a)@]" raw_type t)
    ~either:(fun c tl m e ->
      fprintf ppf "@[<hov1>RFeither(%B,@,%a,@,%B,@,@[<1>ref%t@])@]" c
        raw_type_list tl m
        (fun ppf ->
          match e with None -> fprintf ppf " RFnone"
          | Some f -> fprintf ppf "@,@[<1>(%a)@]" raw_field f))
    rf

let raw_type_expr ppf t =
  visited := []; kind_vars := []; kind_count := 0;
  raw_type ppf t;
  visited := []; kind_vars := []

let () = Btype.print_raw := raw_type_expr

(* Normalize paths *)

let set_printing_env env =
  printing_env :=
    if !Clflags.real_paths then Env.empty
    else env

let wrap_printing_env env f =
  set_printing_env (Env.update_short_paths env);
  try_finally f ~always:(fun () -> set_printing_env Env.empty)

let wrap_printing_env ?error:_ env f =
  Env.without_cmis (wrap_printing_env env) f

type type_result = Short_paths.type_result =
  | Nth of int
  | Path of int list option * Path.t

type type_resolution = Short_paths.type_resolution =
  | Nth of int
  | Subst of int list
  | Id

let apply_subst ns args =
  List.map (List.nth args) ns

let apply_subst_opt nso args =
  match nso with
  | None -> args
  | Some ns -> apply_subst ns args

let apply_nth n args =
  List.nth args n

let best_type_path p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then Path(None, p)
  else Short_paths.find_type (Env.short_paths !printing_env) p

let best_type_path_resolution p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then Id
  else Short_paths.find_type_resolution (Env.short_paths !printing_env) p

let best_type_path_simple p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then p
  else Short_paths.find_type_simple (Env.short_paths !printing_env) p

let best_module_type_path p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then p
  else Short_paths.find_module_type (Env.short_paths !printing_env) p

let best_module_path p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then p
  else Short_paths.find_module (Env.short_paths !printing_env) p

let best_class_type_path p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then None, p
  else Short_paths.find_class_type (Env.short_paths !printing_env) p

let best_class_type_path_simple p =
  if !Clflags.real_paths || !printing_env == Env.empty
  then p
  else Short_paths.find_class_type_simple (Env.short_paths !printing_env) p

(* When building a tree for a best type path, we should not disambiguate
   identifiers whenever the short-path algorithm detected a better path than
   the original one.*)
let tree_of_best_type_path p p' =
  if Path.same p p' then tree_of_path (Some Type) p'
  else tree_of_path ~disambiguation:false None p'

(* Print a type expression *)

let proxy ty = Transient_expr.repr (proxy ty)

(* When printing a type scheme, we print weak names.  When printing a plain
   type, we do not.  This type controls that behavior *)
type type_or_scheme = Type | Type_scheme

let is_non_gen mode ty =
  match mode with
  | Type_scheme -> is_Tvar ty && get_level ty <> generic_level
  | Type        -> false

let nameable_row row =
  row_name row <> None &&
  List.for_all
    (fun (_, f) ->
       match row_field_repr f with
       | Reither(c, l, _) ->
           row_closed row && if c then l = [] else List.length l = 1
       | _ -> true)
    (row_fields row)

(* This specialized version of [Btype.iter_type_expr] normalizes and
   short-circuits the traversal of the [type_expr], so that it covers only the
   subterms that would be printed by the type printer. *)
let printer_iter_type_expr f ty =
  match get_desc ty with
  | Tconstr(p, tyl, _) -> begin
      match best_type_path_resolution p with
      | Nth n ->
          f (apply_nth n tyl)
      | Subst ns ->
        List.iter f (apply_subst ns tyl)
      | Id ->
          List.iter f tyl
      end
  | Tvariant row -> begin
      match row_name row with
      | Some(_p, tyl) when nameable_row row ->
          List.iter f tyl
      | _ ->
          iter_row f row
    end
  | Tobject (fi, nm) -> begin
      match !nm with
      | None ->
          let fields, _ = flatten_fields fi in
          List.iter
            (fun (_, kind, ty) ->
               if field_kind_repr kind = Fpublic then
                 f ty)
            fields
      | Some (_, l) ->
          List.iter f (List.tl l)
    end
  | Tfield(_, kind, ty1, ty2) ->
      if field_kind_repr kind = Fpublic then
        f ty1;
      f ty2
  | _ ->
      Btype.iter_type_expr f ty

module Names : sig
  val reset_names : unit -> unit

  val add_named_vars : type_expr -> unit
  val add_subst : (type_expr * type_expr) list -> unit

  val new_name : unit -> string
  val new_var_name : non_gen:bool -> type_expr -> unit -> string

  val name_of_type : (unit -> string) -> transient_expr -> string
  val check_name_of_type : non_gen:bool -> transient_expr -> unit

  val remove_names : transient_expr list -> unit

  val with_local_names : (unit -> 'a) -> 'a

  (* Refresh the weak variable map in the toplevel; for [print_items], which is
     itself for the toplevel *)
  val refresh_weak : unit -> unit
end = struct
  (* We map from types to names, but not directly; we also store a substitution,
     which maps from types to types.  The lookup process is
     "type -> apply substitution -> find name".  The substitution is presumed to
     be acyclic. *)
  let names = ref ([] : (transient_expr * string) list)
  let name_subst = ref ([] : (transient_expr * transient_expr) list)
  let name_counter = ref 0
  let named_vars = ref ([] : string list)
  let visited_for_named_vars = ref ([] : transient_expr list)

  let weak_counter = ref 1
  let weak_var_map = ref TypeMap.empty
  let named_weak_vars = ref String.Set.empty

  let reset_names () =
    names := [];
    name_subst := [];
    name_counter := 0;
    named_vars := [];
    visited_for_named_vars := []

  let add_named_var tty =
    match tty.desc with
      Tvar (Some name) | Tunivar (Some name) ->
        if List.mem name !named_vars then () else
        named_vars := name :: !named_vars
    | _ -> ()

  let rec add_named_vars ty =
    let tty = Transient_expr.repr ty in
    let px = proxy ty in
    if not (List.memq px !visited_for_named_vars) then begin
      visited_for_named_vars := px :: !visited_for_named_vars;
      match tty.desc with
      | Tvar _ | Tunivar _ ->
          add_named_var tty
        | _ ->
          printer_iter_type_expr add_named_vars ty
    end

  let rec substitute ty =
    match List.assq ty !name_subst with
    | ty' -> substitute ty'
    | exception Not_found -> ty

  let add_subst subst =
    name_subst :=
      List.map (fun (t1,t2) -> Transient_expr.repr t1, Transient_expr.repr t2)
        subst
      @ !name_subst

  let name_is_already_used name =
    List.mem name !named_vars
    || List.exists (fun (_, name') -> name = name') !names
    || String.Set.mem name !named_weak_vars

  let rec new_name () =
    let name =
      if !name_counter < 26
      then String.make 1 (Char.chr(97 + !name_counter))
      else String.make 1 (Char.chr(97 + !name_counter mod 26)) ^
            Int.to_string(!name_counter / 26) in
    incr name_counter;
    if name_is_already_used name then new_name () else name

  let rec new_weak_name ty () =
    let name = "weak" ^ Int.to_string !weak_counter in
    incr weak_counter;
    if name_is_already_used name then new_weak_name ty ()
    else begin
        named_weak_vars := String.Set.add name !named_weak_vars;
        weak_var_map := TypeMap.add ty name !weak_var_map;
        name
      end

  let new_var_name ~non_gen ty () =
    if non_gen then new_weak_name ty ()
    else new_name ()

  let name_of_type name_generator t =
    (* We've already been through repr at this stage, so t is our representative
       of the union-find class. *)
    let t = substitute t in
    try List.assq t !names with Not_found ->
      try TransientTypeMap.find t !weak_var_map with Not_found ->
      let name =
        match t.desc with
          Tvar (Some name) | Tunivar (Some name) ->
            (* Some part of the type we've already printed has assigned another
             * unification variable to that name. We want to keep the name, so
             * try adding a number until we find a name that's not taken. *)
            let available name =
              List.for_all
                (fun (_, name') -> name <> name')
                !names
            in
            if available name then name
            else
              let suffixed i = name ^ Int.to_string i in
              let i = Misc.find_first_mono (fun i -> available (suffixed i)) in
              suffixed i
        | _ ->
            (* No name available, create a new one *)
            name_generator ()
      in
      (* Exception for type declarations *)
      if name <> "_" then names := (t, name) :: !names;
      name

  let check_name_of_type ~non_gen px =
    let name_gen = new_var_name ~non_gen (Transient_expr.type_expr px) in
    ignore(name_of_type name_gen px)

  let remove_names tyl =
    let tyl = List.map substitute tyl in
    names := List.filter (fun (ty,_) -> not (List.memq ty tyl)) !names

  let with_local_names f =
    let old_names = !names in
    let old_subst = !name_subst in
    names      := [];
    name_subst := [];
    try_finally
      ~always:(fun () ->
        names      := old_names;
        name_subst := old_subst)
      f

  let refresh_weak () =
    let refresh t name (m,s) =
      if is_non_gen Type_scheme t then
        begin
          TypeMap.add t name m,
          String.Set.add name s
        end
      else m, s in
    let m, s =
      TypeMap.fold refresh !weak_var_map (TypeMap.empty ,String.Set.empty) in
    named_weak_vars := s;
    weak_var_map := m
end

let reserve_names ty =
  normalize_type ty;
  Names.add_named_vars ty

let visited_objects = ref ([] : transient_expr list)
let aliased = ref ([] : transient_expr list)
let delayed = ref ([] : transient_expr list)
let printed_aliases = ref ([] : transient_expr list)

(* [printed_aliases] is a subset of [aliased] that records only those aliased
   types that have actually been printed; this allows us to avoid naming loops
   that the user will never see. *)

let add_delayed t =
  if not (List.memq t !delayed) then delayed := t :: !delayed

let is_aliased_proxy px = List.memq px !aliased

let add_alias_proxy px =
  if not (is_aliased_proxy px) then
    aliased := px :: !aliased

let add_alias ty = add_alias_proxy (proxy ty)

let add_printed_alias_proxy ~non_gen px =
  Names.check_name_of_type ~non_gen px;
  printed_aliases := px :: !printed_aliases

let add_printed_alias ty = add_printed_alias_proxy (proxy ty)

let aliasable ty =
  match get_desc ty with
    Tvar _ | Tunivar _ | Tpoly _ -> false
  | Tconstr (p, _, _) -> begin
      match best_type_path_resolution p with
      | Nth _ -> false
      | Subst _ | Id -> true
    end
  | _ -> true

(* let namable_row row =
  row.row_name <> None &&
  List.for_all
    (fun (_, f) ->
       match row_field_repr f with
       | Reither(c, l, _, _) ->
           row.row_closed && if c then l = [] else List.length l = 1
       | _ -> true)
    row.row_fields *)
let should_visit_object ty =
  match get_desc ty with
  | Tvariant row -> not (static_row row)
  | Tobject _ -> opened_object ty
  | _ -> false

(*let rec mark_loops_rec visited ty =
  let ty = repr ty in
  let px = proxy ty in
  if List.memq px visited && aliasable ty then add_alias px else
    let visited = px :: visited in
    match ty.desc with
    | Tvar _ -> add_named_var ty
    | Tarrow(_, ty1, ty2, _) ->
        mark_loops_rec visited ty1; mark_loops_rec visited ty2
    | Ttuple tyl -> List.iter (mark_loops_rec visited) tyl
    | Tconstr(p, tyl, _) -> begin
        match best_type_path_resolution p with
        | Nth n ->
            mark_loops_rec visited (apply_nth n tyl)
        | Subst ns ->
          List.iter (mark_loops_rec visited) (apply_subst ns tyl)
        | Id ->
            List.iter (mark_loops_rec visited) tyl
      end
    | Tpackage (_, fl) ->
        List.iter (fun (_n, ty) -> mark_loops_rec visited ty) fl
    | Tvariant row ->
        if List.memq px !visited_objects then add_alias px else
         begin
          let row = row_repr row in
          if not (static_row row) then
            visited_objects := px :: !visited_objects;
          match row.row_name with
          | Some(_p, tyl) when namable_row row ->
              List.iter (mark_loops_rec visited) tyl
          | _ ->
              iter_row (mark_loops_rec visited) row
         end
    | Tobject (fi, nm) ->
        if List.memq px !visited_objects then add_alias px else
         begin
          if opened_object ty then
            visited_objects := px :: !visited_objects;
          begin match !nm with
          | None ->
              let fields, _ = flatten_fields fi in
              List.iter
                (fun (_, kind, ty) ->
                  if field_kind_repr kind = Fpresent then
                    mark_loops_rec visited ty)
                fields
          | Some (_, l) ->
              List.iter (mark_loops_rec visited) (List.tl l)
          end
        end
    | Tfield(_, kind, ty1, ty2) when field_kind_repr kind = Fpresent ->
        mark_loops_rec visited ty1; mark_loops_rec visited ty2
    | Tfield(_, _, _, ty2) ->
        mark_loops_rec visited ty2
    | Tnil -> ()
    | Tsubst _ -> ()  (* we do not print arguments *)
    | Tlink _ -> fatal_error "Printtyp.mark_loops_rec (2)"
    | Tpoly (ty, tyl) ->
        List.iter (fun t -> add_alias t) tyl;
        mark_loops_rec visited ty
    | Tunivar _ -> add_named_var ty *)
let rec mark_loops_rec visited ty =
  let px = proxy ty in
  if List.memq px visited && aliasable ty then add_alias_proxy px else
    let tty = Transient_expr.repr ty in
      let visited = px :: visited in
    match tty.desc with
    | Tvariant _ | Tobject _ ->
        if List.memq px !visited_objects then add_alias_proxy px else begin
          if should_visit_object ty then
              visited_objects := px :: !visited_objects;
          printer_iter_type_expr (mark_loops_rec visited) ty
          end
    | Tpoly(ty, tyl) ->
        List.iter add_alias tyl;
          mark_loops_rec visited ty
    | _ ->
        printer_iter_type_expr (mark_loops_rec visited) ty
let mark_loops ty =
  mark_loops_rec [] ty;;

let prepare_type ty =
  reserve_names ty;
  mark_loops ty;;

let reset_loop_marks () =
  visited_objects := []; aliased := []; delayed := []; printed_aliases := []

let reset_except_context () =
  Names.reset_names (); reset_loop_marks ()

let reset () =
  Conflicts.reset ();
  reset_except_context ()

let prepare_for_printing tyl =
  reset_except_context ();
  List.iter prepare_type tyl

let add_type_to_preparation = prepare_type

(* Disabled in classic mode when printing an unification error *)
let print_labels = ref true

let alias_nongen_row mode px ty =
    match get_desc ty with
    | Tvariant _ | Tobject _ ->
        if is_non_gen mode (Transient_expr.type_expr px) then
          add_alias_proxy px
    | _ -> ()

let rec tree_of_typexp mode ty =
  let px = proxy ty in
  if List.memq px !printed_aliases && not (List.memq px !delayed) then
   let non_gen = is_non_gen mode (Transient_expr.type_expr px) in
   let name = Names.name_of_type (Names.new_var_name ~non_gen ty) px in
   Otyp_var (non_gen, name) else

  let pr_typ () =
    let tty = Transient_expr.repr ty in
    match tty.desc with
    | Tvar _ ->
        let non_gen = is_non_gen mode ty in
        let name_gen = Names.new_var_name ~non_gen ty in
        Otyp_var (non_gen, Names.name_of_type name_gen tty)
    | Tarrow(l, ty1, ty2, _) ->
        let lab =
          if !print_labels || is_optional l then string_of_label l else ""
        in
        let t1 =
          if is_optional l then
            match get_desc ty1 with
            | Tconstr(path, [ty], _)
              when Path.same path Predef.path_option ->
                tree_of_typexp mode ty
            | _ -> Otyp_stuff "<hidden>"
          else tree_of_typexp mode ty1 in
        Otyp_arrow (lab, t1, tree_of_typexp mode ty2)
    | Ttuple tyl ->
        Otyp_tuple (tree_of_typlist mode tyl)
    | Tconstr(p, tyl, _abbrev) -> begin
        match best_type_path p with
        | Nth n -> tree_of_typexp mode (apply_nth n tyl)
        | Path(nso, p) ->
            let tyl' = apply_subst_opt nso tyl in
            Otyp_constr (tree_of_path (Some Type) p, tree_of_typlist mode tyl')
      end
    | Tvariant row ->
      let Row {fields; name; closed; _} = row_repr row in
        let fields =
          if closed then
            List.filter (fun (_, f) -> row_field_repr f <> Rabsent)
              fields
          else fields in
        let present =
          List.filter
            (fun (_, f) ->
               match row_field_repr f with
               | Rpresent _ -> true
               | _ -> false)
            fields in
        let all_present = List.length present = List.length fields in
        begin match name with
        | Some(p, tyl) when nameable_row row ->
            let out_variant =
              match best_type_path p with
              | Nth n -> tree_of_typexp mode (apply_nth n tyl)
              | Path(s, p) ->
                let id = tree_of_path (Some Type) p in
                let args = tree_of_typlist mode (apply_subst_opt s tyl) in
                Otyp_constr (id, args)
            in
            if closed && all_present then
              out_variant
            else
              let tags =
                if all_present then None else Some (List.map fst present) in
              Otyp_variant (Ovar_typ out_variant, closed, tags)
        | _ ->
            let fields = List.map (tree_of_row_field mode) fields in
            let tags =
              if all_present then None else Some (List.map fst present) in
              Otyp_variant (Ovar_fields fields, closed, tags)
        end
    | Tobject (fi, nm) ->
        tree_of_typobject mode fi !nm
    | Tnil | Tfield _ ->
        tree_of_typobject mode ty None
    | Tsubst _ ->
        (* This case should only happen when debugging the compiler *)
        Otyp_stuff "<Tsubst>"
    | Tlink _ ->
        fatal_error "Printtyp.tree_of_typexp"
    | Tpoly (ty, []) ->
        tree_of_typexp mode ty
    | Tpoly (ty, tyl) ->
        (*let print_names () =
          List.iter (fun (_, name) -> prerr_string (name ^ " ")) !names;
          prerr_string "; " in *)
        if tyl = [] then tree_of_typexp mode ty else begin
          let tyl = List.map Transient_expr.repr tyl in
          let old_delayed = !delayed in
          (* Make the names delayed, so that the real type is
             printed once when used as proxy *)
          List.iter add_delayed tyl;
          let tl = List.map (Names.name_of_type Names.new_name) tyl in
          let tr = Otyp_poly (tl, tree_of_typexp mode ty) in
          (* Forget names when we leave scope *)
          Names.remove_names tyl;
          delayed := old_delayed; tr
        end
    | Tunivar _ ->
        Otyp_var (false, Names.name_of_type Names.new_name tty)
    | Tpackage (p, fl) ->
        let p = best_module_type_path p in
        let fl =
          List.map
            (fun (li, ty) -> (
              String.concat "." (Longident.flatten li),
              tree_of_typexp mode ty
            )) fl in
        Otyp_module (tree_of_path (Some Module_type) p, fl)
  in
  if List.memq px !delayed then delayed := List.filter ((!=) px) !delayed;
  alias_nongen_row mode px ty;
  if is_aliased_proxy px && aliasable ty then begin
    let non_gen = is_non_gen mode (Transient_expr.type_expr px) in
    add_printed_alias_proxy ~non_gen px;
    (* add_printed_alias chose a name, thus the name generator
       doesn't matter.*)
    let alias = Names.name_of_type (Names.new_var_name ~non_gen ty) px in
    Otyp_alias {non_gen;  aliased = pr_typ (); alias } end
  else pr_typ ()

and tree_of_row_field mode (l, f) =
    match row_field_repr f with
  | Rpresent None | Reither(true, [], _) -> (l, false, [])
  | Rpresent(Some ty) -> (l, false, [tree_of_typexp mode ty])
  | Reither(c, tyl, _) ->
        if c (* contradiction: constant constructor with an argument *)
      then (l, true, tree_of_typlist mode tyl)
      else (l, false, tree_of_typlist mode tyl)
    | Rabsent -> (l, false, [] (* actually, an error *))

and tree_of_typlist mode tyl =
  List.map (tree_of_typexp mode) tyl

and tree_of_typobject mode fi nm =
  begin match nm with
  | None ->
      let pr_fields fi =
        let (fields, rest) = flatten_fields fi in
        let present_fields =
          List.fold_right
            (fun (n, k, t) l ->
               match field_kind_repr k with
               | Fpublic -> (n, t) :: l
               | _ -> l)
            fields [] in
        let sorted_fields =
          List.sort
            (fun (n, _) (n', _) -> String.compare n n') present_fields in
        tree_of_typfields mode rest sorted_fields in
      let (fields, open_row) = pr_fields fi in
      Otyp_object {fields; open_row}
  | Some (p, _ty :: tyl) ->
      let args = tree_of_typlist mode tyl in
      let p' = best_type_path_simple p in
      Otyp_class (tree_of_best_type_path p p', args)
  | _ ->
      fatal_error "Printtyp.tree_of_typobject"
  end

and tree_of_typfields mode rest = function
  | [] ->
      let open_row =
        match get_desc rest with
        | Tvar _ | Tunivar _ | Tconstr _-> true
        | Tnil -> false
        | _ -> fatal_error "typfields (1)"
      in
      ([], open_row)
  | (s, t) :: l ->
      let field = (s, tree_of_typexp mode t) in
      let (fields, rest) = tree_of_typfields mode rest l in
      (field :: fields, rest)

let typexp mode ppf ty =
  !Oprint.out_type ppf (tree_of_typexp mode ty)

let prepared_type_expr ppf ty = typexp Type ppf ty
let prepared_type_scheme ppf ty = typexp Type_scheme ppf ty

let type_expr ppf ty =
  (* [type_expr] is used directly by error message printers,
     we mark eventual loops ourself to avoid any misuse and stack overflow *)
  prepare_for_printing [ty];
  prepared_type_expr ppf ty

(* "Half-prepared" type expression: [ty] should have had its names reserved, but
   should not have had its loops marked. *)
let type_expr_with_reserved_names ppf ty =
  reset_loop_marks ();
  mark_loops ty;
  prepared_type_expr ppf ty

let shared_type_scheme ppf ty =
  prepare_type ty;
  typexp Type_scheme ppf ty

let type_scheme ppf ty =
  prepare_for_printing [ty];
  prepared_type_scheme ppf ty

let type_path ppf p =
  let p = best_class_type_path_simple p in
  let t = tree_of_path (Some Type) p in
  !Oprint.out_ident ppf t

let tree_of_type_scheme ty =
  prepare_for_printing [ty];
  tree_of_typexp Type_scheme ty

(* Print one type declaration *)

let tree_of_constraints params =
  List.fold_right
    (fun ty list ->
       let ty' = unalias ty in
       if proxy ty != proxy ty' then
         let tr = tree_of_typexp Type_scheme ty in
         (tr, tree_of_typexp Type_scheme ty') :: list
       else list)
    params []

let filter_params tyl =
  let params =
    List.fold_left
      (fun tyl ty ->
        if List.exists (eq_type ty) tyl
        then newty2 ~level:generic_level (Ttuple [ty]) :: tyl
        else ty :: tyl)
      (* Two parameters might be identical due to a constraint but we need to
         print them differently in order to make the output syntactically valid.
         We use [Ttuple [ty]] because it is printed as [ty]. *)
      (* Replacing fold_left by fold_right does not work! *)
      [] tyl
  in List.rev params

let prepare_type_constructor_arguments = function
  | Cstr_tuple l -> List.iter prepare_type l
  | Cstr_record l -> List.iter (fun l -> prepare_type l.ld_type) l

let tree_of_label l =
  (Ident.name l.ld_id, l.ld_mutable = Mutable, tree_of_typexp Type l.ld_type)

let tree_of_constructor_arguments = function
  | Cstr_tuple l -> tree_of_typlist Type l
  | Cstr_record l -> [ Otyp_record (List.map tree_of_label l) ]

let tree_of_single_constructor cd =
  let name = Ident.name cd.cd_id in
  let ret = Option.map (tree_of_typexp Type) cd.cd_res in
  let args = tree_of_constructor_arguments cd.cd_args in
  {
      ocstr_name = name;
      ocstr_args = args;
      ocstr_return_type = ret;
  }

(* When printing GADT constructor, we need to forget the naming decision we took
  for the type parameters and constraints. Indeed, in
  {[
  type 'a t = X: 'a -> 'b t
   ]}
  It is fine to print both the type parameter ['a] and the existentially
  quantified ['a] in the definition of the constructor X as ['a]
 *)
let tree_of_constructor_in_decl cd =
  match cd.cd_res with
  | None -> tree_of_single_constructor cd
  | Some _ -> Names.with_local_names (fun () -> tree_of_single_constructor cd)

let prepare_decl id decl =
  let params = filter_params decl.type_params in
  begin match decl.type_manifest with
  | Some ty ->
      let vars = free_variables ty in
      List.iter
        (fun ty ->
          if get_desc ty = Tvar (Some "_") && List.exists (eq_type ty) vars
          then set_type_desc ty (Tvar None))
        params
  | None -> ()
  end;
  List.iter add_alias params;
  List.iter prepare_type params;
  List.iter (add_printed_alias ~non_gen:false) params;
  let ty_manifest =
    match decl.type_manifest with
    | None -> None
    | Some ty ->
        let ty =
          (* Special hack to hide variant name *)
          match get_desc ty with
            Tvariant row ->
              begin match row_name row with
                Some (Pident id', _) when Ident.same id id' ->
                  newgenty (Tvariant (set_row_name row None))
              | _ -> ty
              end
          | _ -> ty
        in
        prepare_type ty;
        Some ty
  in
  begin match decl.type_kind with
  | Type_abstract -> ()
  | Type_variant (cstrs, _rep) ->
      List.iter
        (fun c ->
           prepare_type_constructor_arguments c.cd_args;
           Option.iter prepare_type c.cd_res)
        cstrs
  | Type_record(l, _rep) ->
      List.iter (fun l -> prepare_type l.ld_type) l
  | Type_open -> ()
  end;
  ty_manifest, params

let tree_of_type_decl id decl =
  let ty_manifest, params = prepare_decl id decl in
  let type_param =
    function
    | Otyp_var (_, id) -> id
    | _ -> "?"
  in
  let type_defined decl =
    let abstr =
      match decl.type_kind with
        Type_abstract ->
          decl.type_manifest = None || decl.type_private = Private
      | Type_record _ ->
          decl.type_private = Private
      | Type_variant (tll, _rep) ->
          decl.type_private = Private ||
          List.exists (fun cd -> cd.cd_res <> None) tll
      | Type_open ->
          decl.type_manifest = None
    in
    let vari =
      List.map2
        (fun ty v ->
          let is_var = is_Tvar ty in
          if abstr || not is_var then
            let inj =
              decl.type_kind = Type_abstract && Variance.mem Inj v &&
              match decl.type_manifest with
              | None -> true
              | Some ty -> (* only abstract or private row types *)
                  decl.type_private = Private &&
                  Btype.is_constr_row ~allow_ident:true (Btype.row_of_type ty)
            and (co, cn) = Variance.get_upper v in
            (if not cn then Covariant else
             if not co then Contravariant else NoVariance),
            (if inj then Injective else NoInjectivity)
          else (NoVariance, NoInjectivity))
        decl.type_params decl.type_variance
    in
    (Ident.name id,
     List.map2 (fun ty cocn -> type_param (tree_of_typexp Type ty), cocn)
       params vari)
  in
  let tree_of_manifest ty1 =
    match ty_manifest with
    | None -> ty1
    | Some ty -> Otyp_manifest (tree_of_typexp Type ty, ty1)
  in
  let (name, args) = type_defined decl in
  let constraints = tree_of_constraints params in
  let ty, priv, unboxed =
    match decl.type_kind with
    | Type_abstract ->
        begin match ty_manifest with
        | None -> (Otyp_abstract, Public, false)
        | Some ty ->
            tree_of_typexp Type ty, decl.type_private, false
        end
    | Type_variant (cstrs, rep) ->
        tree_of_manifest
          (Otyp_sum (List.map tree_of_constructor_in_decl cstrs)),
        decl.type_private,
        (rep = Variant_unboxed)
    | Type_record(lbls, rep) ->
        tree_of_manifest (Otyp_record (List.map tree_of_label lbls)),
        decl.type_private,
        (match rep with Record_unboxed _ -> true | _ -> false)
    | Type_open ->
        tree_of_manifest Otyp_open,
        decl.type_private,
        false
  in
    { otype_name = name;
      otype_params = args;
      otype_type = ty;
      otype_private = priv;
      otype_immediate = Type_immediacy.of_attributes decl.type_attributes;
      otype_unboxed = unboxed;
      otype_cstrs = constraints }

let add_type_decl_to_preparation id decl =
   ignore @@ prepare_decl id decl

let tree_of_prepared_type_decl id decl =
  tree_of_type_decl id decl

let tree_of_type_decl id decl =
  reset_except_context();
  tree_of_type_decl id decl

let add_constructor_to_preparation c =
  prepare_type_constructor_arguments c.cd_args;
  Option.iter prepare_type c.cd_res

let prepared_constructor ppf c =
  !Oprint.out_constr ppf (tree_of_single_constructor c)

let constructor ppf c =
  reset_except_context ();
  add_constructor_to_preparation c;
  prepared_constructor ppf c

let label ppf l =
  reset_except_context ();
  prepare_type l.ld_type;
  !Oprint.out_label ppf (tree_of_label l)

let tree_of_type_declaration id decl rs =
  Osig_type (tree_of_type_decl id decl, tree_of_rec rs)

let tree_of_prepared_type_declaration id decl rs =
  Osig_type (tree_of_prepared_type_decl id decl, tree_of_rec rs)

let type_declaration id ppf decl =
  !Oprint.out_sig_item ppf (tree_of_type_declaration id decl Trec_first)

let add_type_declaration_to_preparation id decl =
  add_type_decl_to_preparation id decl

let prepared_type_declaration id ppf decl =
  !Oprint.out_sig_item ppf
    (tree_of_prepared_type_declaration id decl Trec_first)

let constructor_arguments ppf a =
  let tys = tree_of_constructor_arguments a in
  !Oprint.out_type ppf (Otyp_tuple tys)

(* Print an extension declaration *)

let extension_constructor_args_and_ret_type_subtree ext_args ext_ret_type =
  let ret = Option.map (tree_of_typexp Type) ext_ret_type in
  let args = tree_of_constructor_arguments ext_args in
  (args, ret)

(* When printing extension constructor, it is important to ensure that
after printing the constructor, we are still in the scope of the constructor.
For GADT constructor, this can be done by printing the type parameters inside
their own isolated scope. This ensures that in
{[
   type 'b t += A: 'b -> 'b any t
]}
the type parameter `'b` is not bound when printing the type variable `'b` from
the constructor definition from the type parameter.

Contrarily, for non-gadt constructor, we must keep the same scope for
the type parameters and the constructor because a type constraint may
have changed the name of the type parameter:
{[
type -'a t = .. constraint <x:'a. 'a t -> 'a> = 'a
(* the universal 'a is here to steal the name 'a from the type parameter *)
type 'a t = X of 'a
]} *)

let add_extension_constructor_to_preparation ext =
  let ty_params = filter_params ext.ext_type_params in
  List.iter add_alias ty_params;
  List.iter prepare_type ty_params;
  prepare_type_constructor_arguments ext.ext_args;
  Option.iter prepare_type ext.ext_ret_type

let prepared_tree_of_extension_constructor
    id ext es
  =
  let type_path = best_type_path_simple ext.ext_type_path in
  let ty_name = Path.name type_path in
  let ty_params = filter_params ext.ext_type_params in
  let type_param =
    function
    | Otyp_var (_, id) -> id
    | _ -> "?"
  in
  let param_scope f =
    match ext.ext_ret_type with
    | None ->
        (* normal constructor: same scope for parameters and the constructor *)
        f ()
    | Some _ ->
        (* gadt constructor: isolated scope for the type parameters *)
        Names.with_local_names f
  in
  let ty_params =
    param_scope
      (fun () ->
         List.iter (add_printed_alias ~non_gen:false) ty_params;
         List.map (fun ty -> type_param (tree_of_typexp Type ty)) ty_params
      )
  in
  let name = Ident.name id in
  let args, ret =
    extension_constructor_args_and_ret_type_subtree
      ext.ext_args
      ext.ext_ret_type
  in
  let ext =
    { oext_name = name;
      oext_type_name = ty_name;
      oext_type_params = ty_params;
      oext_args = args;
      oext_ret_type = ret;
      oext_private = ext.ext_private }
  in
  let es =
    match es with
        Text_first -> Oext_first
      | Text_next -> Oext_next
      | Text_exception -> Oext_exception
  in
    Osig_typext (ext, es)

let tree_of_extension_constructor id ext es =
  reset_except_context ();
  add_extension_constructor_to_preparation ext;
  prepared_tree_of_extension_constructor id ext es

let extension_constructor id ppf ext =
  !Oprint.out_sig_item ppf (tree_of_extension_constructor id ext Text_first)

let prepared_extension_constructor id ppf ext =
  !Oprint.out_sig_item ppf
    (prepared_tree_of_extension_constructor id ext Text_first)

let extension_only_constructor id ppf ext =
  reset_except_context ();
  prepare_type_constructor_arguments ext.ext_args;
  Option.iter prepare_type ext.ext_ret_type;
  let name = Ident.name id in
  let args, ret =
    extension_constructor_args_and_ret_type_subtree
      ext.ext_args
      ext.ext_ret_type
  in
  Format.fprintf ppf "@[<hv>%a@]"
    !Oprint.out_constr {
      ocstr_name = name;
      ocstr_args = args;
      ocstr_return_type = ret;
    }

(* Print a value declaration *)

let tree_of_value_description id decl =
  (* Format.eprintf "@[%a@]@." raw_type_expr decl.val_type; *)
  let id = Ident.name id in
  let ty = tree_of_type_scheme decl.val_type in
  let vd =
    { oval_name = id;
      oval_type = ty;
      oval_prims = [];
      oval_attributes = [] }
  in
  let vd =
    match decl.val_kind with
    | Val_prim p -> Primitive.print p vd
    | _ -> vd
  in
  Osig_value vd

let value_description id ppf decl =
  !Oprint.out_sig_item ppf (tree_of_value_description id decl)

(* Print a class type *)

let method_type priv ty =
  match priv, get_desc ty with
  | Mpublic, Tpoly(ty, tyl) -> (ty, tyl)
  | _ , _ -> (ty, [])

let prepare_method _lab (priv, _virt, ty) =
  let ty, _ = method_type priv ty in
  prepare_type ty

let tree_of_method mode (lab, priv, virt, ty) =
  let (ty, tyl) = method_type priv ty in
  let tty = tree_of_typexp mode ty in
  Names.remove_names (List.map Transient_expr.repr tyl);
  let priv = priv <> Mpublic in
  let virt = virt = Virtual in
  Ocsg_method (lab, priv, virt, tty)

let rec prepare_class_type params = function
  | Cty_constr (_p, tyl, cty) ->
      let row = Btype.self_type_row cty in
      if List.memq (proxy row) !visited_objects
      || not (List.for_all is_Tvar params)
      || List.exists (deep_occur row) tyl
      then prepare_class_type params cty
      else List.iter prepare_type tyl
  | Cty_signature sign ->
      (* Self may have a name *)
      let px = proxy sign.csig_self_row in
      if List.memq px !visited_objects then add_alias_proxy px
      else visited_objects := px :: !visited_objects;
      Vars.iter (fun _ (_, _, ty) -> prepare_type ty) sign.csig_vars;
      Meths.iter prepare_method sign.csig_meths
  | Cty_arrow (_, ty, cty) ->
      prepare_type ty;
      prepare_class_type params cty

let rec tree_of_class_type mode params =
  function
  | Cty_constr (p, tyl, cty) ->
    let row = Btype.self_type_row cty in
      if List.memq (proxy row) !visited_objects
      || not (List.for_all is_Tvar params)
      then
        tree_of_class_type mode params cty
      else begin
        let nso, p = best_class_type_path p in
        let tyl = apply_subst_opt nso tyl in
        let namespace = Namespace.best_class_namespace p in
        Octy_constr (tree_of_path namespace p, tree_of_typlist Type_scheme tyl)
      end
  | Cty_signature sign ->
      let px = proxy sign.csig_self_row in
      let self_ty =
        if is_aliased_proxy px then
          Some
            (Otyp_var (false, Names.name_of_type Names.new_name px))
        else None
      in
      let csil = [] in
      let csil =
        List.fold_left
          (fun csil (ty1, ty2) -> Ocsg_constraint (ty1, ty2) :: csil)
          csil (tree_of_constraints params)
      in
      let all_vars =
        Vars.fold (fun l (m, v, t) all -> (l, m, v, t) :: all) sign.csig_vars []
      in
      (* Consequence of PR#3607: order of Map.fold has changed! *)
      let all_vars = List.rev all_vars in
      let csil =
        List.fold_left
          (fun csil (l, m, v, t) ->
            Ocsg_value (l, m = Mutable, v = Virtual, tree_of_typexp mode t)
            :: csil)
          csil all_vars
      in
      let all_meths =
        Meths.fold
          (fun l (p, v, t) all -> (l, p, v, t) :: all)
          sign.csig_meths []
      in
      let all_meths = List.rev all_meths in
      let csil =
        List.fold_left
          (fun csil meth -> tree_of_method mode meth :: csil)
          csil all_meths
      in
      Octy_signature (self_ty, List.rev csil)
  | Cty_arrow (l, ty, cty) ->
      let lab =
        if !print_labels || is_optional l then string_of_label l else ""
      in
      let tr =
       if is_optional l then
         match get_desc ty with
         | Tconstr(path, [ty], _) when Path.same path Predef.path_option ->
             tree_of_typexp mode ty
         | _ -> Otyp_stuff "<hidden>"
       else tree_of_typexp mode ty in
      Octy_arrow (lab, tr, tree_of_class_type mode params cty)

let class_type ppf cty =
  reset ();
  prepare_class_type [] cty;
  !Oprint.out_class_type ppf (tree_of_class_type Type [] cty)

let tree_of_class_param param variance =
  (match tree_of_typexp Type_scheme param with
    Otyp_var (_, s) -> s
  | _ -> "?"),
  if is_Tvar param then Asttypes.(NoVariance, NoInjectivity)
  else variance

let class_variance =
  let open Variance in let open Asttypes in
  List.map (fun v ->
    (if not (mem May_pos v) then Contravariant else
     if not (mem May_neg v) then Covariant else NoVariance),
    NoInjectivity)

let tree_of_class_declaration id cl rs =
  let params = filter_params cl.cty_params in

  reset_except_context ();
  List.iter add_alias params;
  prepare_class_type params cl.cty_type;
  let px = proxy (Btype.self_type_row cl.cty_type) in
  List.iter prepare_type params;

  List.iter (add_printed_alias ~non_gen:false) params;
  if is_aliased_proxy px then add_printed_alias_proxy ~non_gen:false px;

  let vir_flag = cl.cty_new = None in
  Osig_class
    (vir_flag, Ident.name id,
     List.map2 tree_of_class_param params (class_variance cl.cty_variance),
     tree_of_class_type Type_scheme params cl.cty_type,
     tree_of_rec rs)

let class_declaration id ppf cl =
  !Oprint.out_sig_item ppf (tree_of_class_declaration id cl Trec_first)

let tree_of_cltype_declaration id cl rs =
  let params = cl.clty_params in

  reset_except_context ();
  List.iter add_alias params;
  prepare_class_type params cl.clty_type;
  let px = proxy (Btype.self_type_row cl.clty_type) in
  List.iter prepare_type params;

  List.iter (add_printed_alias ~non_gen:false) params;
  if is_aliased_proxy px then (add_printed_alias_proxy ~non_gen:false) px;

  let sign = Btype.signature_of_class_type cl.clty_type in
  let has_virtual_vars =
    Vars.fold (fun _ (_,vr,_) b -> vr = Virtual || b)
      sign.csig_vars false
  in
  let has_virtual_meths =
    Meths.fold (fun _ (_,vr,_) b -> vr = Virtual || b)
      sign.csig_meths false
  in
  Osig_class_type
    (has_virtual_vars || has_virtual_meths, Ident.name id,
     List.map2 tree_of_class_param params (class_variance cl.clty_variance),
     tree_of_class_type Type_scheme params cl.clty_type,
     tree_of_rec rs)

let cltype_declaration id ppf cl =
  !Oprint.out_sig_item ppf (tree_of_cltype_declaration id cl Trec_first)

(* Print a module type *)

let wrap_env fenv ftree arg =
  let env = !printing_env in
  let env' = Env.update_short_paths (fenv env) in
  set_printing_env env';
  let tree = ftree arg in
  set_printing_env env;
  tree

let dummy =
  {
    type_params = [];
    type_arity = 0;
    type_kind = Type_abstract;
    type_private = Public;
    type_manifest = None;
    type_variance = [];
    type_separability = [];
    type_is_newtype = false;
    type_expansion_scope = Btype.lowest_level;
    type_loc = Location.none;
    type_attributes = [];
    type_immediate = Unknown;
    type_unboxed_default = false;
    type_uid = Uid.internal_not_actually_unique;
  }

(** we hide items being defined from short-path to avoid shortening
    [type t = Path.To.t] into [type t = t].
*)

let ident_sigitem = function
  | Types.Sig_type(ident,_,_,_) ->  {hide=true;ident}
  | Types.Sig_class(ident,_,_,_)
  | Types.Sig_class_type (ident,_,_,_)
  | Types.Sig_module(ident,_, _,_,_)
  | Types.Sig_value (ident,_,_)
  | Types.Sig_modtype (ident,_,_)
  | Types.Sig_typext (ident,_,_,_)   ->  {hide=false; ident }

let hide ids env =
  let hide_id id env =
    (* Global idents cannot be renamed *)
    if id.hide && not (Ident.global id.ident) then
      Env.add_type ~check:false (Ident.rename_no_exn id.ident) dummy env
    else env
  in
  List.fold_right hide_id ids env

let with_hidden_items ids f =
  let with_hidden_in_printing_env ids f =
    wrap_env (hide ids) (Naming_context.with_hidden ids) f
  in
  if not !Clflags.real_paths then
    with_hidden_in_printing_env ids f
  else
    Naming_context.with_hidden ids f

let add_sigitem env x =
  Env.add_signature (Signature_group.flatten x) env

let rec tree_of_modtype ?(ellipsis=false) = function
  | Mty_ident p ->
      let p = best_module_type_path p in
      Omty_ident (tree_of_path (Some Module_type) p)
  | Mty_signature sg ->
      Omty_signature (if ellipsis then [Osig_ellipsis]
                      else tree_of_signature sg)
  | Mty_functor(param, ty_res) ->
      let param, env =
        tree_of_functor_parameter param
      in
      let res = wrap_env env (tree_of_modtype ~ellipsis) ty_res in
      Omty_functor (param, res)
  | Mty_alias p ->
      let p = best_module_path p in
      Omty_alias (tree_of_path (Some Module) p)
  | Mty_for_hole -> Omty_hole

and tree_of_functor_parameter = function
  | Unit ->
      None, fun k -> k
  | Named (param, ty_arg) ->
      let name, env =
        match param with
        | None -> None, fun env -> env
        | Some id ->
            Some (Ident.name id),
            Env.add_module ~arg:true id Mp_present ty_arg
      in
      Some (name, tree_of_modtype ~ellipsis:false ty_arg), env

and tree_of_signature sg =
  wrap_env (fun env -> env)(fun sg ->
      let tree_groups = tree_of_signature_rec !printing_env sg in
      List.concat_map (fun (_env,l) -> List.map snd l) tree_groups
    ) sg

and tree_of_signature_rec env' sg =
  let structured = List.of_seq (Signature_group.seq sg) in
  let collect_trees_of_rec_group group =
    let env = !printing_env in
    let env', group_trees =
       trees_of_recursive_sigitem_group env group
    in
    set_printing_env env';
    (env, group_trees) in
  set_printing_env env';
  List.map collect_trees_of_rec_group structured

and trees_of_recursive_sigitem_group env
    (syntactic_group: Signature_group.rec_group) =
  let display (x:Signature_group.sig_item) = x.src, tree_of_sigitem x.src in
  let env = Env.add_signature syntactic_group.pre_ghosts env in
  match syntactic_group.group with
  | Not_rec x -> add_sigitem env x, [display x]
  | Rec_group items ->
      let ids = List.map (fun x -> ident_sigitem x.Signature_group.src) items in
      List.fold_left add_sigitem env items,
      with_hidden_items ids (fun () -> List.map display items)

and tree_of_sigitem = function
  | Sig_value(id, decl, _) ->
      tree_of_value_description id decl
  | Sig_type(id, decl, rs, _) ->
      tree_of_type_declaration id decl rs
  | Sig_typext(id, ext, es, _) ->
      tree_of_extension_constructor id ext es
  | Sig_module(id, _, md, rs, _) ->
      let ellipsis =
        List.exists (function
          | Parsetree.{attr_name = {txt="..."}; attr_payload = PStr []} -> true
          | _ -> false)
          md.md_attributes in
      tree_of_module id md.md_type rs ~ellipsis
  | Sig_modtype(id, decl, _) ->
      tree_of_modtype_declaration id decl
  | Sig_class(id, decl, rs, _) ->
      tree_of_class_declaration id decl rs
  | Sig_class_type(id, decl, rs, _) ->
      tree_of_cltype_declaration id decl rs

and tree_of_modtype_declaration id decl =
  let mty =
    match decl.mtd_type with
    | None -> Omty_abstract
    | Some mty -> tree_of_modtype mty
  in
  Osig_modtype (Ident.name id, mty)

and tree_of_module id ?ellipsis mty rs =
  Osig_module (Ident.name id, tree_of_modtype ?ellipsis mty, tree_of_rec rs)

let rec functor_parameters ~sep custom_printer = function
  | [] -> ignore
  | [id,param] ->
      Format.dprintf "%t%t"
        (custom_printer param)
        (functor_param ~sep ~custom_printer id [])
  | (id,param) :: q ->
      Format.dprintf "%t%a%t"
        (custom_printer param)
        sep ()
        (functor_param ~sep ~custom_printer id q)
and functor_param ~sep ~custom_printer id q =
  match id with
  | None -> functor_parameters ~sep custom_printer q
  | Some id ->
      Naming_context.with_arg id
        (fun () -> functor_parameters ~sep custom_printer q)



let modtype ppf mty = !Oprint.out_module_type ppf (tree_of_modtype mty)
let modtype_declaration id ppf decl =
  !Oprint.out_sig_item ppf (tree_of_modtype_declaration id decl)

(* For the toplevel: merge with tree_of_signature? *)

let print_items showval env x =
  Names.refresh_weak();
  Conflicts.reset ();
  let extend_val env (sigitem,outcome) = outcome, showval env sigitem in
  let post_process (env,l) = List.map (extend_val env) l in
  List.concat_map post_process @@ tree_of_signature_rec env x

(* Print a signature body (used by -i when compiling a .ml) *)

let print_signature ppf tree =
  fprintf ppf "@[<v>%a@]" !Oprint.out_signature tree

let signature ppf sg =
  fprintf ppf "%a" print_signature (tree_of_signature sg)

(* Print a signature body (used by -i when compiling a .ml) *)
let printed_signature sourcefile ppf sg =
  (* we are tracking any collision event for warning 63 *)
  Conflicts.reset ();
  let t = tree_of_signature sg in
  if Warnings.(is_active @@ Erroneous_printed_signature "")
  && Conflicts.exists ()
  then begin
    let conflicts = Format.asprintf "%t" Conflicts.print_explanations in
    Location.prerr_warning (Location.in_file sourcefile)
      (Warnings.Erroneous_printed_signature conflicts);
    Warnings.check_fatal ()
  end;
  fprintf ppf "%a" print_signature t

(* Trace-specific printing *)

(* A configuration type that controls which trace we print.  This could be
   exposed, but we instead expose three separate
   [report_{unification,equality,moregen}_error] functions.  This also lets us
   give the unification case an extra optional argument without adding it to the
   equality and moregen cases. *)
type 'variety trace_format =
  | Unification : Errortrace.unification trace_format
  | Equality    : Errortrace.comparison  trace_format
  | Moregen     : Errortrace.comparison  trace_format

let incompatibility_phrase (type variety) : variety trace_format -> string =
  function
  | Unification -> "is not compatible with type"
  | Equality    -> "is not equal to type"
  | Moregen     -> "is not compatible with type"

(* Print a unification error *)

let same_path t t' =
  eq_type t t' ||
  match get_desc t, get_desc t' with
  | Tconstr(p,tl,_), Tconstr(p',tl',_) -> begin
      match best_type_path p, best_type_path p' with
      | Nth n, Nth n' when n = n' -> true
      | Path(nso, p), Path(nso', p') when Path.same p p' ->
          let tl = apply_subst_opt nso tl in
          let tl' = apply_subst_opt nso' tl' in
          List.length tl = List.length tl' &&
          List.for_all2 eq_type tl tl'
      | _ -> false
      end
  | _ ->
      false

type 'a diff = Same of 'a | Diff of 'a * 'a

let trees_of_type_expansion mode Errortrace.{ty = t; expanded = t'} =
  reset_loop_marks ();
  mark_loops t;
  if same_path t t'
  then begin add_delayed (proxy t); Same (tree_of_typexp mode t) end
  else begin
    mark_loops t';
    let t' = if proxy t == proxy t' then unalias t' else t' in
    (* beware order matter due to side effect,
       e.g. when printing object types *)
    let first = tree_of_typexp mode t in
    let second = tree_of_typexp mode t' in
    if first = second then Same first
    else Diff(first,second)
  end

let type_expansion ppf = function
  | Same t -> !Oprint.out_type ppf t
  | Diff(t,t') ->
      fprintf ppf "@[<2>%a@ =@ %a@]"  !Oprint.out_type t  !Oprint.out_type t'

let trees_of_trace mode =
  List.map (Errortrace.map_diff (trees_of_type_expansion mode))

let trees_of_type_path_expansion (tp,tp') =
  if Path.same tp tp' then Same(tree_of_path (Some Type) tp) else
    Diff(tree_of_path (Some Type) tp, tree_of_path (Some Type) tp')

let type_path_expansion ppf = function
  | Same p -> !Oprint.out_ident ppf p
  | Diff(p,p') ->
      fprintf ppf "@[<2>%a@ =@ %a@]"
        !Oprint.out_ident p
        !Oprint.out_ident p'

let rec trace fst txt ppf = function
  | {Errortrace.got; expected} :: rem ->
      if not fst then fprintf ppf "@,";
      fprintf ppf "@[Type@;<1 2>%a@ %s@;<1 2>%a@]%a"
       type_expansion got txt type_expansion expected
       (trace false txt) rem
  | _ -> ()

type printing_status =
  | Discard
  | Keep
  | Optional_refinement
  (** An [Optional_refinement] printing status is attributed to trace
      elements that are focusing on a new subpart of a structural type.
      Since the whole type should have been printed earlier in the trace,
      we only print those elements if they are the last printed element
      of a trace, and there is no explicit explanation for the
      type error.
  *)

let diff_printing_status Errortrace.{ got      = {ty = t1; expanded = t1'};
                                      expected = {ty = t2; expanded = t2'} } =
  if  is_constr_row ~allow_ident:true t1'
   || is_constr_row ~allow_ident:true t2'
  then Discard
  else if same_path t1 t1' && same_path t2 t2' then Optional_refinement
  else Keep

let printing_status = function
  | Errortrace.Diff d -> diff_printing_status d
  | Errortrace.Escape {kind = Constraint} -> Keep
  | _ -> Keep

(** Flatten the trace and remove elements that are always discarded
    during printing *)

(* Takes [printing_status] to change behavior for [Subtype] *)
let prepare_any_trace printing_status tr =
  let clean_trace x l = match printing_status x with
    | Keep -> x :: l
    | Optional_refinement when l = [] -> [x]
    | Optional_refinement | Discard -> l
  in
  match tr with
  | [] -> []
  | elt :: rem -> elt :: List.fold_right clean_trace rem []

let prepare_trace f tr =
  prepare_any_trace printing_status (Errortrace.map f tr)

(** Keep elements that are [Diff _ ] and take the decision
    for the last element, require a prepared trace *)
let rec filter_trace keep_last = function
  | [] -> []
  | [Errortrace.Diff d as elt]
    when printing_status elt = Optional_refinement ->
    if keep_last then [d] else []
  | Errortrace.Diff d :: rem -> d :: filter_trace keep_last rem
  | _ :: rem -> filter_trace keep_last rem

let type_path_list =
  Format.pp_print_list ~pp_sep:(fun ppf () -> Format.pp_print_break ppf 2 0)
    type_path_expansion

(* Hide variant name and var, to force printing the expanded type *)
let hide_variant_name t =
  match get_desc t with
  | Tvariant row ->
      let Row {fields; more; name; fixed; closed} = row_repr row in
      if name = None then t else
      newty2 ~level:(get_level t)
        (Tvariant
           (create_row ~fields ~fixed ~closed ~name:None
              ~more:(newvar2 (get_level more))))
  | _ -> t

let prepare_expansion Errortrace.{ty; expanded} =
  let expanded = hide_variant_name expanded in
  reserve_names ty;
  if not (same_path ty expanded) then reserve_names expanded;
  Errortrace.{ty; expanded}

let may_prepare_expansion compact (Errortrace.{ty; expanded} as ty_exp) =
  match get_desc expanded with
    Tvariant _ | Tobject _ when compact ->
      reserve_names ty; Errortrace.{ty; expanded = ty}
  | _ -> prepare_expansion ty_exp

let print_path p =
  Format.dprintf "%a" !Oprint.out_ident (tree_of_path (Some Type) p)

let print_tag ppf = fprintf ppf "`%s"

let print_tags =
  let comma ppf () = Format.fprintf ppf ",@ " in
  Format.pp_print_list ~pp_sep:comma print_tag

let is_unit env ty =
  match get_desc (Ctype.expand_head env ty) with
  | Tconstr (p, _, _) -> Path.same p Predef.path_unit
  | _ -> false

let unifiable env ty1 ty2 =
  let snap = Btype.snapshot () in
  let res =
    try Ctype.unify env ty1 ty2; true
    with Unify _ -> false
  in
  Btype.backtrack snap;
  res

let explanation_diff env t3 t4 : (Format.formatter -> unit) option =
  match get_desc t3, get_desc t4 with
  | Tarrow (_, ty1, ty2, _), _
    when is_unit env ty1 && unifiable env ty2 t4 ->
      Some (fun ppf ->
        fprintf ppf
          "@,@[@{<hint>Hint@}: Did you forget to provide `()' as argument?@]")
  | _, Tarrow (_, ty1, ty2, _)
    when is_unit env ty1 && unifiable env t3 ty2 ->
      Some (fun ppf ->
        fprintf ppf
          "@,@[@{<hint>Hint@}: Did you forget to wrap the expression using \
           `fun () ->'?@]")
  | _ ->
      None

let explain_fixed_row_case ppf = function
  | Errortrace.Cannot_be_closed ->
      fprintf ppf "it cannot be closed"
  | Errortrace.Cannot_add_tags tags ->
      fprintf ppf "it may not allow the tag(s) %a" print_tags tags

let explain_fixed_row pos expl = match expl with
  | Fixed_private ->
    dprintf "The %a variant type is private" Errortrace.print_pos pos
  | Univar x ->
    reserve_names x;
    dprintf "The %a variant type is bound to the universal type variable %a"
      Errortrace.print_pos pos type_expr_with_reserved_names x
  | Reified p ->
    dprintf "The %a variant type is bound to %t"
      Errortrace.print_pos pos (print_path p)
  | Rigid -> ignore

let explain_variant (type variety) : variety Errortrace.variant -> _ = function
  (* Common *)
  | Errortrace.Incompatible_types_for s ->
      Some(dprintf "@,Types for tag `%s are incompatible" s)
  (* Unification *)
  | Errortrace.No_intersection ->
      Some(dprintf "@,These two variant types have no intersection")
  | Errortrace.No_tags(pos,fields) -> Some(
      dprintf
        "@,@[The %a variant type does not allow tag(s)@ @[<hov>%a@]@]"
        Errortrace.print_pos pos
        print_tags (List.map fst fields)
    )
  | Errortrace.Fixed_row (pos,
                          k,
                          (Univar _ | Reified _ | Fixed_private as e)) ->
      Some (
        dprintf "@,@[%t,@ %a@]" (explain_fixed_row pos e)
          explain_fixed_row_case k
      )
  | Errortrace.Fixed_row (_,_, Rigid) ->
      (* this case never happens *)
      None
  (* Equality & Moregen *)
  | Errortrace.Presence_not_guaranteed_for (pos, s) -> Some(
      dprintf
        "@,@[The tag `%s is guaranteed to be present in the %a variant type,\
         @ but not in the %a@]"
        s
        Errortrace.print_pos (Errortrace.swap_position pos)
        Errortrace.print_pos pos
    )
  | Errortrace.Openness pos ->
      Some(dprintf "@,The %a variant type is open and the %a is not"
             Errortrace.print_pos pos
             Errortrace.print_pos (Errortrace.swap_position pos))

let explain_escape pre = function
  | Errortrace.Univ u ->
      reserve_names u;
      Some(
        dprintf "%t@,The universal variable %a would escape its scope"
          pre type_expr_with_reserved_names u)
  | Errortrace.Constructor p -> Some(
      dprintf
        "%t@,@[The type constructor@;<1 2>%a@ would escape its scope@]"
        pre path p
    )
  | Errortrace.Module_type p -> Some(
      dprintf
        "%t@,@[The module type@;<1 2>%a@ would escape its scope@]"
        pre path p
    )
  | Errortrace.Equation Errortrace.{ty = _; expanded = t} ->
      reserve_names t;
      Some(
        dprintf "%t @,@[<hov>This instance of %a is ambiguous:@ %s@]"
          pre type_expr_with_reserved_names t
          "it would escape the scope of its equation"
      )
  | Errortrace.Self ->
      Some (dprintf "%t@,Self type cannot escape its class" pre)
  | Errortrace.Constraint ->
      None

let explain_object (type variety) : variety Errortrace.obj -> _ = function
  | Errortrace.Missing_field (pos,f) -> Some(
      dprintf "@,@[The %a object type has no method %s@]"
        Errortrace.print_pos pos f
    )
  | Errortrace.Abstract_row pos -> Some(
      dprintf
        "@,@[The %a object type has an abstract row, it cannot be closed@]"
        Errortrace.print_pos pos
    )
  | Errortrace.Self_cannot_be_closed ->
      Some (dprintf "@,Self type cannot be unified with a closed object type")

let explanation (type variety) intro prev env
  : (Errortrace.expanded_type, variety) Errortrace.elt -> _ = function
  | Errortrace.Diff {got; expected} ->
    explanation_diff env got.expanded expected.expanded
  | Errortrace.Escape {kind; context} ->
    let pre =
      match context, kind, prev with
      | Some ctx, _, _ ->
        reserve_names ctx;
        dprintf "@[%t@;<1 2>%a@]" intro type_expr_with_reserved_names ctx
      | None, Univ _, Some(Errortrace.Incompatible_fields {name; diff}) ->
        reserve_names diff.got;
        reserve_names diff.expected;
        dprintf "@,@[The method %s has type@ %a,@ \
                 but the expected method type was@ %a@]"
          name
          type_expr_with_reserved_names diff.got
          type_expr_with_reserved_names diff.expected
      | _ -> ignore
    in
    explain_escape pre kind
  | Errortrace.Incompatible_fields { name; _ } ->
    Some(dprintf "@,Types for method %s are incompatible" name)
  | Errortrace.Variant v ->
    explain_variant v
  | Errortrace.Obj o ->
    explain_object o
  | Errortrace.Rec_occur(x,y) ->
    reserve_names x;
    reserve_names y;
    begin match get_desc x with
    | Tvar _ | Tunivar _  ->
        Some(fun ppf ->
          reset_loop_marks ();
          mark_loops x;
          mark_loops y;
          dprintf "@,@[<hov>The type variable %a occurs inside@ %a@]"
            prepared_type_expr x prepared_type_expr y
            ppf)
    | _ ->
        (* We had a delayed unification of the type variable with
           a non-variable after the occur check. *)
        Some ignore
        (* There is no need to search further for an explanation, but
           we don't want to print a message of the form:
             {[ The type int occurs inside int list -> 'a |}
        *)
    end

let mismatch intro env trace =
  Errortrace.explain trace (fun ~prev h -> explanation intro prev env h)

let explain mis ppf =
  match mis with
  | None -> ()
  | Some explain -> explain ppf

let warn_on_missing_def env ppf t =
  match get_desc t with
  | Tconstr (p,_,_) ->
    begin
      try
        ignore(Env.find_type p env : Types.type_declaration)
      with Not_found ->
        fprintf ppf
          "@,@[%a is abstract because no corresponding cmi file was found \
           in path.@]" path p
    end
  | _ -> ()

let prepare_expansion_head empty_tr = function
  | Errortrace.Diff d ->
      Some (Errortrace.map_diff (may_prepare_expansion empty_tr) d)
  | _ -> None

let head_error_printer mode txt_got txt_but = function
  | None -> ignore
  | Some d ->
      let d = Errortrace.map_diff (trees_of_type_expansion mode) d in
      dprintf "%t@;<1 2>%a@ %t@;<1 2>%a"
        txt_got type_expansion d.Errortrace.got
        txt_but type_expansion d.Errortrace.expected

let warn_on_missing_defs env ppf = function
  | None -> ()
  | Some Errortrace.{got      = {ty=te1; expanded=_};
                     expected = {ty=te2; expanded=_} } ->
      warn_on_missing_def env ppf te1;
      warn_on_missing_def env ppf te2

(* [subst] comes out of equality, and is [[]] otherwise *)
let error trace_format mode subst env tr txt1 ppf txt2 ty_expect_explanation =
  reset ();
  (* We want to substitute in the opposite order from [Eqtype] *)
  Names.add_subst (List.map (fun (ty1,ty2) -> ty2,ty1) subst);
  let tr =
    prepare_trace
      (fun ty_exp ->
         Errortrace.{ty_exp with expanded = hide_variant_name ty_exp.expanded})
      tr
  in
  let mis = mismatch txt1 env tr in
  match tr with
  | [] -> assert false
  | elt :: tr ->
    try
      print_labels := not !Clflags.classic;
      let tr = filter_trace (mis = None) tr in
      let head = prepare_expansion_head (tr=[]) elt in
      let tr = List.map (Errortrace.map_diff prepare_expansion) tr in
      let head_error = head_error_printer mode txt1 txt2 head in
      let tr = trees_of_trace mode tr in
      fprintf ppf
        "@[<v>\
          @[%t%t@]%a%t\
         @]"
        head_error
        ty_expect_explanation
        (trace false (incompatibility_phrase trace_format)) tr
        (explain mis);
      if env <> Env.empty
      then warn_on_missing_defs env ppf head;
      Conflicts.print_explanations ppf;
      print_labels := true
    with exn ->
      print_labels := true;
      raise exn

let report_error trace_format ppf mode env tr
      ?(subst = [])
      ?(type_expected_explanation = fun _ -> ())
      txt1 txt2 =
  wrap_printing_env ~error:true env (fun () ->
    error trace_format mode subst env tr txt1 ppf txt2
      type_expected_explanation)

let report_unification_error
      ppf env ({trace} : Errortrace.unification_error) =
  report_error Unification ppf Type env
    ?subst:None trace

let report_equality_error
      ppf mode env ({subst; trace} : Errortrace.equality_error) =
  report_error Equality ppf mode env
    ~subst ?type_expected_explanation:None trace

let report_moregen_error
      ppf mode env ({trace} : Errortrace.moregen_error) =
  report_error Moregen ppf mode env
    ?subst:None ?type_expected_explanation:None trace

let report_comparison_error ppf mode env = function
  | Errortrace.Equality_error error -> report_equality_error ppf mode env error
  | Errortrace.Moregen_error  error -> report_moregen_error  ppf mode env error

module Subtype = struct
  (* There's a frustrating amount of code duplication between this module and
     the outside code, particularly in [prepare_trace] and [filter_trace].
     Unfortunately, [Subtype] is *just* similar enough to have code duplication,
     while being *just* different enough (it's only [Diff]) for the abstraction
     to be nonobvious.  Someday, perhaps... *)

  let printing_status = function
    | Errortrace.Subtype.Diff d -> diff_printing_status d

  let prepare_unification_trace = prepare_trace

  let prepare_trace f tr =
    prepare_any_trace printing_status (Errortrace.Subtype.map f tr)

  let trace filter_trace get_diff fst keep_last txt ppf tr =
    print_labels := not !Clflags.classic;
    try match tr with
      | elt :: tr' ->
        let diffed_elt = get_diff elt in
        let tr =
          trees_of_trace Type
          @@ List.map (Errortrace.map_diff prepare_expansion)
          @@ filter_trace keep_last tr' in
        let tr =
          match fst, diffed_elt with
          | true, Some elt -> elt :: tr
          | _, _ -> tr
        in
        trace fst txt ppf tr;
        print_labels := true
      | _ -> ()
    with exn ->
      print_labels := true;
      raise exn

  let rec filter_subtype_trace keep_last = function
    | [] -> []
    | [Errortrace.Subtype.Diff d as elt]
      when printing_status elt = Optional_refinement ->
        if keep_last then [d] else []
    | Errortrace.Subtype.Diff d :: rem ->
        d :: filter_subtype_trace keep_last rem

  let unification_get_diff = function
    | Errortrace.Diff diff ->
        Some (Errortrace.map_diff (trees_of_type_expansion Type) diff)
    | _ -> None

  let subtype_get_diff = function
    | Errortrace.Subtype.Diff diff ->
        Some (Errortrace.map_diff (trees_of_type_expansion Type) diff)

  let report_error
        ppf
        env
        (Errortrace.Subtype.{trace = tr_sub; unification_trace = tr_unif})
        txt1 =
    wrap_printing_env ~error:true env (fun () ->
      reset ();
      let tr_sub = prepare_trace prepare_expansion tr_sub in
      let tr_unif = prepare_unification_trace prepare_expansion tr_unif in
      let keep_first = match tr_unif with
        | [Obj _ | Variant _ | Escape _ ] | [] -> true
        | _ -> false in
      fprintf ppf "@[<v>%a"
        (trace filter_subtype_trace subtype_get_diff true keep_first txt1)
        tr_sub;
      if tr_unif = [] then fprintf ppf "@]" else
        let mis = mismatch (dprintf "Within this type") env tr_unif in
        fprintf ppf "%a%t%t@]"
          (trace filter_trace unification_get_diff false
             (mis = None) "is not compatible with type") tr_unif
          (explain mis)
          Conflicts.print_explanations
    )
end

let report_ambiguous_type_error ppf env tp0 tpl txt1 txt2 txt3 =
  wrap_printing_env ~error:true env (fun () ->
    reset ();
    let tp0 = trees_of_type_path_expansion tp0 in
      match tpl with
      [] -> assert false
    | [tp] ->
        fprintf ppf
          "@[%t@;<1 2>%a@ \
             %t@;<1 2>%a\
           @]"
          txt1 type_path_expansion (trees_of_type_path_expansion tp)
          txt3 type_path_expansion tp0
    | _ ->
        fprintf ppf
          "@[%t@;<1 2>@[<hv>%a@]\
             @ %t@;<1 2>%a\
           @]"
          txt2 type_path_list (List.map trees_of_type_path_expansion tpl)
          txt3 type_path_expansion tp0)

(* Adapt functions to exposed interface *)
let tree_of_path = tree_of_path None
let tree_of_modtype = tree_of_modtype ~ellipsis:false
let type_expansion mode ppf ty_exp =
  type_expansion ppf (trees_of_type_expansion mode ty_exp)
let tree_of_type_declaration ident td rs =
  with_hidden_items [{hide=true; ident}]
    (fun () -> tree_of_type_declaration ident td rs)

let shorten_type_path env p =
  wrap_printing_env env
    (fun () -> best_type_path_simple p)

let shorten_module_type_path env p =
  wrap_printing_env env
    (fun () -> best_module_type_path p)

let shorten_module_path env p =
  wrap_printing_env env
    (fun () -> best_module_path p)

let shorten_class_type_path env p =
  wrap_printing_env env
    (fun () -> best_class_type_path_simple p)

let () =
  Env.shorten_module_path := shorten_module_path