Error when printing types with -rectypes

[samsa1]

I wrote a small test that fails due to a type error, however the type printing fails to an assertion failure.

(* TEST
  flags = " -rectypes ";
*)

let f (x : ((int -> 'a) as 'a)) = x

let _ = (f = 0)

Output :

File "t.ml", line 7, characters 13-14:
7 | let _ = (f = 0)
                 ^
Error: This expression has type "int" but an expression was expected of type
         "(int -> Fatal error: exception File "ocaml/typing/oprint.ml", line 531, characters 11-17: Assertion failed

[samsa1]

The problem comes from :

flambda-backend/ocaml/typing/oprint.ml

Lines 513 to 531 in 95a2dee

	and print_out_ret rm ppf =
	function
	| Otyp_arrow _ as ty ->
	begin match rm with
	| Orm_not_arrow _ -> assert false
	| Orm_no_parens ->
	print_out_type_1 ppf ty
	| Orm_parens rm ->
	let m_legacy, m_new = partition_modes rm in
	print_out_modes_legacy ppf m_legacy;
	pp_print_char ppf '(';
	print_out_type_1 ppf ty;
	pp_print_char ppf ')';
	print_out_modes_new ppf m_new
	end
	| ty ->
	match rm with
	| Orm_not_arrow rm -> print_out_type_mode ~arg:false rm ppf ty
	| _ -> assert false

that does not handle correctly the case of Otyp_alias with recursive types.
This should maybe be corrected when computing if the next component is an arrow or not at

flambda-backend/ocaml/typing/printtyp.ml

Lines 1587 to 1606 in 95a2dee

	and tree_of_ret_typ_mutating mode acc_mode (m, ty) =
	match get_desc ty with
	| Tarrow _ -> begin
	(* We first try to equate [m] with the [acc_mode]; if that succeeds, we
	can omit parens and modes. *)
	match Alloc.equate (Alloc.of_const acc_mode) m with
	| Ok () ->
	let ty = tree_of_typexp mode acc_mode ty in
	(Orm_no_parens, ty)
	| Error _ ->
	(* In this branch we need to print parens. [m] might have undetermined
	axes and we adopt a similar logic to the [marg] above. *)
	let m = Alloc.zap_to_legacy m in
	let ty = tree_of_typexp mode m ty in
	(Orm_parens (tree_of_modes m), ty)
	end
	| _ ->
	let m = Alloc.zap_to_legacy m in
	let ty = tree_of_typexp mode m ty in
	(Orm_not_arrow (tree_of_modes m), ty)

.

[lpw25]

@riaqn You should probably have a look at this one

[riaqn]

Thanks - I will look next Wednesday.