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PoC %typeof#7870

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134 changes: 131 additions & 3 deletionscompiler/ml/typetexp.ml
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Original file line numberDiff line numberDiff line change
Expand Up@@ -206,14 +206,16 @@ let create_package_mty fake loc env (p, l) =
(* Translation of type expressions *)

let type_variables = ref (Tbl.empty : (string, type_expr) Tbl.t)
let type_param_names = ref ([] : string list)
let univars = ref ([] : (string * type_expr) list)
let pre_univars = ref ([] : type_expr list)
let used_variables = ref (Tbl.empty : (string, type_expr * Location.t) Tbl.t)

let reset_type_variables () =
reset_global_level ();
Ctype.reset_reified_var_counter ();
type_variables := Tbl.empty
type_variables := Tbl.empty;
type_param_names := []

let narrow () = (increase_global_level (), !type_variables)

Expand DownExpand Up@@ -252,6 +254,7 @@ let transl_type_param env styp =
with Not_found ->
let v = new_global_var ~name () in
type_variables := Tbl.add name v !type_variables;
type_param_names := !type_param_names @ [name];
v
in
{
Expand DownExpand Up@@ -565,8 +568,133 @@ and transl_type_aux env policy styp =
pack_txt = p;
})
ty
| Ptyp_extension ext ->
raise (Error_forward (Builtin_attributes.error_of_extension ext))
| Ptyp_extension ext -> (
match ext with
| {txt = "typeof"; loc = ext_loc}, payload -> (
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Wow, this is surprisingly easy.
Might inspire me to take a stab at something like%nameof()

(* %typeof payload must be a single identifier *)
match Ast_payload.as_ident payload with
| Some ({txt = lid; loc = lid_loc} as _ident) ->
(* Lookup the value and embed its (generalized) type.
Important: avoid manufacturing polymorphism from a monomorphic
(weak) type, which would violate the value restriction. We only
allow %typeof on values whose type is a closed type scheme. *)
let _path, desc = find_value env lid_loc lid in
let ty0 = desc.val_type in
let () =
if not (Ctype.closed_schema env ty0) then
let msg =
"Cannot use %typeof on this value, because its type is not fully \
known yet.\n\n"
^ "%typeof needs a value whose type is completely determined at \
this point.\n"
^ "For example, [] or ref([]) don't say what element type they \
hold yet.\n\n" ^ "How to fix:\n"
^ "- Add a type annotation to the value (e.g. let u: array<int> \
= [];).\n"
^ "- Or define the value in a way that makes its type known \
immediately.\n\n"
^ "Note: This is related to the value restriction \
(non-generalizable type variables)."
in
raise (Error_forward (Location.error ~loc:ext_loc msg))
in
(match !type_param_names with
| [] -> ()
| lhs_params ->
let rhs_vars = Ctype.free_variables ty0 in
let rhs_names_opt =
List.map
(fun v ->
match (Ctype.repr v).desc with
| Tvar (Some n) | Tunivar (Some n) -> Some n
| _ -> None)
rhs_vars
in
let mk_params_string names =
match names with
| [] -> "< >"
| _ ->
let parts = List.map (fun n -> "'" ^ n) names in
Printf.sprintf "<%s>" (String.concat ", " parts)
in
let error msg =
raise (Error_forward (Location.error ~loc:ext_loc msg))
in
if List.mem None rhs_names_opt then
error
"This %typeof(...) expression refers to a polymorphic value \
whose type variables have no names.\n\
Name the type variables in the value's type annotation (e.g. \
promise<'response>), and use the same names here in the type \
definition.";
let rhs_named =
List.filter_map
(fun v ->
match (Ctype.repr v).desc with
| Tvar (Some n) | Tunivar (Some n) -> Some (n, v)
| _ -> None)
rhs_vars
in
let rhs_names = List.map fst rhs_named in
let module S = Set.Make (String) in
let s_lhs =
List.fold_left (fun s x -> S.add x s) S.empty lhs_params
in
let s_rhs = List.fold_left (fun s x -> S.add x s) S.empty rhs_names in
(if not (S.equal s_lhs s_rhs) then
let missing = S.elements (S.diff s_rhs s_lhs) in
let extra = S.elements (S.diff s_lhs s_rhs) in
let parts =
( [] |> fun acc ->
if missing <> [] then
acc
@ [
Printf.sprintf "Missing on the left: %s"
(mk_params_string missing);
]
else acc )
|> fun acc ->
if extra <> [] then
acc
@ [
Printf.sprintf "Remove from the left: %s"
(mk_params_string extra);
]
else acc
in
let header =
Printf.sprintf
"This identifier `%s` has type variables %s, but your type \
parameters are %s."
(Longident.last lid)
(mk_params_string rhs_names)
(mk_params_string lhs_params)
in
error
(if parts = [] then header
else header ^ "\n\n" ^ String.concat "\n" parts));
(* Tie variables: unify each LHS param with the corresponding RHS var by name.
%typeof reuses the value's scheme whose vars are distinct; tying
ensures the alias shares those vars (passes closedness, keeps names). *)
List.iter
(fun lhs_name ->
let lhs_param = Tbl.find lhs_name !type_variables in
let rhs_var = List.assoc lhs_name rhs_named in
Ctype.unify_var env lhs_param rhs_var)
lhs_params);
(* Preserve type variable names so that typedecl can enforce exact
name/order mapping against LHS parameters. Since we already ensured
the scheme is closed, we can reuse the original scheme here. *)
let ty = ty0 in
(* Build a core_type node carrying the looked up type; we mark the
desc as any since downstream only consults ctyp_type for typing. *)
ctyp Ttyp_any ty
| None ->
let msg =
"%%typeof expects an identifier. Example: type t = %typeof(x)"
in
raise (Error_forward (Location.error ~loc:ext_loc msg)))
| _ -> raise (Error_forward (Builtin_attributes.error_of_extension ext)))

and transl_poly_type env policy t =
transl_type env policy (Ast_helper.Typ.force_poly t)
Expand Down
10 changes: 10 additions & 0 deletionstests/analysis_tests/tests/src/Hover.res
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Expand Up@@ -281,3 +281,13 @@ module Arr = Belt.Array

type aliased = variant
// ^hov

let myFn = (a, b) => a ++ b->Int.toString

type fnType = %typeof(myFn)
// ^hov

let myFnPartial = myFn("hello", ...)

type fnTypePartial = %typeof(myFnPartial)
// ^hov
6 changes: 6 additions & 0 deletionstests/analysis_tests/tests/src/expected/Hover.res.txt
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Expand Up@@ -348,3 +348,9 @@ Hover src/Hover.res 278:8
Hover src/Hover.res 281:6
{"contents": {"kind": "markdown", "value": "```rescript\ntype aliased = variant\n```\n\n---\n\n```\n \n```\n```rescript\ntype variant = CoolVariant | OtherCoolVariant\n```\nGo to: [Type definition](command:rescript-vscode.go_to_location?%5B%22Hover.res%22%2C251%2C0%5D)\n"}}

Hover src/Hover.res 286:6
{"contents": {"kind": "markdown", "value": "```rescript\ntype fnType = (string, int) => string\n```"}}

Hover src/Hover.res 291:6
{"contents": {"kind": "markdown", "value": "```rescript\ntype fnTypePartial = int => string\n```"}}

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@@ -0,0 +1,13 @@

We've found a bug for you!
/.../fixtures/typeof_mismatch.res:6:28

4 │
5 │ let f: fnType = myFn
6 │ let ff: fnType = (a, b) => a->Int.toString + b
7 │

This has type: string
But this function argument is expecting: int

You can convert string to int with Int.fromString.
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@@ -0,0 +1,19 @@

We've found a bug for you!
/.../fixtures/typeof_non_generalized.res:3:10-16

1 │ let u = []
2 │
3 │ type t = %typeof(u)
4 │

Cannot use %typeof on this value, because its type is not fully known yet.

%typeof needs a value whose type is completely determined at this point.
For example, [] or ref([]) don't say what element type they hold yet.

How to fix:
- Add a type annotation to the value (e.g. let u: array<int> = [];).
- Or define the value in a way that makes its type known immediately.

Note: This is related to the value restriction (non-generalizable type variables).
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@@ -0,0 +1,8 @@

We've found a bug for you!
/.../fixtures/typeof_non_ident.res:1:10-16

1 │ type t = %typeof(1 + 2)
2 │

%%typeof expects an identifier. Example: type t = %typeof(x)
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@@ -0,0 +1,12 @@

We've found a bug for you!
/.../fixtures/typeof_param_count_mismatch.res:3:29-35

1 │ external fetch: string => promise<'response> = "fetch"
2 │
3 │ type fetch<'response, 'x> = %typeof(fetch)
4 │

This identifier `fetch` has type variables <'response>, but your type parameters are <'response, 'x>.

Remove from the left: <'x>
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@@ -0,0 +1,13 @@

We've found a bug for you!
/.../fixtures/typeof_param_name_mismatch.res:3:21-27

1 │ external fetch: string => promise<'response> = "fetch"
2 │
3 │ type fetch<'resp> = %typeof(fetch)
4 │

This identifier `fetch` has type variables <'response>, but your type parameters are <'resp>.

Missing on the left: <'response>
Remove from the left: <'resp>
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@@ -0,0 +1,6 @@
let myFn = (a, b) => a ++ b->Int.toString

type fnType = %typeof(myFn)

let f: fnType = myFn
let ff: fnType = (a, b) => a->Int.toString + b
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@@ -0,0 +1,3 @@
let u = []

type t = %typeof(u)
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@@ -0,0 +1 @@
type t = %typeof(1 + 2)
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@@ -0,0 +1,3 @@
external fetch: string => promise<'response> = "fetch"

type fetch<'response, 'x> = %typeof(fetch)
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@@ -0,0 +1,3 @@
external fetch: string => promise<'response> = "fetch"

type fetch<'resp> = %typeof(fetch)
14 changes: 14 additions & 0 deletionstests/tests/src/Typeof.mjs
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@@ -0,0 +1,14 @@
// Generated by ReScript, PLEASE EDIT WITH CARE


function myFn(a, b) {
return a + b.toString();
}

let f = myFn;

export {
myFn,
f,
}
/* No side effect */
9 changes: 9 additions & 0 deletionstests/tests/src/Typeof.res
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@@ -0,0 +1,9 @@
let myFn = (a, b) => a ++ b->Int.toString

type fnType = %typeof(myFn)

let f: fnType = myFn

external fetch: string => promise<'response> = "fetch"

type fetch<'response> = %typeof(fetch)
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