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atdml: support <ocaml attr=...> on record fields, variant constructors, and payloads
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Lines changed: 232 additions & 17 deletions

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‎CHANGES.md‎

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,9 @@
1+
unreleased
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* atdml: Add support for `<ocaml attr="...">` on record fields, variant constructors,
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and variant payload types to attach ppx attributes (e.g. `[@deriving.ord.ignore]`)
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6+
17
4.1.0 (2026-04-11)
28
------------------
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@@ -124,8 +130,9 @@
124130
(inline expressions); supported on sum types and records
125131
- `<json name="...">` to override JSON field or constructor names
126132
- `<ocaml name="...">` to rename variant constructors in OCaml
127-
- `<ocaml attr="...">` to attach ppx attributes (e.g. `[@@deriving show]`)
128-
to generated type definitions
133+
- `<ocaml attr="...">` to attach ppx attributes to generated type definitions
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(e.g. `[@@deriving show]`), individual record fields, variant constructors,
135+
or variant payload types (e.g. `[@compare.ignore]`)
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- `<ocaml private>` on any type definition forces `private` in the generated
130137
`.mli`; `<ocaml public>` on a primitive alias suppresses the default
131138
`private`, making the alias transparent to callers

‎atdml/src/lib/Codegen.ml‎

Lines changed: 43 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -55,6 +55,9 @@ let annot_schema_ocaml : Atd.Annot.schema_section = {
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Import, "name"; (* <ocaml name="..."> on an import: override OCaml alias *)
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Imported_type, "name"; (* <ocaml name="..."> on an imported type: override type name *)
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Variant, "name"; (* <ocaml name="..."> on a variant constructor *)
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Variant, "attr"; (* <ocaml attr="..."> on a variant constructor: append [@...] *)
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Type_expr, "attr"; (* <ocaml attr="..."> on a variant payload type: append [@...] *)
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Field, "attr"; (* <ocaml attr="..."> on a field: append [@...] *)
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Field, "default"; (* <ocaml default="..."> on a with-default field *)
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Field, "name"; (* <ocaml name="..."> on a field: not supported, warns *)
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]
@@ -210,6 +213,30 @@ let get_ocaml_attr an =
210213
~field:"attr"
211214
an
212215

216+
(* Get <ocaml attr="..."> for a field; value is placed inside [@...] *)
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let get_ocaml_field_attr an =
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Atd.Annot.get_opt_field
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~parse:(fun s -> Some s)
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~sections:["ocaml"]
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~field:"attr"
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an
223+
224+
(* Get <ocaml attr="..."> for a variant constructor; value is placed inside [@...] *)
225+
let get_ocaml_variant_attr an =
226+
Atd.Annot.get_opt_field
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~parse:(fun s -> Some s)
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~sections:["ocaml"]
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~field:"attr"
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an
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232+
(* Get <ocaml attr="..."> for a variant payload type expression; value is placed inside [@...] *)
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let get_ocaml_payload_attr e =
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Atd.Annot.get_opt_field
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~parse:(fun s -> Some s)
236+
~sections:["ocaml"]
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~field:"attr"
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(Atd.Ast.annot_of_type_expr e)
239+
213240
(* Get wrap-related annotations for a 'wrap' type expression.
214241
Supports:
215242
<ocaml module="M"> → uses M.t, M.wrap, M.unwrap
@@ -875,12 +902,21 @@ let gen_type_def ~is_mli env ({A.loc; name; param=params; annot=an; value=e; _}
875902
in
876903
let gen_case (loc, orig_name, an, opt_e) =
877904
let cons_name = vtr (get_ocaml_name orig_name an) in
905+
let cons_attr = match get_ocaml_variant_attr an with
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| None -> ""
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| Some attr -> sprintf " [@%s]" attr
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in
878909
match opt_e with
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| None ->
880-
with_inline_doc (sprintf "| %s%s" tick cons_name) loc an
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with_inline_doc (sprintf "| %s%s%s" tick cons_name cons_attr) loc an
881912
| Some e ->
913+
let payload_str =
914+
match get_ocaml_payload_attr e with
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| None -> type_expr_str env e
916+
| Some attr -> sprintf "(%s [@%s])" (type_expr_str env e) attr
917+
in
882918
with_inline_doc
883-
(sprintf "| %s%s of %s" tick cons_name (type_expr_str env e))
919+
(sprintf "| %s%s of %s%s" tick cons_name payload_str cons_attr)
884920
loc an
885921
in
886922
let hd =
@@ -917,8 +953,12 @@ let gen_type_def ~is_mli env ({A.loc; name; param=params; annot=an; value=e; _}
917953
B.Block
918954
(concat_map
919955
(fun (loc, (fname, _, an), e) ->
956+
let field_attr = match get_ocaml_field_attr an with
957+
| None -> ""
958+
| Some attr -> sprintf " [@%s]" attr
959+
in
920960
with_inline_doc
921-
(sprintf "%s: %s;" (pftr fname) (type_expr_str env e))
961+
(sprintf "%s: %s%s;" (pftr fname) (type_expr_str env e) field_attr)
922962
loc an)
923963
fields);
924964
B.Line "}";

‎atdml/tests/named-snapshots/attr‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,7 @@
22

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type point = {
44
x: float;
5-
y: float;
5+
y: float option [@option];
66
}
77
[@@deriving show]
88

@@ -191,7 +191,7 @@ end
191191

192192
type point = {
193193
x: float;
194-
y: float;
194+
y: float option [@option];
195195
}
196196
[@@deriving show]
197197

‎atdml/tests/named-snapshots/variant_attr‎

Lines changed: 138 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,138 @@
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(* Auto-generated from "variant_attr.atd" by atdml. *)
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type status =
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| Active [@deriving.ord.ignore]
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| Inactive
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| Pending of (int [@deriving.ord.ignore])
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val status_of_yojson : Yojson.Safe.t -> status
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val yojson_of_status : status -> Yojson.Safe.t
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val status_of_json : string -> status
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val json_of_status : status -> string
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module Status : sig
14+
type nonrec t = status
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val of_yojson : Yojson.Safe.t -> t
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val to_yojson : t -> Yojson.Safe.t
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val of_json : string -> t
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val to_json : t -> string
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end
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--- ml ---
22+
(* Auto-generated from "variant_attr.atd" by atdml. *)
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[@@@ocaml.warning "-27-32-33-35-39"]
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(* Inlined runtime — no external dependency needed. *)
26+
module Atdml_runtime = struct
27+
let bad_type expected_type x =
28+
Printf.ksprintf failwith "expected %s, got: %s"
29+
expected_type (Yojson.Safe.to_string x)
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let bad_sum type_name x =
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Printf.ksprintf failwith "invalid variant for type '%s': %s"
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type_name (Yojson.Safe.to_string x)
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let missing_field type_name field_name =
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Printf.ksprintf failwith "missing field '%s' in object of type '%s'"
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field_name type_name
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39+
let bool_of_yojson = function
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| `Bool b -> b
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| x -> bad_type "bool" x
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43+
let yojson_of_bool b = `Bool b
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45+
let int_of_yojson = function
46+
| `Int n -> n
47+
| x -> bad_type "int" x
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49+
let yojson_of_int n = `Int n
50+
51+
let float_of_yojson = function
52+
| `Float f -> f
53+
| `Int n -> Float.of_int n
54+
| x -> bad_type "float" x
55+
56+
let yojson_of_float f = `Float f
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58+
let string_of_yojson = function
59+
| `String s -> s
60+
| x -> bad_type "string" x
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62+
let yojson_of_string s = `String s
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64+
let unit_of_yojson = function
65+
| `Null -> ()
66+
| x -> bad_type "null" x
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68+
let yojson_of_unit () = `Null
69+
70+
let list_of_yojson f = function
71+
| `List xs -> List.map f xs
72+
| x -> bad_type "array" x
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74+
let yojson_of_list f xs = `List (List.map f xs)
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76+
let option_of_yojson f = function
77+
| `String "None" -> None
78+
| `List [`String "Some"; x] -> Some (f x)
79+
| x -> bad_type "option" x
80+
81+
let yojson_of_option f = function
82+
| None -> `String "None"
83+
| Some x -> `List [`String "Some"; f x]
84+
85+
let nullable_of_yojson f = function
86+
| `Null -> None
87+
| x -> Some (f x)
88+
89+
let yojson_of_nullable f = function
90+
| None -> `Null
91+
| Some x -> f x
92+
93+
(* Returns true iff the list has strictly more than [n] elements,
94+
without traversing past element n+1. *)
95+
let rec list_length_gt n = function
96+
| _ :: rest -> if n = 0 then true else list_length_gt (n - 1) rest
97+
| [] -> false
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99+
let assoc_of_yojson f = function
100+
| `Assoc pairs -> List.map (fun (k, v) -> (k, f v)) pairs
101+
| x -> bad_type "object" x
102+
103+
let yojson_of_assoc f xs =
104+
`Assoc (List.map (fun (k, v) -> (k, f v)) xs)
105+
end
106+
107+
type status =
108+
| Active [@deriving.ord.ignore]
109+
| Inactive
110+
| Pending of (int [@deriving.ord.ignore])
111+
112+
let status_of_yojson (x : Yojson.Safe.t) : status =
113+
match x with
114+
| `String "Active" -> Active
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| `String "Inactive" -> Inactive
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| `List [`String "Pending"; v] -> Pending (Atdml_runtime.int_of_yojson v)
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| _ -> Atdml_runtime.bad_sum "status" x
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119+
let yojson_of_status (x : status) : Yojson.Safe.t =
120+
match x with
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| Active -> `String "Active"
122+
| Inactive -> `String "Inactive"
123+
| Pending v -> `List [`String "Pending"; Atdml_runtime.yojson_of_int v]
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125+
let status_of_json s =
126+
status_of_yojson (Yojson.Safe.from_string s)
127+
128+
let json_of_status x =
129+
Yojson.Safe.to_string (yojson_of_status x)
130+
131+
module Status = struct
132+
type nonrec t = status
133+
let of_yojson = status_of_yojson
134+
let to_yojson = yojson_of_status
135+
let of_json = status_of_json
136+
let to_json = json_of_status
137+
end
138+

‎atdml/tests/test.ml‎

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -489,13 +489,23 @@ type shape = [
489489
~atd_src:{|
490490
type point <ocaml attr="deriving show"> = {
491491
x: float;
492-
y: float;
492+
y: float option <ocaml attr="option">;
493493
}
494494

495495
type points <ocaml attr="deriving show"> = point list
496496
|}
497497
;
498498

499+
test_codegen_snapshot "variant attr"
500+
~atd_src:{|
501+
type status = [
502+
| Active <ocaml attr="deriving.ord.ignore">
503+
| Inactive
504+
| Pending of int <ocaml attr="deriving.ord.ignore">
505+
]
506+
|}
507+
;
508+
499509
test_codegen_snapshot "doc"
500510
~atd_src:{|
501511
<doc text="Module-level documentation.">

‎doc/atdml-reference.rst‎

Lines changed: 29 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -419,34 +419,54 @@ Section ``ocaml``
419419
Field ``attr``
420420
""""""""""""""
421421

422-
Position: on a type definition, i.e. on the left-hand side just before the
423-
equal sign ``=``
422+
Position: on a type definition, a record field, a variant constructor, or a
423+
variant payload type expression
424424

425-
Values: the contents of a ppx annotation without the enclosing ``[@@`` and
426-
``]``
425+
Values: the contents of a ppx annotation without the enclosing brackets and
426+
``@`` sigils
427427

428-
Semantics: appends a ppx attribute to the generated OCaml type definition,
429-
in both the ``.mli`` and ``.ml`` files.
428+
Semantics:
430429

431-
Example:
430+
- On a **type definition** (left-hand side just before ``=``), appends a
431+
``[@@attr]`` attribute after the type definition in both the ``.mli`` and
432+
``.ml`` files.
433+
- On a **record field** (after the field type), appends a ``[@attr]``
434+
attribute to that field in the generated type definition.
435+
- On a **variant constructor** (after the constructor name), appends a
436+
``[@attr]`` attribute to that constructor.
437+
- On a **variant payload type** (after the ``of <type>``), wraps the payload
438+
in ``(<type> [@attr])``.
439+
440+
Examples:
432441

433442
.. code:: ocaml
434443
435444
type point <ocaml attr="deriving show, eq"> = {
436445
x: float;
437-
y: float;
446+
y: float <ocaml attr="compare.ignore">;
438447
}
439448
449+
type status = [
450+
| Active <ocaml attr="deriving.ord.ignore">
451+
| Pending of int <ocaml attr="deriving.ord.ignore">
452+
| Inactive
453+
]
454+
440455
translates to
441456

442457
.. code:: ocaml
443458
444459
type point = {
445460
x: float;
446-
y: float;
461+
y: float [@compare.ignore];
447462
}
448463
[@@deriving show, eq]
449464
465+
type status =
466+
| Active [@deriving.ord.ignore]
467+
| Pending of (int [@deriving.ord.ignore])
468+
| Inactive
469+
450470
This is useful for attaching ppx rewriters such as ``ppx_deriving`` or
451471
``ppx_yojson_conv`` to generated types. Note that the ppx library must be
452472
present in the build environment; atdml does not provide it.

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