classify: filter undefined values from JS objects - #86
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The browser PPX emits Js.Undefined.empty for record fields with [@json.option] [@json.drop_default] when the value is None, so the JS object carries a key with an undefined value. Js.Dict.entries exposes those entries, and classify previously tripped on them with "unknown JSON value type: undefined". Filter undefined entries in the `Assoc branch so that dropped fields are unobservable to consumers, matching the intent of [@json.option]. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
andreypopp
requested review from
anmonteiro,
davesnx,
jchavarri and
pedrobslisboa
April 28, 2026 09:52
Comment on lines
+5
to
+15
| let dict_to_list_without_undefined dict = | ||
| let keys = Js.Dict.keys dict in | ||
| let l = Array.length keys in | ||
| let xs = ref [] in | ||
| for i = l - 1 downto 0 do | ||
| let key = Array.unsafe_get keys i in | ||
| let value = Js.Dict.unsafeGet dict key in | ||
| if not ((Obj.magic value : _ Js.Undefined.t) == Js.undefined) then | ||
| xs := (key, value) :: !xs | ||
| done; | ||
| !xs |
Collaborator
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Probably there is some performance issues, but why don't do this:
let dict_to_list_without_undefined dict =
Js.Dict.entries dict
|> Array.to_list
|> List.filter (fun (_, value) ->
not ((Obj.magic value : _ Js.Undefined.t) == Js.undefined))
Collaborator
There was a problem hiding this comment.
Or
let dict_to_list_without_undefined dict =
Array.fold_right
(fun (key, value) acc ->
if not ((Obj.magic value : _ Js.Undefined.t) == Js.undefined) then
(key, value) :: acc
else acc)
(Js.Dict.entries dict) []
Collaborator
Author
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yeah, I wanted to reduce number of allocations as much as possible, so no intermediate lists/arrays.
pedrobslisboa
approved these changes
Apr 28, 2026
pedrobslisboa
left a comment
pedrobslisboa
left a comment
Collaborator
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The comments above are just for curiosity.
| for i = l - 1 downto 0 do | ||
| let key = Array.unsafe_get keys i in | ||
| let value = Js.Dict.unsafeGet dict key in | ||
| if not ((Obj.magic value : _ Js.Undefined.t) == Js.undefined) then |
Collaborator
There was a problem hiding this comment.
Probably the same reason of the other comment, but why not Js.typeof value <> "undefined" in this case instead of Obj.magic?
jchavarri
added a commit
that referenced
this pull request
Jun 29, 2026
* main: (40 commits) Respect nonrec type declarations in json derivers (#94) ppx/test: cover encode behavior for @drop_default variants (#84) allow @@compact_variants to parse ["Tag"] in addition to "Tag" for nullary variants (#93) Make extra JSON fields allowed by default (#92) Fix error messages for `[@@json.compact_variants]` (#91) Revert "Fix error message for @@compact_variants" (#90) Fix error message for @@compact_variants (#87) ppx: add [@json.catch_all] for forward-compatible string enums (#88) classify: filter undefined values from JS objects (#86) Add primitives semantics table to readme (#82) Support @json.compact_variants on polyvariant types (#79) ppx: allow dropping arbitrary values with `[@drop_default]` (#77) .gitignore: .claude upgrade ppxlib to 0.36 / handle Ptyp_open (#60) build with Melange 6 / OCaml 5.4 (#72) fmt: format using OCamlformat 0.28 (#75) fix: use `opam-check-npm-deps` compatible with OPAM 2.5 (#74) native: re_export yojson browser: remove dup of_json_error_to_string native: +of_json_error_to_string ...
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The browser PPX emits Js.Undefined.empty for record fields with [@json.option] [@json.drop_default] when the value is None, so the JS object carries a key with an undefined value. Js.Dict.entries exposes those entries, and classify previously tripped on them with "unknown JSON value type: undefined".
Filter undefined entries in the `Assoc branch so that dropped fields are unobservable to consumers, matching the intent of [@json.option].