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Fix null falling into object branch in untagged variant switch #8253

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Merged
cristianoc merged 1 commit into from
Feb 25, 2026
+64 −14
Merged

Fix null falling into object branch in untagged variant switch #8253

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#### :bug: Bug fix

- Fix compiler crash (`Fatal error: Parmatch.all_record_args`) when matching empty dict/record patterns. https://github.com/rescript-lang/rescript/pull/8246
- Fix `null` falling into the object branch instead of the wildcard when pattern matching on untagged variants with both `Object` and `null` cases. https://github.com/rescript-lang/rescript/pull/8253

#### :memo: Documentation

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16 changes: 15 additions & 1 deletion compiler/core/lam_compile.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -814,6 +814,10 @@ let compile output_prefix =
| _ -> false
in
let clause_is_not_typeof (tag, _) = tag_is_not_typeof tag in
let clause_is_object_typeof = function
| Ast_untagged_variants.Untagged ObjectType, _ -> true
| _ -> false
in
let switch ?default ?declaration e clauses =
let not_typeof_clauses, typeof_clauses =
List.partition clause_is_not_typeof clauses
Expand All @@ -827,7 +831,17 @@ let compile output_prefix =
(E.emit_check (IsInstanceOf (instance_type, Expr e)))
switch_body
~else_:[build_if_chain rest]
| _ -> S.string_switch ?default ?declaration (E.typeof e) typeof_clauses
| _ ->
let typeof_switch () =
S.string_switch ?default ?declaration (E.typeof e) typeof_clauses
in
if has_null_case && List.exists clause_is_object_typeof typeof_clauses
then
match default with
| Some default_body ->
S.if_ (E.is_null e) default_body ~else_:[typeof_switch ()]
| None -> typeof_switch ()
else typeof_switch ()
in
build_if_chain not_typeof_clauses
in
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46 changes: 33 additions & 13 deletions tests/tests/src/js_json_test.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,24 +367,44 @@ Mocha.describe("Js_json_test", () => {
Test_utils.eq("File \"js_json_test.res\", line 314, characters 7-14", Js_json.decodeArray({}), undefined);
Test_utils.eq("File \"js_json_test.res\", line 315, characters 7-14", Js_json.decodeArray(1.23), undefined);
});
Mocha.test("JSON Array/Object switch falls through to wildcard on null", () => {
let classifyArrayOrObject = json => {
if (Array.isArray(json)) {
return json.length;
}
if (json === null) {
return;
}
switch (typeof json) {
case "object" :
Js_dict.get(json, "x");
return 0;
default:
return;
}
};
Test_utils.eq("File \"js_json_test.res\", line 328, characters 7-14", classifyArrayOrObject(null), undefined);
Test_utils.eq("File \"js_json_test.res\", line 329, characters 7-14", classifyArrayOrObject([1]), 1);
Test_utils.eq("File \"js_json_test.res\", line 330, characters 7-14", classifyArrayOrObject({}), 0);
});
Mocha.test("JSON decodeBoolean", () => {
Test_utils.eq("File \"js_json_test.res\", line 319, characters 7-14", Js_json.decodeBoolean("test"), undefined);
Test_utils.eq("File \"js_json_test.res\", line 320, characters 7-14", Js_json.decodeBoolean(true), true);
Test_utils.eq("File \"js_json_test.res\", line 321, characters 7-14", Js_json.decodeBoolean([]), undefined);
Test_utils.eq("File \"js_json_test.res\", line 322, characters 7-14", Js_json.decodeBoolean(null), undefined);
Test_utils.eq("File \"js_json_test.res\", line 323, characters 7-14", Js_json.decodeBoolean({}), undefined);
Test_utils.eq("File \"js_json_test.res\", line 324, characters 7-14", Js_json.decodeBoolean(1.23), undefined);
Test_utils.eq("File \"js_json_test.res\", line 334, characters 7-14", Js_json.decodeBoolean("test"), undefined);
Test_utils.eq("File \"js_json_test.res\", line 335, characters 7-14", Js_json.decodeBoolean(true), true);
Test_utils.eq("File \"js_json_test.res\", line 336, characters 7-14", Js_json.decodeBoolean([]), undefined);
Test_utils.eq("File \"js_json_test.res\", line 337, characters 7-14", Js_json.decodeBoolean(null), undefined);
Test_utils.eq("File \"js_json_test.res\", line 338, characters 7-14", Js_json.decodeBoolean({}), undefined);
Test_utils.eq("File \"js_json_test.res\", line 339, characters 7-14", Js_json.decodeBoolean(1.23), undefined);
});
Mocha.test("JSON decodeNull", () => {
Test_utils.eq("File \"js_json_test.res\", line 328, characters 7-14", Js_json.decodeNull("test"), undefined);
Test_utils.eq("File \"js_json_test.res\", line 329, characters 7-14", Js_json.decodeNull(true), undefined);
Test_utils.eq("File \"js_json_test.res\", line 330, characters 7-14", Js_json.decodeNull([]), undefined);
Test_utils.eq("File \"js_json_test.res\", line 331, characters 7-14", Js_json.decodeNull(null), null);
Test_utils.eq("File \"js_json_test.res\", line 332, characters 7-14", Js_json.decodeNull({}), undefined);
Test_utils.eq("File \"js_json_test.res\", line 333, characters 7-14", Js_json.decodeNull(1.23), undefined);
Test_utils.eq("File \"js_json_test.res\", line 343, characters 7-14", Js_json.decodeNull("test"), undefined);
Test_utils.eq("File \"js_json_test.res\", line 344, characters 7-14", Js_json.decodeNull(true), undefined);
Test_utils.eq("File \"js_json_test.res\", line 345, characters 7-14", Js_json.decodeNull([]), undefined);
Test_utils.eq("File \"js_json_test.res\", line 346, characters 7-14", Js_json.decodeNull(null), null);
Test_utils.eq("File \"js_json_test.res\", line 347, characters 7-14", Js_json.decodeNull({}), undefined);
Test_utils.eq("File \"js_json_test.res\", line 348, characters 7-14", Js_json.decodeNull(1.23), undefined);
});
Mocha.test("JSON serialize/deserialize identity", () => {
let idtest = obj => Test_utils.eq("File \"js_json_test.res\", line 339, characters 27-34", obj, Js_json.deserializeUnsafe(Js_json.serializeExn(obj)));
let idtest = obj => Test_utils.eq("File \"js_json_test.res\", line 354, characters 27-34", obj, Js_json.deserializeUnsafe(Js_json.serializeExn(obj)));
idtest(undefined);
idtest({
hd: [
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15 changes: 15 additions & 0 deletions tests/tests/src/js_json_test.res
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Expand Up @@ -315,6 +315,21 @@ describe(__MODULE__, () => {
eq(__LOC__, J.decodeArray(J.number(1.23)), None)
})

test("JSON Array/Object switch falls through to wildcard on null", () => {
let classifyArrayOrObject = (json: J.t) =>
switch json {
| J.Array(items) => Some(items->Js.Array2.length)
| J.Object(dict) =>
ignore(Js.Dict.get(dict, "x"))
Some(0)
| _ => None
}

eq(__LOC__, classifyArrayOrObject(J.null), None)
eq(__LOC__, classifyArrayOrObject(J.array([J.number(1.)])), Some(1))
eq(__LOC__, classifyArrayOrObject(J.object_(Js.Dict.empty())), Some(0))
})

test("JSON decodeBoolean", () => {
eq(__LOC__, J.decodeBoolean(J.string("test")), None)
eq(__LOC__, J.decodeBoolean(J.boolean(true)), Some(true))
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