refactor: simplify omit handling in UnionValidator and remove unused MaybeOmits struct

mikeedjones · mikeedjones · commit ccd07fa72c8e · 2026-02-09T09:34:09.000Z
diff --git a/pydantic-core/src/validators/union.rs b/pydantic-core/src/validators/union.rs
@@ -110,7 +110,7 @@ impl UnionValidator {
         let old_fields_set_count = state.fields_set_count;
 
         let mut errors = MaybeErrors::new(self.custom_error.as_ref());
-        let mut omits = MaybeOmits::new();
+        let mut should_omit = false;
 
         let mut best_match: Option<(Py<PyAny>, Exactness, Option<usize>)> = None;
 
@@ -159,7 +159,7 @@ impl UnionValidator {
                 },
                 Err(ValError::Omit) => {
                     if best_match.is_none() {
-                        omits.push(choice, label.as_deref());
+                        should_omit = true;
                     }
                 }
                 Err(ValError::LineErrors(lines)) => {
@@ -184,7 +184,7 @@ impl UnionValidator {
             return Ok(best_match);
         }
         // if there were no successful matches, but there was at least one omit, return omit instead of errors
-        if best_match.is_none() && !omits.is_empty() {
+        if best_match.is_none() && should_omit {
             return Err(ValError::Omit);
         }
         // no matches, build errors
@@ -289,24 +289,6 @@ impl<'a> MaybeErrors<'a> {
     }
 }
 
-struct MaybeOmits<'a> {
-    omits: SmallVec<[(&'a CombinedValidator, Option<&'a str>); SMALL_UNION_THRESHOLD]>,
-}
-
-impl<'a> MaybeOmits<'a> {
-    fn new() -> Self {
-        Self { omits: SmallVec::new() }
-    }
-
-    fn push(&mut self, choice: &'a CombinedValidator, label: Option<&'a str>) {
-        self.omits.push((choice, label));
-    }
-
-    fn is_empty(&self) -> bool {
-        self.omits.is_empty()
-    }
-}
-
 #[derive(Debug)]
 pub struct TaggedUnionValidator {
     discriminator: Discriminator,
diff --git a/tests/types/test_union.py b/tests/types/test_union.py
@@ -74,3 +74,25 @@ class Container2(pydantic.BaseModel):
     # as nested unions were individually attempted with each of strict and lax checking,
     # and the discriminators also incurred an extra attempt at each check level too.
     assert MyModel.field_a_serializer_calls == 2
+
+
+def test_list_union_omit():
+    OmitList = list[pydantic.OnErrorOmit[int] | pydantic.OnErrorOmit[bool]]
+    ta = pydantic.TypeAdapter(OmitList)
+    assert ta.validate_python([1, 'True', 'foo', '2', False, 'bar']) == [1, True, 2, False]
+
+
+def test_typed_dict_union_omit():
+    class TD(TypedDict):
+        # arguably this should fail on schema build since `x` is a
+        # required field, and setting the type to `OnErrorOmit`
+        # effectively makes it optional.
+        x: pydantic.OnErrorOmit[int] | pydantic.OnErrorOmit[bool]
+
+    ta = pydantic.TypeAdapter(TD)
+    assert ta.validate_python({'x': 1}) == {'x': 1}
+    assert ta.validate_python({'x': 'True'}) == {'x': True}
+
+    # test to document the behaviour that if all options in the union fail,
+    # the field is omitted, even if it is required in the TypedDict.
+    assert ta.validate_python({'x': 'foo'}) == {}
