Fix: dataclass InitVars shouldn't be required on serialization

src/serializers/type_serializers/dataclass.rs

@@ -43,15 +43,17 @@ impl BuildSerializer for DataclassArgsBuilder {
 
             let key_py: Py<PyString> = PyString::new(py, &name).into();
 
-            if field_info.get_as(intern!(py, "serialization_exclude"))? == Some(true) {
-                fields.insert(name, SerField::new(py, key_py, None, None, true));
-            } else {
-                let schema = field_info.get_as_req(intern!(py, "schema"))?;
-                let serializer = CombinedSerializer::build(&schema, config, definitions)
-                    .map_err(|e| py_schema_error_type!("Field `{}`:\n  {}", index, e))?;
-
-                let alias = field_info.get_as(intern!(py, "serialization_alias"))?;
-                fields.insert(name, SerField::new(py, key_py, alias, Some(serializer), true));
+            if !field_info.get_as(intern!(py, "init_only"))?.unwrap_or(false) {
+                if field_info.get_as(intern!(py, "serialization_exclude"))? == Some(true) {
+                    fields.insert(name, SerField::new(py, key_py, None, None, true));
+                } else {
+                    let schema = field_info.get_as_req(intern!(py, "schema"))?;
+                    let serializer = CombinedSerializer::build(&schema, config, definitions)
+                        .map_err(|e| py_schema_error_type!("Field `{}`:\n  {}", index, e))?;
+
+                    let alias = field_info.get_as(intern!(py, "serialization_alias"))?;
+                    fields.insert(name, SerField::new(py, key_py, alias, Some(serializer), true));
+                }
             }
         }
 

tests/serializers/test_dataclasses.py

@@ -192,3 +192,45 @@ class Model:
     m = v.validate_python({'extra': 'extra'})
 
     assert s.to_python(m) == {'extra': 'extra bam!'}
+
+
+def test_dataclass_initvar_not_required_on_union_ser() -> None:
+    @dataclasses.dataclass
+    class Foo:
+        x: int
+        init_var: dataclasses.InitVar[int] = 1
+
+    @dataclasses.dataclass
+    class Bar:
+        x: int
+
+    schema = core_schema.union_schema(
+        [
+            core_schema.dataclass_schema(
+                Foo,
+                core_schema.dataclass_args_schema(
+                    'Foo',
+                    [
+                        core_schema.dataclass_field(name='x', schema=core_schema.int_schema()),
+                        core_schema.dataclass_field(
+                            name='init_var',
+                            init_only=True,
+                            schema=core_schema.with_default_schema(core_schema.int_schema(), default=1),
+                        ),
+                    ],
+                ),
+                ['x'],
+                post_init=True,
+            ),
+            core_schema.dataclass_schema(
+                Bar,
+                core_schema.dataclass_args_schema(
+                    'Bar', [core_schema.dataclass_field(name='x', schema=core_schema.int_schema())]
+                ),
+                ['x'],
+            ),
+        ]
+    )
+
+    s = SchemaSerializer(schema)
+    assert s.to_python(Foo(x=1), warnings='error') == {'x': 1}