WIP

python/pydantic_core/core_schema.py

@@ -1437,6 +1437,30 @@ def uuid_schema(
     )
 
 
+class NestedSchema(TypedDict, total=False):
+    type: Required[Literal['nested']]
+    cls: Required[Type[Any]]
+    # Should return `(CoreSchema, SchemaValidator, SchemaSerializer)` but this requires a forward ref
+    get_info: Required[Callable[[], Any]]
+    metadata: Any
+    serialization: SerSchema
+
+def nested_schema(
+    *,
+    cls: Type[Any],
+    get_info: Callable[[], Any],
+    metadata: Any = None,
+    serialization: SerSchema | None = None
+) -> NestedSchema:
+    return _dict_not_none(
+        type='nested',
+        cls=cls,
+        get_info=get_info,
+        metadata=metadata,
+        serialization=serialization
+    )
+
+
 class IncExSeqSerSchema(TypedDict, total=False):
     type: Required[Literal['include-exclude-sequence']]
     include: Set[int]
@@ -3866,6 +3890,7 @@ def definition_reference_schema(
         DefinitionReferenceSchema,
         UuidSchema,
         ComplexSchema,
+        NestedSchema,
     ]
 elif False:
     CoreSchema: TypeAlias = Mapping[str, Any]
@@ -3922,6 +3947,7 @@ def definition_reference_schema(
     'definition-ref',
     'uuid',
     'complex',
+    'nested',
 ]
 
 CoreSchemaFieldType = Literal['model-field', 'dataclass-field', 'typed-dict-field', 'computed-field']

src/py_gc.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
 
 use ahash::AHashMap;
 use enum_dispatch::enum_dispatch;
@@ -58,6 +58,25 @@ impl<T: PyGcTraverse> PyGcTraverse for Option<T> {
     }
 }
 
+impl<T: PyGcTraverse, E> PyGcTraverse for Result<T, E> {
+    fn py_gc_traverse(&self, visit: &PyVisit<'_>) -> Result<(), PyTraverseError> {
+        match self {
+            Ok(v) => T::py_gc_traverse(v, visit),
+            // FIXME(BoxyUwU): Lol
+            Err(_) => Ok(()),
+        }
+    }
+}
+
+impl<T: PyGcTraverse> PyGcTraverse for OnceLock<T> {
+    fn py_gc_traverse(&self, visit: &PyVisit<'_>) -> Result<(), PyTraverseError> {
+        match self.get() {
+            Some(item) => T::py_gc_traverse(item, visit),
+            None => Ok(()),
+        }
+    }
+}
+
 /// A crude alternative to a "derive" macro to help with building PyGcTraverse implementations
 macro_rules! impl_py_gc_traverse {
     ($name:ty { }) => {

src/serializers/shared.rs

@@ -143,6 +143,7 @@ combined_serializer! {
         Recursive: super::type_serializers::definitions::DefinitionRefSerializer;
         Tuple: super::type_serializers::tuple::TupleSerializer;
         Complex: super::type_serializers::complex::ComplexSerializer;
+        Nested: super::type_serializers::nested::NestedSerializer;
     }
 }
 
@@ -254,6 +255,7 @@ impl PyGcTraverse for CombinedSerializer {
             CombinedSerializer::Tuple(inner) => inner.py_gc_traverse(visit),
             CombinedSerializer::Uuid(inner) => inner.py_gc_traverse(visit),
             CombinedSerializer::Complex(inner) => inner.py_gc_traverse(visit),
+            CombinedSerializer::Nested(inner) => inner.py_gc_traverse(visit),
         }
     }
 }

src/serializers/type_serializers/mod.rs

@@ -16,6 +16,7 @@ pub mod json_or_python;
 pub mod list;
 pub mod literal;
 pub mod model;
+pub mod nested;
 pub mod nullable;
 pub mod other;
 pub mod set_frozenset;

src/serializers/type_serializers/nested.rs

@@ -0,0 +1,135 @@
+use std::{borrow::Cow, sync::OnceLock};
+
+use pyo3::{
+    intern,
+    types::{PyAnyMethods, PyDict, PyDictMethods, PyTuple, PyType},
+    Bound, Py, PyAny, PyObject, PyResult, Python,
+};
+
+use crate::{
+    definitions::DefinitionsBuilder,
+    serializers::{
+        shared::{BuildSerializer, TypeSerializer},
+        CombinedSerializer, Extra,
+    },
+    SchemaSerializer,
+};
+
+#[derive(Debug)]
+pub struct NestedSerializer {
+    model: Py<PyType>,
+    name: String,
+    get_serializer: Py<PyAny>,
+    serializer: OnceLock<PyResult<Py<SchemaSerializer>>>,
+}
+
+impl_py_gc_traverse!(NestedSerializer {
+    model,
+    get_serializer,
+    serializer
+});
+
+impl BuildSerializer for NestedSerializer {
+    const EXPECTED_TYPE: &'static str = "nested";
+
+    fn build(
+        schema: &Bound<'_, PyDict>,
+        _config: Option<&Bound<'_, PyDict>>,
+        _definitions: &mut DefinitionsBuilder<CombinedSerializer>,
+    ) -> PyResult<CombinedSerializer> {
+        let py = schema.py();
+
+        let get_serializer = schema
+            .get_item(intern!(py, "get_info"))?
+            .expect("Invalid core schema for `nested` type, no `get_info`")
+            .unbind();
+
+        let model = schema
+            .get_item(intern!(py, "cls"))?
+            .expect("Invalid core schema for `nested` type, no `model`")
+            .downcast::<PyType>()
+            .expect("Invalid core schema for `nested` type, not a `PyType`")
+            .clone();
+
+        let name = model.getattr(intern!(py, "__name__"))?.extract()?;
+
+        Ok(CombinedSerializer::Nested(NestedSerializer {
+            model: model.clone().unbind(),
+            name,
+            get_serializer,
+            serializer: OnceLock::new(),
+        }))
+    }
+}
+
+impl NestedSerializer {
+    fn nested_serializer<'py>(&self, py: Python<'py>) -> PyResult<&Py<SchemaSerializer>> {
+        self.serializer
+            .get_or_init(|| {
+                Ok(self
+                    .get_serializer
+                    .bind(py)
+                    .call((), None)?
+                    .downcast::<PyTuple>()?
+                    .get_item(2)?
+                    .downcast::<SchemaSerializer>()?
+                    .clone()
+                    .unbind())
+            })
+            .as_ref()
+            .map_err(|e| e.clone_ref(py))
+    }
+}
+
+impl TypeSerializer for NestedSerializer {
+    fn to_python(
+        &self,
+        value: &Bound<'_, PyAny>,
+        include: Option<&Bound<'_, PyAny>>,
+        exclude: Option<&Bound<'_, PyAny>>,
+        mut extra: &Extra,
+    ) -> PyResult<PyObject> {
+        let mut guard = extra.recursion_guard(value, self.model.as_ptr() as usize)?;
+
+        self.nested_serializer(value.py())?
+            .bind(value.py())
+            .get()
+            .serializer
+            .to_python(value, include, exclude, guard.state())
+    }
+
+    fn json_key<'a>(&self, key: &'a Bound<'_, PyAny>, extra: &Extra) -> PyResult<Cow<'a, str>> {
+        self.nested_serializer(key.py())?
+            .bind(key.py())
+            .get()
+            .serializer
+            .json_key(key, extra)
+    }
+
+    fn serde_serialize<S: serde::ser::Serializer>(
+        &self,
+        value: &Bound<'_, PyAny>,
+        serializer: S,
+        include: Option<&Bound<'_, PyAny>>,
+        exclude: Option<&Bound<'_, PyAny>>,
+        mut extra: &Extra,
+    ) -> Result<S::Ok, S::Error> {
+        use super::py_err_se_err;
+
+        let mut guard = extra
+            .recursion_guard(value, self.model.as_ptr() as usize)
+            .map_err(py_err_se_err)?;
+
+        self.nested_serializer(value.py())
+            // FIXME(BoxyUwU): Don't unwrap this
+            .unwrap()
+            .bind(value.py())
+            .get()
+            .serializer
+            .serde_serialize(value, serializer, include, exclude, guard.state())
+    }
+
+    fn get_name(&self) -> &str {
+        &self.name
+    }
+}

src/validators/mod.rs

@@ -49,6 +49,7 @@ mod list;
 mod literal;
 mod model;
 mod model_fields;
+mod nested;
 mod none;
 mod nullable;
 mod set;
@@ -584,6 +585,7 @@ pub fn build_validator(
         definitions::DefinitionRefValidator,
         definitions::DefinitionsValidatorBuilder,
         complex::ComplexValidator,
+        nested::NestedValidator,
     )
 }
 
@@ -738,6 +740,8 @@ pub enum CombinedValidator {
     // input dependent
     JsonOrPython(json_or_python::JsonOrPython),
     Complex(complex::ComplexValidator),
+    // Schema for reusing an existing validator
+    Nested(nested::NestedValidator),
 }
 
 /// This trait must be implemented by all validators, it allows various validators to be accessed consistently,

src/validators/model.rs

@@ -77,7 +77,7 @@ impl BuildValidator for ModelValidator {
 
         let class: Bound<'_, PyType> = schema.get_as_req(intern!(py, "cls"))?;
         let sub_schema = schema.get_as_req(intern!(py, "schema"))?;
-        let validator = build_validator(&sub_schema, config.as_ref(), definitions)?;
+        let validator: CombinedValidator = build_validator(&sub_schema, config.as_ref(), definitions)?;
         let name = class.getattr(intern!(py, "__name__"))?.extract()?;
 
         Ok(Self {

src/validators/nested.rs

@@ -0,0 +1,115 @@
+use std::sync::OnceLock;
+
+use pyo3::{
+    intern,
+    types::{PyAnyMethods, PyDict, PyDictMethods, PyTuple, PyTupleMethods, PyType},
+    Bound, Py, PyAny, PyObject, PyResult, Python,
+};
+
+use crate::{
+    definitions::DefinitionsBuilder,
+    errors::{ErrorTypeDefaults, ValError, ValResult},
+    input::Input,
+    recursion_guard::RecursionGuard,
+};
+
+use super::{BuildValidator, CombinedValidator, SchemaValidator, ValidationState, Validator};
+
+#[derive(Debug)]
+pub struct NestedValidator {
+    cls: Py<PyType>,
+    name: String,
+    get_validator: Py<PyAny>,
+    validator: OnceLock<PyResult<Py<SchemaValidator>>>,
+}
+
+impl_py_gc_traverse!(NestedValidator {
+    cls,
+    get_validator,
+    validator
+});
+
+impl BuildValidator for NestedValidator {
+    const EXPECTED_TYPE: &'static str = "nested";
+
+    fn build(
+        schema: &Bound<'_, PyDict>,
+        _config: Option<&Bound<'_, PyDict>>,
+        _definitions: &mut DefinitionsBuilder<super::CombinedValidator>,
+    ) -> PyResult<super::CombinedValidator> {
+        let py = schema.py();
+
+        let get_validator = schema.get_item(intern!(py, "get_info"))?.unwrap().unbind();
+
+        let cls = schema
+            .get_item(intern!(py, "cls"))?
+            .unwrap()
+            .downcast::<PyType>()?
+            .clone();
+
+        let name = cls.getattr(intern!(py, "__name__"))?.extract()?;
+
+        Ok(CombinedValidator::Nested(NestedValidator {
+            cls: cls.clone().unbind(),
+            name,
+            get_validator: get_validator,
+            validator: OnceLock::new(),
+        }))
+    }
+}
+
+impl NestedValidator {
+    fn nested_validator<'py>(&self, py: Python<'py>) -> PyResult<&Py<SchemaValidator>> {
+        self.validator
+            .get_or_init(|| {
+                Ok(self
+                    .get_validator
+                    .bind(py)
+                    .call((), None)?
+                    .downcast::<PyTuple>()?
+                    .get_item(1)?
+                    .downcast::<SchemaValidator>()?
+                    .clone()
+                    .unbind())
+            })
+            .as_ref()
+            .map_err(|e| e.clone_ref(py))
+    }
+}
+
+impl Validator for NestedValidator {
+    fn validate<'py>(
+        &self,
+        py: Python<'py>,
+        input: &(impl Input<'py> + ?Sized),
+        state: &mut ValidationState<'_, 'py>,
+    ) -> ValResult<PyObject> {
+        let Some(id) = input.as_python().map(py_identity) else {
+            return self
+                .nested_validator(py)?
+                .bind(py)
+                .get()
+                .validator
+                .validate(py, input, state);
+        };
+
+        // Python objects can be cyclic, so need recursion guard
+        let Ok(mut guard) = RecursionGuard::new(state, id, self.cls.as_ptr() as usize) else {
+            return Err(ValError::new(ErrorTypeDefaults::RecursionLoop, input));
+        };
+
+        self.nested_validator(py)?
+            .bind(py)
+            .get()
+            .validator
+            .validate(py, input, guard.state())
+    }
+
+    fn get_name(&self) -> &str {
+        &self.name
+    }
+}
+
+fn py_identity(obj: &Bound<'_, PyAny>) -> usize {
+    obj.as_ptr() as usize
+}