fix memory leak in create_class (pydantic#58)

src/validators/model_class.rs

@@ -1,11 +1,11 @@
 use std::os::raw::c_int;
 use std::ptr::null_mut;
 
-use pyo3::conversion::{AsPyPointer, FromPyPointer};
+use pyo3::conversion::AsPyPointer;
 use pyo3::exceptions::PyTypeError;
 use pyo3::prelude::*;
 use pyo3::types::{PyDict, PyTuple, PyType};
-use pyo3::{ffi, intern, ToBorrowedObject};
+use pyo3::{ffi, intern};
 
 use crate::build_tools::{py_error, SchemaDict};
 use crate::errors::{as_internal, context, err_val_error, ErrorKind, InputValue, ValError, ValResult};
@@ -67,7 +67,7 @@ impl Validator for ModelClassValidator {
             )
         } else {
             let output = self.validator.validate(py, input, extra, slots)?;
-            unsafe { self.create_class(py, output).map_err(as_internal) }
+            self.create_class(py, output).map_err(as_internal)
         }
     }
 
@@ -99,51 +99,48 @@ impl Validator for ModelClassValidator {
 }
 
 impl ModelClassValidator {
-    unsafe fn create_class(&self, py: Python, output: PyObject) -> PyResult<PyObject> {
-        let t: &PyTuple = output.extract(py)?;
-        let model_dict = t.get_item(0)?;
-        let fields_set = t.get_item(1)?;
+    fn create_class(&self, py: Python, output: PyObject) -> PyResult<PyObject> {
+        let (model_dict, fields_set): (&PyAny, &PyAny) = output.extract(py)?;
 
         // based on the following but with the second argument of new_func set to an empty tuple as required
         // https://github.com/PyO3/pyo3/blob/d2caa056e9aacc46374139ef491d112cb8af1a25/src/pyclass_init.rs#L35-L77
         let args = PyTuple::empty(py);
         let raw_type = self.class.as_ref(py).as_type_ptr();
-        let instance_ptr = match (*raw_type).tp_new {
-            Some(new_func) => {
-                let obj = new_func(raw_type, args.as_ptr(), null_mut());
-                if obj.is_null() {
-                    return Err(PyErr::fetch(py));
-                } else {
-                    obj
-                }
+        let instance = unsafe {
+            // Safety: raw_type is known to be a non-null type object pointer
+            match (*raw_type).tp_new {
+                // Safety: the result of new_func is guaranteed to be either an owned pointer or null on error returns.
+                Some(new_func) => PyObject::from_owned_ptr_or_err(
+                    py,
+                    // Safety: the non-null pointers are known to be valid, and it's allowed to call tp_new with a
+                    // null kwargs dict.
+                    new_func(raw_type, args.as_ptr(), null_mut()),
+                )?,
+                None => return Err(PyTypeError::new_err("base type without tp_new")),
             }
-            None => return Err(PyTypeError::new_err("base type without tp_new")),
         };
 
-        force_setattr(instance_ptr, py, intern!(py, "__dict__"), model_dict)?;
-        force_setattr(instance_ptr, py, intern!(py, "__fields_set__"), fields_set)?;
+        let instance_ref = instance.as_ref(py);
+        force_setattr(py, instance_ref, intern!(py, "__dict__"), model_dict)?;
+        force_setattr(py, instance_ref, intern!(py, "__fields_set__"), fields_set)?;
 
-        match PyAny::from_borrowed_ptr_or_opt(py, instance_ptr) {
-            Some(instance) => Ok(instance.into()),
-            None => Err(PyTypeError::new_err("failed to create instance of class")),
-        }
+        Ok(instance)
     }
 }
 
-/// copied and modified from
-/// https://github.com/PyO3/pyo3/blob/d2caa056e9aacc46374139ef491d112cb8af1a25/src/instance.rs#L587-L597
-/// to use `PyObject_GenericSetAttr` thereby bypassing `__setattr__` methods on the instance,
-/// see https://github.com/PyO3/pyo3/discussions/2321 for discussion
-pub fn force_setattr<N, V>(obj: *mut ffi::PyObject, py: Python<'_>, attr_name: N, value: V) -> PyResult<()>
+pub fn force_setattr<N, V>(py: Python<'_>, obj: &PyAny, attr_name: N, value: V) -> PyResult<()>
 where
     N: ToPyObject,
     V: ToPyObject,
 {
-    attr_name.with_borrowed_ptr(py, move |attr_name| {
-        value.with_borrowed_ptr(py, |value| unsafe {
-            error_on_minusone(py, ffi::PyObject_GenericSetAttr(obj, attr_name, value))
-        })
-    })
+    let attr_name = attr_name.to_object(py);
+    let value = value.to_object(py);
+    unsafe {
+        error_on_minusone(
+            py,
+            ffi::PyObject_GenericSetAttr(obj.as_ptr(), attr_name.as_ptr(), value.as_ptr()),
+        )
+    }
 }
 
 // Defined here as it's not exported by pyo3