Make IntoPyObject for Bound & Borrowed more generic

Author: bschoenmaeckers

newsfragments/5831.added.md

@@ -0,0 +1 @@
+Add `Borrowed::as_bound`

newsfragments/5831.changed.md

@@ -0,0 +1 @@
+Make `IntoPyObject` for `Bound` & `Borrowed` more generic

src/conversion.rs

@@ -127,16 +127,16 @@ pub(crate) mod private {
     }
 }
 
-impl<'py, T: PyTypeCheck> IntoPyObject<'py> for Bound<'py, T> {
+impl<'py, T: PyTypeCheck> IntoPyObject<'py> for Bound<'_, T> {
     type Target = T;
     type Output = Bound<'py, Self::Target>;
     type Error = Infallible;
 
     #[cfg(feature = "experimental-inspect")]
     const OUTPUT_TYPE: PyStaticExpr = T::TYPE_HINT;
 
-    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
-        Ok(self)
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        Ok(self.unbind().into_bound(py))
     }
 }
 
@@ -148,8 +148,8 @@ impl<'a, 'py, T: PyTypeCheck> IntoPyObject<'py> for &'a Bound<'py, T> {
     #[cfg(feature = "experimental-inspect")]
     const OUTPUT_TYPE: PyStaticExpr = T::TYPE_HINT;
 
-    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
-        Ok(self.as_borrowed())
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        Ok(self.as_unbound().bind_borrowed(py))
     }
 }
 
@@ -161,8 +161,8 @@ impl<'a, 'py, T: PyTypeCheck> IntoPyObject<'py> for Borrowed<'a, 'py, T> {
     #[cfg(feature = "experimental-inspect")]
     const OUTPUT_TYPE: PyStaticExpr = T::TYPE_HINT;
 
-    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
-        Ok(self)
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        Ok(self.as_unbound().bind_borrowed(py))
     }
 }
 
@@ -174,8 +174,8 @@ impl<'a, 'py, T: PyTypeCheck> IntoPyObject<'py> for &Borrowed<'a, 'py, T> {
     #[cfg(feature = "experimental-inspect")]
     const OUTPUT_TYPE: PyStaticExpr = T::TYPE_HINT;
 
-    fn into_pyobject(self, _py: Python<'py>) -> Result<Self::Output, Self::Error> {
-        Ok(*self)
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        Ok(self.as_unbound().bind_borrowed(py))
     }
 }
 

src/instance.rs

@@ -1075,6 +1075,14 @@ impl<'a, 'py, T> Borrowed<'a, 'py, T> {
     pub unsafe fn cast_unchecked<U>(self) -> Borrowed<'a, 'py, U> {
         Borrowed(self.0, PhantomData, self.2)
     }
+
+    /// Removes the connection for this `Borrowed<T>` from the [`Python<'py>`] token,
+    /// allowing it to cross thread boundaries, without transferring ownership.
+    #[inline]
+    pub fn as_unbound(&self) -> &'a Py<T> {
+        // Safety: NonNull<ffi::PyObject> is layout-compatible with Py<T>
+        unsafe { NonNull::from(&self.0).cast().as_ref() }
+    }
 }
 
 impl<'a, T: PyClass> Borrowed<'a, '_, T> {