adjust definition of Py2Borrowed to enable PyBytes implementation

Author: davidhewitt

src/instance.rs

@@ -230,7 +230,11 @@ unsafe impl<T> AsPyPointer for Py2<'_, T> {
 /// The advantage of this over `&Py2` is that it avoids the need to have a pointer-to-pointer, as Py2
 /// is already a pointer to a PyObject.
 #[repr(transparent)]
-pub(crate) struct Py2Borrowed<'a, 'py, T>(NonNull<ffi::PyObject>, PhantomData<&'a Py2<'py, T>>); // TODO is it useful to have the generic form?
+pub(crate) struct Py2Borrowed<'a, 'py, T>(
+    NonNull<ffi::PyObject>,
+    PhantomData<&'a Py<T>>,
+    Python<'py>,
+); // TODO is it useful to have the generic form?
 
 impl<'a, 'py> Py2Borrowed<'a, 'py, PyAny> {
     /// # Safety
@@ -241,18 +245,18 @@ impl<'a, 'py> Py2Borrowed<'a, 'py, PyAny> {
         py: Python<'py>,
         ptr: *mut ffi::PyObject,
     ) -> PyResult<Self> {
-        NonNull::new(ptr).map_or_else(|| Err(PyErr::fetch(py)), |ptr| Ok(Self(ptr, PhantomData)))
+        NonNull::new(ptr).map_or_else(
+            || Err(PyErr::fetch(py)),
+            |ptr| Ok(Self(ptr, PhantomData, py)),
+        )
     }
 
     /// # Safety
     /// This is similar to `std::slice::from_raw_parts`, the lifetime `'a` is completely defined by
     /// the caller and it's the caller's responsibility to ensure that the reference this is
     /// derived from is valid for the lifetime `'a`.
-    pub(crate) unsafe fn from_ptr_or_opt(
-        _py: Python<'py>,
-        ptr: *mut ffi::PyObject,
-    ) -> Option<Self> {
-        NonNull::new(ptr).map(|ptr| Self(ptr, PhantomData))
+    pub(crate) unsafe fn from_ptr_or_opt(py: Python<'py>, ptr: *mut ffi::PyObject) -> Option<Self> {
+        NonNull::new(ptr).map(|ptr| Self(ptr, PhantomData, py))
     }
 
     /// # Safety
@@ -263,6 +267,7 @@ impl<'a, 'py> Py2Borrowed<'a, 'py, PyAny> {
         Self(
             NonNull::new(ptr).unwrap_or_else(|| crate::err::panic_after_error(py)),
             PhantomData,
+            py,
         )
     }
 }
@@ -273,6 +278,7 @@ impl<'a, 'py, T> From<&'a Py2<'py, T>> for Py2Borrowed<'a, 'py, T> {
         Self(
             unsafe { NonNull::new_unchecked(instance.as_ptr()) },
             PhantomData,
+            instance.py(),
         )
     }
 }
@@ -852,6 +858,10 @@ impl<T> Py<T> {
         Py2(py, ManuallyDrop::new(self))
     }
 
+    pub(crate) fn attach_borrow<'a, 'py>(&'a self, py: Python<'py>) -> Py2Borrowed<'a, 'py, T> {
+        Py2Borrowed(self.0, PhantomData, py)
+    }
+
     /// Returns whether `self` and `other` point to the same object. To compare
     /// the equality of two objects (the `==` operator), use [`eq`](PyAny::eq).
     ///

src/types/bytes.rs

@@ -127,10 +127,8 @@ impl Py<PyBytes> {
     /// Gets the Python bytes as a byte slice. Because Python bytes are
     /// immutable, the result may be used for as long as the reference to
     /// `self` is held, including when the GIL is released.
-    pub fn as_bytes<'a>(&'a self, _py: Python<'_>) -> &'a [u8] {
-        // Safety: `Py2Borrowed` has the same layout as `Py`
-        let borrowed: Py2Borrowed<'a, '_, PyBytes> = unsafe { std::mem::transmute_copy(self) };
-        borrowed.as_bytes()
+    pub fn as_bytes<'a>(&'a self, py: Python<'_>) -> &'a [u8] {
+        self.attach_borrow(py).as_bytes()
     }
 }