limit 'py: 'a on Borrowed

Author: davidhewitt

pyo3-macros-backend/src/method.rs

@@ -125,15 +125,9 @@ impl FnType {
             FnType::FnClass(span) | FnType::FnNewClass(span) => {
                 let py = syn::Ident::new("py", Span::call_site());
                 let slf: Ident = syn::Ident::new("_slf", Span::call_site());
-                let allow_deprecated = if cfg!(feature = "gil-refs") {
-                    quote!()
-                } else {
-                    quote!(#[allow(deprecated)])
-                };
                 quote_spanned! { *span =>
                     #[allow(clippy::useless_conversion)]
-                    #allow_deprecated
-                    ::std::convert::Into::into(_pyo3::types::PyType::from_type_ptr(#py, #slf.cast())),
+                    ::std::convert::Into::into(_pyo3::types::PyType::from_type_ptr_borrowed(#py, #slf.cast())),
                 }
             }
             FnType::FnModule(span) => {

src/instance.rs

@@ -256,7 +256,9 @@ unsafe impl<T> AsPyPointer for Bound<'_, T> {
 ///
 /// Similarly, this type is `Copy` and `Clone`, like a shared reference (`&T`).
 #[repr(transparent)]
-pub struct Borrowed<'a, 'py, T>(NonNull<ffi::PyObject>, PhantomData<&'a Py<T>>, Python<'py>);
+pub struct Borrowed<'a, 'py, T>(NonNull<ffi::PyObject>, PhantomData<&'a Py<T>>, Python<'py>)
+where
+    'py: 'a;
 
 impl<'py, T> Borrowed<'_, 'py, T> {
     /// Creates a new owned `Bound` from this borrowed reference by increasing the reference count.
@@ -1318,6 +1320,21 @@ where
     }
 }
 
+impl<'py, T> std::convert::From<Borrowed<'py, 'py, T>> for &'py T::AsRefTarget
+where
+    T: HasPyGilRef,
+{
+    fn from(borrowed: Borrowed<'py, 'py, T>) -> Self {
+        borrowed.into_gil_ref()
+    }
+}
+
+impl<'py, T> std::convert::From<Borrowed<'py, 'py, T>> for Py<T> {
+    fn from(borrowed: Borrowed<'py, 'py, T>) -> Self {
+        borrowed.to_owned().unbind()
+    }
+}
+
 impl<T> std::convert::From<Py<T>> for PyObject
 where
     T: AsRef<PyAny>,

src/types/bytes.rs

@@ -129,7 +129,8 @@ impl Py<PyBytes> {
     /// 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] {
-        self.bind_borrowed(py).as_bytes()
+        // Safety: lifetime of the borrow can extend beyond py.
+        unsafe { std::mem::transmute(self.bind_borrowed(py).as_bytes()) }
     }
 }
 

src/types/string.rs

@@ -407,7 +407,8 @@ impl Py<PyString> {
     /// the GIL lifetime.
     #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
     pub fn to_str<'a>(&'a self, py: Python<'_>) -> PyResult<&'a str> {
-        self.bind_borrowed(py).to_str()
+        // Safety: lifetime of the borrow can extend beyond py.
+        unsafe { std::mem::transmute(self.bind_borrowed(py).to_str()) }
     }
 
     /// Converts the `PyString` into a Rust string, avoiding copying when possible.
@@ -418,7 +419,8 @@ impl Py<PyString> {
     /// Because `str` objects are immutable, the returned slice is independent of
     /// the GIL lifetime.
     pub fn to_cow<'a>(&'a self, py: Python<'_>) -> PyResult<Cow<'a, str>> {
-        self.bind_borrowed(py).to_cow()
+        // Safety: lifetime of the borrow can extend beyond py.
+        unsafe { std::mem::transmute(self.bind_borrowed(py).to_cow()) }
     }
 
     /// Converts the `PyString` into a Rust string.
@@ -429,7 +431,8 @@ impl Py<PyString> {
     /// Because `str` objects are immutable, the returned slice is independent of
     /// the GIL lifetime.
     pub fn to_string_lossy<'a>(&'a self, py: Python<'_>) -> Cow<'a, str> {
-        self.bind_borrowed(py).to_string_lossy()
+        // Safety: lifetime of the borrow can extend beyond py.
+        unsafe { std::mem::transmute(self.bind_borrowed(py).to_string_lossy()) }
     }
 }
 

tests/ui/invalid_pymethods.stderr

@@ -179,11 +179,11 @@ error: macros cannot be used as items in `#[pymethods]` impl blocks
 197 |     macro_invocation!();
     |     ^^^^^^^^^^^^^^^^
 
-error[E0277]: the trait bound `i32: From<&PyType>` is not satisfied
+error[E0277]: the trait bound `i32: From<pyo3::Borrowed<'_, '_, PyType>>` is not satisfied
   --> tests/ui/invalid_pymethods.rs:46:45
    |
 46 |     fn classmethod_wrong_first_argument(_x: i32) -> Self {
-   |                                             ^^^ the trait `From<&PyType>` is not implemented for `i32`
+   |                                             ^^^ the trait `From<pyo3::Borrowed<'_, '_, PyType>>` is not implemented for `i32`
    |
    = help: the following other types implement trait `From<T>`:
              <i32 as From<bool>>
@@ -192,4 +192,4 @@ error[E0277]: the trait bound `i32: From<&PyType>` is not satisfied
              <i32 as From<u8>>
              <i32 as From<u16>>
              <i32 as From<NonZeroI32>>
-   = note: required for `&PyType` to implement `Into<i32>`
+   = note: required for `pyo3::Borrowed<'_, '_, PyType>` to implement `Into<i32>`

tests/ui/invalid_result_conversion.stderr

@@ -5,8 +5,8 @@ error[E0277]: the trait bound `PyErr: From<MyError>` is not satisfied
    | ^^^^^^^^^^^^^ the trait `From<MyError>` is not implemented for `PyErr`
    |
    = help: the following other types implement trait `From<T>`:
-             <PyErr as From<PyBorrowError>>
              <PyErr as From<std::io::Error>>
+             <PyErr as From<PyBorrowError>>
              <PyErr as From<PyBorrowMutError>>
              <PyErr as From<PyDowncastError<'a>>>
              <PyErr as From<DowncastError<'_, '_>>>