Add support for arbitrary arrays

build.rs

@@ -902,6 +902,27 @@ fn abi3_without_interpreter() -> Result<()> {
     Ok(())
 }
 
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = core::str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    pieces.next()?.parse().ok()
+}
+
+fn manage_min_const_generics() {
+    let rustc_minor_version = match rustc_minor_version() {
+        Some(inner) => inner,
+        None => return,
+    };
+    if rustc_minor_version >= 51 {
+        println!("cargo:rustc-cfg=min_const_generics");
+    }
+}
+
 fn main() -> Result<()> {
     // If PYO3_NO_PYTHON is set with abi3, we can build PyO3 without calling Python.
     // We only check for the abi3-py3{ABI3_MAX_MINOR} because lower versions depend on it.
@@ -961,5 +982,7 @@ fn main() -> Result<()> {
         println!("cargo:rustc-cfg=__pyo3_ci");
     }
 
+    manage_min_const_generics();
+
     Ok(())
 }

src/types/list.rs

@@ -178,6 +178,7 @@ where
     }
 }
 
+#[cfg(min_const_generics)]
 macro_rules! array_impls {
     ($($N:expr),+) => {
         $(
@@ -193,11 +194,22 @@ macro_rules! array_impls {
     }
 }
 
+#[cfg(min_const_generics)]
 array_impls!(
     0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
     26, 27, 28, 29, 30, 31, 32
 );
 
+#[cfg(not(min_const_generics))]
+impl<T, const N: usize> IntoPy<PyObject> for [T; N]
+where
+    T: ToPyObject,
+{
+    fn into_py(self, py: Python) -> PyObject {
+        self.as_ref().to_object(py)
+    }
+}
+
 impl<T> ToPyObject for Vec<T>
 where
     T: ToPyObject,

src/types/mod.rs

@@ -244,3 +244,40 @@ mod slice;
 mod string;
 mod tuple;
 mod typeobject;
+
+#[cfg(min_const_generics)]
+struct ArrayGuard<T, const N: usize> {
+    dst: *mut T,
+    initialized: usize,
+}
+
+#[cfg(min_const_generics)]
+impl<T, const N: usize> Drop for ArrayGuard<T, N> {
+    fn drop(&mut self) {
+        debug_assert!(self.initialized <= N);
+        let initialized_part = core::ptr::slice_from_raw_parts_mut(self.dst, self.initialized);
+        unsafe {
+            core::ptr::drop_in_place(initialized_part);
+        }
+    }
+}
+
+#[cfg(min_const_generics)]
+fn try_create_array<E, F, T, const N: usize>(mut cb: F) -> Result<[T; N], E>
+where
+    F: FnMut(usize) -> Result<T, E>,
+{
+    let mut array: core::mem::MaybeUninit<[T; N]> = core::mem::MaybeUninit::uninit();
+    let mut guard: ArrayGuard<T, N> = ArrayGuard {
+        dst: array.as_mut_ptr() as _,
+        initialized: 0,
+    };
+    unsafe {
+        for (idx, value_ptr) in (&mut *array.as_mut_ptr()).iter_mut().enumerate() {
+            core::ptr::write(value_ptr, cb(idx)?);
+            guard.initialized += 1;
+        }
+        core::mem::forget(guard);
+        Ok(array.assume_init())
+    }
+}

src/types/sequence.rs

@@ -257,6 +257,7 @@ impl PySequence {
     }
 }
 
+#[cfg(not(min_const_generics))]
 macro_rules! array_impls {
     ($($N:expr),+) => {
         $(
@@ -305,11 +306,46 @@ macro_rules! array_impls {
     }
 }
 
+#[cfg(not(min_const_generics))]
 array_impls!(
     0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
     26, 27, 28, 29, 30, 31, 32
 );
 
+#[cfg(all(min_const_generics, not(feature = "nightly")))]
+impl<'a, T, const N: usize> FromPyObject<'a> for [T; N]
+where
+    T: FromPyObject<'a>,
+{
+    #[cfg(not(feature = "nightly"))]
+    fn extract(obj: &'a PyAny) -> PyResult<Self> {
+        create_array_from_obj(obj)
+    }
+
+    #[cfg(feature = "nightly")]
+    default fn extract(obj: &'a PyAny) -> PyResult<Self> {
+        create_array_from_obj(obj)
+    }
+}
+
+#[cfg(all(min_const_generics, feature = "nightly"))]
+impl<'source, T, const N: usize> FromPyObject<'source> for [T; N]
+where
+    for<'a> T: FromPyObject<'a> + crate::buffer::Element,
+{
+    fn extract(obj: &'source PyAny) -> PyResult<Self> {
+        let mut array = create_array_from_obj(obj)?;
+        if let Ok(buf) = crate::buffer::PyBuffer::get(obj) {
+            if buf.dimensions() == 1 && buf.copy_to_slice(obj.py(), &mut array).is_ok() {
+                buf.release(obj.py());
+                return Ok(array);
+            }
+            buf.release(obj.py());
+        }
+        Ok(array)
+    }
+}
+
 impl<'a, T> FromPyObject<'a> for Vec<T>
 where
     T: FromPyObject<'a>,
@@ -345,6 +381,21 @@ where
     }
 }
 
+#[cfg(min_const_generics)]
+fn create_array_from_obj<'s, T, const N: usize>(obj: &'s PyAny) -> PyResult<[T; N]>
+where
+    T: FromPyObject<'s>,
+{
+    let seq = <PySequence as PyTryFrom>::try_from(obj)?;
+    crate::types::try_create_array(|idx| {
+        seq.get_item(idx as isize)
+            .map_err(|_| {
+                exceptions::PyBufferError::new_err("Slice length does not match buffer length.")
+            })?
+            .extract::<T>()
+    })
+}
+
 fn extract_sequence<'s, T>(obj: &'s PyAny) -> PyResult<Vec<T>>
 where
     T: FromPyObject<'s>,
@@ -357,6 +408,7 @@ where
     Ok(v)
 }
 
+#[cfg(not(min_const_generics))]
 fn extract_sequence_into_slice<'s, T>(obj: &'s PyAny, slice: &mut [T]) -> PyResult<()>
 where
     T: FromPyObject<'s>,
@@ -706,6 +758,7 @@ mod test {
         assert!(v == [1, 2, 3, 4]);
     }
 
+    #[cfg(not(min_const_generics))]
     #[test]
     fn test_extract_bytearray_to_array() {
         let gil = Python::acquire_gil();
@@ -718,6 +771,23 @@ mod test {
         assert!(&v == b"abc");
     }
 
+    #[cfg(min_const_generics)]
+    #[test]
+    fn test_extract_bytearray_to_array() {
+        let gil = Python::acquire_gil();
+        let py = gil.python();
+        let v: [u8; 33] = py
+            .eval(
+                "bytearray(b'abcabcabcabcabcabcabcabcabcabcabc')",
+                None,
+                None,
+            )
+            .unwrap()
+            .extract()
+            .unwrap();
+        assert!(&v == b"abcabcabcabcabcabcabcabcabcabcabc");
+    }
+
     #[test]
     fn test_extract_bytearray_to_vec() {
         let gil = Python::acquire_gil();