Add nightly-optimizations feature

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+## Added
+- Gate some optimizations needing specialization in a `nightly-optimizations` feature (disabled by default). [#927](https://github.com/PyO3/pyo3/pull/927)
 
 ## [0.10.0] - 2020-05-14
 ### Fixed

Cargo.toml

@@ -48,6 +48,10 @@ python3 = []
 # so that the module can also be used with statically linked python interpreters.
 extension-module = []
 
+# Use this feature to enable optimizations only possible on nightly Rust.
+# (Dependent on specialization.)
+nightly-optimizations = []
+
 # The stable cpython abi as defined in PEP 384. Currently broken with
 # many compilation errors. Pull Requests working towards fixing that
 # are welcome.

src/conversion.rs

@@ -104,6 +104,20 @@ impl<T> ToBorrowedObject for T
 where
     T: ToPyObject,
 {
+    #[cfg(not(nightly_optimizations))]
+    fn with_borrowed_ptr<F, R>(&self, py: Python, f: F) -> R
+    where
+        F: FnOnce(*mut ffi::PyObject) -> R,
+    {
+        let ptr = self.to_object(py).into_ptr();
+        let result = f(ptr);
+        unsafe {
+            ffi::Py_XDECREF(ptr);
+        }
+        result
+    }
+
+    #[cfg(nightly_optimizations)]
     default fn with_borrowed_ptr<F, R>(&self, py: Python, f: F) -> R
     where
         F: FnOnce(*mut ffi::PyObject) -> R,
@@ -117,6 +131,7 @@ where
     }
 }
 
+#[cfg(nightly_optimizations)]
 impl<T> ToBorrowedObject for T
 where
     T: ToPyObject + AsPyPointer,

src/types/sequence.rs

@@ -1,5 +1,6 @@
 // Copyright (c) 2017-present PyO3 Project and Contributors
 
+#[cfg(nightly_optimizations)]
 use crate::buffer;
 use crate::err::{self, PyDowncastError, PyErr, PyResult};
 use crate::exceptions;
@@ -265,13 +266,22 @@ macro_rules! array_impls {
             where
                 T: Copy + Default + FromPyObject<'a>,
             {
+                #[cfg(not(nightly_optimizations))]
+                fn extract(obj: &'a PyAny) -> PyResult<Self> {
+                    let mut array = [T::default(); $N];
+                    extract_sequence_into_slice(obj, &mut array)?;
+                    Ok(array)
+                }
+
+                #[cfg(nightly_optimizations)]
                 default fn extract(obj: &'a PyAny) -> PyResult<Self> {
                     let mut array = [T::default(); $N];
                     extract_sequence_into_slice(obj, &mut array)?;
                     Ok(array)
                 }
             }
 
+            #[cfg(nightly_optimizations)]
             impl<'source, T> FromPyObject<'source> for [T; $N]
             where
                 for<'a> T: Copy + Default + FromPyObject<'a> + buffer::Element,
@@ -304,11 +314,18 @@ impl<'a, T> FromPyObject<'a> for Vec<T>
 where
     T: FromPyObject<'a>,
 {
+    #[cfg(not(nightly_optimizations))]
+    fn extract(obj: &'a PyAny) -> PyResult<Self> {
+        extract_sequence(obj)
+    }
+
+    #[cfg(nightly_optimizations)]
     default fn extract(obj: &'a PyAny) -> PyResult<Self> {
         extract_sequence(obj)
     }
 }
 
+#[cfg(nightly_optimizations)]
 impl<'source, T> FromPyObject<'source> for Vec<T>
 where
     for<'a> T: FromPyObject<'a> + buffer::Element + Copy,