Add an Into<NonNull<T>> impl for Box<T>

Author: dwijnand

src/liballoc/boxed.rs

@@ -479,6 +479,15 @@ impl From<Box<str>> for Box<[u8]> {
     }
 }
 
+#[allow(incoherent_fundamental_impls)]
+#[unstable(feature = "box_into_raw_non_null", issue = "47336")]
+impl<T: ?Sized> Into<NonNull<T>> for Box<T> {
+    #[inline]
+    fn into(self) -> NonNull<T> {
+        Box::into_unique(self).into()
+    }
+}
+
 impl Box<dyn Any> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/boxed_test.rs

@@ -148,3 +148,11 @@ fn boxed_slice_from_iter() {
     assert_eq!(boxed.len(), 100);
     assert_eq!(boxed[7], 7);
 }
+
+#[test]
+fn to_nonnull() {
+    let boxed: Box<i32> = Box::from(0);
+    let ptr: std::ptr::NonNull<i32> = boxed.into();
+    let deref = unsafe { *ptr.as_ref() };
+    assert_eq!(deref, 0);
+}