Auto merge of #56998 - dwijnand:from-Arc/Rc-to-NonNull, r=<try>

Add Into<NonNull<T>> impls for Arc<T>/Rc<T>

/cc @withoutboats who mentioned to me this might be worth adding to the standard library, in withoutboats/smart#4
/cc @kennytm who last year didn't love the idea of having an Into<NonNull<T>> for Box<T>, in #46952

src/liballoc/boxed.rs

@@ -527,6 +527,15 @@ 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

@@ -138,3 +138,11 @@ 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);
+}

src/liballoc/rc.rs

@@ -1176,6 +1176,14 @@ impl<T> From<Vec<T>> for Rc<[T]> {
  }
 }
 
+#[unstable(feature = "rc_into_nonnull", reason = "newly added", issue = "0")]
+impl<T: ?Sized> Into<NonNull<T>> for Rc<T> {
+ #[inline]
+ fn into(self) -> NonNull<T> {
+ unsafe { NonNull::new_unchecked(Rc::into_raw(self) as *mut _) }
+ }
+}
+
 /// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
 /// managed value. The value is accessed by calling [`upgrade`] on the `Weak`
 /// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.

src/liballoc/sync.rs

@@ -1572,6 +1572,14 @@ impl<T> From<Vec<T>> for Arc<[T]> {
  }
 }
 
+#[unstable(feature = "arc_into_nonnull", reason = "newly added", issue = "0")]
+impl<T: ?Sized> Into<NonNull<T>> for Arc<T> {
+ #[inline]
+ fn into(self) -> NonNull<T> {
+ unsafe { NonNull::new_unchecked(Arc::into_raw(self) as *mut _) }
+ }
+}
+
 #[cfg(test)]
 mod tests {
  use std::boxed::Box;

src/liballoc/tests/arc.rs

@@ -85,3 +85,10 @@ fn eq() {
  assert!(!(x != x));
  assert_eq!(*x.0.borrow(), 0);
 }
+
+#[test]
+fn to_nonnull() {
+ let ptr: std::ptr::NonNull<i32> = Arc::new(0).into();
+ let deref = unsafe { *ptr.as_ref() };
+ assert_eq!(deref, 0);
+}

src/liballoc/tests/rc.rs

@@ -85,3 +85,10 @@ fn eq() {
  assert!(!(x != x));
  assert_eq!(*x.0.borrow(), 0);
 }
+
+#[test]
+fn to_nonnull() {
+ let ptr: std::ptr::NonNull<i32> = Rc::new(0).into();
+ let deref = unsafe { *ptr.as_ref() };
+ assert_eq!(deref, 0);
+}