Rollup merge of rust-lang#130822 - bjoernager:non-null-from-ref, r=dtolnay

Add `from_ref` and `from_mut` constructors to `core::ptr::NonNull`.

Relevant tracking issue: rust-lang#130823

The `core::ptr::NonNull` type should have the convenience constructors `from_ref` and `from_mut` for parity with `core::ptr::from_ref` and `core::ptr::from_mut`.

Although the type in question already implements `From<&T>` and `From<&mut T>`, these new functions also carry the ability to be used in constant expressions (due to not being behind a trait).

Author: matthiaskrgr

core/src/lib.rs

@@ -153,6 +153,7 @@
 #![feature(isqrt)]
 #![feature(lazy_get)]
 #![feature(link_cfg)]
+#![feature(non_null_from_ref)]
 #![feature(offset_of_enum)]
 #![feature(panic_internals)]
 #![feature(ptr_alignment_type)]

core/src/ptr/non_null.rs

@@ -230,6 +230,24 @@ impl<T: ?Sized> NonNull<T> {
         }
     }
 
+    /// Converts a reference to a `NonNull` pointer.
+    #[unstable(feature = "non_null_from_ref", issue = "130823")]
+    #[rustc_const_unstable(feature = "non_null_from_ref", issue = "130823")]
+    #[inline]
+    pub const fn from_ref(r: &T) -> Self {
+        // SAFETY: A reference cannot be null.
+        unsafe { NonNull { pointer: r as *const T } }
+    }
+
+    /// Converts a mutable reference to a `NonNull` pointer.
+    #[unstable(feature = "non_null_from_ref", issue = "130823")]
+    #[rustc_const_unstable(feature = "non_null_from_ref", issue = "130823")]
+    #[inline]
+    pub const fn from_mut(r: &mut T) -> Self {
+        // SAFETY: A mutable reference cannot be null.
+        unsafe { NonNull { pointer: r as *mut T } }
+    }
+
     /// Performs the same functionality as [`std::ptr::from_raw_parts`], except that a
     /// `NonNull` pointer is returned, as opposed to a raw `*const` pointer.
     ///
@@ -1753,9 +1771,8 @@ impl<T: ?Sized> From<&mut T> for NonNull<T> {
     ///
     /// This conversion is safe and infallible since references cannot be null.
     #[inline]
-    fn from(reference: &mut T) -> Self {
-        // SAFETY: A mutable reference cannot be null.
-        unsafe { NonNull { pointer: reference as *mut T } }
+    fn from(r: &mut T) -> Self {
+        NonNull::from_mut(r)
     }
 }
 
@@ -1765,8 +1782,7 @@ impl<T: ?Sized> From<&T> for NonNull<T> {
     ///
     /// This conversion is safe and infallible since references cannot be null.
     #[inline]
-    fn from(reference: &T) -> Self {
-        // SAFETY: A reference cannot be null.
-        unsafe { NonNull { pointer: reference as *const T } }
+    fn from(r: &T) -> Self {
+        NonNull::from_ref(r)
     }
 }