Add 'from_ref' and 'from_mut' constructors to 'core::ptr::NonNull'; A…

…dd 'must_use' attribute to 'core::ptr::NonNull' constructors;

library/core/src/lib.rs

@@ -174,6 +174,7 @@
 #![feature(isqrt)]
 #![feature(lazy_get)]
 #![feature(link_cfg)]
+#![feature(non_null_from_ref)]
 #![feature(offset_of_enum)]
 #![feature(panic_internals)]
 #![feature(ptr_alignment_type)]

library/core/src/ptr/non_null.rs

@@ -191,6 +191,7 @@ impl<T: ?Sized> NonNull<T> {
     /// ```
     #[stable(feature = "nonnull", since = "1.25.0")]
     #[rustc_const_stable(feature = "const_nonnull_new_unchecked", since = "1.25.0")]
+    #[must_use]
     #[inline]
     pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
         // SAFETY: the caller must guarantee that `ptr` is non-null.
@@ -220,6 +221,7 @@ impl<T: ?Sized> NonNull<T> {
     /// ```
     #[stable(feature = "nonnull", since = "1.25.0")]
     #[rustc_const_unstable(feature = "const_nonnull_new", issue = "93235")]
+    #[must_use]
     #[inline]
     pub const fn new(ptr: *mut T) -> Option<Self> {
         if !ptr.is_null() {
@@ -230,6 +232,26 @@ impl<T: ?Sized> NonNull<T> {
         }
     }
 
+    /// Converts a reference to a `NonNull` pointer.
+    #[unstable(feature = "non_null_from_ref", issue = "none")]
+    #[rustc_const_unstable(feature = "non_null_from_ref", issue = "none")]
+    #[must_use]
+    #[inline]
+    pub const fn from_ref(r: &T) -> Self {
+        // SAFETY: A reference cannot be null.
+        unsafe { NonNull { pointer: reference as *const T } }
+    }
+
+    /// Converts a mutable reference to a `NonNull` pointer.
+    #[unstable(feature = "non_null_from_ref", issue = "none")]
+    #[rustc_const_unstable(feature = "non_null_from_ref", issue = "none")]
+    #[must_use]
+    #[inline]
+    pub const fn from_mut(r: &mut T) -> Self {
+        // SAFETY: A mutable reference cannot be null.
+        unsafe { NonNull { pointer: reference 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 +1775,8 @@ 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 +1786,7 @@ 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)
     }
 }