Add to_raw_parts methods to *const, *mut, and NonNull

These are not named `into_` because they do not consume their receiver
since raw pointers are `Copy`.

Author: SimonSapin

library/core/src/ptr/const_ptr.rs

@@ -48,6 +48,17 @@ impl<T: ?Sized> *const T {
         self as _
     }
 
+    /// Decompose a (possibly wide) pointer into is address and metadata components.
+    ///
+    /// The pointer can be later reconstructed with [`from_raw_parts`].
+    #[cfg(not(bootstrap))]
+    #[unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[rustc_const_unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[inline]
+    pub const fn to_raw_parts(self) -> (*const (), <T as super::Pointee>::Metadata) {
+        (self.cast(), super::metadata(self))
+    }
+
     /// Returns `None` if the pointer is null, or else returns a shared reference to
     /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
     /// must be used instead.

library/core/src/ptr/metadata.rs

@@ -28,8 +28,9 @@ pub trait Pointee {
 pub trait Thin = Pointee<Metadata = ()>;
 
 /// Extract the metadata component of a pointer.
+#[rustc_const_unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
 #[inline]
-pub fn metadata<T: ?Sized>(ptr: *const T) -> <T as Pointee>::Metadata {
+pub const fn metadata<T: ?Sized>(ptr: *const T) -> <T as Pointee>::Metadata {
     // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
     // and PtrComponents<T> have the same memory layouts. Only std can make this
     // guarantee.

library/core/src/ptr/mut_ptr.rs

@@ -47,6 +47,17 @@ impl<T: ?Sized> *mut T {
         self as _
     }
 
+    /// Decompose a (possibly wide) pointer into is address and metadata components.
+    ///
+    /// The pointer can be later reconstructed with [`from_raw_parts_mut`].
+    #[cfg(not(bootstrap))]
+    #[unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[rustc_const_unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[inline]
+    pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
+        (self.cast(), super::metadata(self))
+    }
+
     /// Returns `None` if the pointer is null, or else returns a shared reference to
     /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
     /// must be used instead.

library/core/src/ptr/non_null.rs

@@ -193,6 +193,17 @@ impl<T: ?Sized> NonNull<T> {
         }
     }
 
+    /// Decompose a (possibly wide) pointer into is address and metadata components.
+    ///
+    /// The pointer can be later reconstructed with [`NonNull::from_raw_parts`].
+    #[cfg(not(bootstrap))]
+    #[unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[rustc_const_unstable(feature = "ptr_metadata", issue = /* FIXME */ "none")]
+    #[inline]
+    pub const fn to_raw_parts(self) -> (NonNull<()>, <T as super::Pointee>::Metadata) {
+        (self.cast(), super::metadata(self.as_ptr()))
+    }
+
     /// Acquires the underlying `*mut` pointer.
     #[stable(feature = "nonnull", since = "1.25.0")]
     #[rustc_const_stable(feature = "const_nonnull_as_ptr", since = "1.32.0")]