Use NonNull::without_provenance within the standard library

This API removes the need for several `unsafe` blocks, and leads to
clearer code.

alloc/src/lib.rs

@@ -126,6 +126,7 @@
 #![feature(local_waker)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array_transpose)]
+#![feature(nonnull_provenance)]
 #![feature(panic_internals)]
 #![feature(pattern)]
 #![feature(pin_coerce_unsized_trait)]

alloc/src/rc.rs

@@ -252,6 +252,7 @@ use core::intrinsics::abort;
 use core::iter;
 use core::marker::{PhantomData, Unsize};
 use core::mem::{self, ManuallyDrop, align_of_val_raw};
+use core::num::NonZeroUsize;
 use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, LegacyReceiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 #[cfg(not(no_global_oom_handling))]
@@ -3027,12 +3028,7 @@ impl<T> Weak<T> {
     #[rustc_const_stable(feature = "const_weak_new", since = "1.73.0")]
     #[must_use]
     pub const fn new() -> Weak<T> {
-        Weak {
-            ptr: unsafe {
-                NonNull::new_unchecked(ptr::without_provenance_mut::<RcInner<T>>(usize::MAX))
-            },
-            alloc: Global,
-        }
+        Weak { ptr: NonNull::without_provenance(NonZeroUsize::MAX), alloc: Global }
     }
 }
 
@@ -3054,12 +3050,7 @@ impl<T, A: Allocator> Weak<T, A> {
     #[inline]
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub fn new_in(alloc: A) -> Weak<T, A> {
-        Weak {
-            ptr: unsafe {
-                NonNull::new_unchecked(ptr::without_provenance_mut::<RcInner<T>>(usize::MAX))
-            },
-            alloc,
-        }
+        Weak { ptr: NonNull::without_provenance(NonZeroUsize::MAX), alloc }
     }
 }
 

alloc/src/sync.rs

@@ -18,6 +18,7 @@ use core::intrinsics::abort;
 use core::iter;
 use core::marker::{PhantomData, Unsize};
 use core::mem::{self, ManuallyDrop, align_of_val_raw};
+use core::num::NonZeroUsize;
 use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, LegacyReceiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 use core::pin::{Pin, PinCoerceUnsized};
@@ -2687,12 +2688,7 @@ impl<T> Weak<T> {
     #[rustc_const_stable(feature = "const_weak_new", since = "1.73.0")]
     #[must_use]
     pub const fn new() -> Weak<T> {
-        Weak {
-            ptr: unsafe {
-                NonNull::new_unchecked(ptr::without_provenance_mut::<ArcInner<T>>(usize::MAX))
-            },
-            alloc: Global,
-        }
+        Weak { ptr: NonNull::without_provenance(NonZeroUsize::MAX), alloc: Global }
     }
 }
 
@@ -2717,12 +2713,7 @@ impl<T, A: Allocator> Weak<T, A> {
     #[inline]
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub fn new_in(alloc: A) -> Weak<T, A> {
-        Weak {
-            ptr: unsafe {
-                NonNull::new_unchecked(ptr::without_provenance_mut::<ArcInner<T>>(usize::MAX))
-            },
-            alloc,
-        }
+        Weak { ptr: NonNull::without_provenance(NonZeroUsize::MAX), alloc }
     }
 }
 

core/src/alloc/layout.rs

@@ -233,8 +233,7 @@ impl Layout {
     #[must_use]
     #[inline]
     pub const fn dangling(&self) -> NonNull<u8> {
-        // SAFETY: align is guaranteed to be non-zero
-        unsafe { NonNull::new_unchecked(crate::ptr::without_provenance_mut::<u8>(self.align())) }
+        NonNull::without_provenance(self.align.as_nonzero())
     }
 
     /// Creates a layout describing the record that can hold a value

std/src/io/error/repr_bitpacked.rs

@@ -103,7 +103,8 @@
 //! the time.
 
 use core::marker::PhantomData;
-use core::ptr::{self, NonNull};
+use core::num::NonZeroUsize;
+use core::ptr::NonNull;
 
 use super::{Custom, ErrorData, ErrorKind, RawOsError, SimpleMessage};
 
@@ -176,7 +177,7 @@ impl Repr {
         let utagged = ((code as usize) << 32) | TAG_OS;
         // Safety: `TAG_OS` is not zero, so the result of the `|` is not 0.
         let res = Self(
-            unsafe { NonNull::new_unchecked(ptr::without_provenance_mut(utagged)) },
+            NonNull::without_provenance(unsafe { NonZeroUsize::new_unchecked(utagged) }),
             PhantomData,
         );
         // quickly smoke-check we encoded the right thing (This generally will
@@ -193,7 +194,7 @@ impl Repr {
         let utagged = ((kind as usize) << 32) | TAG_SIMPLE;
         // Safety: `TAG_SIMPLE` is not zero, so the result of the `|` is not 0.
         let res = Self(
-            unsafe { NonNull::new_unchecked(ptr::without_provenance_mut(utagged)) },
+            NonNull::without_provenance(unsafe { NonZeroUsize::new_unchecked(utagged) }),
             PhantomData,
         );
         // quickly smoke-check we encoded the right thing (This generally will

std/src/lib.rs

@@ -342,6 +342,7 @@
 #![feature(lazy_get)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_write_slice)]
+#![feature(nonnull_provenance)]
 #![feature(panic_can_unwind)]
 #![feature(panic_internals)]
 #![feature(pin_coerce_unsized_trait)]