Rollup merge of rust-lang#130164 - RalfJung:const_ptr_as_ref, r=dtolnay

move some const fn out of the const_ptr_as_ref feature

When a `const fn` is still `#[unstable]`, it should generally use the same feature to track its regular stability and const-stability. Then when that feature moves towards stabilization we can decide whether the const-ness can be stabilized as well, or whether it should be moved into a new feature.

Also, functions like `ptr::as_ref` (which returns an `Option<&mut T>`) require `is_null`, which is tricky and blocked on some design concerns (see rust-lang#74939). So move those to the is_null feature gate, as they should be stabilized together with `ptr.is_null()`.

Affects rust-lang#91822, rust-lang#122034, rust-lang#75402, rust-lang#74939

core/src/ptr/const_ptr.rs

@@ -270,7 +270,7 @@ impl<T: ?Sized> *const T {
     /// }
     /// ```
     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
     #[inline]
     pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
         // SAFETY: the caller must guarantee that `self` is valid
@@ -302,7 +302,7 @@ impl<T: ?Sized> *const T {
     /// ```
     // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized.
     #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
     #[inline]
     #[must_use]
     pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T {
@@ -336,7 +336,7 @@ impl<T: ?Sized> *const T {
     /// ```
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
     where
         T: Sized,
@@ -1664,7 +1664,7 @@ impl<T> *const [T] {
     /// [allocated object]: crate::ptr#allocated-object
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
         if self.is_null() {
             None

core/src/ptr/mut_ptr.rs

@@ -261,7 +261,7 @@ impl<T: ?Sized> *mut T {
     /// }
     /// ```
     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
     #[inline]
     pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
         // SAFETY: the caller must guarantee that `self` is valid for a
@@ -295,7 +295,7 @@ impl<T: ?Sized> *mut T {
     /// ```
     // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized.
     #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
     #[inline]
     #[must_use]
     pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T {
@@ -334,7 +334,7 @@ impl<T: ?Sized> *mut T {
     /// ```
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
     where
         T: Sized,
@@ -580,7 +580,7 @@ impl<T: ?Sized> *mut T {
     /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
     /// ```
     #[stable(feature = "ptr_as_ref", since = "1.9.0")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
     #[inline]
     pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
         // SAFETY: the caller must guarantee that `self` is be valid for
@@ -616,7 +616,7 @@ impl<T: ?Sized> *mut T {
     /// ```
     // FIXME: mention it in the docs for `as_mut` and `as_uninit_mut` once stabilized.
     #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
     #[inline]
     #[must_use]
     pub const unsafe fn as_mut_unchecked<'a>(self) -> &'a mut T {
@@ -639,7 +639,7 @@ impl<T: ?Sized> *mut T {
     /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
     where
         T: Sized,
@@ -2016,7 +2016,7 @@ impl<T> *mut [T] {
     /// [allocated object]: crate::ptr#allocated-object
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
         if self.is_null() {
             None
@@ -2068,7 +2068,7 @@ impl<T> *mut [T] {
     /// [allocated object]: crate::ptr#allocated-object
     #[inline]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
         if self.is_null() {
             None

core/src/ptr/non_null.rs

@@ -133,7 +133,7 @@ impl<T: Sized> NonNull<T> {
     #[inline]
     #[must_use]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_ref<'a>(self) -> &'a MaybeUninit<T> {
         // SAFETY: the caller must guarantee that `self` meets all the
         // requirements for a reference.
@@ -157,7 +157,7 @@ impl<T: Sized> NonNull<T> {
     #[inline]
     #[must_use]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_mut<'a>(self) -> &'a mut MaybeUninit<T> {
         // SAFETY: the caller must guarantee that `self` meets all the
         // requirements for a reference.
@@ -1563,7 +1563,7 @@ impl<T> NonNull<[T]> {
     #[inline]
     #[must_use]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_slice<'a>(self) -> &'a [MaybeUninit<T>] {
         // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
         unsafe { slice::from_raw_parts(self.cast().as_ptr(), self.len()) }
@@ -1628,7 +1628,7 @@ impl<T> NonNull<[T]> {
     #[inline]
     #[must_use]
     #[unstable(feature = "ptr_as_uninit", issue = "75402")]
-    #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
+    #[rustc_const_unstable(feature = "ptr_as_uninit", issue = "75402")]
     pub const unsafe fn as_uninit_slice_mut<'a>(self) -> &'a mut [MaybeUninit<T>] {
         // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
         unsafe { slice::from_raw_parts_mut(self.cast().as_ptr(), self.len()) }