Stabilize alloc_layout_extra

GrigorenkoPV · GrigorenkoPV · commit d45e7f6d37a3 · 2025-12-19T16:54:36.000+03:00
diff --git a/compiler/rustc_codegen_cranelift/patches/0027-sysroot_tests-128bit-atomic-operations.patch b/compiler/rustc_codegen_cranelift/patches/0027-sysroot_tests-128bit-atomic-operations.patch
@@ -14,11 +14,10 @@ diff --git a/coretests/tests/lib.rs b/coretests/tests/lib.rs
 index 1e336bf..35e6f54 100644
 --- a/coretests/tests/lib.rs
 +++ b/coretests/tests/lib.rs
-@@ -2,5 +2,4 @@
+@@ -2,4 +2,3 @@
  // tidy-alphabetical-start
 -#![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
  #![cfg_attr(test, feature(cfg_select))]
- #![feature(alloc_layout_extra)]
  #![feature(array_ptr_get)]
 diff --git a/coretests/tests/atomic.rs b/coretests/tests/atomic.rs
 index b735957..ea728b6 100644
diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
@@ -184,7 +184,7 @@ impl Global {
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
-            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling_ptr(), 0)),
             // SAFETY: `layout` is non-zero in size,
             size => unsafe {
                 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
@@ -314,7 +314,7 @@ unsafe impl Allocator for Global {
             // SAFETY: conditions must be upheld by the caller
             0 => unsafe {
                 self.deallocate(ptr, old_layout);
-                Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
+                Ok(NonNull::slice_from_raw_parts(new_layout.dangling_ptr(), 0))
             },
 
             // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
@@ -834,7 +834,7 @@ impl<T: ?Sized + CloneToUninit, A: Allocator> Box<T, A> {
         }
         let layout = Layout::for_value::<T>(src);
         let (ptr, guard) = if layout.size() == 0 {
-            (layout.dangling(), None)
+            (layout.dangling_ptr(), None)
         } else {
             // Safety: layout is non-zero-sized
             let ptr = alloc.allocate(layout)?.cast();
diff --git a/library/alloc/src/boxed/thin.rs b/library/alloc/src/boxed/thin.rs
@@ -245,7 +245,7 @@ impl<H> WithHeader<H> {
                 // Some paranoia checking, mostly so that the ThinBox tests are
                 // more able to catch issues.
                 debug_assert!(value_offset == 0 && T::IS_ZST && H::IS_ZST);
-                layout.dangling()
+                layout.dangling_ptr()
             } else {
                 let ptr = alloc::alloc(layout);
                 if ptr.is_null() {
@@ -282,7 +282,7 @@ impl<H> WithHeader<H> {
                 // Some paranoia checking, mostly so that the ThinBox tests are
                 // more able to catch issues.
                 debug_assert!(value_offset == 0 && size_of::<T>() == 0 && size_of::<H>() == 0);
-                layout.dangling()
+                layout.dangling_ptr()
             } else {
                 let ptr = alloc::alloc(layout);
                 if ptr.is_null() {
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
@@ -86,7 +86,6 @@
 // Library features:
 // tidy-alphabetical-start
 #![cfg_attr(not(no_global_oom_handling), feature(string_replace_in_place))]
-#![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(array_into_iter_constructors)]
 #![feature(ascii_char)]
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
@@ -261,7 +261,7 @@ use core::panic::{RefUnwindSafe, UnwindSafe};
 #[cfg(not(no_global_oom_handling))]
 use core::pin::Pin;
 use core::pin::PinCoerceUnsized;
-use core::ptr::{self, NonNull, drop_in_place};
+use core::ptr::{self, Alignment, NonNull, drop_in_place};
 #[cfg(not(no_global_oom_handling))]
 use core::slice::from_raw_parts_mut;
 use core::{borrow, fmt, hint};
@@ -3847,11 +3847,11 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> usize {
     // and extern types, the input safety requirement is currently enough to
     // satisfy the requirements of align_of_val_raw; this is an implementation
     // detail of the language that must not be relied upon outside of std.
-    unsafe { data_offset_align(align_of_val_raw(ptr)) }
+    unsafe { data_offset_align(Alignment::new_unchecked(align_of_val_raw(ptr))) }
 }
 
 #[inline]
-fn data_offset_align(align: usize) -> usize {
+fn data_offset_align(align: Alignment) -> usize {
     let layout = Layout::new::<RcInner<()>>();
     layout.size() + layout.padding_needed_for(align)
 }
@@ -4478,7 +4478,7 @@ impl<T: ?Sized, A: Allocator> UniqueRcUninit<T, A> {
 
     /// Returns the pointer to be written into to initialize the [`Rc`].
     fn data_ptr(&mut self) -> *mut T {
-        let offset = data_offset_align(self.layout_for_value.align());
+        let offset = data_offset_align(self.layout_for_value.alignment());
         unsafe { self.ptr.as_ptr().byte_add(offset) as *mut T }
     }
 
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
@@ -26,7 +26,7 @@ use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Lega
 use core::ops::{Residual, Try};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 use core::pin::{Pin, PinCoerceUnsized};
-use core::ptr::{self, NonNull};
+use core::ptr::{self, Alignment, NonNull};
 #[cfg(not(no_global_oom_handling))]
 use core::slice::from_raw_parts_mut;
 use core::sync::atomic::Ordering::{Acquire, Relaxed, Release};
@@ -4208,11 +4208,11 @@ unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> usize {
     // and extern types, the input safety requirement is currently enough to
     // satisfy the requirements of align_of_val_raw; this is an implementation
     // detail of the language that must not be relied upon outside of std.
-    unsafe { data_offset_align(align_of_val_raw(ptr)) }
+    unsafe { data_offset_align(Alignment::new_unchecked(align_of_val_raw(ptr))) }
 }
 
 #[inline]
-fn data_offset_align(align: usize) -> usize {
+fn data_offset_align(align: Alignment) -> usize {
     let layout = Layout::new::<ArcInner<()>>();
     layout.size() + layout.padding_needed_for(align)
 }
@@ -4258,7 +4258,7 @@ impl<T: ?Sized, A: Allocator> UniqueArcUninit<T, A> {
 
     /// Returns the pointer to be written into to initialize the [`Arc`].
     fn data_ptr(&mut self) -> *mut T {
-        let offset = data_offset_align(self.layout_for_value.align());
+        let offset = data_offset_align(self.layout_for_value.alignment());
         unsafe { self.ptr.as_ptr().byte_add(offset) as *mut T }
     }
 
diff --git a/library/alloctests/lib.rs b/library/alloctests/lib.rs
@@ -14,7 +14,6 @@
 //
 // Library features:
 // tidy-alphabetical-start
-#![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(array_into_iter_constructors)]
 #![feature(assert_matches)]
diff --git a/library/alloctests/tests/boxed.rs b/library/alloctests/tests/boxed.rs
@@ -104,7 +104,7 @@ pub struct ConstAllocator;
 unsafe impl Allocator for ConstAllocator {
     fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
-            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling_ptr(), 0)),
             _ => unsafe {
                 let ptr = core::intrinsics::const_allocate(layout.size(), layout.align());
                 Ok(NonNull::new_unchecked(ptr as *mut [u8; 0] as *mut [u8]))
diff --git a/library/alloctests/tests/lib.rs b/library/alloctests/tests/lib.rs
@@ -1,5 +1,4 @@
 #![feature(allocator_api)]
-#![feature(alloc_layout_extra)]
 #![feature(iter_array_chunks)]
 #![feature(assert_matches)]
 #![feature(wtf8_internals)]
diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
@@ -217,10 +217,11 @@ impl Layout {
     /// be that of a valid pointer, which means this must not be used
     /// as a "not yet initialized" sentinel value.
     /// Types that lazily allocate must track initialization by some other means.
-    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
+    #[stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
     #[must_use]
     #[inline]
-    pub const fn dangling(&self) -> NonNull<u8> {
+    pub const fn dangling_ptr(&self) -> NonNull<u8> {
         NonNull::without_provenance(self.align.as_nonzero())
     }
 
@@ -250,29 +251,23 @@ impl Layout {
     }
 
     /// Returns the amount of padding we must insert after `self`
-    /// to ensure that the following address will satisfy `align`
-    /// (measured in bytes).
+    /// to ensure that the following address will satisfy `alignment`.
     ///
-    /// e.g., if `self.size()` is 9, then `self.padding_needed_for(4)`
+    /// e.g., if `self.size()` is 9, then `self.padding_needed_for(alignment4)`
+    /// (where `alignment4.as_usize() == 4`)
     /// returns 3, because that is the minimum number of bytes of
     /// padding required to get a 4-aligned address (assuming that the
     /// corresponding memory block starts at a 4-aligned address).
     ///
-    /// The return value of this function has no meaning if `align` is
-    /// not a power-of-two.
-    ///
-    /// Note that the utility of the returned value requires `align`
+    /// Note that the utility of the returned value requires `alignment`
     /// to be less than or equal to the alignment of the starting
     /// address for the whole allocated block of memory. One way to
-    /// satisfy this constraint is to ensure `align <= self.align()`.
-    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
-    #[must_use = "this returns the padding needed, \
-                  without modifying the `Layout`"]
+    /// satisfy this constraint is to ensure `alignment.as_usize() <= self.align()`.
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[must_use = "this returns the padding needed, without modifying the `Layout`"]
     #[inline]
-    pub const fn padding_needed_for(&self, align: usize) -> usize {
-        // FIXME: Can we just change the type on this to `Alignment`?
-        let Some(align) = Alignment::new(align) else { return usize::MAX };
-        let len_rounded_up = self.size_rounded_up_to_custom_align(align);
+    pub const fn padding_needed_for(&self, alignment: Alignment) -> usize {
+        let len_rounded_up = self.size_rounded_up_to_custom_align(alignment);
         // SAFETY: Cannot overflow because the rounded-up value is never less
         unsafe { unchecked_sub(len_rounded_up, self.size) }
     }
@@ -335,14 +330,15 @@ impl Layout {
     /// layout of the array and `offs` is the distance between the start
     /// of each element in the array.
     ///
+    /// Does not include padding after the trailing element.
+    ///
     /// (That distance between elements is sometimes known as "stride".)
     ///
     /// On arithmetic overflow, returns `LayoutError`.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(alloc_layout_extra)]
     /// use std::alloc::Layout;
     ///
     /// // All rust types have a size that's a multiple of their alignment.
@@ -353,17 +349,32 @@ impl Layout {
     /// // But you can manually make layouts which don't meet that rule.
     /// let padding_needed = Layout::from_size_align(6, 4).unwrap();
     /// let repeated = padding_needed.repeat(3).unwrap();
-    /// assert_eq!(repeated, (Layout::from_size_align(24, 4).unwrap(), 8));
+    /// assert_eq!(repeated, (Layout::from_size_align(22, 4).unwrap(), 8));
+    ///
+    /// // Repeating an element zero times has zero size, but keeps the alignment (like `[T; 0]`)
+    /// let repeated = normal.repeat(0).unwrap();
+    /// assert_eq!(repeated, (Layout::from_size_align(0, 4).unwrap(), 12));
+    /// let repeated = padding_needed.repeat(0).unwrap();
+    /// assert_eq!(repeated, (Layout::from_size_align(0, 4).unwrap(), 8));
     /// ```
-    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
+    #[stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn repeat(&self, n: usize) -> Result<(Self, usize), LayoutError> {
+        // FIXME(const-hack): the following could be way shorter with `?`
         let padded = self.pad_to_align();
-        if let Ok(repeated) = padded.repeat_packed(n) {
-            Ok((repeated, padded.size()))
+        let Ok(result) = (if let Some(k) = n.checked_sub(1) {
+            let Ok(repeated) = padded.repeat_packed(k) else {
+                return Err(LayoutError);
+            };
+            repeated.extend_packed(*self)
         } else {
-            Err(LayoutError)
-        }
+            debug_assert!(n == 0);
+            self.repeat_packed(0)
+        }) else {
+            return Err(LayoutError);
+        };
+        Ok((result, padded.size()))
     }
 
     /// Creates a layout describing the record for `self` followed by
@@ -443,7 +454,8 @@ impl Layout {
     /// aligned.
     ///
     /// On arithmetic overflow, returns `LayoutError`.
-    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
+    #[stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn repeat_packed(&self, n: usize) -> Result<Self, LayoutError> {
         if let Some(size) = self.size.checked_mul(n) {
@@ -460,7 +472,8 @@ impl Layout {
     /// and is not incorporated *at all* into the resulting layout.
     ///
     /// On arithmetic overflow, returns `LayoutError`.
-    #[unstable(feature = "alloc_layout_extra", issue = "55724")]
+    #[stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "alloc_layout_extra", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     pub const fn extend_packed(&self, next: Self) -> Result<Self, LayoutError> {
         // SAFETY: each `size` is at most `isize::MAX == usize::MAX/2`, so the
diff --git a/library/coretests/tests/alloc.rs b/library/coretests/tests/alloc.rs
@@ -6,7 +6,7 @@ fn const_unchecked_layout() {
     const SIZE: usize = 0x2000;
     const ALIGN: usize = 0x1000;
     const LAYOUT: Layout = unsafe { Layout::from_size_align_unchecked(SIZE, ALIGN) };
-    const DANGLING: NonNull<u8> = LAYOUT.dangling();
+    const DANGLING: NonNull<u8> = LAYOUT.dangling_ptr();
     assert_eq!(LAYOUT.size(), SIZE);
     assert_eq!(LAYOUT.align(), ALIGN);
     assert_eq!(Some(DANGLING), NonNull::new(ptr::without_provenance_mut(ALIGN)));
diff --git a/library/coretests/tests/lib.rs b/library/coretests/tests/lib.rs
@@ -1,7 +1,6 @@
 // tidy-alphabetical-start
 #![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
 #![cfg_attr(test, feature(cfg_select))]
-#![feature(alloc_layout_extra)]
 #![feature(array_ptr_get)]
 #![feature(array_try_from_fn)]
 #![feature(array_try_map)]
diff --git a/library/std/src/alloc.rs b/library/std/src/alloc.rs
@@ -142,7 +142,7 @@ impl System {
     #[inline]
     fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
-            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling_ptr(), 0)),
             // SAFETY: `layout` is non-zero in size,
             size => unsafe {
                 let raw_ptr = if zeroed {
@@ -266,7 +266,7 @@ unsafe impl Allocator for System {
             // SAFETY: conditions must be upheld by the caller
             0 => unsafe {
                 Allocator::deallocate(self, ptr, old_layout);
-                Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
+                Ok(NonNull::slice_from_raw_parts(new_layout.dangling_ptr(), 0))
             },
 
             // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
@@ -367,7 +367,6 @@
 //
 // Library features (alloc):
 // tidy-alphabetical-start
-#![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(clone_from_ref)]
 #![feature(get_mut_unchecked)]

Original file line number	Diff line number	Diff line change
`@@ -834,7 +834,7 @@ impl<T: ?Sized + CloneToUninit, A: Allocator> Box<T, A> {`
`834`	`834`	`}`
`835`	`835`	`let layout = Layout::for_value::<T>(src);`
`836`	`836`	`let (ptr, guard) = if layout.size() == 0 {`
`837`		`- (layout.dangling(), None)`
	`837`	`+ (layout.dangling_ptr(), None)`
`838`	`838`	`} else {`
`839`	`839`	`// Safety: layout is non-zero-sized`
`840`	`840`	`let ptr = alloc.allocate(layout)?.cast();`
Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,4 @@`
`1`	`1`	`#![feature(allocator_api)]`
`2`		`-#![feature(alloc_layout_extra)]`
`3`	`2`	`#![feature(iter_array_chunks)]`
`4`	`3`	`#![feature(assert_matches)]`
`5`	`4`	`#![feature(wtf8_internals)]`