Rollup merge of #132455 - RalfJung:const_alloc_layout, r=dtolnay

make const_alloc_layout feature gate only about functions that are already stable
The const_alloc_layout feature gate has two kinds of functions: those that are stable, but not yet const-stable, and those that are fully unstable.
I think we should split that up. So this PR makes const_alloc_layout just about functions that are already stable but waiting for const-stability; all the other functions now have their constness guarded by the gate that also guards their regular stability.
Cc #67521

Author: GuillaumeGomez

library/core/src/alloc/layout.rs

@@ -216,7 +216,7 @@ impl Layout {
 /// [trait object]: ../../book/ch17-02-trait-objects.html
 /// [extern type]: ../../unstable-book/language-features/extern-types.html
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
-#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
+#[rustc_const_unstable(feature = "layout_for_ptr", issue = "69835")]
 #[must_use]
 pubconstunsafefnfor_value_raw<T: ?Sized>(t:*constT) -> Self{
 // SAFETY: we pass along the prerequisites of these functions to the caller
@@ -232,7 +232,6 @@ impl Layout {
 /// sentinel value. Types that lazily allocate must track initialization by
 /// some other means.
 #[unstable(feature = "alloc_layout_extra", issue = "55724")]
-#[rustc_const_unstable(feature = "alloc_layout_extra", issue = "55724")]
 #[must_use]
 #[inline]
 pubconstfndangling(&self) -> NonNull<u8>{
@@ -256,6 +255,7 @@ impl Layout {
 /// `align` violates the conditions listed in [`Layout::from_size_align`].
 #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
+#[cfg_attr(not(bootstrap), rustc_const_stable_indirect)]
 #[inline]
 pubconstfnalign_to(&self,align:usize) -> Result<Self,LayoutError>{
 ifletSome(align) = Alignment::new(align){
@@ -282,7 +282,6 @@ impl Layout {
 /// 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")]
-#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
 #[must_use = "this returns the padding needed, \
  without modifying the `Layout`"]
 #[inline]
@@ -332,6 +331,7 @@ impl Layout {
 /// to the layout's current size.
 #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
+#[cfg_attr(not(bootstrap), rustc_const_stable_indirect)]
 #[must_use = "this returns a new `Layout`, \
  without modifying the original"]
 #[inline]
@@ -374,7 +374,6 @@ impl Layout {
 /// assert_eq!(repeated, (Layout::from_size_align(24, 4).unwrap(), 8));
 /// ```
 #[unstable(feature = "alloc_layout_extra", issue = "55724")]
-#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
 #[inline]
 pubconstfnrepeat(&self,n:usize) -> Result<(Self,usize),LayoutError>{
 let padded = self.pad_to_align();
@@ -432,6 +431,7 @@ impl Layout {
 /// ```
 #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
+#[cfg_attr(not(bootstrap), rustc_const_stable_indirect)]
 #[inline]
 pubconstfnextend(&self,next:Self) -> Result<(Self,usize),LayoutError>{
 let new_align = Alignment::max(self.align, next.align);
@@ -463,7 +463,6 @@ impl Layout {
 ///
 /// On arithmetic overflow, returns `LayoutError`.
 #[unstable(feature = "alloc_layout_extra", issue = "55724")]
-#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
 #[inline]
 pubconstfnrepeat_packed(&self,n:usize) -> Result<Self,LayoutError>{
 ifletSome(size) = self.size.checked_mul(n){
@@ -481,7 +480,6 @@ impl Layout {
 ///
 /// On arithmetic overflow, returns `LayoutError`.
 #[unstable(feature = "alloc_layout_extra", issue = "55724")]
-#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
 #[inline]
 pubconstfnextend_packed(&self,next:Self) -> Result<Self,LayoutError>{
 // SAFETY: each `size` is at most `isize::MAX == usize::MAX/2`, so the
@@ -497,6 +495,7 @@ impl Layout {
 /// `isize::MAX`, returns `LayoutError`.
 #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]
 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
+#[cfg_attr(not(bootstrap), rustc_const_stable_indirect)]
 #[inline]
 pubconstfnarray<T>(n:usize) -> Result<Self,LayoutError>{
 // Reduce the amount of code we need to monomorphize per `T`.