make Cell unstably const

Author: RalfJung

library/core/src/cell.rs

@@ -494,8 +494,9 @@ impl<T> Cell<T> {
 /// ```
 #[inline]
 #[stable(feature = "move_cell", since = "1.17.0")]
+#[rustc_const_unstable(feature = "const_cell", issue = "131283")]
 #[rustc_confusables("swap")]
-pubfnreplace(&self,val:T) -> T{
+pubconstfnreplace(&self,val:T) -> T{
 // SAFETY: This can cause data races if called from a separate thread,
 // but `Cell` is `!Sync` so this won't happen.
  mem::replace(unsafe{&mut*self.value.get()}, val)
@@ -535,7 +536,8 @@ impl<T: Copy> Cell<T> {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-pubfnget(&self) -> T{
+#[rustc_const_unstable(feature = "const_cell", issue = "131283")]
+pubconstfnget(&self) -> T{
 // SAFETY: This can cause data races if called from a separate thread,
 // but `Cell` is `!Sync` so this won't happen.
 unsafe{*self.value.get()}
@@ -613,7 +615,8 @@ impl<T: ?Sized> Cell<T> {
 /// ```
 #[inline]
 #[stable(feature = "cell_get_mut", since = "1.11.0")]
-pubfnget_mut(&mutself) -> &mutT{
+#[rustc_const_unstable(feature = "const_cell", issue = "131283")]
+pubconstfnget_mut(&mutself) -> &mutT{
 self.value.get_mut()
 }
 
@@ -632,7 +635,8 @@ impl<T: ?Sized> Cell<T> {
 /// ```
 #[inline]
 #[stable(feature = "as_cell", since = "1.37.0")]
-pubfnfrom_mut(t:&mutT) -> &Cell<T>{
+#[rustc_const_unstable(feature = "const_cell", issue = "131283")]
+pubconstfnfrom_mut(t:&mutT) -> &Cell<T>{
 // SAFETY: `&mut` ensures unique access.
 unsafe{&*(t as*mutTas*constCell<T>)}
 }
@@ -686,7 +690,8 @@ impl<T> Cell<[T]> {
 /// assert_eq!(slice_cell.len(), 3);
 /// ```
 #[stable(feature = "as_cell", since = "1.37.0")]
-pubfnas_slice_of_cells(&self) -> &[Cell<T>]{
+#[rustc_const_unstable(feature = "const_cell", issue = "131283")]
+pubconstfnas_slice_of_cells(&self) -> &[Cell<T>]{
 // SAFETY: `Cell<T>` has the same memory layout as `T`.
 unsafe{&*(selfas*constCell<[T]>as*const[Cell<T>])}
 }
@@ -706,7 +711,8 @@ impl<T, const N: usize> Cell<[T; N]> {
 /// let array_cell: &[Cell<i32>; 3] = cell_array.as_array_of_cells();
 /// ```
 #[unstable(feature = "as_array_of_cells", issue = "88248")]
-pubfnas_array_of_cells(&self) -> &[Cell<T>;N]{
+#[rustc_const_unstable(feature = "as_array_of_cells", issue = "88248")]
+pubconstfnas_array_of_cells(&self) -> &[Cell<T>;N]{
 // SAFETY: `Cell<T>` has the same memory layout as `T`.
 unsafe{&*(selfas*constCell<[T;N]>as*const[Cell<T>;N])}
 }