Rollup merge of rust-lang#124049 - slanterns:const_io_structs_stabilize, r=jhpratt

Stabilize `const_io_structs`

This PR stabilizes `const_io_structs`.

Tracking issue: rust-lang#78812.
Implementation PR: rust-lang#78811.

FCPs already completed in the tracking issue.

Closes rust-lang#78812.

``@rustbot`` label: +T-libs-api

r? libs-api

Author: RalfJung

library/std/src/io/cursor.rs

@@ -95,7 +95,7 @@ impl<T> Cursor<T> {
     /// # force_inference(&buff);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+    #[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
     pub const fn new(inner: T) -> Cursor<T> {
         Cursor { pos: 0, inner }
     }
@@ -132,7 +132,7 @@ impl<T> Cursor<T> {
     /// let reference = buff.get_ref();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+    #[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
     pub const fn get_ref(&self) -> &T {
         &self.inner
     }
@@ -178,7 +178,7 @@ impl<T> Cursor<T> {
     /// assert_eq!(buff.position(), 1);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+    #[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
     pub const fn position(&self) -> u64 {
         self.pos
     }

library/std/src/io/util.rs

@@ -51,7 +51,7 @@ pub struct Empty;
 /// ```
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+#[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
 pub const fn empty() -> Empty {
     Empty
 }
@@ -173,7 +173,7 @@ pub struct Repeat {
 /// ```
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+#[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
 pub const fn repeat(byte: u8) -> Repeat {
     Repeat { byte }
 }
@@ -276,7 +276,7 @@ pub struct Sink;
 /// ```
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_io_structs", issue = "78812")]
+#[rustc_const_stable(feature = "const_io_structs", since = "CURRENT_RUSTC_VERSION")]
 pub const fn sink() -> Sink {
     Sink
 }

library/std/src/lib.rs

@@ -407,7 +407,6 @@
 // tidy-alphabetical-start
 #![feature(const_collections_with_hasher)]
 #![feature(const_hash)]
-#![feature(const_io_structs)]
 #![feature(const_ip)]
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]