std: Stabilize the thread_local_const_init feature

This commit is intended to follow the stabilization disposition of the
FCP that has now finished in #84223. This stabilizes the ability to flag
thread local initializers as `const` expressions which enables the macro
to generate more efficient code for accessing it, notably removing
runtime checks for initialization.

More information can also be found in #84223 as well as the tests where
the feature usage was removed in this PR.

Closes #84223

compiler/rustc_middle/src/lib.rs

@@ -51,7 +51,6 @@
 #![feature(control_flow_enum)]
 #![feature(associated_type_defaults)]
 #![feature(iter_zip)]
-#![feature(thread_local_const_init)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(try_reserve_kind)]

compiler/rustc_query_system/src/lib.rs

@@ -5,7 +5,6 @@
 #![feature(iter_zip)]
 #![feature(let_else)]
 #![feature(min_specialization)]
-#![feature(thread_local_const_init)]
 #![feature(extern_types)]
 
 #[macro_use]

compiler/rustc_span/src/lib.rs

@@ -20,7 +20,6 @@
 #![feature(negative_impls)]
 #![feature(nll)]
 #![feature(min_specialization)]
-#![feature(thread_local_const_init)]
 
 #[macro_use]
 extern crate rustc_macros;

library/std/src/lib.rs

@@ -216,10 +216,7 @@
 // std may use features in a platform-specific way
 #![allow(unused_features)]
 #![feature(rustc_allow_const_fn_unstable)]
-#![cfg_attr(
-    test,
-    feature(internal_output_capture, print_internals, update_panic_count, thread_local_const_init)
-)]
+#![cfg_attr(test, feature(internal_output_capture, print_internals, update_panic_count))]
 #![cfg_attr(
     all(target_vendor = "fortanix", target_env = "sgx"),
     feature(slice_index_methods, coerce_unsized, sgx_platform)

library/std/src/thread/local.rs

@@ -164,7 +164,6 @@ macro_rules! __thread_local_inner {
     (@key $t:ty, const $init:expr) => {{
         #[cfg_attr(not(windows), inline)] // see comments below
         unsafe fn __getit() -> $crate::option::Option<&'static $t> {
-            const _REQUIRE_UNSTABLE: () = $crate::thread::require_unstable_const_init_thread_local();
             const INIT_EXPR: $t = $init;
 
             // wasm without atomics maps directly to `static mut`, and dtors

library/std/src/thread/mod.rs

@@ -204,13 +204,6 @@ pub use self::local::os::Key as __OsLocalKeyInner;
 #[doc(hidden)]
 pub use self::local::statik::Key as __StaticLocalKeyInner;
 
-// This is only used to make thread locals with `const { .. }` initialization
-// expressions unstable. If and/or when that syntax is stabilized with thread
-// locals this will simply be removed.
-#[doc(hidden)]
-#[unstable(feature = "thread_local_const_init", issue = "84223")]
-pub const fn require_unstable_const_init_thread_local() {}
-
 ////////////////////////////////////////////////////////////////////////////////
 // Builder
 ////////////////////////////////////////////////////////////////////////////////

src/test/codegen/auxiliary/thread_local_aux.rs

@@ -1,5 +1,4 @@
 #![crate_type = "lib"]
-#![feature(thread_local_const_init)]
 
 use std::cell::Cell;
 

src/test/codegen/thread-local.rs

@@ -6,7 +6,6 @@
 // ignore-android does not use #[thread_local]
 
 #![crate_type = "lib"]
-#![feature(thread_local_const_init)]
 
 extern crate thread_local_aux as aux;
 

src/test/ui/feature-gates/thread-local-const-init.rs

@@ -1,4 +0,0 @@
-thread_local!(static X: u32 = const { 0 });
-//~^ ERROR: use of unstable library feature 'thread_local_const_init'
-
-fn main() {}

src/test/ui/feature-gates/thread-local-const-init.stderr

@@ -1,13 +0,0 @@
-error[E0658]: use of unstable library feature 'thread_local_const_init'
-  --> $DIR/thread-local-const-init.rs:1:1
-   |
-LL | thread_local!(static X: u32 = const { 0 });
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #84223 <https://github.com/rust-lang/rust/issues/84223> for more information
-   = help: add `#![feature(thread_local_const_init)]` to the crate attributes to enable
-   = note: this error originates in the macro `$crate::__thread_local_inner` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.