From 9835e2ae736235810b4ea1c162ca5e65c547e770 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sat, 18 May 2024 04:49:50 +0200
Subject: Merging upstream version 1.71.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 library/std/src/thread/local.rs | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

(limited to 'library/std/src/thread/local.rs')

diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs
index 7fdf03acc..1b86d898c 100644
--- a/library/std/src/thread/local.rs
+++ b/library/std/src/thread/local.rs
@@ -18,8 +18,8 @@ use crate::fmt;
 /// target platform. It is instantiated with the [`thread_local!`] macro and the
 /// primary method is the [`with`] method.
 ///
-/// The [`with`] method yields a reference to the contained value which cannot be
-/// sent across threads or escape the given closure.
+/// The [`with`] method yields a reference to the contained value which cannot
+/// outlive the current thread or escape the given closure.
 ///
 /// [`thread_local!`]: crate::thread_local
 ///
@@ -134,10 +134,28 @@ impl<T: 'static> fmt::Debug for LocalKey<T> {
 /// thread_local! {
 ///     pub static FOO: RefCell<u32> = RefCell::new(1);
 ///
-///     #[allow(unused)]
 ///     static BAR: RefCell<f32> = RefCell::new(1.0);
 /// }
-/// # fn main() {}
+///
+/// FOO.with(|foo| assert_eq!(*foo.borrow(), 1));
+/// BAR.with(|bar| assert_eq!(*bar.borrow(), 1.0));
+/// ```
+///
+/// This macro supports a special `const {}` syntax that can be used
+/// when the initialization expression can be evaluated as a constant.
+/// This can enable a more efficient thread local implementation that
+/// can avoid lazy initialization. For types that do not
+/// [need to be dropped][crate::mem::needs_drop], this can enable an
+/// even more efficient implementation that does not need to
+/// track any additional state.
+///
+/// ```
+/// use std::cell::Cell;
+/// thread_local! {
+///     pub static FOO: Cell<u32> = const { Cell::new(1) };
+/// }
+///
+/// FOO.with(|foo| assert_eq!(foo.get(), 1));
 /// ```
 ///
 /// See [`LocalKey` documentation][`std::thread::LocalKey`] for more
@@ -153,23 +171,23 @@ macro_rules! thread_local {
     () => {};
 
     ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => (
-        $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, const $init);
+        $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, const $init);
         $crate::thread_local!($($rest)*);
     );
 
     ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }) => (
-        $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, const $init);
+        $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, const $init);
     );
 
     // process multiple declarations
     ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => (
-        $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
+        $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
         $crate::thread_local!($($rest)*);
     );
 
     // handle a single declaration
     ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr) => (
-        $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
+        $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
     );
 }
 
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