From 1ac5d7dcde57c3f4baa975d79dbdb57dfdb2489c Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Wed, 10 Nov 2021 10:55:30 -0800
Subject: [PATCH] std: Tweak expansion of thread-local const
This commit tweaks the expansion of `thread_local!` when combined with a
`const { ... }` value to help ensure that the rules which apply to
`const { ... }` blocks will be the same as when they're stabilized.
Previously with this invocation:
thread_local!(static NAME: Type = const { init_expr });
this would generate (on supporting platforms):
#[thread_local]
static NAME: Type = init_expr;
instead the macro now expands to:
const INIT_EXPR: Type = init_expr;
#[thread_local]
static NAME: Type = INIT_EXPR;
with the hope that because `init_expr` is defined as a `const` item then
it's not accidentally allowing more behavior than if it were put into a
`static`. For example on the stabilization issue [this example][ex] now
gives the same error both ways.
[ex]: https://github.com/rust-lang/rust/issues/84223#issuecomment-953384298
---
library/std/src/thread/local.rs | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs
index c53290ec0c7..b27db876176 100644
--- a/library/std/src/thread/local.rs
+++ b/library/std/src/thread/local.rs
@@ -165,6 +165,7 @@ macro_rules! __thread_local_inner {
#[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
// aren't implemented because thread dtors aren't really a thing
@@ -174,7 +175,7 @@ macro_rules! __thread_local_inner {
// block.
#[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))]
{
- static mut VAL: $t = $init;
+ static mut VAL: $t = INIT_EXPR;
Some(&VAL)
}
@@ -184,18 +185,17 @@ macro_rules! __thread_local_inner {
not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
))]
{
+ #[thread_local]
+ static mut VAL: $t = INIT_EXPR;
+
// If a dtor isn't needed we can do something "very raw" and
// just get going.
if !$crate::mem::needs_drop::<$t>() {
- #[thread_local]
- static mut VAL: $t = $init;
unsafe {
return Some(&VAL)
}
}
- #[thread_local]
- static mut VAL: $t = $init;
// 0 == dtor not registered
// 1 == dtor registered, dtor not run
// 2 == dtor registered and is running or has run
@@ -242,7 +242,7 @@ macro_rules! __thread_local_inner {
))]
{
#[inline]
- const fn __init() -> $t { $init }
+ const fn __init() -> $t { INIT_EXPR }
static __KEY: $crate::thread::__OsLocalKeyInner<$t> =
$crate::thread::__OsLocalKeyInner::new();
#[allow(unused_unsafe)]