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std: Tweak expansion of thread-local const

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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
This commit is contained in:
Alex Crichton 2021-11-10 10:55:30 -08:00
parent 68ca579406
commit 1ac5d7dcde
1 changed files with 6 additions and 6 deletions
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12
library/std/src/thread/local.rs
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@ -165,6 +165,7 @@ macro_rules! __thread_local_inner {
#[cfg_attr(not(windows), inline)] // see comments below #[cfg_attr(not(windows), inline)] // see comments below
unsafe fn __getit() -> $crate::option::Option<&'static $t> { unsafe fn __getit() -> $crate::option::Option<&'static $t> {
const _REQUIRE_UNSTABLE: () = $crate::thread::require_unstable_const_init_thread_local(); 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 // wasm without atomics maps directly to `static mut`, and dtors
// aren't implemented because thread dtors aren't really a thing // aren't implemented because thread dtors aren't really a thing
@ -174,7 +175,7 @@ macro_rules! __thread_local_inner {
// block. // block.
#[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))] #[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))]
{ {
static mut VAL: $t = $init; static mut VAL: $t = INIT_EXPR;
Some(&VAL) Some(&VAL)
} }
@ -184,18 +185,17 @@ macro_rules! __thread_local_inner {
not(all(target_arch = "wasm32", not(target_feature = "atomics"))), not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
))] ))]
{ {
#[thread_local]
static mut VAL: $t = INIT_EXPR;
// If a dtor isn't needed we can do something "very raw" and // If a dtor isn't needed we can do something "very raw" and
// just get going. // just get going.
if !$crate::mem::needs_drop::<$t>() { if !$crate::mem::needs_drop::<$t>() {
#[thread_local]
static mut VAL: $t = $init;
unsafe { unsafe {
return Some(&VAL) return Some(&VAL)
} }
} }
#[thread_local]
static mut VAL: $t = $init;
// 0 == dtor not registered // 0 == dtor not registered
// 1 == dtor registered, dtor not run // 1 == dtor registered, dtor not run
// 2 == dtor registered and is running or has run // 2 == dtor registered and is running or has run
@ -242,7 +242,7 @@ macro_rules! __thread_local_inner {
))] ))]
{ {
#[inline] #[inline]
const fn __init() -> $t { $init } const fn __init() -> $t { INIT_EXPR }
static __KEY: $crate::thread::__OsLocalKeyInner<$t> = static __KEY: $crate::thread::__OsLocalKeyInner<$t> =
$crate::thread::__OsLocalKeyInner::new(); $crate::thread::__OsLocalKeyInner::new();
#[allow(unused_unsafe)] #[allow(unused_unsafe)]