Allow any const expression blocks in thread_local!
#116392
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@rustbot label +T-libs-api +A-thread-locals +A-macros -T-libs |
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thread_local!const expression blocks in thread_local!
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r? @m-ou-se for T-libs-api FCP since this is a user-facing stable API change. |
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| /// pub static FOO: Cell<u32> = const { | ||
| /// let value = 1; | ||
| /// Cell::new(value) | ||
| /// }; |
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It's good to have a test that checks this works, but I don't think we should make the documentation example more verbose/complicated than necessary.
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@rfcbot merge Summary: // Allowed today:
thread_local! {
pub static A: Cell<u32> = const { Cell::new(value) };
}
// Disallowed today, but allowed after this PR:
thread_local! {
pub static B: Cell<u32> = const {
let value = 1;
Cell::new(value)
};
} |
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Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members: No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See this document for info about what commands tagged team members can give me. |
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🔔 This is now entering its final comment period, as per the review above. 🔔 |
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LGTM. I hope this won't have an unexpected interaction with #![allow(incomplete_features)]
#![feature(const_closures)]
#![feature(type_alias_impl_trait)]
type Closure = impl Fn();
thread_local! {
pub static X: Closure = const || {};
}@rfcbot reviewed |
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The final comment period, with a disposition to merge, as per the review above, is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed. This will be merged soon. |
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@rustbot author |
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@nvzqz this is waiting on #116392 (review) to be addressed. |
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Jan 22, 2024
Allow any `const` expression blocks in `thread_local!` This PR contains a rebase of the macro change from rust-lang#116392, together with adding a test under library/std/tests. Testing this feature by making the documentation's example code needlessly more complicated was not appropriate as pointed out in rust-lang#116392 (review). Without the macro change, this new test would fail to build as follows: ```console error: no rules expected the token `let` --> library/std/tests/thread.rs:26:13 | 26 | let value = 1; | ^^^ no rules expected this token in macro call | note: while trying to match meta-variable `$init:expr` --> library/std/src/thread/local.rs:189:69 | 189 | ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => ( | ^^^^^^^^^^ ``` Closes rust-lang#116392.
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Allow any `const` expression blocks in `thread_local!` This PR contains a rebase of the macro change from rust-lang#116392, together with adding a test under library/std/tests. Testing this feature by making the documentation's example code needlessly more complicated was not appropriate as pointed out in rust-lang#116392 (review). Without the macro change, this new test would fail to build as follows: ```console error: no rules expected the token `let` --> library/std/tests/thread.rs:26:13 | 26 | let value = 1; | ^^^ no rules expected this token in macro call | note: while trying to match meta-variable `$init:expr` --> library/std/src/thread/local.rs:189:69 | 189 | ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => ( | ^^^^^^^^^^ ``` Closes rust-lang#116392.
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Rollup merge of rust-lang#120181 - dtolnay:tlconst, r=thomcc Allow any `const` expression blocks in `thread_local!` This PR contains a rebase of the macro change from rust-lang#116392, together with adding a test under library/std/tests. Testing this feature by making the documentation's example code needlessly more complicated was not appropriate as pointed out in rust-lang#116392 (review). Without the macro change, this new test would fail to build as follows: ```console error: no rules expected the token `let` --> library/std/tests/thread.rs:26:13 | 26 | let value = 1; | ^^^ no rules expected this token in macro call | note: while trying to match meta-variable `$init:expr` --> library/std/src/thread/local.rs:189:69 | 189 | ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => ( | ^^^^^^^^^^ ``` Closes rust-lang#116392.
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Previously only a single expression could be allowed within the
constblock. This change allows for statements to precede the final expression, similarly to real inlineconstexpressions.This works by taking
$initas ablockinthread_local!and passing it tothread_local_inner!, where it is accepted as anexpr.