Allow any `const` expression blocks in `thread_local!` #116392

nvzqz · 2023-10-03T18:47:59Z

Previously only a single expression could be allowed within the const block. This change allows for statements to precede the final expression, similarly to real inline const expressions.

This works by taking $init as a block in thread_local! and passing it to thread_local_inner!, where it is accepted as an expr.

rustbot · 2023-10-03T18:48:08Z

r? @Mark-Simulacrum

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nvzqz · 2023-10-03T18:49:36Z

@rustbot label +T-libs-api +A-thread-locals +A-macros -T-libs

Mark-Simulacrum · 2023-10-07T20:06:48Z

r? @m-ou-se for T-libs-api FCP since this is a user-facing stable API change.

m-ou-se · 2023-11-28T14:50:37Z

library/std/src/thread/local.rs

+///     pub static FOO: Cell<u32> = const {
+///         let value = 1;
+///         Cell::new(value)
+///     };


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.

m-ou-se · 2023-11-28T14:54:15Z

@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)
    };
}

rfcbot · 2023-11-28T14:54:20Z

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.

rfcbot · 2023-11-28T15:23:57Z

🔔 This is now entering its final comment period, as per the review above. 🔔

dtolnay · 2023-11-29T02:25:46Z

LGTM.

I hope this won't have an unexpected interaction with const_closures (#106003). But this is clearly worth doing anyway.

#![allow(incomplete_features)]
#![feature(const_closures)]
#![feature(type_alias_impl_trait)]

type Closure = impl Fn();

thread_local! {
    pub static X: Closure = const || {};
}

@rfcbot reviewed

rfcbot · 2023-12-08T15:24:02Z

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.

dtolnay · 2023-12-08T16:13:34Z

@rustbot author

dtolnay · 2024-01-12T04:29:24Z

@nvzqz this is waiting on #116392 (review) to be addressed.

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.

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.

Allow any expression blocks in thread_local!

0d3dff9

rustbot assigned Mark-Simulacrum Oct 3, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 3, 2023

nvzqz changed the title ~~Allow any expression blocks in thread_local!~~ Allow any const expression blocks in thread_local! Oct 3, 2023

rustbot assigned m-ou-se and unassigned Mark-Simulacrum Oct 7, 2023

Mark-Simulacrum added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Oct 7, 2023

m-ou-se reviewed Nov 28, 2023

View reviewed changes

rfcbot removed the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Nov 28, 2023

rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. to-announce Announce this issue on triage meeting and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Dec 8, 2023

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 8, 2023

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 8, 2023

apiraino removed the to-announce Announce this issue on triage meeting label Dec 14, 2023

dtolnay assigned dtolnay and unassigned m-ou-se Jan 12, 2024

dtolnay mentioned this pull request Jan 21, 2024

Allow any const expression blocks in thread_local! #120181

Merged

bors closed this in d3761de Jan 22, 2024

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Allow any `const` expression blocks in `thread_local!` #116392

Allow any `const` expression blocks in `thread_local!` #116392

nvzqz commented Oct 3, 2023 •

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m-ou-se Nov 28, 2023

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Allow any const expression blocks in thread_local! #116392

Allow any const expression blocks in thread_local! #116392

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Allow any `const` expression blocks in `thread_local!` #116392

Allow any `const` expression blocks in `thread_local!` #116392

nvzqz commented Oct 3, 2023 •

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rfcbot commented Nov 28, 2023 •

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