`const` blocks as a `mod` item #149174

GrigorenkoPV · 2025-11-21T12:02:00Z

Tracking issue: #149226

This adds support for writing const { ... } as an item in a module. In the current implementation, this is a unique AST item that gets lowered to const _: () = const { ... }; in HIR.

rustfmt support included.

TODO:

pub const { ... } does not make sense (see Add warn-by-default lint for visibility on const _ declarations #147136). Reject it. Should this be rejected by the parser or smth?
Improve diagnostics (preferably they should not mention the fake _ ident).

rustbot · 2025-11-29T21:40:07Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

rustbot · 2025-11-29T21:40:09Z

r? @jdonszelmann

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jdonszelmann · 2026-01-06T16:02:48Z

@GrigorenkoPV feel like updating the last comments and finishing this up?

rustbot · 2026-01-21T16:39:46Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

ytmimi · 2026-01-23T15:06:46Z

tests/ui/parser/const-block-items/inner-attr.rs

+// ATTENTION: if we ever start accepting inner attributes here, make sure `rustfmt` can handle them.
+//            see: https://github.com/rust-lang/rustfmt/issues/6158


Thank you 🙏🏼

ytmimi

All good for the rustfmt changes

View changes since this review

GrigorenkoPV · 2026-01-24T13:12:36Z

@rustbot ready

jdonszelmann · 2026-01-24T13:29:02Z

@bors r=me,ytmimi

rust-bors · 2026-01-24T13:29:09Z

📌 Commit d144915 has been approved by me,ytmimi

It is now in the queue for this repository.

GrigorenkoPV · 2026-01-24T13:54:58Z

📌 Commit d144915 has been approved by me,ytmimi

It is now in the queue for this repository.

I don't think bors has managed to properly parse "me" as an alias in this context.

@ghost

Rollup of 4 pull requests Successful merges: - #149174 (`const` blocks as a `mod` item) - #151282 (THIR patterns: Explicitly distinguish `&pin` from plain `&`/`&mut`) - #151593 (miri subtree update) - #151516 (Do not emit errors on non-metaitem diagnostic attr input) r? @ghost

Rollup merge of #149174 - GrigorenkoPV:const_block_item, r=me,ytmimi `const` blocks as a `mod` item Tracking issue: #149226 This adds support for writing `const { ... }` as an item in a module. In the current implementation, this is a unique AST item that gets lowered to `const _: () = const { ... };` in HIR. rustfmt support included. TODO: - `pub const { ... }` does not make sense (see #147136). Reject it. Should this be rejected by the parser or smth? - Improve diagnostics (preferably they should not mention the fake `_` ident).

@ghost

Rollup of 4 pull requests Successful merges: - rust-lang/rust#149174 (`const` blocks as a `mod` item) - rust-lang/rust#151282 (THIR patterns: Explicitly distinguish `&pin` from plain `&`/`&mut`) - rust-lang/rust#151593 (miri subtree update) - rust-lang/rust#151516 (Do not emit errors on non-metaitem diagnostic attr input) r? @ghost

@ghost

…iaskrgr Rollup of 4 pull requests Successful merges: - rust-lang#149174 (`const` blocks as a `mod` item) - rust-lang#151282 (THIR patterns: Explicitly distinguish `&pin` from plain `&`/`&mut`) - rust-lang#151593 (miri subtree update) - rust-lang#151516 (Do not emit errors on non-metaitem diagnostic attr input) r? @ghost

GrigorenkoPV force-pushed the const_block_item branch from 7ec6ad3 to 0b65188 Compare November 21, 2025 12:08