make `rustc_allow_const_fn_unstable` an actual `rustc_attrs` attribute#152749

cyrgani · 2026-02-17T10:12:31Z

It is already named like one, but used to have its own feature gate, which this PR now removes in favor of just using #![feature(rustc_attrs)].

Most of the diff is just the line number changes in malformed-attrs.stderr.

rustbot · 2026-02-17T10:12:34Z

⚠️ #[rustc_allow_const_fn_unstable] needs careful audit to avoid accidentally exposing unstable
implementation details on stable.

cc @rust-lang/wg-const-eval

rustbot · 2026-02-17T10:12:39Z

r? @mati865

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fmease · 2026-02-17T12:58:55Z

compiler/rustc_feature/src/removed.rs

     Some("removed in favor of `#![register_tool]`"), 66070),
    (removed, rust_2018_preview, "1.76.0", None,
     Some("2018 Edition preview is no longer relevant")),
+    (removed, rustc_allow_const_fn_unstable, "CURRENT_RUSTC_VERSION", Some(69399), Some("merged into `#![feature(rustc_attrs)]`")),


I wonder if there's actual merit in keeping track of removed internal features 🤔. After all, in theory nobody other than stdlib authors should've used and should use this attribute. Context: I'm always eager to get rid of unnecessary baggage.

(#69399 isn't even a proper tracking issue ^^).

agree with fmease here

Removed it.
That said, I was told to do the opposite in #152746 (comment) earlier today.

Thanks for bringing this up. As a general rule, we indeed want to keep track of removed features, so users have an easier time migrating. Of course, there are probably gray areas where the opinion of reviewers might diverge.

In the case of the now removed 5723 feature, I don't know if it was truly necessary to keep books, I haven't looked into it. It depends on the ecosystem impact I feel like. Still, keeping record is the safe & generally desired default.

Specifically in the case of the specially flagged internal features however (which are only a thing since 2 years ago maybe?) I'm set on 'purging the archives' since I don't care about providing hypothetical users who aren't stdlib devs further internal information for migrating a feature they shouldn't've used in the first place. rustc carries enough historical baggage, I don't want to increase it.

jdonszelmann · 2026-02-17T13:23:34Z

r? me

jdonszelmann · 2026-02-17T13:24:47Z

I think this one should just be properly removed

jdonszelmann · 2026-02-17T13:24:52Z

@rustbot author

rustbot · 2026-02-17T13:24:56Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

jdonszelmann · 2026-02-17T22:49:00Z

I think this is genuinely nicest, and it's internal anyway. If someone cares enough, undo that decision, but it's an @bors r+ rollup from me

rust-bors · 2026-02-17T22:49:03Z

📌 Commit 83ef505 has been approved by jdonszelmann

It is now in the queue for this repository.

…zelmann make `rustc_allow_const_fn_unstable` an actual `rustc_attrs` attribute It is already named like one, but used to have its own feature gate, which this PR now removes in favor of just using `#![feature(rustc_attrs)]`. Most of the diff is just the line number changes in `malformed-attrs.stderr`.

Rollup of 19 pull requests Successful merges: - #145399 (Unify wording of resolve error) - #150473 (tail calls: fix copying non-scalar arguments to callee) - #152637 (Add a note about elided lifetime) - #152657 (std: move `exit` out of PAL) - #152729 (compiler: Don't mark `SingleUseConsts` MIR pass as "required for soundness") - #152753 (remove the explicit error for old `rental` versions) - #152758 (Remove ShallowInitBox.) - #151530 (Fix invalid `mut T` suggestion for `&mut T` in missing lifetime error) - #152179 (Add documentation note about signed overflow direction) - #152474 (Implement opt-bisect-limit for MIR) - #152509 (tests/ui/test-attrs: add annotations for reference rules) - #152672 (std: use libc version of `_NSGetArgc`/`_NSGetArgv`) - #152711 (resolve: Disable an assert that no longer holds) - #152732 (add regression test for 147958) - #152745 (Fix ICE in `suggest_param_env_shadowing` with incompatible args) - #152749 (make `rustc_allow_const_fn_unstable` an actual `rustc_attrs` attribute) - #152756 (Miri: recursive validity: also recurse into Boxes) - #152770 (carryless_mul: mention the base) - #152778 (Update tracking issue number for final_associated_functions)

Rollup of 20 pull requests Successful merges: - #145399 (Unify wording of resolve error) - #150473 (tail calls: fix copying non-scalar arguments to callee) - #152637 (Add a note about elided lifetime) - #152729 (compiler: Don't mark `SingleUseConsts` MIR pass as "required for soundness") - #152751 (Rename dep node "fingerprints" to distinguish key and value hashes) - #152753 (remove the explicit error for old `rental` versions) - #152758 (Remove ShallowInitBox.) - #151530 (Fix invalid `mut T` suggestion for `&mut T` in missing lifetime error) - #152179 (Add documentation note about signed overflow direction) - #152474 (Implement opt-bisect-limit for MIR) - #152509 (tests/ui/test-attrs: add annotations for reference rules) - #152672 (std: use libc version of `_NSGetArgc`/`_NSGetArgv`) - #152711 (resolve: Disable an assert that no longer holds) - #152725 (Rework explanation of CLI lint level flags) - #152732 (add regression test for 147958) - #152745 (Fix ICE in `suggest_param_env_shadowing` with incompatible args) - #152749 (make `rustc_allow_const_fn_unstable` an actual `rustc_attrs` attribute) - #152756 (Miri: recursive validity: also recurse into Boxes) - #152770 (carryless_mul: mention the base) - #152778 (Update tracking issue number for final_associated_functions)

Rollup merge of #152749 - cyrgani:rustc-allow-const, r=jdonszelmann make `rustc_allow_const_fn_unstable` an actual `rustc_attrs` attribute It is already named like one, but used to have its own feature gate, which this PR now removes in favor of just using `#![feature(rustc_attrs)]`. Most of the diff is just the line number changes in `malformed-attrs.stderr`.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 17, 2026

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rust-cloud-vms bot force-pushed the rustc-allow-const branch from 68ff184 to e335f96 Compare February 17, 2026 12:00

fmease approved these changes Feb 17, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 17, 2026

make rustc_allow_const_fn_unstable an actual rustc_attrs attribute

83ef505

rust-cloud-vms bot force-pushed the rustc-allow-const branch from e335f96 to 83ef505 Compare February 17, 2026 20:16

cyrgani added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 17, 2026

rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 17, 2026

jhpratt mentioned this pull request Feb 18, 2026

Rollup of 12 pull requests #152776

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jhpratt mentioned this pull request Feb 18, 2026

Rollup of 20 pull requests #152781

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jhpratt mentioned this pull request Feb 18, 2026

Rollup of 19 pull requests #152782

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Zalathar mentioned this pull request Feb 18, 2026

Rollup of 20 pull requests #152785

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rust-bors bot merged commit e53dd52 into rust-lang:main Feb 18, 2026
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rustbot added this to the 1.95.0 milestone Feb 18, 2026

cyrgani deleted the rustc-allow-const branch February 18, 2026 18:23

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