Lower attributes for functions without bodies by JonathanBrouwer · Pull Request #162761 · rust-lang/rust

JonathanBrouwer · 2026-09-14T11:37:56Z

This is a temporary solution to get the bug fixed.
I'm going to see if we can move the function hir::Params from hir::Body to hir::FnSig, this would cleanly fix this bug and would undo most of this PR. That is a large project which might take me some time to complete, so I'd prefer to get the bug fixed first with this workaround.

Maybe r? @jdonszelmann since you have context?
cc @mejrs cause you're probably interested

rustbot · 2026-09-14T11:38:02Z

jdonszelmann is currently at their maximum review capacity.
They may take a while to respond.

jdonszelmann · 2026-09-14T12:50:21Z


 warning: the `must_use` attribute cannot be used on function params
-  --> $DIR/param-attrs-builtin-attrs.rs:40:7
+  --> $DIR/param-attrs-builtin-attrs.rs:29:7


the check for these warnings should go, since it causes double emissions

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Let's fix this in a follow-up PR, it will be quite a big diff to remove this error and replace it by target checking consistently

JonathanBrouwer · 2026-09-14T12:51:16Z

@rust-lang/lang Is this a PR that you would want to take a look at?
This makes the following code, which was incorrectly allowed, no longer compile.
I believe there is some decision that for attribute fixes a ping was enough? I can't find that tho

fn help(x: fn(#[rustc_splat] usize)) {}

JonathanBrouwer · 2026-09-14T13:05:10Z

@rustbot ready

jdonszelmann · 2026-09-14T13:08:25Z

r=me then after some acknowledgement from t-lang. I think it falls under the same rule as earlier breaking changes in attrs (i.e. notify t-lang but do the change) but let them acknowledge that. Notably, this attribute is rather new, it's unlikely anyone depends on this.

JonathanBrouwer · 2026-09-14T13:56:21Z

Just in case
@bors try @rust-timer queue

Lower attributes for functions without bodies

teor2345

Apart from the comment tweak, this looks like what I'd expect to happen for splat. Thank you for this fix!

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teor2345

Did we also want to backport this to beta or stable?

Sorry for the multiple notifications 🙂

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teor2345 · 2026-09-14T14:37:29Z

    //~| ERROR allow, cfg, cfg_attr, deny, expect, forbid, and warn are the only allowed built-in attributes
 }

+trait Test {


I don't know if it's worth duplicating the trait, type, and extern tests in the splat feature gate test, up to you.

https://github.com/rust-lang/rust/blob/ada41e1ce81819f01577c0ee40ccbd6fc41384e8/tests/ui/feature-gates/feature-gate-splat.rs

I think it's not worth duplicating the test

rust-bors · 2026-09-14T14:55:52Z

☀️ Try build successful (CI)
Build commit: ed70b09 (ed70b094daccd48a86a95d8b0acdc0dfb125b3d0)
Base parent: ed77b7b (ed77b7b8699e342c2dc842c83cb5fe4025252ee8)

scottmcm · 2026-09-23T17:12:35Z

Agreed that this was clearly never supposed to be stable.

@rfcbot reviewed

teor2345 · 2026-09-23T18:18:08Z

Agreed that this was clearly never supposed to be stable.

@rfcbot reviewed

Triage note: after an hour, @scottmcm's box hasn't been ticked by the bot yet, so I ticket it manually.
(This doesn't change whether the FCP is over the threshold.)

rust-rfcbot · 2026-10-03T17:14:14Z

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.

rustbot · 2026-10-03T20:44:50Z

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.

JonathanBrouwer · 2026-10-03T20:46:08Z

r=me then after some acknowledgement from t-lang.

@bors r=jdonszelmann

rust-bors · 2026-10-03T20:46:11Z

📋 This PR cannot be approved because it currently has the following labels: proposed-final-comment-period, S-waiting-on-t-lang.

JonathanBrouwer · 2026-10-03T20:46:50Z

@bors r=jdonszelmann

rust-bors · 2026-10-03T20:46:54Z

📌 Commit 9c9d810 has been tentatively approved by jdonszelmann

It will be put into the queue for this repository once PR CI succeeds.

@jdonszelmann

… r=jdonszelmann Lower attributes for functions without bodies Fixes rust-lang#162639 This is a temporary solution to get the bug fixed. I'm going to see if we can move the function `hir::Param`s from `hir::Body` to `hir::FnSig`, this would cleanly fix this bug and would undo most of this PR. That is a large project which might take me some time to complete, so I'd prefer to get the bug fixed first with this workaround. Maybe r? @jdonszelmann since you have context? cc @mejrs cause you're probably interested

Rollup of 18 pull requests Successful merges: - #158102 (When compiling without a specified `--edition`, emit a message) - #162027 (std: add `fs::rename_noreplace`) - #162761 (Lower attributes for functions without bodies) - #163161 (implement FCW for `rustc_allowed_through_unstable_modules` items) - #163613 (Tweak the rendering of "not general enough" errors on the old trait solver) - #162062 (core: fix the docs of PanicInfo::location) - #163140 (document safety requirements for atomic intrinsics) - #163342 (Don't imply incorrect things about `Global` in the docs of `System`) - #163445 (Add safety comments for alloc::str) - #163503 (Mark Rc strong/weak count methods must_use) - #163548 (fs::set_permissions_nofollow: Android support, test cleanup) - #163585 ([triagebot] Create `debugger_visualizer` assign group) - #163597 (Add `SplitPathsRef` implementation for motor to make std build) - #163602 (Move media & home dirs tests to fs tests.) - #163667 (Finalize changes on expect messages for library/core/src/fmt/mod.rs) - #163682 ([rustdoc] Correctly link to (imported) enum variants with "jump to def") - #163683 (Fix GCC codegen backend comment in bootstrap) - #163703 (Move more `rustdoc-html tests` in the right location) Failed merges: - #161491 (Rip out old solver coherence)

Rollup of 18 pull requests Successful merges: - #158102 (When compiling without a specified `--edition`, emit a message) - #162761 (Lower attributes for functions without bodies) - #163161 (implement FCW for `rustc_allowed_through_unstable_modules` items) - #163613 (Tweak the rendering of "not general enough" errors on the old trait solver) - #162062 (core: fix the docs of PanicInfo::location) - #163140 (document safety requirements for atomic intrinsics) - #163342 (Don't imply incorrect things about `Global` in the docs of `System`) - #163445 (Add safety comments for alloc::str) - #163503 (Mark Rc strong/weak count methods must_use) - #163548 (fs::set_permissions_nofollow: Android support, test cleanup) - #163585 ([triagebot] Create `debugger_visualizer` assign group) - #163597 (Add `SplitPathsRef` implementation for motor to make std build) - #163602 (Move media & home dirs tests to fs tests.) - #163667 (Finalize changes on expect messages for library/core/src/fmt/mod.rs) - #163682 ([rustdoc] Correctly link to (imported) enum variants with "jump to def") - #163683 (Fix GCC codegen backend comment in bootstrap) - #163703 (Move more `rustdoc-html tests` in the right location) - #163725 (some crashes fixed with next-solver) Failed merges: - #161491 (Rip out old solver coherence)

@jdonszelmann

Rollup merge of #162761 - JonathanBrouwer:lower-param-attrs, r=jdonszelmann Lower attributes for functions without bodies Fixes #162639 This is a temporary solution to get the bug fixed. I'm going to see if we can move the function `hir::Param`s from `hir::Body` to `hir::FnSig`, this would cleanly fix this bug and would undo most of this PR. That is a large project which might take me some time to complete, so I'd prefer to get the bug fixed first with this workaround. Maybe r? @jdonszelmann since you have context? cc @mejrs cause you're probably interested

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. labels Sep 14, 2026

rustbot assigned jdonszelmann Sep 14, 2026

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JonathanBrouwer force-pushed the lower-param-attrs branch 3 times, most recently from 29274ef to 5bf5ae2 Compare September 14, 2026 12:28

jdonszelmann requested changes Sep 14, 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 Sep 14, 2026

JonathanBrouwer force-pushed the lower-param-attrs branch from 5bf5ae2 to e6552cd Compare September 14, 2026 13:05

rustbot 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 Sep 14, 2026

JonathanBrouwer added the S-waiting-on-t-lang Status: Awaiting decision from T-lang label Sep 14, 2026

JonathanBrouwer mentioned this pull request Sep 14, 2026

Remove the FnParamForbiddenAttr diagnostic #162770

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 14, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 14, 2026

Auto merge of #162761 - JonathanBrouwer:lower-param-attrs, r=<try>

ed70b09

Lower attributes for functions without bodies

teor2345 approved these changes Sep 14, 2026

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traviscross added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. and removed P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang labels Sep 23, 2026

rust-rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. to-announce Announce this issue on triage meeting labels Oct 3, 2026

rustbot mentioned this pull request Oct 3, 2026

Tracking issue for release notes of #162761: Lower attributes for functions without bodies #163709

Open

JonathanBrouwer added 3 commits October 3, 2026 22:40

Route fn_hir_id into lower_fn_decl

465aca6

Add regression tests

539bfe3

Lower attributes for functions without bodies

9c9d810

JonathanBrouwer force-pushed the lower-param-attrs branch from cad361c to 9c9d810 Compare October 3, 2026 20:44

JonathanBrouwer removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. S-waiting-on-t-lang Status: Awaiting decision from T-lang labels Oct 3, 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 Oct 3, 2026

traviscross added the waived-reference-pr This language change does not need a Reference PR. label Oct 3, 2026

jhpratt mentioned this pull request Oct 3, 2026

Rollup of 18 pull requests #163729

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jhpratt mentioned this pull request Oct 4, 2026

Rollup of 18 pull requests #163735

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rust-bors Bot merged commit dc179d7 into rust-lang:main Oct 4, 2026
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rustbot added this to the 1.101.0 milestone Oct 4, 2026

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