Stop rustfmt deleting attributes in fn params by teor2345 · Pull Request #161709 · rust-lang/rust

teor2345 · 2026-08-25T00:07:57Z

Currently, rustfmt deletes attributes in function type parameters, for example:

type F = fn(#[rustc_splat] ());

Becomes:

type F = fn(());

Playground

This is an annoying and confusing bug, and causes formatted code to silently change meaning, or fail compilation.

This PR cherry-picks the fix and tests from rust-lang/rustfmt#6590 to rust-lang/rust.

We're discussing a potential beta backport in Zulip #t-rustfmt > Attributes in fn type deleted on stable but not nightly, which is why this PR is separate to the subtree sync.

Tracking issue: #153629

This formatting bug impacts splatted function pointers
We just published a "call for experiment" blog post, including experiments with splatted function pointers

r? @ytmimi

ytmimi · 2026-08-25T01:07:27Z

@teor2345 you can r=me once CI is green

jieyouxu · 2026-08-25T01:34:15Z

@bors r=ytmimi rollup

rust-bors · 2026-08-25T01:34:18Z

📌 Commit 6a1074e has been approved by ytmimi

It is now in the queue for this repository.

@ytmimi

…, r=ytmimi Stop rustfmt deleting attributes in fn params Currently, rustfmt deletes attributes in function type parameters, for example: ```rust type F = fn(#[rustc_splat] ()); ``` Becomes: ```rust type F = fn(()); ``` [Playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=f56e4727022f44a6e5c937c1521830f9) This is an annoying and confusing bug, and causes formatted code to silently change meaning, or fail compilation. This PR cherry-picks the fix and tests from rust-lang/rustfmt#6590 to `rust-lang/rust`. We're discussing a potential beta backport in [Zulip #t-rustfmt > Attributes in fn type deleted on stable but not nightly](https://rust-lang.zulipchat.com/#narrow/channel/357797-t-rustfmt/topic/Attributes.20in.20fn.20type.20deleted.20on.20stable.20but.20not.20nightly/with/618688539), which is why this PR is separate to the subtree sync. Tracking issue: rust-lang#153629 - This formatting bug impacts splatted function pointers - We just published [a "call for experiment" blog post](https://blog.rust-lang.org/inside-rust/2026/08/19/overloading-experiment/), including experiments with splatted function pointers r? @ytmimi

Rollup of 9 pull requests Successful merges: - #160533 (dirfd dir operations (3/4)) - #161294 (add crashtests [6/N]) - #160392 (library: motor: bump moto-rt ABI ver to 17) - #161646 (interpret: fix after_local_read handling) - #160819 (Rework `div_ceil` for nonzero integers) - #161591 (run `classify-runtime-const` test for `f128`) - #161680 (renovate: add lockfile update warning) - #161702 (Use `drop_guard` in some places in {core,alloc,std}) - #161709 (Stop rustfmt deleting attributes in fn params)

…uwer Rollup of 10 pull requests Successful merges: - #160533 (dirfd dir operations (3/4)) - #161294 (add crashtests [6/N]) - #160392 (library: motor: bump moto-rt ABI ver to 17) - #161646 (interpret: fix after_local_read handling) - #161682 (Update books) - #160819 (Rework `div_ceil` for nonzero integers) - #161204 (core: Make funnel shifts panic only if overflow checks are enabled) - #161591 (run `classify-runtime-const` test for `f128`) - #161680 (renovate: add lockfile update warning) - #161709 (Stop rustfmt deleting attributes in fn params)

teor2345 · 2026-08-25T08:09:32Z

We talked about a possible beta backport in Zulip. I'm nominating before it merges because I'm off work for the next few days, and I might forget.

@rustbot beta-nominate T-rustdoc

rustbot · 2026-08-25T08:09:35Z

Error: The feature nominate is not enabled in this repository.
To enable it add its section in the triagebot.toml in the root of the repository.

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #triagebot on Zulip.

teor2345 · 2026-08-25T08:12:49Z

Oops, I was following https://forge.rust-lang.org/triagebot/nominate.html#configuration
But I think it's just

@rustbot label +beta-nominated

@ytmimi

Rollup merge of #161709 - teor2345:rustfmt-fn-param-attr-bug, r=ytmimi Stop rustfmt deleting attributes in fn params Currently, rustfmt deletes attributes in function type parameters, for example: ```rust type F = fn(#[rustc_splat] ()); ``` Becomes: ```rust type F = fn(()); ``` [Playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=f56e4727022f44a6e5c937c1521830f9) This is an annoying and confusing bug, and causes formatted code to silently change meaning, or fail compilation. This PR cherry-picks the fix and tests from rust-lang/rustfmt#6590 to `rust-lang/rust`. We're discussing a potential beta backport in [Zulip #t-rustfmt > Attributes in fn type deleted on stable but not nightly](https://rust-lang.zulipchat.com/#narrow/channel/357797-t-rustfmt/topic/Attributes.20in.20fn.20type.20deleted.20on.20stable.20but.20not.20nightly/with/618688539), which is why this PR is separate to the subtree sync. Tracking issue: #153629 - This formatting bug impacts splatted function pointers - We just published [a "call for experiment" blog post](https://blog.rust-lang.org/inside-rust/2026/08/19/overloading-experiment/), including experiments with splatted function pointers r? @ytmimi

rustbot · 2026-08-25T17:10:34Z

beta backport approved as per rustfmt team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels are handled by them.

[beta] bump stage0, plus backports - Bump stage0 to stable 1.98.0 - fix buggy MaybeDangling<&T> validation logic #161125 - resolving cyclic glob vis-max #161024 - Check for missing rustfmt in the stdarch intrinsic test step sooner #161641 - Uplift rustfmt macro formatting fix #161370 - Stop rustfmt deleting attributes in fn params #161709 r? me

…uwer Rollup of 10 pull requests Successful merges: - rust-lang/rust#160533 (dirfd dir operations (3/4)) - rust-lang/rust#161294 (add crashtests [6/N]) - rust-lang/rust#160392 (library: motor: bump moto-rt ABI ver to 17) - rust-lang/rust#161646 (interpret: fix after_local_read handling) - rust-lang/rust#161682 (Update books) - rust-lang/rust#160819 (Rework `div_ceil` for nonzero integers) - rust-lang/rust#161204 (core: Make funnel shifts panic only if overflow checks are enabled) - rust-lang/rust#161591 (run `classify-runtime-const` test for `f128`) - rust-lang/rust#161680 (renovate: add lockfile update warning) - rust-lang/rust#161709 (Stop rustfmt deleting attributes in fn params)

[beta] bump stage0, plus backports - Bump stage0 to stable 1.98.0 - fix buggy MaybeDangling<&T> validation logic #161125 - resolving cyclic glob vis-max #161024 - Check for missing rustfmt in the stdarch intrinsic test step sooner #161641 - Uplift rustfmt macro formatting fix #161370 - Stop rustfmt deleting attributes in fn params #161709 - Bust sccache's cache #161384 r? me

CPunisher added 4 commits August 25, 2026 09:35

Fix

95b56fe

Add variadic test

27f59f4

Add trait fn tests

3159d9f

Add test for issue 6607

6a1074e

teor2345 self-assigned this Aug 25, 2026

teor2345 added C-bug Category: This is a bug. T-rustfmt Relevant to the rustfmt team, which will review and decide on the PR/issue. F-splat `#![feature(splat)]` https://github.com/rust-lang/rust/issues/153629 labels Aug 25, 2026

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rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 25, 2026

teor2345 mentioned this pull request Aug 25, 2026

Add more splat fn type tests #161711

Open

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 Aug 25, 2026

Zalathar mentioned this pull request Aug 25, 2026

Rollup of 9 pull requests #161715

Closed

JonathanBrouwer mentioned this pull request Aug 25, 2026

Rollup of 10 pull requests #161719

Merged

rustbot added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Aug 25, 2026

rust-bors Bot merged commit c887061 into rust-lang:main Aug 25, 2026
13 checks passed

rustbot added this to the 1.100.0 milestone Aug 25, 2026

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Aug 25, 2026

cuviper mentioned this pull request Aug 25, 2026

[beta] bump stage0, plus backports #161422

Merged

cuviper modified the milestones: 1.100.0, 1.99.0 Aug 25, 2026

cuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Aug 25, 2026

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Stop rustfmt deleting attributes in fn params - #161709

Stop rustfmt deleting attributes in fn params#161709
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