Add unnecessary_trailing_comma lint - #16530

nyurik · 2026-02-07T08:30:52Z

This matches cargo fmt behavior but for format!(...) -style macro calls.

To make this PR easier to review, it moves all linting of the clippy code to #16533

Suggest removing an unnecessary trailing comma before the closing parenthesis in single-line format-like macro invocations (e.g. println!, format!, write!). The lint currently only runs on format-like macros because it relies on format-argument parsing; arbitrary user macros are not supported to avoid incorrect suggestions.

Lint is in the style group (allow-by-default)
Single-line only: multi-line macro invocations are not linted
Machine-applicable fix: removes the trailing comma

// catches this
debug!("Foo={}", 1,);

// suggests this
debug!("Foo={}", 1);

Closes #13965

changelog: [unnecessary_trailing_comma]: new lint to remove trailing commas in a single-line format macro usage

rustbot · 2026-02-07T08:30:57Z

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github-actions · 2026-02-07T08:47:00Z

Lintcheck changes for f72e055

Lint	Added	Removed	Changed
`clippy::unnecessary_trailing_comma`	17	0	0

This comment will be updated if you push new changes

rustbot · 2026-02-07T09:07:09Z

Some changes occurred in clippy_lints/src/doc

cc @notriddle

samueltardieu · 2026-02-08T08:53:08Z

The style category is warn-by-default. There is a risk that this lint is too opinionated for a warn-by-default category. Also, we don't usually lint for formatting as this is handled by rustfmt.

nyurik · 2026-02-08T09:15:33Z

@samueltardieu this lint is essentially the missing piece for a single line macro calls that cargo fmt already does for regular function calls. I don't think anyone would ever want to have println!("...",) -- most of these are simply accidental leftovers for when multiline formats get reformatted as a single line. The only reason cargo fmt cannot do it is that it requires type resolution to ensure correct detection. Note that --fix should work perfectly for this lint. I honestly think this is a "style" as anything could possibly get.

Jarcho · 2026-02-09T19:04:13Z

FCP started: https://rust-lang.zulipchat.com/#narrow/channel/257328-clippy/topic/FCP.3A.20.60unnecessary_trailing_comma.60/with/572863765

…g#16533) This noop PR makes the new comma-removing lint PR less noisy, allowing it focus only on the new functionality See rust-lang#16530 changelog: none

…n, r=mati865 style: remove unneeded trailing commas Make format-like macro calls look similar to what `cargo fmt` does automatically - remove trailing commas. When removing a comma, I also inlined some variables for consistency and clarity. I'm working on a [clippy lint](rust-lang/rust-clippy#16530) to make this process automatic.

Rollup merge of #152372 - nyurik:clippy-rustc_trait_selection, r=mati865 style: remove unneeded trailing commas Make format-like macro calls look similar to what `cargo fmt` does automatically - remove trailing commas. When removing a comma, I also inlined some variables for consistency and clarity. I'm working on a [clippy lint](rust-lang/rust-clippy#16530) to make this process automatic.

rustbot · 2026-02-13T19:40:51Z

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

nyurik

thx, fixed

@rustbot ready.

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Jarcho

Looks good. Can you squash down the commits please.

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Suggest removing an unnecessary trailing comma before the closing parenthesis in single-line format-like macro invocations (e.g. println!, format!, write!). The lint currently only runs on format-like macros because it relies on format-argument parsing; arbitrary user macros are not supported to avoid incorrect suggestions. - Lint is in the `style` group (allow-by-default) - Single-line only: multi-line macro invocations are not linted - Machine-applicable fix: removes the trailing comma

rustbot · 2026-02-17T19:30:53Z

This PR was rebased onto a different master 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.

nyurik · 2026-02-17T19:31:27Z

thx @Jarcho, rebased and squashed

Jarcho

Thank you.

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Keep new_instead_of_clear entry and incorporate all lint entries from master: unnecessary_trailing_comma (pedantic, rust-lang#16530), disallowed_fields, manual_checked_ops, duration_suboptimal_units, and manual_take. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rustbot assigned Jarcho Feb 7, 2026

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chore: remove unnecessary trailing commas in format strings #16533

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style: remove unneeded trailing commas rust-lang/rust#152372

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Merged via the queue into rust-lang:master with commit 38321c8 Feb 23, 2026
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g-plane mentioned this pull request Mar 17, 2026

unnecessary_trailing_comma appears in 1.94 section in changelog #16721

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nyurik deleted the unnecessary_trailing_comma branch April 16, 2026 17:23

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