Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::unnecessary_trailing_comma: unnecessary trailing comma

What it meansSuggests removing an unnecessary trailing comma before the closing parenthesis in single-line macro invocations. It is in the pedantic group and off by default.

What you see

warning: unnecessary trailing comma
 --> main.rs:3:21
  |
3 | println!("Foo={}", 1,);
  |                     ^ help: remove the trailing comma
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_trailing_comma
  = note: `-W clippy::unnecessary-trailing-comma` implied by `-W clippy::pedantic`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

The trailing comma is redundant and removing it is more consistent with how rustfmt formats regular function calls.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

println!("Foo={}", 1,);

Write this instead

println!("Foo={}", 1);

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
unnecessary_trailing_comma = "warn"

In code

#![warn(clippy::unnecessary_trailing_comma)]

One run

cargo clippy -- -W clippy::unnecessary-trailing-comma

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.95.0added in Rust

Clippy's own documentation

What it does

Suggests removing an unnecessary trailing comma before the closing parenthesis in single-line macro invocations.

Why is this bad?

The trailing comma is redundant and removing it is more consistent with how rustfmt formats regular function calls.

Known limitations

This lint currently only runs on format-like macros (e.g. format!, println!, write!) because it relies on format-argument parsing; applying it to arbitrary user macros could cause incorrect suggestions. It may be extended to other macros in the future. Only single-line macro invocations are linted.

Example

println!("Foo={}", 1,);

Use instead:

println!("Foo={}", 1);

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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