Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::possible_missing_comma: possibly missing a comma here

What it meansChecks for possible missing comma in an array. It lints if an array element is a binary operator expression and it lies on two lines. It is in the correctness group and denied by default (the build fails).

What you see

error: possibly missing a comma here
 --> main.rs:4:15
  |
4 |     -1, -2, -3 // <= no comma here
  |               ^
  |
  = note: to remove this lint, add a comma or write the expr in a single line
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#possible_missing_comma
  = note: `#[deny(clippy::possible_missing_comma)]` on by default

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?

This could lead to unexpected results.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let a = &[
    -1, -2, -3 // <= no comma here
    -4, -5, -6
];

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::possible_missing_comma)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
possible_missing_comma = "allow"

One run

cargo clippy -- -A clippy::possible-missing-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.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for possible missing comma in an array. It lints if an array element is a binary operator expression and it lies on two lines.

Why is this bad?

This could lead to unexpected results.

Example

let a = &[
    -1, -2, -3 // <= no comma here
    -4, -5, -6
];

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

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