Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::empty_structs_with_brackets: found empty brackets on struct declaration

What it meansFinds structs without fields (a so-called “empty struct”) that are declared with brackets. It is in the restriction group and off by default.

What you see

warning: found empty brackets on struct declaration
 --> main.rs:3:14
  |
3 | struct Cookie {}
  |              ^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#empty_structs_with_brackets
  = note: requested on the command line with `-W clippy::empty-structs-with-brackets`
  = help: remove the brackets

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?

Empty brackets after a struct declaration can be omitted, and it may be desirable to do so consistently for style. However, removing the brackets also introduces a public constant named after the struct, so this is not just a syntactic simplification but an API change, and adding them back is a breaking API change.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

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

Flagged

struct Cookie {}
struct Biscuit();

Write this instead

struct Cookie;
struct Biscuit;

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]
empty_structs_with_brackets = "warn"

In code

#![warn(clippy::empty_structs_with_brackets)]

One run

cargo clippy -- -W clippy::empty-structs-with-brackets

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.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.62.0added in Rust

Clippy's own documentation

What it does

Finds structs without fields (a so-called “empty struct”) that are declared with brackets.

Why restrict this?

Empty brackets after a struct declaration can be omitted, and it may be desirable to do so consistently for style.

However, removing the brackets also introduces a public constant named after the struct, so this is not just a syntactic simplification but an API change, and adding them back is a breaking API change.

Example

struct Cookie {}
struct Biscuit();

Use instead:

struct Cookie;
struct Biscuit;

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

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