Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::empty_enum_variants_with_brackets: enum variant has empty brackets

What it meansFinds enum variants without fields that are declared with empty brackets. It is in the restriction group and off by default.

What you see

warning: enum variant has empty brackets
 --> main.rs:5:14
  |
5 |     HasNoData(),       // redundant parentheses
  |              ^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#empty_enum_variants_with_brackets
  = note: requested on the command line with `-W clippy::empty-enum-variants-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 enum variant declaration are redundant and 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 variant, 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 (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

enum MyEnum {
    HasData(u8),
    HasNoData(),       // redundant parentheses
    NoneHereEither {}, // redundant braces
}

Write this instead

enum MyEnum {
    HasData(u8),
    HasNoData,
    NoneHereEither,
}

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_enum_variants_with_brackets = "warn"

In code

#![warn(clippy::empty_enum_variants_with_brackets)]

One run

cargo clippy -- -W clippy::empty-enum-variants-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

1.77.0added in Rust

Clippy's own documentation

What it does

Finds enum variants without fields that are declared with empty brackets.

Why restrict this?

Empty brackets after a enum variant declaration are redundant and 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 variant, so this is not just a syntactic simplification but an API change, and adding them back is a breaking API change.

Example

enum MyEnum {
    HasData(u8),
    HasNoData(),       // redundant parentheses
    NoneHereEither {}, // redundant braces
}

Use instead:

enum MyEnum {
    HasData(u8),
    HasNoData,
    NoneHereEither,
}

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

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