Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::unneeded_field_pattern: you matched a field with a wildcard pattern, consider using `..` instead

What it meansChecks for structure field patterns bound to wildcards. It is in the restriction group and off by default.

What you see

warning: you matched a field with a wildcard pattern, consider using `..` instead
 --> main.rs:6:11
  |
6 |     Foo { a: _, b: 0, .. } => {},
  |           ^^^^
  |
  = help: try with `Foo { b: 0, .. }`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unneeded_field_pattern
  = note: requested on the command line with `-W clippy::unneeded-field-pattern`

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?

Using .. instead is shorter and leaves the focus on the fields that are actually bound.

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

let f = Foo { a: 0, b: 0, c: 0 };

match f {
    Foo { a: _, b: 0, .. } => {},
    Foo { a: _, b: _, c: _ } => {},
}

Write this instead

let f = Foo { a: 0, b: 0, c: 0 };

match f {
    Foo { b: 0, .. } => {},
    Foo { .. } => {},
}

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]
unneeded_field_pattern = "warn"

In code

#![warn(clippy::unneeded_field_pattern)]

One run

cargo clippy -- -W clippy::unneeded-field-pattern

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

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for structure field patterns bound to wildcards.

Why restrict this?

Using .. instead is shorter and leaves the focus on the fields that are actually bound.

Example

let f = Foo { a: 0, b: 0, c: 0 };

match f {
    Foo { a: _, b: 0, .. } => {},
    Foo { a: _, b: _, c: _ } => {},
}

Use instead:

let f = Foo { a: 0, b: 0, c: 0 };

match f {
    Foo { b: 0, .. } => {},
    Foo { .. } => {},
}

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

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