Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::unneeded_wildcard_pattern: this pattern is unneeded as the `..` pattern can match that element

What it meansChecks for tuple and struct patterns with a wildcard pattern (_) is next to a rest pattern (..). NOTE: While _, .. means there is at least one element left, .. means there are 0 or more elements left. This can make a difference when refactoring, but shouldn’t result in errors in the refactored code, since the wildcard pattern isn’t used anyway. It is in the complexity group and warns by default.

What you see

warning: this pattern is unneeded as the `..` pattern can match that element
 --> main.rs:4:22
  |
4 |     TupleStruct(0, .., _) => (),
  |                      ^^^ help: remove it
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unneeded_wildcard_pattern
  = note: `#[warn(clippy::unneeded_wildcard_pattern)]` 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?

The wildcard pattern is unneeded as the rest pattern can match that element as well.

Code that does something simple in a complicated way. Warns by default.

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

match t {
    TupleStruct(0, .., _) => (),
    _ => (),
}

Write this instead

match t {
    TupleStruct(0, ..) => (),
    _ => (),
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
unneeded_wildcard_pattern = "allow"

One run

cargo clippy -- -A clippy::unneeded-wildcard-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.

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.40.0added in Rust

Clippy's own documentation

What it does

Checks for tuple and struct patterns with a wildcard pattern (_) is next to a rest pattern (..).

NOTE: While _, .. means there is at least one element left, .. means there are 0 or more elements left. This can make a difference when refactoring, but shouldn’t result in errors in the refactored code, since the wildcard pattern isn’t used anyway.

Why is this bad?

The wildcard pattern is unneeded as the rest pattern can match that element as well.

Example

match t {
    TupleStruct(0, .., _) => (),
    _ => (),
}

Use instead:

match t {
    TupleStruct(0, ..) => (),
    _ => (),
}

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

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