clippy::used_underscore_binding: used underscore-prefixed binding

What you see

warning: used underscore-prefixed binding
 --> main.rs:4:9
  |
4 | let y = _x + 1; // Here we are using `_x`, even though it has a leading
  |         ^^
  |
note: binding is defined here
 --> main.rs:3:5
  |
3 | let _x = 0;
  |     ^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#used_underscore_binding
  = note: `-W clippy::used-underscore-binding` implied by `-W clippy::pedantic`

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?

A single leading underscore is usually used to indicate that a binding will not be used. Using such a binding breaks this expectation.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

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

Flagged

let _x = 0;
let y = _x + 1; // Here we are using `_x`, even though it has a leading
                // underscore. We should rename `_x` to `x`

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

[lints.clippy]
used_underscore_binding = "warn"

#![warn(clippy::used_underscore_binding)]

cargo clippy -- -W clippy::used-underscore-binding

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.