clippy::no_effect_underscore_binding: binding to `_` prefixed variable with no side-effect

What you see

warning: binding to `_` prefixed variable with no side-effect
 --> main.rs:3:5
  |
3 | let _i_serve_no_purpose = 1;
  |     ^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#no_effect_underscore_binding
  = note: `-W clippy::no-effect-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?

Unlike dead code, these bindings are actually executed. However, as they have no effect and shouldn’t be used further on, all they do is make the code less readable.

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 _i_serve_no_purpose = 1;

Turn it off, or on

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

[lints.clippy]
no_effect_underscore_binding = "warn"

#![warn(clippy::no_effect_underscore_binding)]

cargo clippy -- -W clippy::no-effect-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.