Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::redundant_locals: redundant redefinition of a binding `a`

What it meansChecks for redundant redefinitions of local bindings. It is in the suspicious group and warns by default.

What you see

warning: redundant redefinition of a binding `a`
 --> main.rs:4:1
  |
4 | let a = a;
  | ^^^^^^^^^^
  |
help: `a` is initially defined here
 --> main.rs:3:5
  |
3 | let a = 0;
  |     ^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#redundant_locals
  = note: `#[warn(clippy::redundant_locals)]` 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?

Redundant redefinitions of local bindings do not change behavior other than variable’s lifetimes and are likely to be unintended. These rebindings can be intentional to shorten the lifetimes of variables because they affect when the Drop implementation is called. Other than that, they do not affect your code’s meaning but they may affect rustc’s stack allocation.

Code that is most likely wrong or useless. Warns by default.

How to fix it

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

Flagged

let a = 0;
let a = a;

fn foo(b: i32) {
    let b = b;
}

Write this instead

let a = 0;
// no redefinition with the same name

fn foo(b: i32) {
  // no redefinition with the same name
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
redundant_locals = "allow"

One run

cargo clippy -- -A clippy::redundant-locals

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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.73.0added in Rust

Clippy's own documentation

What it does

Checks for redundant redefinitions of local bindings.

Why is this bad?

Redundant redefinitions of local bindings do not change behavior other than variable’s lifetimes and are likely to be unintended.

These rebindings can be intentional to shorten the lifetimes of variables because they affect when the Drop implementation is called. Other than that, they do not affect your code’s meaning but they may affect rustc’s stack allocation.

Example

let a = 0;
let a = a;

fn foo(b: i32) {
    let b = b;
}

Use instead:

let a = 0;
// no redefinition with the same name

fn foo(b: i32) {
  // no redefinition with the same name
}

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

Up next

Also worth your time

Did this answer your question?