Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::self_assignment: self-assignment of `a.x` to `a.x`

What it meansChecks for explicit self-assignments. It is in the correctness group and denied by default (the build fails).

What you see

error: self-assignment of `a.x` to `a.x`
 --> main.rs:8:5
  |
8 |     a.x = a.x;
  |     ^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#self_assignment
  = note: `#[deny(clippy::self_assignment)]` 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?

Self-assignments are redundant and unlikely to be intentional.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

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

Flagged

struct Event {
    x: i32,
}

fn copy_position(a: &mut Event, b: &Event) {
    a.x = a.x;
}

Write this instead

struct Event {
    x: i32,
}

fn copy_position(a: &mut Event, b: &Event) {
    a.x = b.x;
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
self_assignment = "allow"

One run

cargo clippy -- -A clippy::self-assignment

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.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

1.48.0added in Rust

Clippy's own documentation

What it does

Checks for explicit self-assignments.

Why is this bad?

Self-assignments are redundant and unlikely to be intentional.

Known problems

If expression contains any deref coercions or indexing operations they are assumed not to have any side effects.

Example

struct Event {
    x: i32,
}

fn copy_position(a: &mut Event, b: &Event) {
    a.x = a.x;
}

Should be:

struct Event {
    x: i32,
}

fn copy_position(a: &mut Event, b: &Event) {
    a.x = b.x;
}

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

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