clippy::misrefactored_assign_op: variable appears on both sides of an assignment operation

What you see

warning: variable appears on both sides of an assignment operation
 --> main.rs:6:1
  |
6 | a += a + b;
  | ^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#misrefactored_assign_op
  = note: `#[warn(clippy::misrefactored_assign_op)]` on by default
help: did you mean `a = a + b` or `a = a + a + b`? Consider replacing it with
  |
6 - a += a + b;
6 + a += b;
  |
help: or
  |
6 - a += a + b;
6 + a = a + a + b;
  |

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?

Most likely these are bugs where one meant to write a op= b.

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

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

let mut a = 5;
let b = 2;
// ...
a += a + b;

Turn it off, or on

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

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

[lints.clippy]
misrefactored_assign_op = "allow"

cargo clippy -- -A clippy::misrefactored-assign-op

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.