clippy::inverted_saturating_sub: inverted arithmetic check before subtraction

What you see

error: inverted arithmetic check before subtraction
 --> main.rs:6:19
  |
6 | let result = if a > b { b - a } else { 0 };
  |                   ^     ----- help: try replacing it with: `a - b`
  |
note: this subtraction underflows when `b < a`
 --> main.rs:6:25
  |
6 | let result = if a > b { b - a } else { 0 };
  |                         ^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#inverted_saturating_sub
  = note: `#[deny(clippy::inverted_saturating_sub)]` 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?

This could result in an underflow and is most likely not what the user wants. If this was intended to be a saturated subtraction, consider using the saturating_sub method directly.

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 (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

let a = 12u32;
let b = 13u32;

let result = if a > b { b - a } else { 0 };

Write this instead

let a = 12u32;
let b = 13u32;

let result = a.saturating_sub(b);

Turn it off, or on

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

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

[lints.clippy]
inverted_saturating_sub = "allow"

cargo clippy -- -A clippy::inverted-saturating-sub

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.