clippy::neg_cmp_op_on_partial_ord: the use of negated comparison operators on partially ordered types produces code that is hard to read and refactor, please consider using the `partial_cmp` method instead, to make it clear that the two values could be incomparable

What you see

warning: the use of negated comparison operators on partially ordered types produces code that is hard to read and refactor, please consider using the `partial_cmp` method instead, to make it clear that the two values could be incomparable
 --> main.rs:6:25
  |
6 | let not_less_or_equal = !(a <= b);
  |                         ^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#neg_cmp_op_on_partial_ord
  = note: `#[warn(clippy::neg_cmp_op_on_partial_ord)]` 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?

These operators make it easy to forget that the underlying types actually allow not only three potential Orderings (Less, Equal, Greater) but also a fourth one (Uncomparable). This is especially easy to miss if the operator based comparison result is negated.

Code that does something simple in a complicated way. Warns by default.

How to fix it

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

Flagged

let a = 1.0;
let b = f64::NAN;

let not_less_or_equal = !(a <= b);

Write this instead

use std::cmp::Ordering;

let _not_less_or_equal = match a.partial_cmp(&b) {
    None | Some(Ordering::Greater) => true,
    _ => false,
};

Turn it off, or on

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

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

[lints.clippy]
neg_cmp_op_on_partial_ord = "allow"

cargo clippy -- -A clippy::neg-cmp-op-on-partial-ord

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.