`clippy::non_canonical_partial_ord_impl` warns for canonical forwarding implementation

Lint Name

clippy::non_canonical_partial_ord_impl

Reproducer

use std::cmp::Ordering;

struct A {
    inner: i32,
    cache: i32,
}

impl PartialEq for A {
    fn eq(&self, other: &A) -> bool {
        self.inner == other.inner
    }
}

impl Eq for A {}

impl PartialOrd for A {
    fn partial_cmp(&self, other: &A) -> Option<Ordering> {
        self.inner.partial_cmp(&other.inner)
    }
}

impl Ord for A {
    fn cmp(&self, other: &A) -> Ordering {
        self.inner.cmp(&other.inner)
    }
}

Results in this warning:

warning: non-canonical implementation of `partial_cmp` on an `Ord` type
  --> 16:1
   |
16 | /  impl PartialOrd for A {
17 | |      fn partial_cmp(&self, other: &A) -> Option<Ordering> {
   | | __________________________________________________________-
18 | ||         self.inner.partial_cmp(&other.inner)
19 | ||     }
   | ||_____- help: change this to: `{ Some(self.cmp(other)) }`
20 | |  }
   | |__^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#non_canonical_partial_ord_impl
   = note: `#[warn(clippy::non_canonical_partial_ord_impl)]` on by default

But I expected no warning for this rather canonical forwarding of traits to one particular member.

Version

rustc 1.84.0 (9fc6b4312 2025-01-07)
binary: rustc
commit-hash: 9fc6b43126469e3858e2fe86cafb4f0fd5068869
commit-date: 2025-01-07
host: x86_64-unknown-linux-gnu
release: 1.84.0
LLVM version: 19.1.5

Start with the clippy::non_canonical_partial_ord_impl lint and the Rust reproducer in the issue. Inspect how the lint recognizes canonical PartialOrd implementations and compare that behavior with the shown forwarding implementation. Done means the reproducer no longer produces an incorrect warning while genuinely non-canonical implementations remain diagnosed.