The issue concerns this line:
https://github.com/rust-lang/rust-clippy/blob/98c4a49db8c305c468646715b773fa9b6ec7049a/clippy_lints/src/derive.rs#L350

The line is 130 characters long, which exceeds the max_width declared in the rustfmt.toml file:
https://github.com/rust-lang/rust-clippy/blob/98c4a49db8c305c468646715b773fa9b6ec7049a/rustfmt.toml#L1

Yet none of these commands produce a change or error:

cargo fmt
rustfmt clippy_lints/src/derive.rs
cargo +nightly fmt
rustfmt +nightly clippy_lints/src/derive.rs

(Re +nightly, recall Clippy uses a rust-toolchain file.)