Useless check for chars

[xamgore]

Summary

to_ascii_lowercase is totally fine.

Lint Name

clippy::manual_ignore_case_cmp

Reproducer

I tried this code:

let x: char = 'a';
if x.to_ascii_lowercase() == 's' { ... }

I saw this happen:

manual case-insensitive ASCII comparison Help: for further information visit https://rust-lang.github.io/rust-clippy/master/index. html#manual_ignore_case_cmp Note: `#[warn(clippy::manual_ignore_case_cmp)]` on by default Help: consider using `.eq_ignore_ascii_case()` instead

let x: char = 'a';
if x.eq_ignore_ascii_case(&'s') { ... }

pub const fn eq_ignore_ascii_case(&self, other: &char) -> bool {
    self.to_ascii_lowercase() == other.to_ascii_lowercase()
}

Version

rustc 1.84.0 (9fc6b4312 2025-01-07)
binary: rustc
commit-hash: 9fc6b43126469e3858e2fe86cafb4f0fd5068869
commit-date: 2025-01-07
host: aarch64-apple-darwin
release: 1.84.0
LLVM version: 19.1.5

Additional Labels

No response

[alex-semenyuk]

This is performance lint.

Why is this bad?
The eq_ignore_ascii_case method is faster because it does not allocate memory for the new strings, and it is more readable.

[xamgore]

How does comparing strings relate to comparing chars? For strings the lint is totally legal, while for chars it's meaningless, isn't it?