Suggest using is_ascii_lowercase / is_ascii_uppercase

[leonardo-m]

What it does

This simple lint suggests to replace matches!() on full upper/lower case ranges with the built-in methods.

Lint Name

use_is_ascii_lower_upper_case

Category

style

Advantage

The code is simpler, it contains less tokens.

Drawbacks

None, I think.

Example

#![warn(clippy::all)]
#![warn(clippy::nursery)]
#![warn(clippy::pedantic)]
fn main() {
    assert!(matches!('x', 'a' ..= 'z'));
    assert!(matches!('X', 'A' ..= 'Z'));
    assert!(matches!(b'x', b'a' ..= b'z'));
    assert!(matches!(b'X', b'A' ..= b'Z'));
}

Could be written as:

#![warn(clippy::all)]
#![warn(clippy::nursery)]
#![warn(clippy::pedantic)]
fn main() {
    assert!('x'.is_ascii_lowercase());
    assert!(b'x'.is_ascii_lowercase());
    assert!('X'.is_ascii_uppercase());
    assert!(b'X'.is_ascii_uppercase());    
}

[oppiliappan]

this should be applicable to 'a'..='z'.contains(&c) as well.

[koka831]

@rustbot claim

[koka831]

It might be better to use matches! macro when given pattern contains multiple conditions.

assert!(matches!(foo, 'A'..='Z' | 'a'..='z'));

// should be?
assert!(foo.is_ascii_uppercase() || foo.is_ascii_lowercase())

Of course it'd be great to suggest to use is_ascii_alphabetic in that case.

[xFrednet]

It might be better to use matches! macro when given pattern contains multiple conditions.

For the given example, suggesting is_ascii_alphabetic would be ideal, but also a lot more work to implement. So my suggestion would be to first focus on is_ascii_uppercase and is_ascii_lowercase. The lint can always be improved later :)

Though, I would try to find a more general lint name like manual_is_ascii_check. Then we can also use that for is_ascii_digit. The lint description could also say that these is_ascii_ functions are often const :)

[koka831]

The lint can always be improved later :)

Yes, that's true. we'll start small and then grow it.
So I'll try to handle matches! macro with single range as suggested above.

I would try to find a more general lint name like manual_is_ascii_check

👍

[koka831]

@xFrednet can we close this? Or leave it open until #9290 (comment) get covered?:)

[xFrednet]

Oh yes, we can close this. Thank you for the ping and the implementation! :)