Lint bit width

[alv-around]

Fixes #16876

Current state:

• suggests change of T::BITS - x.leading_zeros() for uints
• suggests change of NonZero::<T>::BITS - x.leading_zeros() for NonZero (see comment)

Description

rust 1.97 introduces the method bit_width() for uints and NonZero (docs), this will make the manual computation redundant and unnecessary.

Example

let x: u32 = b'101';
let bit_width = u32::BITS - x.leading_zeros();

Can be replaced with:

let x: u32 = b'101';
let bit_width = x.bit_width();

changelog: [manual_bit_width]: Added a lint to detect bit_width implementations.

I have

• Followed [lint naming conventions][lint_naming]
• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation
• Run cargo dev fmt

[rustbot]

r? @dswij

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[alv-around]

Same as in the previous comment

View changes since the review

[sorairolake]

NonZero::<T>::BITS - x.leading_zeros() returns u32, and x.bit_width() returns NonZero<u32>, where x is NonZero<T>. Therefore, these are not equivalent.

[alv-around]

NonZero::<T>::BITS - x.leading_zeros() returns u32, and x.bit_width() returns NonZero<u32>, where x is NonZero<T>. Therefore, these are not equivalent.

Good catch! I remove support NonZero::<T>::BITS - x.leading_zeros() case.