clippy::manual_bit_width: manual implementation of `bit_width`

What you see

warning: manual implementation of `bit_width`
 --> main.rs:4:17
  |
4 | let bit_width = u32::BITS - x.leading_zeros();
  |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_bit_width
  = note: `-W clippy::manual-bit-width` implied by `-W clippy::pedantic`
help: try
  |
4 - let bit_width = u32::BITS - x.leading_zeros();
4 + let bit_width = x.bit_width();
  |

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

Manual reimplementations of bit_width increase code complexity for little benefit.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

let x: u32 = 5;
let bit_width = u32::BITS - x.leading_zeros();

Write this instead

let x: u32 = 5;
let bit_width = x.bit_width();

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

[lints.clippy]
manual_bit_width = "warn"

#![warn(clippy::manual_bit_width)]

cargo clippy -- -W clippy::manual-bit-width

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.