Summary

The manual_is_power_of_two lint:

• may suggest invalid code by not adding required parentheses
• suggest invalid code by not checking the MSRV in a const context

Reproducer

I tried this code:

#![allow(unused)]
#![warn(clippy::manual_is_power_of_two)]
#[clippy::msrv = "1.0.0"]
const fn f(a: i32) -> bool {
    a as u32 & (a as u32 - 1) == 0
}
fn main() {}

I expected to see this happen: either no suggestion, or a suggestion to use (a as u32).count_ones() == 1.

Instead, this happened:

warning: manually reimplementing `is_power_of_two`
 --> u.rs:6:5
  |
6 |     a as u32 & (a as u32 - 1) == 0
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `.is_power_of_two()`: `a as u32.is_power_of_two()`

Not only .is_power_of_two() cannot be used in a const context below Rust 1.32.0, but also the suggestion a as u32.is_power_of_two() lacks parentheses around a as u32.

Version

rustc 1.87.0-nightly (1aeb99d24 2025-03-19)
binary: rustc
commit-hash: 1aeb99d248e1b0069110cb03c6f1dcc7b36fd7f3
commit-date: 2025-03-19
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Additional Labels

@rustbot label +Isuggestion-causes-error
@rustbot claim