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Recommend NonZero*::new.unwrap() over NonZero*::new_unchecked in consts #13991

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zacknewman opened this issue Jan 13, 2025 · 2 comments · Fixed by #13993
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Recommend NonZero*::new.unwrap() over NonZero*::new_unchecked in consts #13991

zacknewman opened this issue Jan 13, 2025 · 2 comments · Fixed by #13993
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@samueltardieu
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A-lint Area: New lints

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@zacknewman
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zacknewman commented Jan 13, 2025 •
edited by rustbot
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What it does

Just found out that Option::unwrap is now a const fn; had I not ran into that, I wouldn't have changed my use of NonZero*::new_unchecked for const variables.

Advantage

  • Removes one more case where unsafe code is needed.

Drawbacks

  • Conflicts with unwrap_used.

Example

use core::num::NonZeroUsize;
const FOO: NonZeroUsize = unsafe { NonZeroUsize::new_unchecked(1) };

Could be written as:

use core::num::NonZeroUsize;
const FOO: NonZeroUsize =  NonZeroUsize::new(1).unwrap();
@zacknewman zacknewman added the A-lint Area: New lints label Jan 13, 2025
@zacknewman zacknewman changed the title Recommend NonZero*:new.unwrap() over NonZero*::new_unchecked in consts Recommend NonZero*::new.unwrap() over NonZero*::new_unchecked in consts Jan 13, 2025
@samueltardieu
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@samueltardieu samueltardieu mentioned this issue Jan 13, 2025
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github-merge-queue bot pushed a commit that referenced this issue Jan 15, 2025
@Manishearth
New lint useless-nonzero-new_unchecked (#13993)
25d319d 
changelog: [`useless-nonzero-new_unchecked`]: new lint

Close #13991

### What it does

Checks for `NonZero*::new_unchecked(<literal>)` being used in a `const`
context.

### Why is this bad?

Using `NonZero*::new_unchecked()` is an `unsafe` function and requires
an `unsafe` context. When used with an
integer literal in a `const` context, `NonZero*::new().unwrap()` will
provide the same result with identical
runtime performances while not requiring `unsafe`.

### Example
```no_run
const PLAYERS: NonZeroUsize = unsafe { NonZeroUsize::new_unchecked(3) };
```
Use instead:
```no_run
const PLAYERS: NonZeroUsize = NonZeroUsize::new(3).unwrap();
```
@leonardo-m
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To avoid seeing the unwrap, sometimes I'd like to use a compile-time function like this:

const FOO: NonZeroUsize = non_zero<usize, 1>();

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New lint useless-nonzero-new_unchecked samueltardieu/rust-clippy
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@samueltardieu @zacknewman @leonardo-m