Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::nonnull_unchecked_on_box_ptr: use of `NonNull::new_unchecked` with `Box::into_raw`

What it meansChecks for unsafe usage of NonNull::new_unchecked(Box::into_raw(x)), and suggests calling NonNull::from_mut(Box::leak(x)) instead. It is in the complexity group and warns by default.

What you see

warning: use of `NonNull::new_unchecked` with `Box::into_raw`
 --> main.rs:5:11
  |
5 | let ptr = unsafe { NonNull::new_unchecked(Box::into_raw(one)) };
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::into_non_null(one)`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#nonnull_unchecked_on_box_ptr
  = note: `#[warn(clippy::nonnull_unchecked_on_box_ptr)]` on by default

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?

NonNull::new_unchecked is an unsafe function, which we don’t need to call at all if we can instead use a mutable reference.

Code that does something simple in a complicated way. Warns by default.

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

use std::ptr::NonNull;
let one = Box::new(1);
let ptr = unsafe { NonNull::new_unchecked(Box::into_raw(one)) };

Write this instead

use std::ptr::NonNull;
let one = Box::new(1);
let ptr = NonNull::from_mut(Box::leak(one));

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::nonnull_unchecked_on_box_ptr)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
nonnull_unchecked_on_box_ptr = "allow"

One run

cargo clippy -- -A clippy::nonnull-unchecked-on-box-ptr

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.

Settings in clippy.toml

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

Complexitygroup

warndefault level

yesfixed by cargo clippy --fix

1.98.0added in Rust

Clippy's own documentation

What it does

Checks for unsafe usage of NonNull::new_unchecked(Box::into_raw(x)), and suggests calling NonNull::from_mut(Box::leak(x)) instead.

Why is this bad?

NonNull::new_unchecked is an unsafe function, which we don’t need to call at all if we can instead use a mutable reference.

Example

use std::ptr::NonNull;
let one = Box::new(1);
let ptr = unsafe { NonNull::new_unchecked(Box::into_raw(one)) };

Use instead:

use std::ptr::NonNull;
let one = Box::new(1);
let ptr = NonNull::from_mut(Box::leak(one));

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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