Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::unnecessary_safety_comment: statement has unnecessary safety comment

What it meansChecks for // SAFETY: comments on safe code. It is in the restriction group and off by default.

What you see

warning: statement has unnecessary safety comment
 --> main.rs:7:1
  |
7 | let ptr = NonNull::new(a).unwrap();
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
help: consider removing the safety comment
 --> main.rs:6:4
  |
6 | // SAFETY: references are guaranteed to be non-null.
  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_safety_comment
  = note: requested on the command line with `-W clippy::unnecessary-safety-comment`

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?

Safe code has no safety requirements, so there is no need to describe safety invariants.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

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 a = &mut 42;

// SAFETY: references are guaranteed to be non-null.
let ptr = NonNull::new(a).unwrap();

Write this instead

use std::ptr::NonNull;
let a = &mut 42;

let ptr = NonNull::new(a).unwrap();

Turn it off, or on

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

Whole crate (Cargo.toml)

[lints.clippy]
unnecessary_safety_comment = "warn"

In code

#![warn(clippy::unnecessary_safety_comment)]

One run

cargo clippy -- -W clippy::unnecessary-safety-comment

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.

Restrictiongroup

allowdefault level

yesfixed by cargo clippy --fix

1.67.0added in Rust

Clippy's own documentation

What it does

Checks for // SAFETY: comments on safe code.

Why restrict this?

Safe code has no safety requirements, so there is no need to describe safety invariants.

Example

use std::ptr::NonNull;
let a = &mut 42;

// SAFETY: references are guaranteed to be non-null.
let ptr = NonNull::new(a).unwrap();

Use instead:

use std::ptr::NonNull;
let a = &mut 42;

let ptr = NonNull::new(a).unwrap();

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

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