Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::infinite_loop: infinite loop detected

What it meansChecks for infinite loops in a function where the return type is not ! and lint accordingly. It is in the restriction group and off by default.

What you see

warning: infinite loop detected
 --> main.rs:4:5
  |
4 | /     loop {
5 | |         // do something
6 | |     }
  | |_____^
  |
  = help: if this is not intended, try adding a `break` or `return` to the loop
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#infinite_loop
  = note: requested on the command line with `-W clippy::infinite-loop`
help: if this is intentional, consider specifying `!` as function return
  |
3 | fn run_forever() -> ! {
  |                  ++++

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?

Making the return type ! serves as documentation that the function does not return. If the function is not intended to loop infinitely, then this lint may detect a bug.

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 does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

fn run_forever() {
    loop {
        // do something
    }
}

Write this instead

fn run_forever() -> ! {
    loop {
        // do something
    }
}

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]
infinite_loop = "warn"

In code

#![warn(clippy::infinite_loop)]

One run

cargo clippy -- -W clippy::infinite-loop

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

nofixed by cargo clippy --fix

1.76.0added in Rust

Clippy's own documentation

What it does

Checks for infinite loops in a function where the return type is not ! and lint accordingly.

Why restrict this?

Making the return type ! serves as documentation that the function does not return. If the function is not intended to loop infinitely, then this lint may detect a bug.

Example

fn run_forever() {
    loop {
        // do something
    }
}

If infinite loops are as intended:

fn run_forever() -> ! {
    loop {
        // do something
    }
}

Otherwise add a break or return condition:

fn run_forever() {
    loop {
        // do something
        if condition {
            break;
        }
    }
}

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

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