Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::panic_in_result_fn: used `panic!()` or assertion in a function that returns `Result`

What it meansChecks for usage of panic! or assertions in a function whose return type is Result. It is in the restriction group and off by default.

What you see

warning: used `panic!()` or assertion in a function that returns `Result`
 --> main.rs:3:1
  |
3 | / fn result_with_panic() -> Result<bool, String>
4 | | {
5 | |     panic!("error");
6 | | }
  | |_^
  |
  = help: `panic!()` or assertions should not be used in a function that returns `Result` as `Result` is expected to return an error instead of crashing
note: return Err() instead of panicking
 --> main.rs:5:5
  |
5 |     panic!("error");
  |     ^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#panic_in_result_fn
  = note: requested on the command line with `-W clippy::panic-in-result-fn`

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?

For some codebases, it is desirable for functions of type result to return an error instead of crashing. Hence panicking macros should be avoided.

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. Change the code by hand:

Flagged

fn result_with_panic() -> Result<bool, String>
{
    panic!("error");
}

Write this instead

fn result_without_panic() -> Result<bool, String> {
    Err(String::from("error"))
}

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]
panic_in_result_fn = "warn"

In code

#![warn(clippy::panic_in_result_fn)]

One run

cargo clippy -- -W clippy::panic-in-result-fn

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

1.48.0added in Rust

Clippy's own documentation

What it does

Checks for usage of panic! or assertions in a function whose return type is Result.

Why restrict this?

For some codebases, it is desirable for functions of type result to return an error instead of crashing. Hence panicking macros should be avoided.

Known problems

Functions called from a function returning a Result may invoke a panicking macro. This is not checked.

Example

fn result_with_panic() -> Result<bool, String>
{
    panic!("error");
}

Use instead:

fn result_without_panic() -> Result<bool, String> {
    Err(String::from("error"))
}

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

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