Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::manual_assert: only a `panic!` in `if`-then statement

What it meansDetects if-then-panic! that can be replaced with assert!. It is in the pedantic group and off by default.

What you see

warning: only a `panic!` in `if`-then statement
 --> main.rs:4:1
  |
4 | / if !sad_people.is_empty() {
5 | |     panic!("there are sad people: {:?}", sad_people);
6 | | }
  | |_^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_assert
  = note: `-W clippy::manual-assert` implied by `-W clippy::pedantic`
help: replace `if`-then-`panic!` with `assert!`
  |
4 - if !sad_people.is_empty() {
5 -     panic!("there are sad people: {:?}", sad_people);
6 - }
4 + assert!(sad_people.is_empty(), "there are sad people: {:?}", sad_people)
  |

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?

assert! is simpler than if-then-panic!.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

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

let sad_people: Vec<&str> = vec![];
if !sad_people.is_empty() {
    panic!("there are sad people: {:?}", sad_people);
}

Write this instead

let sad_people: Vec<&str> = vec![];
assert!(sad_people.is_empty(), "there are sad people: {:?}", sad_people);

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]
manual_assert = "warn"

In code

#![warn(clippy::manual_assert)]

One run

cargo clippy -- -W clippy::manual-assert

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.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.57.0added in Rust

Clippy's own documentation

What it does

Detects if-then-panic! that can be replaced with assert!.

Why is this bad?

assert! is simpler than if-then-panic!.

Example

let sad_people: Vec<&str> = vec![];
if !sad_people.is_empty() {
    panic!("there are sad people: {:?}", sad_people);
}

Use instead:

let sad_people: Vec<&str> = vec![];
assert!(sad_people.is_empty(), "there are sad people: {:?}", sad_people);

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

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