Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::unit_cmp: Checks for comparisons to unit

What it meansChecks for comparisons to unit. This includes all binary comparisons (like == and <) and asserts. It is in the correctness group and denied by default (the build fails).

Does it matter?

Unit is always equal to itself, and thus is just a clumsily written constant. Mostly this happens when someone accidentally adds semicolons at the end of the operands.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

if {
    foo();
} == {
    bar();
} {
    baz();
}

Write this instead

{
    foo();
    bar();
    baz();
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
unit_cmp = "allow"

One run

cargo clippy -- -A clippy::unit-cmp

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.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for comparisons to unit. This includes all binary comparisons (like == and <) and asserts.

Why is this bad?

Unit is always equal to itself, and thus is just a clumsily written constant. Mostly this happens when someone accidentally adds semicolons at the end of the operands.

Example

if {
    foo();
} == {
    bar();
} {
    baz();
}

is equal to

{
    foo();
    bar();
    baz();
}

For asserts:

assert_eq!({ foo(); }, { bar(); });

will always succeed

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

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