Clippy lint · Style · checked with Clippy 0.1.99

clippy::needless_return_with_question_mark: Checks for return statements on Err paired with the ? operator

What it meansChecks for return statements on Err paired with the ? operator. It is in the style group and warns by default.

Does it matter?

The return is unnecessary. Returns may be used to add attributes to the return expression. Return statements with attributes are therefore be accepted by this lint.

Code that works but is not idiomatic Rust. Warns by default.

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

fn foo(x: usize) -> Result<(), Box<dyn Error>> {
    if x == 0 {
        return Err(...)?;
    }
    Ok(())
}

Write this instead

fn foo(x: usize) -> Result<(), Box<dyn Error>> {
    if x == 0 {
        Err(...)?;
    }
    Ok(())
}

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
needless_return_with_question_mark = "allow"

One run

cargo clippy -- -A clippy::needless-return-with-question-mark

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.

Stylegroup

warndefault level

yesfixed by cargo clippy --fix

1.73.0added in Rust

Clippy's own documentation

What it does

Checks for return statements on Err paired with the ? operator.

Why is this bad?

The return is unnecessary.

Returns may be used to add attributes to the return expression. Return statements with attributes are therefore be accepted by this lint.

Example

fn foo(x: usize) -> Result<(), Box<dyn Error>> {
    if x == 0 {
        return Err(...)?;
    }
    Ok(())
}

simplify to

fn foo(x: usize) -> Result<(), Box<dyn Error>> {
    if x == 0 {
        Err(...)?;
    }
    Ok(())
}

if paired with try_err, use instead:

fn foo(x: usize) -> Result<(), Box<dyn Error>> {
    if x == 0 {
        return Err(...);
    }
    Ok(())
}

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

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