Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::unnecessary_wraps: this function's return value is unnecessarily wrapped by `Option`

What it meansChecks for private functions that only return Ok or Some. It is in the pedantic group and off by default.

What you see

warning: this function's return value is unnecessarily wrapped by `Option`
  --> main.rs:3:1
   |
 3 | fn get_cool_number(a: bool, b: bool) -> Option<i32> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#unnecessary_wraps
   = note: `-W clippy::unnecessary-wraps` implied by `-W clippy::pedantic`
help: remove `Option` from the return type...
   |
 3 - fn get_cool_number(a: bool, b: bool) -> Option<i32> {
 3 + fn get_cool_number(a: bool, b: bool) -> i32 {
   |
help: ...and then remove the surrounding `Some()` from returning expressions
   |
 5 ~         return 50;
 6 |     }
 7 |     if a {
 8 ~         0
 9 |     } else {
10 ~         10
   |

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?

It is not meaningful to wrap values when no None or Err is returned.

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

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 get_cool_number(a: bool, b: bool) -> Option<i32> {
    if a && b {
        return Some(50);
    }
    if a {
        Some(0)
    } else {
        Some(10)
    }
}

Write this instead

fn get_cool_number(a: bool, b: bool) -> i32 {
    if a && b {
        return 50;
    }
    if a {
        0
    } else {
        10
    }
}

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]
unnecessary_wraps = "warn"

In code

#![warn(clippy::unnecessary_wraps)]

One run

cargo clippy -- -W clippy::unnecessary-wraps

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.

Settings in clippy.toml

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

Pedanticgroup

allowdefault level

nofixed by cargo clippy --fix

1.50.0added in Rust

Clippy's own documentation

What it does

Checks for private functions that only return Ok or Some.

Why is this bad?

It is not meaningful to wrap values when no None or Err is returned.

Known problems

There can be false positives if the function signature is designed to fit some external requirement.

Example

fn get_cool_number(a: bool, b: bool) -> Option<i32> {
    if a && b {
        return Some(50);
    }
    if a {
        Some(0)
    } else {
        Some(10)
    }
}

Use instead:

fn get_cool_number(a: bool, b: bool) -> i32 {
    if a && b {
        return 50;
    }
    if a {
        0
    } else {
        10
    }
}

Configuration

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

(default: true)

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

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