clippy::boxed_local: local variable doesn't need to be boxed here

What you see

warning: local variable doesn't need to be boxed here
 --> main.rs:3:8
  |
3 | fn foo(x: Box<u32>) {}
  |        ^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#boxed_local
  = note: `#[warn(clippy::boxed_local)]` on by default

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?

This is an unnecessary allocation, and bad for performance. It is only necessary to allocate if you wish to move the box into something.

Code that could be written to run faster. Warns by default.

How to fix it

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

Flagged

fn foo(x: Box<u32>) {}

Write this instead

fn foo(x: u32) {}

Turn it off, or on

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

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

[lints.clippy]
boxed_local = "allow"

cargo clippy -- -A clippy::boxed-local

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

• too-large-for-stack: The maximum size of objects (in bytes) that will be linted. Larger objects are ok on the heap