clippy::missing_inline_in_public_items: missing `#[inline]` on a publicly callable function

What you see

warning: missing `#[inline]` on a publicly callable function
 --> main.rs:1:1
  |
1 | pub fn foo() {} // missing #[inline]
  | ^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#missing_inline_in_public_items
  = note: requested on the command line with `-W clippy::missing-inline-in-public-items`

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?

When a function is not marked #[inline], it is not a “small” candidate for automatic inlining, and LTO is not in use, then it is not possible for the function to be inlined into the code of any crate other than the one in which it is defined. Depending on the role of the function and the relationship of the crates, this could significantly reduce performance. Certain types of crates might intend for most of the methods in their public API to be able to be inlined across crates even when LTO is disabled. This lint allows those crates to require all exported methods to be #[inline] by default, and then opt out for specific methods where this might not make sense.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

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

Flagged

pub fn foo() {} // missing #[inline]
fn ok() {} // ok
#[inline] pub fn bar() {} // ok
#[inline(always)] pub fn baz() {} // ok

pub trait Bar {
  fn bar(); // ok
  fn def_bar() {} // missing #[inline]
}

struct Baz;
impl Baz {
    fn private() {} // ok
}

impl Bar for Baz {
  fn bar() {} // ok - Baz is not exported
}

pub struct PubBaz;
impl PubBaz {
    fn private() {} // ok
    pub fn not_private() {} // missing #[inline]
}

impl Bar for PubBaz {
    fn bar() {} // missing #[inline]
    fn def_bar() {} // missing #[inline]
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

[lints.clippy]
missing_inline_in_public_items = "warn"

#![warn(clippy::missing_inline_in_public_items)]

cargo clippy -- -W clippy::missing-inline-in-public-items

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.