Silence clippy lints for #[instrument] on async functions for crates that warn on implicit_return

[mjbshaw]

The macro expands to a trialing if statement that is used as an implicit return value for the function. That works, but for users who set implicit_return = "deny" then this results in triggering clippy.

Motivation

See rust-lang/rust-clippy#16676

Minimum reproducible example:

Cargo.toml:

[package]
name = "clippy-implicit-return-instrument-repro"
edition = "2024"

[dependencies]
tracing = { version = "0.1.44", features = ["attributes"] }

[lints.clippy]
implicit_return = "deny"

src/lib.rs:

#[tracing::instrument]
pub async fn run() {
}

If you then run cargo clippy you get this result:

error: missing `return` statement
 --> src/lib.rs:1:1
  |
1 | #[tracing::instrument]
  | ^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#implicit_return
  = note: requested on the command line with `-D clippy::implicit-return`
  = note: this error originates in the attribute macro `tracing::instrument` (in Nightly builds, run with -Z macro-backtrace for more info)

Solution

#[allow(clippy::implicit_return)] on the trailing return so it doesn't trigger clippy.