clippy::double-must-use emitted for #[must_use] on async fn

[garryod]

Summary

As of 1.67 (Pull Request), the #[must_use] hint is applied to the Output of a Future when use on an async fn. With this change clippy now reports a false positive double-must-use in the context of async fns.

Lint Name

double-must-use

Reproducer

I tried this code:

#[must_use]
pub async fn new_reliable(room_url: impl Into<String>) -> (Self, MessageLoopFuture) {
    ...
}

I saw this happen:

error: this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]`
Error:    --> matchbox_socket/src/webrtc_socket/socket.rs:139:5
    |
139 |     pub async fn new_unreliable(room_url: impl Into<String>) -> (Self, MessageLoopFuture) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: either add some descriptive text or remove the attribute
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#double_must_use
    = note: `-D clippy::double-must-use` implied by `-D warnings`

I expected to see this happen:

No warning

Version

rustc 1.68.0 (2c8cc3432 2023-03-06)
binary: rustc
commit-hash: 2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74
commit-date: 2023-03-06
host: x86_64-unknown-linux-gnu
release: 1.68.0
LLVM version: 15.0.6

Additional Labels

No response

[blyxyas]

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