Disable clippy error around generated main function

[vic1707]

The current implementation of embassy_executor::main and generated code causes clippy to complain even when using an empty function (for demonstration purposes).

error: future cannot be sent between threads safely
  --> src/main.rs:22:1
   |
22 | #[embassy_executor::main]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `____embassy_main_task` is not `Send`
   |
note: captured value is not `Send`
  --> src/main.rs:23:15
   |
23 | async fn main(_spawner: Spawner) {}
   |               ^^^^^^^^ has type `embassy_executor::Spawner` which is not `Send`
   = note: `*mut ()` doesn't implement `core::marker::Send`
note: captured value is not `Send`
  --> src/main.rs:23:15
   |
23 | async fn main(_spawner: Spawner) {}
   |               ^^^^^^^^ has type `embassy_executor::Spawner` which is not `Send`
   = note: `*mut ()` doesn't implement `core::marker::Sync`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#future_not_send
   = note: `-D clippy::future-not-send` implied by `-D clippy::nursery`
   = help: to override `-D clippy::nursery` add `#[allow(clippy::future_not_send)]`

---

Currently the only way to make said error/warning go away is to put

#![allow(clippy::future_not_send)]

at the top of the module calling embassy_executor::main.
Users unfortunately can't put the allow attribute like this (attribute gets removed during expansion).

#[embassy_executor::main]
#[allow(clippy::future_not_send)]
async fn main(_spawner: Spawner) {}

nor

#[allow(clippy::future_not_send)]
#[embassy_executor::main]
async fn main(_spawner: Spawner) {}

Adding the attribute directly in the expanded code makes clippy happy.

Note: This might not be the ideal fix (maybe allowing async fn main(_spawner: SendSpawner) {} would work but I don't have enough knowledge on embassy to know if that's faceable or wished).
Adding the attribute seems like a good compromise, being quick and easy to maintain (maybe using expect can be better but it requires a relatively new version of rust)

[Dirbaio]

thanks!

(clippy::future_not_send is a very dubious lint anyway especially for embedded. Many futures are not Send in embedded, and that's perfectly okay!)

[vic1707]

Thank you, I certainly wasn't expecting a reply that quickly!

(clippy::future_not_send is a very dubious lint anyway especially for embedded. Many futures are not Send in embedded, and that's perfectly okay!)

Thank you for the advice! First time doing embedded and async in Rust so I'll keep that in mind 👌