Compile success when generic parameter is possibly not "Send", but compile fail if said parameter is in a tuple

[david0u0]

async_trait ersion: 0.1.83
rustc version: rustc 1.84.0-beta.5 (0857a8e32 2024-12-27)

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Below is the minimum code that can reproduce this. With the function "test_success", async trait doesn't care about "S" being Send or not, but when I put it into a tuple (bool, &mut S), suddenly it starts to complain that "S" cannot be send between threads.

use async_trait::async_trait;

#[async_trait]
trait Test<S> {
    async fn test_success(&self, _s: &mut S) {}
    // async fn test_fail(&self, _s: (bool, &mut S)) {}
}

Here's the error message:

   Compiling playground v0.0.1 (/playground)
error[E0277]: `S` cannot be sent between threads safely
 --> src/lib.rs:6:51
  |
6 |     async fn test_fail(&self, _s: (bool, &mut S)) {}
  |                                                   ^^
  |                                                   |
  |                                                   `S` cannot be sent between threads safely
  |                                                   within this `{async block@src/lib.rs:6:51: 6:53}`
  |
  = note: required because it appears within the type `&mut S`
  = note: required because it appears within the type `(bool, &mut S)`
note: required because it's used within this `async` block
 --> src/lib.rs:6:51
  |
6 |     async fn test_fail(&self, _s: (bool, &mut S)) {}
  |                                                   ^^
  = note: required for the cast from `Pin<Box<{async block@src/lib.rs:6:51: 6:53}>>` to `Pin<Box<(dyn Future<Output = ()> + Send + 'async_trait)>>`
help: consider restricting type parameter `S`
  |
4 | trait Test<S: std::marker::Send> {
  |             +++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to 1 previous error

---

I'm not sure what should be the correct behavior, but these two scenario seem logically the same. So I think they should either both compile fail or pass.

Thanks for this amazing crate!