Broken async trait on Rust 1.81 and above

[jon-chuang]

Bug Report

error: implementation of `std::marker::Send` is not general enough

    |
87  |       ) -> Result<Response<ServerDecodeMessage>, Status> {
    |  ________________________________________________________^
146 | |         }
147 | |     }
    | |_____^ implementation of `std::marker::Send` is not general enough
    |
    = note: `std::marker::Send` would have to be implemented for the type `&[u32]`
    = note: ...but `std::marker::Send` is actually implemented for the type `&'0 [u32]`, for some specific lifetime `'0`

No repro

Version

tonic = "0.12.3"

Platform

Macos and Ubuntu

More Info

See these Rustc issues unfixed for 5 years:

• Higher ranked lifetime error when tryng to see that a future is send. rust-lang/rust#114046
• Lifetime bounds in auto trait impls prevent trait from being implemented on generators rust-lang/rust#64552
• Incorrect "implementation of Send is not general enough" error with lifetimed Send impl used in async fn rust-lang/rust#96865

[jon-chuang]

This is actually a broken rustc issue that thankfully provides us with the clearest and most enlightening of error messages. The fix has nothing to do with the error message 👍