Removing async_trait dependency as for Rust 1.75

[JasterV]

Hello there!

Since Rust 1.75 was released and async traits are now supported natively, there is no need to keep relying on the async_trait crate.

How hard would it be to get rid of this dependency? Are there any plans for it yet?

[bikeshedder]

I have asked that same question myself. At the time of this writing the Rust compiler warns against using async fn for public traits. It could be changed into -> impl Future<...> though I have not tried that, yet:

https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html#dynamic-dispatch

Traits that use -> impl Trait and async fn are not object-safe, which means they lack support for dynamic dispatch. We plan to provide utilities that enable dynamic dispatch in an upcoming version of the trait-variant crate.

In theory this should be no limiting factor as the Manager is a generic and there should be no dynamic dispatch happening.

I need to look into that. I guess there are dragons lurking. 🐉

[Johnabell]

I guess there are dragons lurking. 🐉

There are definitely considerations regarding the use of this feature in public traits in particular this write up is a good summary: https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html#where-the-gaps-lie. Moving away from async_trait might change the implicit bounds that are applied to the return types and consequently the returned Future might no longer be Send which could be problematic for multi-threaded async runtimes (and represent a breaking change). Additionally, the fact that the traits are no longer considered object safe should also be considered a breaking change.

[bikeshedder]

I just gave this a try:

• Remove async_trait dependency #297

I had to change some detail in the deadpool-postgres crate as the swappable TLS implementation caused some issues. I solved it via cloning the config structure inside the Connect trait I provided to make this object safe.

[bikeshedder]

I just merged that PR. All tests passed and it seams to be working just fine.

If I don't encounter any blocker I will release the next deadpool version without async_trait. 🎉

[JasterV]

Damn that is so cool! I'm glad that my comment started all this, thank you for your blazingly fast response!

[JasterV]

Also thank you for updating the edition of the crate to the latest 2021 and bumping dependencies :D