Slow compilation of route definitions

[Nutomic]

Our project uses actix-web 4.10 and has a file with about 200 lines of route and service definitions. By moving this file to a separate crate I noticed that it takes around 60s to compile (tested with 1.81, 1.86, nightly-2025-04-27).

You can reproduce it with the following commands:

git clone https://github.com/LemmyNet/lemmy.git --recursive --branch api-routes-crate
cd lemmy
cargo build --timings -p lemmy_api_routes

My question is, are you aware of this kind of problem with slow compilation and possible workarounds? Do you know if this has been reported to compiler developers already?

[robjtede]

Thanks for flagging this. It's not something that's been reported before.

That certainly is a long time for that file; we're not doing anything crazy with generics for it to explode by number of routes.

I'll have a dig soon.

[Nutomic]

Strangely moving the file to a separate crate made it much slower. On the main branch the file is in the same crate as main(), and that only takes ~25s.

I will wait for your results and open an issue in the Rust repo then.

[Nutomic]

Went ahead and opened an issue for rustc: rust-lang/rust#140944