error[E0670]: async fn is not permitted in the 2015 edition

[kanekv]

I'm getting this error in the output. It doesn't break anything though.

[matklad]

I think this works as expected? This error comes from cargo check and it indeed is true that async fn is not supported on 2015 edition

[kanekv]

Probably it's cargo problem then (should it report that if project is on 2018 edition).

[zkat]

@kanekv @matklad can you reopen this? I'm getting the same error -- but it only happens through rust-analyzer. For some reason, it seems to think the project is on 2015, but it's definitely on 2018, and cargo check doesn't complain at all, so this seems to be an ra bug. I can reproduce it just by having an async fn in a file.

And yes, it's definitely breaking something: It's preventing format-on-save from working, so I keep committing bad fmt stuff 😅

[matklad]

@zkat a minimal reproducible example will help here. For formatting, we just use rustfmt, so my guess would be that something's odd with the way Cargo project is setup.

[davidbarsky]

I saw this error in a minimal project that didn't have a rustfmt.toml. I was able to make the errors go away by creating a rustfmt.toml and adding an edition = "2018" to it.

[zkat]

@matklad The repro is so small, it's not even worth putting up on a repo:

1. Install VS Code Insiders edition.
2. install rust-analyzer using the instructions in the readme
3. make sure cargo fmt is actually installed in the system
4. use stable as the default rust channel
5. cargo new bug-repro --lib
6. Edit lib.rs and add the following code, then save the file and look at the Output pane's Rust Analyzer Language Server tab.:

pub async fn foo() -> Result<(), std::error::Error> { Ok(())
}

FWIW, @davidbarsky's suggestion of adding a rustfmt.toml file fixed this for me.

[zkat]

Looks like this behavior is (somewhat) intentional, as rustfmt isn't aware of Cargo.toml unless invoked through cargo itself: https://github.com/rust-lang/rustfmt#rusts-editions. But I feel as though it's a bug for rust-analyzer to not be Cargo.toml aware if it detects that it's that kind of project?

[matklad]

I'd say that this is out of scope, for now. it will be in scope once we switch to rustfmt as a library (which isn't goint to happen any time soon). Closing as a dupe of #2146 (which contains some more rational).

[malaire]

I'm getting this error in some projects with Sublime Text and rust-analyzer, but not all. The --edition 2018 switch is not being passed to rustfmt.

[ArshiAAkhavan]

it seems that the issue still remains
i have rust-analyzer 0.0.0 (caf23f291 2022-07-11) and i use vim and i can't get it to format my code unless i set the edition in rustfmt.toml

[AustinHellerRepo]

Just in case someone else made the same mistake I did, I was having this issue where it was stating that my edition was 2015 because I made the mistake of changing my "main.rs" filename to something else and did not specify a target in my "Cargo.toml" file. Changing the name back was the first issue, but then I learned that I had to use $ cargo run in order to ensure that my packages were visible.

[romainds-tech]

I solved the problem by adding

edition = "2021"

just below [package] in Cargo.toml

[LefterisJP]

I solved the problem by adding

edition = "2021"

just below [package] in Cargo.toml

For us putting this in cargo.toml does not seem to have an effect. But adding a rustfmt.toml with the same value as per the docs works.

[djhunter67]

I saw this error in a minimal project that didn't have a rustfmt.toml. I was able to make the errors go away by creating a rustfmt.toml and adding an edition = "2018" to it.

This fixed it!