RustFmt does not take into account edition from Cargo.toml

[jonhoo]

• rust.vim version: 97fdc4e

Steps to reproduce:

$ cargo new --bin edition-fmt
$ cd edition-fmt
$ grep edition Cargo.toml
edition = "2018"
$ echo 'fn main() { async { 1; }; }' > src/main.rs

Expected vs. actual behavior:

Expected:

Open src/main.rs in editor and run :RustFmt. The file should now look like this:

fn main() {
    async {
        1;
    };
}

Actual:

Open src/main.rs in editor and run :RustFmt. You get the error:

error: expected identifier, found `1`

This is because rustfmt is run, which defaults to the 2015 edition (where async isn't supported). The rustfmt command does not take into account edition from Cargo.toml. It is possible to work around this by doing:

$ echo 'edition = "2018"' > rustfmt.toml

But remembering to do this in all projects is a bit of a pain, and is not very discoverable. I believe the reason why rustfmt is used over cargo fmt is to support formatting only certain paths, and to support formatting even when operating on Rust files not in a cargo project, but the cost here seems too high. Is there some way we can get both that functionality and have sensible support for edition as specified in Cargo.toml?

[bcmyers]

Hey @jonhoo. Nice to see we're having the same issue. I solved it by putting the following in my .vimrc:

let g:rustfmt_options = '--edition 2018'

This of course sets the edition globally; so it's no good if you're still working on both 2015 and 2018 projects. It's also odd that 2018 is not the default.

In any case, for a more comprehensive solution, it'd be nice to see the edition being picked up automatically from the Cargo.toml as you suggest.

In the meantime, though, this workaround works for me as I don't have any 2015 projects.

[chris-morgan]

I think we need either a way of telling rustfmt to get options from Cargo.toml (as a fallback for rustfmt.toml, which I think would be acceptable still for projects that don’t use Cargo), or for cargo fmt to expose a means of only formatting a single file, which it doesn’t look to at present. Either way, I think this needs to be a rustfmt issue, to provide the hooks that we need. I’m too lazy right now to file such an issue myself; I invite others to.

[bcmyers]

In the meantime @chris-morgan, shouldn't rust.vim default to the 2018 edition (in the absense of a rustfmt.toml)? As people start using async/await, this is going to become an issue for a lot of users.

[chris-morgan]

Sounds not ideal, but overall reasonable. Patch accepted.

[alexryndin]

Sounds not ideal, but overall reasonable. Patch accepted.

Hi, will this patch be available in master?

[da-x]

@alexryndin I pushed to master now. @mhinz I amended your commit a bit, should work now whether rustfmt.toml exists or not.