cargo fmt cannot be used for formatting a single rust buffer

[jenanwise]

In #87 / #88, the rustfmt formatter was switched from calling rustfmt directly to using cargo fmt so that it would respect Cargo.toml. Unfortunately, cargo fmt cannot format a single file. It will actually format all the files in the crate. When combined with --emit=stdout (as in current master), this will spit out all the crate's src into the current buffer on save.

See discussion in rust-lang/rustfmt#4074

There doesn't appear to be a way to respect Cargo.toml while formatting a single buffer.

[lassik]

Thanks for reporting the bug. I don't use Rust myself, so I'll follow your recommendations on what to do.

Skimming that rustfmt thread, I got the impression that the problem is there's no simple way to run rustfmt so that it parses the same config file cargo fmt parses. And when we run cargo fmt we are almost guaranteed to format extra files in addition to the one we want.

[lassik]

Does this imply that Rust formatting currently cannot be made work properly for projects using non-standard formatter settings? In other words, we need to wait for the rustfmt and/or cargo fmt maintainers to add a command line flag for editor plugins.

[jenanwise]

Skimming that rustfmt thread, I got the impression that the problem is there's no simple way to run rustfmt so that it parses the same config file cargo fmt parses. And when we run cargo fmt we are almost guaranteed to format extra files in addition to the one we want.

That's correct, at least for now.

Does this imply that Rust formatting currently cannot be made work properly for projects using non-standard formatter settings?

Not quite. rustfmt respects settings in the project's rustfmt.toml. As far as I am aware, the only real rustfmt config option that matters in Cargo.toml is edition. By default, rustfmt uses the "2015" edition, which does not allow the async keyword. Cargo.toml specifies the Rust edition for the project, so using cargo fmt gets you automatic edition config for free, but other configuration options still go in rustfmt.toml (even when using cargo fmt).

It's worth noting that the next major release of rustfmt will default to the "2018" edition.

My recommendation would be to revert #88 and advise users to create a rustfmt.toml if they need any configuration. That seems to be the recommendation for editor integrations from the rustlang team for now.

[lassik]

And you can set the edition in rustfmt.toml just as well as in Cargo.toml, so people using 2018 can solve their problem simply by creating the former file. That sounds very reasonable indeed. Let's do it.

[lassik]

OK, pushed a fix to master. Please test and close this issue if it solves the problem. Thanks for an excellent bug report!

[jenanwise]

It works, thank you!