Refine rustfmt

[kchibisov]

That's just a prototype how it should look to apply nightly rustfmt with a bit more involved rules.

There's no intent to do that before the new keyboard API rework.

[MarijnS95]

I personally quite like this grouping, are we missing an option?

[madsmtm]

I dislike it, I find that it makes merge conflicts harder

[maroider]

I've personally switched to imports_granularity = "Item" in my current personal project to make my life easier on that front, but it does tend to create massive walls of use statements.

[kchibisov]

I personally hate the grouping current winit is using, and personally I don't have it in Wayland backend, since rustfmt doesn't enforce it. It just nearly impossible to read it and rebase. Or maybe I've just used to Module option.

[aloucks]

For what it's worth, +nightly was originally used as the formatting check, but caused problems for contributors who weren't using nightly Rust. See also: #1074

[madsmtm]

We agreed to do this in today's meeting, though only after a few of the larger in-flight PRs have been merged.

I raised the concern that users would have to run cargo +nightly fmt, and that their editor would be set to run the stable rustfmt by default. My concerns would be assuaged if we:

1. Added a note about this to CONTRIBUTING.md, perhaps noting that you can configure rust-analyzer.rustfmt.extraArgs with ["+nightly"] to make this work by default.
2. Changed the CI step to be called "Check nightly formatting".

[madsmtm]

I assume the only thing you've changed is rustfmt.toml. Had a look at it, I agree with all the options, though I think you might get trouble with reorder_impl_items until madsmtm/objc2#479 is resolved, so might want to wait with that.

[kchibisov]

The only thing I could change is comment width to 80, so it's a bit more compact, but that's about it.

[daxpedda]

unstable_features is missing.

I would also like to add the following:

• error_on_unformatted
• format_macro_bodies
• format_macro_matchers
• hex_literal_case

I'm also against the following rules because they move away from the default Rust style:

• match_block_trailing_comma
• overflow_delimited_expr
• use_small_heuristics

[daxpedda]

This is deprecated, I don't think we need that in Rustfmt.

[daxpedda]

This can be removed, its default is already true.

[kchibisov]

And use_small is the main reason for me to change it, because the code is way easier to read with it, since it's more compact.