Format our code with rustfmt

[tetsuharuohzeki]

I think we should do this.

[tetsuharuohzeki]

cc: @Manishearth ?

[jdm]

Ms2ger and I have filed a lot of issues each time we've tried rustfmt on Servo. We could certainly start running it on particular files that don't end up with terrible output.

[Manishearth]

It's not ready yet. I periodically try running it on Servo.

[frewsxcv]

Anyone know how Go projects incorporate gofmt (or Rust w/ rustfmt) into project workflows? Require that it get used pre-commit and checked via CI? Have the build system automatically format upon check-in (which sounds scary)? Something else?

[tetsuharuohzeki]

I think it would be better to check in CI the commited files as tidy which we're running. It's not enough?

[Manishearth]

Checked via CI I think. Similar to how clippy checks update_lints or how servo checks lockfile_changed.

I'd rather not gate CI on rustfmt though. I'm slightly more okay with it if we use circleci or something for tidy+fmt to get separate and immediate status icons from the long build.

[Manishearth]

So I've been poking around, and rustfmt seems to be much more stable now.

The following toml config is pretty nice for servo

reorder_imports = true
reorder_imported_names = true
max_width = 120
ideal_width = 80
normalize_comments = false

normalize_comments prevents the license comment from being reformatted to use line comments instead of block comments. We might want to do that anyway, but it's nice to reduce the impact of the first run.

rustfmt currently doesn't reorder extern crates. Furthermore, it reformats #[attr] extern crate foo; into two lines, which breaks tidy (tidy only asks for the sorting of extern crate lines which do not have attributes, since the ones with attributes usually have special requirements for ordering). We'll need to change this a bit and/or add extern crate sorting to rustfmt.

I would like to reformat everything and slowly make rustfmt part of CI checks. Perhaps removing the corresponding tidy checks.

Thoughts? @jdm @Ms2ger @wafflespeanut

[jdm]

I'm open to that plan. I think adding extern crate reordering to rustfmt makes the most sense.

[wafflespeanut]

It'd be wonderful to have rustfmt in tree. Also, tidy's sorting isn't that great right now (#9259). We can improve it in tidy, but rustfmt should do this better. I never imagined that rustfmt could be integrated so easily 😄

[pyfisch]

🎉 rustfmt now works well on servo with this config:

match_block_trailing_comma = true
binop_separator = "Back"
error_on_line_overflow = false

It can be installed with rustup install rustfmt-preview for servo and run with cargo fmt --package layout for individual packages like layout.

The formatting works with ./mach test-tidy but the long (>100 character) imports need to be formatted by hand.

[atouchet]

Is this done now?

[CYBAI]

Done by #22126 !