[idea] Use rustfmt in CI for style checks

[marmistrz]

This could prevent many style review comments in PRs.

[Susurrus]

I used to run this for my projects but found that it was unstable. I don't believe it's reasonable at this point to use rustfmt in CI, especially since it'll likely point out many errors unrelated to the current PR. I think this would be a good thing to do for 1.0, however. Same with running Clippy on all PRs.

[dingxiangfei2009]

@Susurrus Shall we reconsider enabling this check today? I mean rustfmt is pretty stable now in 2019.

[posborne]

I think enabling a rustfmt check in CI at this point would be very reasonable and is something I have started to add to a lot of projects including ones with significant churn at the day job.

This can be done via cargo fmt --all -- --check.

[SUPERCILEX]

@rtzoeller Pretty sure this was fixed by #1748

[pacak]

I'm not sure. Try checking out and running cargo fmt -- src/*.rs. I'm getting a big diff if I do this.

[SUPERCILEX]

Huh, it seems like we're running into this issue: rust-lang/rustfmt#3253