Running rustfmt on rust-lang/rust codebase

[dtolnay]

Filing this to track https://internals.rust-lang.org/t/running-rustfmt-on-rust-lang-rust-and-other-rust-lang-repositories/8732 in a way that doesn't get locked every 90 days, since I believe we all still want this to happen.

Using rustfmt would have several wins:

• Adopt a uniform style, of course
• But also resolve problems that contributors have either:
  • trying to figure out our style (heh, good luck)
  • accidentally running rustfmt on stuff that drags in a lot of auxiliary diffs

There are obviously two main approaches:

• Flag day
• Gradual transition

I am partial to “flag day” myself, but I could go either way.

There is another question too: how to keep things formatted? In my ideal world, this would be fairly painless, but I’m not sure how best to achieve that (one idea I had was a rustfmtbot that runs rustfmt on people’s PRs and pushes commits automatically, but that does not exist afaik).

[Centril]

The compiler team decided to move forward with enforcing formatting in the repo in rust-lang/compiler-team#80 and the plan is being implemented in #65939.

[Centril]

Closing as done.