Add option to skip generated files

[Timmmm]

There's a growing de facto standard to mark generated files by putting @generated in a comment at the top of the file. E.g. check the top of Cargo.lock.

It would be great if there were an option to have Rustfmt skip files that contain @generated.

[topecongiro]

I have seen @Generated annotation in Java, but to be honest, I have not seen usages of @generated in the Rust community besides Cargo.lock. @Timmmm Are you aware of any tools/projects that add // @generated comment on generated files?

[Timmmm]

Capnp does (I added that change). I also have an internal tool that does.

Phabricator supports it and shows files containing @generated as collapsed in diff views by default (you can still expand them). For reference here is the diff that added it to Cargo.lock.

[topecongiro]

Thank you for your information. It seems reasonable to have the option in rustfmt.

[stepancheg]

@generated is a standard way to mark a file as generated in Phabricator.

Would be nice if rustfmt supported that out of the box.