mixed_attributes_style should allow mixing outer cfgs and inner doccomments

[apoelstra]

Summary

The mixed_attributes_style treats doccomments as attributes, which I suppose they technically are, but this is not how users perceive them. It is common with modules to use inner doccomments (and inner style lints, clippy allows, etc., for that matter, but ok, I can accept that the lint doesn't like that) while having outer cfg gates for features.

Reproducer

I tried this code:

#[cfg(test)]
mod tests {
    //! Doccomment for my tests module
}

This triggers the lint:

warning: item has both inner and outer attributes
 --> src/main.rs:2:1
  |
2 | / #[cfg(test)]
3 | | mod tests {
4 | |     //! Doccomment for my tests module
  | |______________________________________^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mixed_attributes_style
  = note: `#[warn(clippy::mixed_attributes_style)]` on by default

warning: `clippy-demo` (bin "clippy-demo") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.30s

But I think either fix would be more confusing to read (either add a #![cfg(test)] which I have literally never seen in Rust code, or move the doccomment out, which makes it much harder for readers of the code to see that this is a module-level "header comment").

Version

rustc 1.73.0 (cc66ad468 2023-10-03)
binary: rustc
commit-hash: cc66ad468955717ab92600c770da8c1601a4ff33
commit-date: 2023-10-03
host: x86_64-unknown-linux-gnu
release: 1.73.0
LLVM version: 17.0.2

Additional Labels

No response

[J-ZhengLi]

This might be not as intended @rustbot claim

[jdygert-spok]

IMO this is a more general problem than doc comments. Many attributes have a "preferred" location. A common case is #[cfg(test)] or #[test] outside, and #![allow(...)] inside.

A more general solution would be to only trigger the lint when the same attribute is both outer and inner on an item.

[workingjubilee]

Yeah, I kind of hate this lint as it doesn't seem consistent with how I use attributes at all. I most definitely have that "this attribute goes here, this attribute goes here" pattern.

[nyurik]

I also noticed this lint when running cargo +nightly clippy -p martin-tile-utils on https://github.com/maplibre/martin (observed in b92a407):

warning: item has both inner and outer attributes
   --> martin-tile-utils/src/lib.rs:281:1
    |
281 | / #[cfg(test)]
282 | | mod tests {
283 | |     #![allow(clippy::unreadable_literal)]
    | |_________________________________________^