Tracking issue for inclusion of `derive` in lint `unused_attributes`

[Havvy]

The following code emits an unsquelchable warning.

#![crate_type="lib"]

#[derive()]
struct Struct;

warning: empty trait list in `derive`
 --> src/lib.rs:4:1
  |
4 | #[derive()]
  | ^^^^^^^^^^^

This warning should have a named lint unused_derive that is a part of the unused group of lints.

This warning should be a part of unused_attributes.

[petrochenkov]

empty trait list in derive should have a lint name

... and that name is unused_attributes.

[clintfred]

#[allow(unused_attributes)]
#[derive()]

Does not appear to squelch the warning for me...

[Centril]

It seems eminently reasonable to me to include #[derive()] in unused_attributes since it is an attribute applied with no effect; so let's kick off fcp for that.

@rfcbot merge

[rfcbot]

Team member @Centril has proposed to merge this. The next step is review by the rest of the tagged teams:

• @Centril
• @aturon
• @cramertj
• @eddyb
• @joshtriplett
• @nikomatsakis
• @nrc
• @pnkfelix
• @scottmcm
• @withoutboats

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[zackmdavis]

Implementing this as part of the existing UnusedAttributes pass would be complicated by #45216, but it might also be possible to implement where the existing "empty trait list" warning is issued (possibly as a buffered early lint).

[Havvy]

I need to make UnusedAttributes a buffered early lint for the same thing with cfg_attr.

[joshtriplett]

Seems reasonable. And a macro that might end up with an empty derive list should have no problem turning off unused_attributes locally.

[scottmcm]

@rfcbot reviewed

I certainly agree with moving warnings to lints.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.