`duplicated_attributes` false positive on lint reasons (and other attributes too)

[kpreid]

Summary

When two lint reasons are the same, duplicated_attributes lints and suggests that one of them should be removed. This would change the meaning.

Besides the specific case of allow(..., reason = ...), I also observe that the implementation seems to be making the assumption that, unless otherwise specified, all attributes’ syntax can be interpreted as a tree of shared prefixes like use foo::{bar, baz} is. That's not true; it's up to the attribute’s definition how its contents are interpreted. If that false assumption were removed, then #13238 would also be fixed, and #12619 (rustc_on_unimplemented) wouldn't need a special case.

Lint Name

duplicated_attributes

Reproducer

I tried this code:

#![allow(missing_docs, reason = "library for internal use only")]
#![allow(
    exported_private_dependencies,
    reason = "library for internal use only"
)]

I saw this happen:

warning: duplicated attribute
 --> src/lib.rs:4:5
  |
4 |     reason = "library for internal use only"
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
note: first defined here
 --> src/lib.rs:1:24
  |
1 | #![allow(missing_docs, reason = "library for internal use only")]
  |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: remove this attribute
 --> src/lib.rs:4:5
  |
4 |     reason = "library for internal use only"
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#duplicated_attributes
  = note: `#[warn(clippy::duplicated_attributes)]` on by default

Expected: No lint

Version

rustc 1.83.0-nightly (4ac7bcbaa 2024-09-04)
binary: rustc
commit-hash: 4ac7bcbaad8d6fd7a51bdf1b696cbc3ba4c796cf
commit-date: 2024-09-04
host: x86_64-apple-darwin
release: 1.83.0-nightly
LLVM version: 19.1.0

Additional Labels

No response

[samueltardieu]

This has been fixed.

[Veetaha]

#12619 (rustc_on_unimplemented) wouldn't need a special case.

True! bon has an attribute with the semantics very similar to rustc_on_unimplemented causing a false-positive lint:

#[derive(bon::Builder)]
#[builder(on(String, into), on(PathBuf, into))]
pub struct Example {}

Here, double into is fine according to #[builder(on())] semantics.

However, it gets a warning:

warning: duplicated attribute
 --> crates/sandbox/src/main.rs:2:41
  |
2 | #[builder(on(String, into), on(PathBuf, into))]
  |                                         ^^^^
  |
note: first defined here
 --> crates/sandbox/src/main.rs:2:22
  |
2 | #[builder(on(String, into), on(PathBuf, into))]
  |                      ^^^^
help: remove this attribute
 --> crates/sandbox/src/main.rs:2:41
  |
2 | #[builder(on(String, into), on(PathBuf, into))]
  |                                         ^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#duplicated_attributes
  = note: `#[warn(clippy::duplicated_attributes)]` on by default

@samueltardieu I tried the latest nightly and I still see a false-positive for bon's attributes

cargo 1.88.0-nightly (864f74d4e 2025-04-11)