unused_import indicates a very perplexing span on nightly-2023-11-30

Code

Cargo.toml

[package]
name = "unused_import"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

[features]
feature_1 = []
feature_2 = []

lib.rs:

pub mod seed;

#[cfg(feature = "feature_1")]
mod feature_1;
#[cfg(feature = "feature_1")]
pub use feature_1::*;

#[cfg(feature = "feature_2")]
mod feature_2;
#[cfg(feature = "feature_2")]
pub use feature_2::*;

seed.rs:

pub struct Seed(u128);

feature_1.rs:

pub use super::seed::Seed;

feature_2.rs:

pub use crate::seed::Seed;

Current output

cargo +nightly-2023-11-30 build --features=feature_1,feature_2
   Compiling unused_import_false_positive v0.1.0 (/home/arthur/Documents/zama/code/unused_import_false_positive)
warning: unused import: `crate::seed::Seed`
 --> src/feature_2.rs:1:9
  |
1 | pub use crate::seed::Seed;
  |         ^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused import: `feature_2::*`
  --> src/lib.rs:11:9
   |
11 | pub use feature_2::*;
   |         ^^^^^^^^^^^^

warning: `unused_import_false_positive` (lib) generated 2 warnings (run `cargo fix --lib -p unused_import_false_positive` to apply 2 suggestions)
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s

Desired output

cargo +nightly-2023-11-30 build --features=feature_1,feature_2
   Compiling unused_import_false_positive v0.1.0 (/home/arthur/Documents/zama/code/unused_import_false_positive)
warning: unused import: `crate::seed::Seed`
 --> src/feature_2.rs:1:9
  |
1 | pub use crate::seed::Seed;
  |         ^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused import: `feature_2::*`
  --> src/lib.rs:11:9
   |
11 | pub use feature_2::*;
   |         ^^^^^^^^^^^^

Because `Seed` is already publicly exported here:

  --> src/lib.rs:11:9
   |
 6 | pub use feature_1::*;
   |         ^^^^^^^^^^^^


warning: `unused_import_false_positive` (lib) generated 2 warnings (run `cargo fix --lib -p unused_import_false_positive` to apply 2 suggestions)
    Finished dev [unoptimized + debuginfo] target(s) in 0.04s

Rationale and extra context

Not sure why multiple exports of the same type have been deemed bad or worth a lint (or maybe it's a side effect of changes on the unused_import detection) but I was in a larger project where I could not figure out why this started popping up when updating to the latest nightly.

Also for whatever reason on the bigger project I did not get the lib.rs reference, here I guess the project is small enough that the compiler manages to give the information.

Other cases

No response

Anything else?

No response

Reproduce the report with the Cargo.toml feature definitions and lib.rs, seed.rs, feature_1.rs, and feature_2.rs examples using the shown nightly build command. Start by examining the unused_import diagnostics for the two feature re-exports and determine whether the duplicate public export is expected. Done means the behavior is clarified and covered by a regression case if a compiler change is needed.