FP unused_trait_names

[matthiaskrgr]

Summary

.

Lint Name

unused_trait_names

Reproducer

I tried this code:

#![warn(clippy::unused_trait_names)]
#![feature(decl_macro)]

mod m {
    pub trait Tr {
        fn method(&self) {}
    }

    impl Tr for u8 {}
}

macro gen_import($Br: ident) {
    use m::Tr as $Br;
}
gen_import!(Br);

fn main() {
    0u8.method();
}

I saw this happen:

warning: importing trait that is only used anonymously
  --> src/main.rs:13:12
   |
13 |     use m::Tr as $Br;
   |            ^^ help: use: `Tr as _`
14 | }
15 | gen_import!(Br);
   | --------------- in this macro invocation
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unused_trait_names
note: the lint level is defined here
  --> src/main.rs:1:9
   |
1  | #![warn(clippy::unused_trait_names)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this warning originates in the macro `gen_import` (in Nightly builds, run with -Z macro-backtrace for more info)

suggestion

#![warn(clippy::unused_trait_names)]
#![feature(decl_macro)]

mod m {
    pub trait Tr {
        fn method(&self) {}
    }

    impl Tr for u8 {}
}

macro gen_import($Br: ident) {
    use m::Tr as _ as $Br;
}
gen_import!(Br);

fn main() {
    0u8.method();
}

does not compile

error: expected `;`, found keyword `as`
  --> src/main.rs:13:20
   |
13 |     use m::Tr as _ as $Br;
   |                    ^^ expected `;`
14 | }
15 | gen_import!(Br);
   | --------------- in this macro invocation
   |
   = note: this error originates in the macro `gen_import` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0599]: no method named `method` found for type `u8` in the current scope
  --> src/main.rs:18:9
   |
6  |         fn method(&self) {}
   |            ------ the method is available for `u8` here
...
18 |     0u8.method();
   |         ^^^^^^ method not found in `u8`error: expected `;`, found keyword `as`
  --> src/main.rs:13:20
   |
13 |     use m::Tr as _ as $Br;
   |                    ^^ expected `;`
14 | }
15 | gen_import!(Br);
   | --------------- in this macro invocation
   |
   = note: this error originates in the macro `gen_import` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0599]: no method named `method` found for type `u8` in the current scope
  --> src/main.rs:18:9
   |
6  |         fn method(&self) {}
   |            ------ the method is available for `u8` here
...
18 |     0u8.method();
   |         ^^^^^^ method not found in `u8`
   |
   = help: items from traits can only be used if the trait is in scope
help: trait `Tr` which provides `method` is implemented but not in scope; perhaps you want to import it
   |
4  + use crate::m::Tr;
   |

For more information about this error, try `rustc --explain E0599`.
   |
   = help: items from traits can only be used if the trait is in scope
help: trait `Tr` which provides `method` is implemented but not in scope; perhaps you want to import it
   |
4  + use crate::m::Tr;
   |

For more information about this error, try `rustc --explain E0599`.

Version

Additional Labels

No response

[matthiaskrgr]

rustc 1.89.0-nightly (1bbd62e54 2025-05-29)
binary: rustc
commit-hash: 1bbd62e547ba5cc08ccb44c27def3d33195d2dd5
commit-date: 2025-05-29
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

[profetia]

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