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type alias incorrectly flagged as unused when solely used in impl header #58593
Description
Consider the following code (play):
type T = ();
struct S<X>(X);
impl Clone for S<T> { fn clone(&self) -> Self { S(()) } }
fn main() {
let s = S(());
drop(s.clone());
}Today this emits the following warning diagnostic:
warning: type alias is never used: `T`
--> src/main.rs:1:1
|
1 | type T = ();
| ^^^^^^^^^^^^
|
= note: #[warn(dead_code)] on by default
But that type alias is not dead code. It is used in the impl Clone for S<T> { ... }, as one can see by trying to recompile the code after commenting out the type alias.
Activity
oli-obk commentedon Feb 20, 2019
Previous instances of related (or possibly the same) problems:
varkor commentedon Mar 29, 2019
I think this is essentially the same problem as #59333 (comment).
istankovic commentedon Oct 20, 2023
Seems to be fixed. Tested with 1.73 and got no warnings.
KaiTomotake commentedon Jan 23, 2026
@rustbot claim
KaiTomotake commentedon Jan 23, 2026
Oops, looks like there was already someone ahead of me.
tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rszakrad commentedon Sep 21, 2026
This looks covereed by
tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rsadded in #141407 can be closed.