Suggest unused lifetime parameters

Code

type Foo<'a> = ();

fn foo<'a>() -> Foo<'a> { () }

fn main() {
    foo();
}

Current output

Success

Desired output

warning: lifetime parameter `'a` is never used
 --> src/main.rs:1:10
  |
1 | type Foo<'a> = ();
  |          ^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: lifetime parameter `'a` is never used
 --> src/main.rs:3:8
  |
3 | fn foo<'a>() -> Foo<'a> { () }
  |        ^^

Rationale and extra context

No response

Other cases

No response

Anything else?

No response

Start by compiling the Rust snippet from the issue and compare the current output with the requested warnings for both unused lifetime parameters. Trace the compiler's unused-parameter diagnostics and related tests, then add coverage showing warnings for the type alias and function cases. Done means the example emits the expected warnings without changing valid lifetime behavior.