Possible unit_arg false positive when passing `Default::default()` as function parameter resolving to unit value

Lint name: unit_arg

I tried this code (Playground):

#[derive(Debug)]
struct Foo;

trait Factory: Sized {
    type Options: Default;

    fn create(options: Self::Options) -> Self;
}

impl Factory for Foo {
    type Options = ();

    fn create(_: Self::Options) -> Self {
        Foo
    }
}

fn main() {
    let x = Foo::create(Default::default());

    println!("{:?}", x);
}

In my real use case, the same pattern is employed for generalizing the passing of default options to a creator function, irrespective of implementation.

I expected this not to trigger unit_arg, and most importantly, not to recommend moving Default::default(); to the front while leaving a literal unit value in its stead, which could be incompatible with other implementations of Factory:

error: passing a unit value to a function
  --> src/main.rs:21:13
   |
21 |     let x = Foo::create(Default::default());
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: the lint level is defined here
  --> src/main.rs:1:9
   |
1  | #![deny(clippy::unit_arg)]
   |         ^^^^^^^^^^^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unit_arg
help: move the expression in front of the call and replace it with the unit literal `()`
   |
21 |     let x = {
22 |         Default::default();
23 |         Foo::create(())
24 |     };
   |

Meta

• cargo clippy -V: clippy 0.1.52 (9bc8c42 2021-05-09), also occurs in 0.1.54 (2021-06-09 eab201d)
• rustc -Vv:

  rustc 1.52.1 (9bc8c42bb 2021-05-09)
  binary: rustc
  commit-hash: 9bc8c42bb2f19e745a63f3445f1ac248fb015e53
  commit-date: 2021-05-09
  host: x86_64-unknown-linux-gnu
  release: 1.52.1
  LLVM version: 12.0.0
  

Start by running the reported Rust example with the unit_arg lint enabled and inspect the lint's implementation and existing tests. Confirm that Default::default() is resolved as a unit value only for this implementation, then add coverage and ensure the lint no longer recommends replacing a potentially generic default argument with ().