Error when using _ as name for Bound argument in class method

[michaeljones]

We are using _ as an argument name for the &Bound<'_, PyType> argument to a classmethod and I get the following error:

error: Expected typed argument
   --> project/src/lib.rs:107:9
    |
107 |         _: &Bound<'_, PyType>,
    |         ^

error: could not compile `nrf-probe-py` (lib) due to 1 previous error

If I rename it to bound or _bound then the error goes away. The argument isn't used in our current implementations.

Is that expected?

[termoshtt]

I guess it causes from #[pyfunction] rather than #[gen_stub_pyfunction].

#[pyfunction]
fn test_empty(_: Bound<'_, PyType>) {
    println!("test_empty");
}

will causes

error: wildcard argument names are not supported
  --> examples/pure/src/lib.rs:89:15
   |
89 | fn test_empty(_: Bound<'_, PyType>) {
   |               ^

[michaeljones]

I should have provided more of an example. It is failing on a impl method rather than a function and it is working without the pyo3-stub-gen annotation. The code looks like:

#[gen_stub_pymethods]
#[pymethods]
impl ObjectData {
    #[classmethod]
    fn from_map(
        _: &Bound<'_, PyType>,
        dict: HashMap<u32, Vec<u8>>,
    ) -> Result<Self, Error> {
       // ...
    }
}

It works without the #[gen_stub_pymethods] part. Does that seem meaningfully different to the pyfunction setup?