Invalid macro rewrite in PySequenceProtocol (0.6.0)

[althonos]

🐛 Bug Reports

The signature of __setitem__ for PySequenceProtocol implementations is not rewritten the right way, and the wrong argument is replaced. See example.

🌍 Environment

• Your operating system and version: Linux (Archlinux)
• Your python version: 3.7
• How did you install python (e.g. apt or pyenv)? Did you use a virtualenv?: pacman -S python
• Your rust version (rustc --version): rustc 1.35.0-nightly (94fd04589 2019-03-21)
• Are you using the latest pyo3 version? Have you tried using latest master (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")? Tried with both v0.6.0 and master.

💥 Reproducing

Minimal example:

#[macro_use]
extern crate pyo3;
use pyo3::prelude::*;
use pyo3::PySequenceProtocol;

#[pyclass]
pub struct MyList {
    elems: Vec<u8>
}

#[pyproto]
impl PySequenceProtocol for MyList {
  fn __setitem__(&mut self, key: isize, item: u8) -> PyResult<()> {
    self.elems[key as usize] = item;
  }
}

When trying to compile, the compiler will fail with:

error[E0053]: method `__setitem__` has an incompatible type for trait
  --> src/lib.rs:15:3
   |
15 |   fn __setitem__(&mut self, key: isize, item: u8) -> PyResult<()> {
   |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected isize, found associated type
   |
   = note: expected type `fn(&'p mut MyList, isize, <MyList as pyo3::sequence::PySequenceSetItemProtocol<'p>>::Value) -> <MyList as pyo3::sequence::PySequenceSetItemProtocol<'p>>::Result`
              found type `fn(&'p mut MyList, <MyList as pyo3::sequence::PySequenceSetItemProtocol<'p>>::Value, u8) -> <MyList as pyo3::sequence::PySequenceSetItemProtocol<'p>>::Result`

After running cargo expand, the actual signature generated by the pyproto macro is:

impl<'p> PySequenceProtocol<'p> for MyList {
    fn __setitem__(
        &'p mut self,
        key: <MyList as pyo3::class::sequence::PySequenceSetItemProtocol<'p>>::Value,
        item: u8,
    ) -> <MyList as pyo3::class::sequence::PySequenceSetItemProtocol<'p>>::Result {
        self.elems[key as usize] = item;
    }
}

where it should be (if I'm not mistaken):

impl<'p> PySequenceProtocol<'p> for MyList {
    fn __setitem__(
        &'p mut self,
        key: isize,
        item: <MyList as pyo3::class::sequence::PySequenceSetItemProtocol<'p>>::Value,
    ) -> <MyList as pyo3::class::sequence::PySequenceSetItemProtocol<'p>>::Result {
        self.elems[key as usize] = item;
    }
}

[althonos]

Closed by #423.