#[pyproto] can break lifetime elision

[davidhewitt]

🐛 Bug Reports

🌍 Environment

• Your PyO3 version: 0.11.1
• Have you tried using latest PyO3 master?`: yes

💥 Reproducing

This sample code looks correct according to lifetime elision rules:

#[pyproto]
impl PyIterProtocol for Foo {
    fn __iter__(slf: PyRef<Self>) -> PyRef<Self> {
        slf
    }
}

But it doesn't compile successfully:

error[E0106]: missing lifetime specifier
  --> src/main.rs:26:44
   |
26 |     fn __iter__(slf: PyRef<Self>) -> PyRef<Self> {
   |                                            ^ expected named lifetime parameter
   |
help: consider using the `'p` lifetime
   |
26 |     fn __iter__(slf: PyRef<Self>) -> PyRef<'p, Self> {
   |                                            ^^^

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'p` due to
 conflicting requirements
  --> src/main.rs:26:50
   |
26 |       fn __iter__(slf: PyRef<Self>) -> PyRef<Self> {
   |  __________________________________________________^
27 | |         slf
28 | |     }
   | |_____^
   |
note: first, the lifetime cannot outlive the lifetime `'p` as defined on the impl at
24:1...
  --> src/main.rs:24:1
   |
24 | #[pyproto]
   | ^^^^^^^^^^
note: ...so that the types are compatible
  --> src/main.rs:26:50
   |
26 |       fn __iter__(slf: PyRef<Self>) -> PyRef<Self> {
   |  __________________________________________________^
27 | |         slf
28 | |     }
   | |_____^
   = note: expected `pyo3::class::iter::PyIterIterProtocol<'p>`
              found `pyo3::class::iter::PyIterIterProtocol<'_>`
   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the expression is assignable
  --> src/main.rs:27:9
   |
27 |         slf
   |         ^^^
   = note: expected `pyo3::pycell::PyRef<'static, _>`
              found `pyo3::pycell::PyRef<'_, _>`
   = note: this error originates in an attribute macro (in Nightly builds, run with -
Z macro-backtrace for more info)

It might be nice to adjust the pyproto proc macro so that this works.

[davidhewitt]

This got resolved in #1093