overflow evaluating requirement for `&pyo3::Bound<'_, _>: pyo3::IntoPyObject<'_>`

Found while attempting to upgrade pydantic-core to test out PyO3 main.

Consider the following code from 0.22.

use pyo3::prelude::*;

pub trait Foo<'py>: ToPyObject {}

fn takes_foo<'py>(foo: impl Foo<'py>) {}

... this compiles fine, and is a useful pattern. Unfortunately, the upgrade path for this seems difficult in our current 0.23 draft.

Given the ToPyObject super trait (i.e. by-ref conversion), the simple thing I tried is:

use pyo3::prelude::*;

pub trait Foo<'py>
where
    for<'a> &'a Self: IntoPyObject<'py>,
{
}

fn takes_foo<'py>(foo: impl Foo<'py>) {}

Unfortunately, this immediately blows up the compiler with a recursion error:

error[E0275]: overflow evaluating the requirement `&pyo3::Bound<'_, _>: pyo3::IntoPyObject<'_>`
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`pyo3_scratch`)
  = note: required for `&&pyo3::Bound<'_, _>` to implement `pyo3::IntoPyObject<'_>`
  = note: 126 redundant requirements hidden
  = note: required for `&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&...` to implement `for<'a> pyo3::IntoPyObject<'py>`
  = note: the full name for the type has been written to '/Users/david/Dev/pyo3-scratch/target/debug/deps/pyo3_scratch.long-type-2493199481127865716.txt'
  = note: consider using `--verbose` to print the full type name to the console

Start with the standalone Rust reproducer in the issue and compare the 0.22 ToPyObject pattern with the 0.23 IntoPyObject bound. Trace the recursive trait requirements reported by the compiler; done means an equivalent trait pattern compiles without overflow and provides a viable upgrade path. No source file or test is named.