E0716 "temporary value dropped while borrowed" in #[pyfunction]

[thejcannon]

Bug Description

👋 Love PyO3!

Upgrading from 0.16 to 0.18 I'm seeing the following compiler error:

error[E0716]: temporary value dropped while borrowed
    --> src/externs/interface.rs:1024:17
     |
1021 | #[pyfunction]
     | -------------
     | |           |
     | |           temporary value is freed at the end of this statement
     | borrow later used here
...
1024 |   py_scheduler: &'py PyScheduler,
     |                 ^ creates a temporary value which is freed while still in use
     |
     = note: consider using a `let` binding to create a longer lived value

The code in question looks like:

#[pyclass]
struct PyScheduler(Scheduler);

// ...

#[pyfunction]
fn scheduler_metrics<'py>(
  py: Python<'py>,
  py_scheduler: &'py PyScheduler,
  py_session: &'py PySession,
) -> HashMap<&'py str, i64> {
  py_scheduler
    .0
    .core
    .executor
    .enter(|| py.allow_threads(|| py_scheduler.0.metrics(&py_session.0)))
}

Steps to Reproduce

(Try and compile the code)

Backtrace

No response

Your operating system and version

Ubuntu 20

Your Python version (python --version)

3.8

Your Rust version (rustc --version)

rustc 1.69.0 (84c898d65 2023-04-16)

Your PyO3 version

0.18.3

How did you install python? Did you use a virtualenv?

apt and no venv

Additional Info

No response

[adamreichold]

I am able to reproduce and the seems to stem from returning HashMap<&'py str, i64> instead of e.g. HashMap<String, i64>.