Weird clippy issue when vecs are used in signature

[iajoiner]

Bug Description

Clippy produces weird warning when vec is used in signature. Moreover it is impossible to turn that warning off at the level of the function.

Steps to Reproduce

use pyo3::prelude::*;

#[pyfunction]
#[pyo3(signature = (
    _data = vec![],
))]
pub fn foo(
    _data: Vec<i32>,
) {
}

Put the code above in a new binary or lib crate and run cargo clippy.

You should see a warning like this:

Checking pycatch v0.1.0 (/home/iajoiner/Documents/tests/pycatch)
warning: redundant closure
 --> src/main.rs:6:13
  |
6 |       _data = vec![],
  |  _____________^
7 | | ))]
8 | | pub fn foo(
9 | |     _data: Vec<i32>,
  | |______________^ help: replace the closure with `Vec::new`: `std::vec::Vec::new`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_closure
  = note: `#[warn(clippy::redundant_closure)]` on by default

warning: `pycatch` (bin "pycatch") generated 1 warning
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s

Backtrace

No response

Your operating system and version

Ubuntu 22.04

Your Python version (python --version)

Python 3.10.6

Your Rust version (rustc --version)

rustc 1.67.1 (d5a82bbd2 2023-02-07)

Your PyO3 version

0.18.1

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

I think it came with Ubuntu.
Yes.

Additional Info

No response

[iajoiner]

Corresponding clippy issue: rust-lang/rust-clippy#10378

[davidhewitt]

Thanks for the report! PyO3 places this default into a closure in the generated code, so the lint is correctly identifying a case which looks like it could technically be reduced if handwritten. In practice I think there's not much we can do except silence the warning, which #2990 implements.