Unable to specify keyword-only arguments

[sunjay]

🌍 Environment

• Your operating system and version: Linux Mint 19.3
• Your python version: Python 3.6.9
• How did you install python (e.g. apt or pyenv)? Did you use a virtualenv?: Using apt, no virtualenv
• Your Rust version (rustc --version): rustc 1.44.1 (c7087fe00 2020-06-17)
• Your PyO3 version: 0.11.1
• Have you tried using latest PyO3 master (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")?: yes

💥 Reproducing

Minimal reproduction:

#[pyfunction("*", a, b)]
fn sum(a: usize, b: usize) -> usize {
    a + b
}

This is valid and should be allowed. The arguments a and b are keyword-only, which means that this function needs to be called as sum(a=3, b=3).

Compiling this produces the error:

error: Positional argument or varargs(*) is not allowed after *
   --> src/lib.rs:3:19
    |
  3 | #[pyfunction("*", a, b)]
    |                   ^

error: aborting due to previous error

The equivalent Python code that works with Python 3:

def sum(*, a, b):
    return a + b

I think this is related to #790 and the subsequent changes made in #792.

[kngwyu]

Thank you for reporting!
It looks like I misunderstood this syntax 😓

[dvermd]

If nobody's already taken this one, I'll give it a try

[davidhewitt]

@dvermd please do! I'm happy to answer any questions and review your PR 👍

[dvermd]

I'm thinking of replacing the booleans has_kw, has_varargs and has_kwargs in pyfunctions.rs by an enum or a state machine. This part is defining the function.
Is there also any code validating the parameters when calling a function ?

[davidhewitt]

Sounds good

Is there also any code validating the parameters when calling a function ?

I think you're looking for parse_fn_args

[kngwyu]

Thanks.

I'm thinking of replacing the booleans has_kw, has_varargs and has_kwargs in pyfunctions.rs by an enum or a state machine. This part is defining the function.

The current code is already a state machine and I don't think abstracting it more is so meaningful.
What we need is just to treat arguments after * as keyword-only arguments in add_work