Allow inline struct, enum, fn and mod inside of declarative modules

[Tpt]

This PR lifts restrictions on the content of declarative modules.

It also allows to add #[pymodule_export] to:

• struct with #[pyclass]
• enum with #[pyclass]
• fn with #[pyfunction]
• mod with #[pymodule]

Open question: do we want to require adding #[pymodule_export] to the elements to be exported or do we export automatically all elements with #[pyclass], #[pyfunction] or #[pymodule]?

Example:

#[pymodule]
mod declarative_module {
    #[pymodule_export]
    #[pymodule]
    mod inner {
        #[pymodule_export]
        #[pyfunction]
        fn triple(x: usize) -> usize {
            x * 3
        }

        #[pymodule_export]
        #[pyclass]
        struct Struct;

        #[pymethods]
        impl Struct {
            #[new]
            fn new() -> Self {
                Self
            }
        }
    }
}

[davidhewitt]

Thanks for this follow-up, I am very excited to see this feature coming together after so long!

Open question: do we want to require adding #[pymodule_export] to the elements to be exported or do we export automatically all elements with #[pyclass], #[pyfunction] or #[pymodule]?

Great question! I think automatic is likely to lead to nicer-reading code (a lot less repetition), so I'd prefer that.

If there are reasons users don't want to export they could just move the code outside the module. Or we could add a #[pyo3(no_export)] option if users really ask for it, but I'm not convinced that's necessary to add right now...

[Tpt]

@davidhewitt Thank you for the reviews!

Great question! I think automatic is likely to lead to nicer-reading code (a lot less repetition), so I'd prefer that.

If there are reasons users don't want to export they could just move the code outside the module. Or we could add a #[pyo3(no_export)] option if users really ask for it, but I'm not convinced that's necessary to add right now...

Perfect! Done!

[davidhewitt]

Fantastic, imo this leads to a beautiful result I've wanted for years! Thanks 🙏

[davidhewitt]

Very nice way to reuse the existing machinery!

[davidhewitt]

Same thing about the changelog entry not being needed here, I'll remove.