Consider support for unit variants in complex enums

[mkovaxx]

Allow the following:

pyo3/tests/ui/invalid_pyclass_enum.rs

Lines 18 to 22 in d1b0722

	#[pyclass]
	enum NoUnitVariants {
	StructVariant { field: i32 },
	UnitVariant,
	}

[davidhewitt]

My stance remains the same as #3582 (comment) that the difference between complex enums and "simple" enums is enough that it's confusing for users to allow unit enums in complex enums.

So unless there are new ideas which could move this forwards, I'm inclined to keep the current status quo and worry about other things 😄

[mkovaxx]

I tend to agree; this would mostly be a cosmetic improvement that might not be worth the added complexity.

[davidhewitt]

In which case let's close this for now, there's many other things on the PyO3 issue tracker which could benefit from attention and don't have such design drawbacks.