Make `TzInner` public

[kylebarron]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

In pyo3-arrow, I'm converting from Arrow scalars to Python objects.

Prior to pyo3 0.23.4, pyo3 handled the object conversion by converting all time zones to a fixed offset, but as of pyo3 0.23.4, pyo3 requires the Tz implementation to implement IntoPyObject, and arrow_array::timezone::Tz does not.

One way to fix this is to converting all time zones to a fixed offset manually, e.g.

let dt: chrono::DateTime<arrow_array::timezone::Tz> = ...;
dt.fixed_offset().into_py_any(py)?

But this loses timezone information. It would be ideal to convert all timezone information into the Python scalar. But TzInner is private:

arrow-rs/arrow-array/src/timezone.rs

Lines 81 to 85 in a0c3186

	#[derive(Debug, Copy, Clone)]
	enum TzInner {
	Timezone(chrono_tz::Tz),
	Offset(FixedOffset),
	}

So we have no way to access the underlying chrono_tz::Tz out of the Tz.

Describe the solution you'd like

Make TzInner public.

Describe alternatives you've considered

Always convert to a fixed offset, but this will lose any timezone information.

Additional context

[tustvold]

I wonder if we could instead just convert back to a string?

[kylebarron]

Up to you. I think being able to access the chrono_tz::Tz would be slightly easier for me (as chrono_tz::Tz implements IntoPyObject) but I can understand why converting back to a string may be a preferred public API.

[tustvold]

Given arrow_array::Tz is supposed to be a helper, as opposed to a canonical representation, DataType is in terms of Arc<str> not Tz, I think using strings would be the most consistent way to handle this