feat!: remove deprecations for 1.4.0 release

[agoose77]

Per the wiki:

• typestr argument will be removed from Form objects.
• Form.type_from_behavior(...) will be removed in favour of Form.type.
• ak.typetracer.empty_if_typetracer will be removed in favour of ak.typetracer.length_zero_if_typetracer.
• UnionArray.simplified's merge argument will be removed.
• The built-in string and categorical behaviors will be removed.

[agoose77]

Hmm, looks like we probably shouldn't remove the ak.behaviors.string module (or categorical) just yet; any pickles whose array class is defined in these modules will thus fail to load. I propose to wait, and eventually we'll be able to remove these outright. Let's bump the removal to 6-12 months?

[codecov]

Codecov Report

Merging #2688 (da12418) into main (a5efdfe) will increase coverage by 0.05%.
The diff coverage is 84.84%.

Additional details and impacted files

Files Changed	Coverage Δ
src/awkward/__init__.py	96.96% <ø> (-0.18%)	⬇️
src/awkward/behaviors/categorical.py	0.00% <0.00%> (-71.43%)	⬇️
src/awkward/forms/form.py	82.12% <ø> (+0.43%)	⬆️
src/awkward/typetracer.py	87.09% <ø> (+2.48%)	⬆️
src/awkward/types/optiontype.py	81.48% <60.00%> (+2.79%)	⬆️
src/awkward/types/unknowntype.py	84.00% <71.42%> (+4.58%)	⬆️
src/awkward/behaviors/string.py	100.00% <100.00%> (+36.36%)	⬆️
src/awkward/contents/unionarray.py	85.57% <100.00%> (+0.07%)	⬆️
src/awkward/types/listtype.py	95.74% <100.00%> (+3.29%)	⬆️
src/awkward/types/numpytype.py	94.68% <100.00%> (+1.68%)	⬆️
... and 4 more

[jpivarski]

Thanks for making each deprecated feature removal a separate commit; it was much easier to review each commit separately!

Hmm, looks like we probably shouldn't remove the ak.behaviors.string module (or categorical) just yet; any pickles whose array class is defined in these modules will thus fail to load. I propose to wait, and eventually we'll be able to remove these outright. Let's bump the removal to 6-12 months?

Good point—to maintain backward pickle compatibility, we can never fully remove them. But they can become hollow shells of their former selves, like the ak._ext.Form and subclasses in

awkward/src/awkward/_ext.py

Lines 3 to 17 in 519bba6

	from awkward.forms import (
	BitMaskedForm,
	ByteMaskedForm,
	EmptyForm,
	Form,
	IndexedForm,
	IndexedOptionForm,
	ListForm,
	ListOffsetForm,
	NumpyForm,
	RecordForm,
	RegularForm,
	UnionForm,
	UnmaskedForm,
	)

If all we're trying to do is have pickle.load not fail on old data, the ak.behaviors.string.StringBehavior etc. classes must continue to exist at that address, but they don't have to be special classes. We can keep the string.py and categorical.py modules in behaviors/, but StringBehavior etc. can be alternate names for ak.Array (i.e. no special class for them). After unpickling, the arrays would no longer carry any residue of pickle having declared that they should have these classes.

If anyone asks why we have these pass-throughs, the answer can be the same as for _ext.py: to preserve old pickles. (A comment can explain that in-situ.) That would minimize cognitive overhead.

[agoose77]

Hmm, the thought had occurred to me but I dismissed it as non-viable. I'm not sure why, though; it's a good idea!

Now this can merge :)