Small warnings refactor at next major release

[trexfeathers]

📰 Custom Issue

#5498 revealed several existing uses of warning subcategories that could not be changed without it being breaking. These should therefore be addressed at the next major release, to make Iris' use of warnings as rational/unsurprising as possible.

iris/lib/iris/fileformats/nimrod_load_rules.py

Lines 35 to 41 in 257be15

	class TranslationWarning(IrisNimrodTranslationWarning):
	"""
	Backwards compatible form of :class:`iris.exceptions.IrisNimrodTranslationWarning`.
	"""
	# TODO: remove at the next major release.
	pass

iris/lib/iris/fileformats/_nc_load_rules/helpers.py

Lines 327 to 333 in 257be15

	class UnknownCellMethodWarning(iris.exceptions.IrisUnknownCellMethodWarning):
	"""
	Backwards compatible form of :class:`iris.exceptions.IrisUnknownCellMethodWarning`.
	"""
	# TODO: remove at the next major release.
	pass

iris/lib/iris/fileformats/nimrod_load_rules.py

Lines 35 to 41 in 257be15

	class TranslationWarning(IrisNimrodTranslationWarning):
	"""
	Backwards compatible form of :class:`iris.exceptions.IrisNimrodTranslationWarning`.
	"""
	# TODO: remove at the next major release.
	pass

iris/lib/iris/__init__.py

Lines 178 to 179 in 257be15

	# TODO: next major release: set IrisDeprecation to subclass
	# DeprecationWarning instead of UserWarning.