Deprecation of `Dataset.update()` returning a dataset object

[VeckoTheGecko]

What is your issue?

Version: latest

#4932 mentions that the return value of Dataset.update() will be removed in v0.21 (released Jan 28, 2022).

xarray/xarray/core/dataset.py

Lines 5547 to 5553 in fd7c765

	Returns
	-------
	updated : Dataset
	Updated dataset. Note that since the update is in-place this is the input
	dataset.
	It is deprecated since version 0.17 and scheduled to be removed in 0.21.

This functionality wasn't removed yet due to #5630 (comment).

I don't think there was a tracking issue for that PR comment before.

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[VeckoTheGecko]

Seems like this has already been given considerable thought, so not sure how useful making this issue is. I feel like I'm dusting off old bones in the codebase 😅 . Maintainers, what would be the best way forward?

• make the dataset subclass (which as shoyer said, might be difficult to get right)
• remove " and scheduled to be removed in 0.21."
• leave as is? something else?

[keewis]

I'd personally vote for completing the deprecation cycle (which was started about three years ago), but not sure how disruptive this would be.