DatasetView class breaks Liskov's rule.

What is your issue?

Working on migrating the datatree.py module into xarray/core revealed that the DatasetView class, which implements Dataset while disabling methods to mutate the object, breaks Liskov's substitution principle. The type for one of the overloads of DatasetView.__getitem__ is more general than the corresponding Dataset.__getitem__ signature (due to the use of Self in the Dataset signature).

# In Dataset:
class Dataset(...):
    ...
    @overload
    def __getitem__(self, key: Iterable[Hashable]) -> Self: ...

The use of Self means that signature inherited from the superclass has a return type of DatasetView, but the DatasetView signature is overridden to have a return type of Dataset (the more generalised parent).

To avoid this, a couple of implementations were attempted:

• A class that tries to intercept the methods that mutate the Dataset using getattr. This does not catch the __setitem__ method, as it is a Magic Method, and those aren't affected by getattr.
• A Metaclass that can intercept Magic Methods, too. Implementation was inspired from here. I didn't get it to fully work, and eventually realised this was getting too complicated given the scope of the original problem.
• A mix-in for the mutating methods. I couldn't get this to work in the timescale agreed upon.
• Resorting back to ignoring the mypy errors for now, so we can proceed with the migration (given that there isn't a significant implementation concern identified from these type issues).

Also note, there is a tangentially-related known mypy error when a property setter accepts an argument of a different type to the property itself (https://github.com/python/mypy/issues/3004). This affects the assignment of Dataset objects to the DataTree.ds property. (Separate issue, but related)

Start by reading xarray/core/dataset.py around the Dataset.getitem signature and the datatree.py migration linked in the issue. Compare the DatasetView overrides and the attempted interception, metaclass, and mix-in approaches. Done requires a decided design that preserves DatasetView's mutation restrictions while resolving the reported mypy incompatibility; no specific test is named.