Raise a better error when an array/store already exists

It would be helpful for users and downstream libraries if the error thrown when attempting to create an array that already exists on disk was more specific. For example, this error isn’t very clear and it isn’t easy to wrap in error handling logic:

import zarr
zarr.create((10, 10), store='/tmp/test.zarr')
zarr.create((10, 10), store='/tmp/test.zarr')
# ValueError: path '' contains an array

This could perhaps raise a FileExistsError or at least include a message that describes the condition more clearly.

[Carreau]

#590 from 3 weeks ago does already include subclasses of ValueError with more informative names and make the stacktrace more explicit as to where the error come from.

Though we do need to remove the helper function in favor of custom exception and I’m was waiting for #546 to get in as it did conflict and was bigger.

Once this is in we can more precise error messages, but there will still be some layer of indirection with the store.

[rabernat]

👍 We often hit these errors with cloud storage (e.g. s3fs) and users get very confused.

@eric-czech’s suggestions make sense to me.