Zarr not cleaning up after MetadataError

[ivirshup]

Minimal, reproducible code sample, a copy-pastable example if possible

import zarr

z = zarr.open("tmp.zarr")
z.create_dataset(
    "throws_error",
    data=["a", "b", "c"],
    dtype=[("a", object), ("b", object)]
)  # Throws an error
assert "throws_error" in z  # The key is set
z["throws_error"]  # Access throws an error

Problem description

For certain failures to write an array, zarr isn't cleaning up after itself. I expected that there wouldn't be an entry for the key if setting the value failed.

Version and installation information

• zarr v2.3.2
• numcodecs v0.6.3
• python v3.7.4
• On a mac
• With pip installed zarr and numcodecs