S3FileSystem.du() FileNotFoundError for paths with empty prefixes

[andyfarmerboy]

The .du() method returns a FileNotFoundError if any terminal prefix trees at or below the path root do not contain any files.

path = 'bucket/empty-prefix/'  
print(S3FileSystem.du(path))

#> FileNotFoundError

# (Expected) 
# 0

The method returns a numeric value as expected if all prefixes contain files.

[martindurant]

Agreed that this should work. See the general discussion at fsspec/filesystem_spec#562 - we could do with a comprehensive set of tests for the object storage backends with paths with/without terminal "/", and with/without deeper-nested contents, across the several methods that do this kind of work.

For now, there is a chance that this particular issue is already fixed on main (soon to be released), because find, used by du, no longer uses the prefix/delimiter approach when maxdepth is not specified.

[ianthomas23]

I have confirmed that this has already been fixed, and I've submitted a PR (#803) to ensure there are no future regressions.