Infinite recursion in walk() when S3 bucket contains object with key /

We've run into a reproducible issue where calling walk() on an S3 bucket causes infinite recursion if the bucket contains an object with the key /

This happens because:

• S3 allows an object to be created with the key /
• ls() returns it as a "directory" (i.e. common prefix /)
• walk() sees that as a subdirectory and recurses into it
• But that "subdirectory" is just the bucket root again → leading to infinite recursion
• This eventually leads to a RecursionError: maximum recursion depth exceeded.

Let us know if this is something you'd consider filtering out at the s3fs level. Happy to provide a test case or additional details!

Thanks for the great library 🙏

Start by locating the Python implementation of walk() and its use of ls(), then reproduce the case with an S3 object whose key is /. Trace how the returned common prefix is treated as a child directory; done means the case no longer recurses indefinitely and a regression test covers it.