url_to_fs with DirFileSystem

[pjw91]

Is the url dir:///usr/lib valid for url_to_fs?

It raises the following exception currently:

Traceback (most recent call last):
  File "/dev/shm/newfs/a.py", line 4, in <module>
    d=fsspec.url_to_fs('dir:///ext/stag')
  File "/dev/shm/newfs/.venv/lib/python3.14/site-packages/fsspec/core.py", line 432, in url_to_fs
    fs = filesystem(protocol, **inkwargs)
  File "/dev/shm/newfs/.venv/lib/python3.14/site-packages/fsspec/registry.py", line 325, in filesystem
    return cls(**storage_options)
  File "/dev/shm/newfs/.venv/lib/python3.14/site-packages/fsspec/spec.py", line 84, in __call__
    obj = super().__call__(*args, **kwargs, **strip_tokenize_options)
  File "/dev/shm/newfs/.venv/lib/python3.14/site-packages/fsspec/implementations/dirfs.py", line 48, in __init__
    self.path = fs._strip_protocol(path)
                ~~~~~~~~~~~~~~~~~~^^^^^^
  File "/dev/shm/newfs/.venv/lib/python3.14/site-packages/fsspec/implementations/local.py", line 256, in _strip_protocol
    if path.startswith("file://"):
       ^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'startswith'

It seems that in url_to_fs() :

    # chain = [('/usr/lib', 'dir', {})]
    for i, ch in enumerate(reversed(chain)):
        urls, protocol, kw = ch
        if i == len(chain) - 1:
            inkwargs = dict(**kw, **inkwargs)
            inkwargs['fo'] = urls    # BUGGY: <--- lack this line
            continue
        inkwargs["target_options"] = dict(**kw, **inkwargs)
        inkwargs["target_protocol"] = protocol
        inkwargs["fo"] = urls
    urlpath, protocol, _ = chain[0]
    fs = filesystem(protocol, **inkwargs)
    return fs, urlpath

When chain = [('/usr/lib', 'dir', {})], neither fo or path is assigned in inkwargs, thus the instantiate fs = filesystem(protocol, **inkwargs) becomes fs = filesystem('dir', **{}) and lacks path for DirFileSystem

[martindurant]

The correct call is:

fsspec.core.url_to_fs("dir::file:///usr/lib")
or
fsspec.core.url_to_fs("dir::///usr/lib"

Here, "::" is the fsspec way to separate the path parts, and dirFS needs a specific filesystem/path to work on. "file" is the default one, but you could have given any known protocol in the second part of the URL.