GDriveFileSystem: Raise FIleNotFoundError on ls. (#283)

* GDriveFileSystem: Raise `FIleNotFoundError` on `ls`.

Per https://github.com/iterative/dvc/issues/9607

* Update pydrive2/fs/spec.py

Co-authored-by: Ruslan Kuprieiev <kupruser@gmail.com>

* black

* Test for empty dir in ls (#284)

* test_ls: create dir

mkdir in GDriveFileSystem is a noop.

---------

Co-authored-by: Ruslan Kuprieiev <kupruser@gmail.com>
Co-authored-by: skshetry <18718008+skshetry@users.noreply.github.com>
Co-authored-by: Saugat Pachhai (सौगात) <suagatchhetri@outlook.com>

pydrive2/fs/spec.py

@@ -434,7 +434,9 @@ def ls(self, path, detail=False):
             dir_ids = self._path_to_item_ids(base)
 
         if not dir_ids:
-            return None
+            raise FileNotFoundError(
+                errno.ENOENT, os.strerror(errno.ENOENT), path
+            )
 
         root_path = posixpath.join(bucket, base)
         contents = []

pydrive2/test/test_fs.py

@@ -116,8 +116,11 @@ def test_rm(fs, remote_dir):
     assert not fs.exists(remote_dir + "/dir/c/a")
 
 
-def test_ls(fs, remote_dir):
-    fs.mkdir(remote_dir + "dir/")
+def test_ls(fs: GDriveFileSystem, remote_dir):
+    _, base = fs.split_path(remote_dir + "dir/")
+    fs._path_to_item_ids(base, create=True)
+    assert fs.ls(remote_dir + "dir/") == []
+
     files = set()
     for no in range(8):
         file = remote_dir + f"dir/test_{no}"
@@ -138,6 +141,11 @@ def by_name(details):
     assert dirs == expected
 
 
+def test_ls_non_existing_dir(fs, remote_dir):
+    with pytest.raises(FileNotFoundError):
+        fs.ls(remote_dir + "dir/")
+
+
 def test_find(fs, remote_dir):
     fs.mkdir(remote_dir + "/dir")