Remove breaking check about auto_mkdir for FSSpecStore

changes/3193.bugfix.rst

@@ -0,0 +1,2 @@
+Removed an unnecessary check from ``_fsspec._make_async`` that would raise an exception when
+creating a read-only store backed by a local file system with ``auto_mkdir`` set  to ``False``.

src/zarr/storage/_fsspec.py

@@ -56,18 +56,12 @@ def _make_async(fs: AbstractFileSystem) -> AsyncFileSystem:
         fs_dict["asynchronous"] = True
         return fsspec.AbstractFileSystem.from_json(json.dumps(fs_dict))
 
-    # Wrap sync filesystems with the async wrapper
-    if type(fs) is fsspec.implementations.local.LocalFileSystem and not fs.auto_mkdir:
-        raise ValueError(
-            f"LocalFilesystem {fs} was created with auto_mkdir=False but Zarr requires the filesystem to automatically create directories"
-        )
     if fsspec_version < parse_version("2024.12.0"):
         raise ImportError(
             f"The filesystem '{fs}' is synchronous, and the required "
             "AsyncFileSystemWrapper is not available. Upgrade fsspec to version "
             "2024.12.0 or later to enable this functionality."
         )
-
     from fsspec.implementations.asyn_wrapper import AsyncFileSystemWrapper
 
     return AsyncFileSystemWrapper(fs, asynchronous=True)

tests/test_store/test_fsspec.py

@@ -365,7 +365,7 @@ def test_open_fsmap_file_raises(tmp_path: pathlib.Path) -> None:
     fsspec = pytest.importorskip("fsspec.implementations.local")
     fs = fsspec.LocalFileSystem(auto_mkdir=False)
     mapper = fs.get_mapper(tmp_path)
-    with pytest.raises(ValueError, match="LocalFilesystem .*"):
+    with pytest.raises(FileNotFoundError, match="No such file or directory: .*"):
         array_roundtrip(mapper)
 
 
@@ -426,3 +426,17 @@ async def test_delete_dir_wrapped_filesystem(tmp_path: Path) -> None:
     assert await store.exists("foo-bar/zarr.json")
     assert not await store.exists("foo/zarr.json")
     assert not await store.exists("foo/c/0")
+
+
+@pytest.mark.skipif(
+    parse_version(fsspec.__version__) < parse_version("2024.12.0"),
+    reason="No AsyncFileSystemWrapper",
+)
+async def test_with_read_only_auto_mkdir(tmp_path: Path) -> None:
+    """
+    Test that creating a read-only copy of a store backed by the local file system does not error
+    if auto_mkdir is False.
+    """
+
+    store_w = FsspecStore.from_url(f"file://{tmp_path}", storage_options={"auto_mkdir": False})
+    _ = store_w.with_read_only()