Make async instances from sync fsmap objects

Author: maxrjones

src/zarr/storage/_fsspec.py

@@ -3,6 +3,8 @@
 import warnings
 from typing import TYPE_CHECKING, Any
 
+from fsspec import AbstractFileSystem
+
 from zarr.abc.store import (
     ByteRequest,
     OffsetByteRequest,
@@ -16,7 +18,6 @@
 if TYPE_CHECKING:
     from collections.abc import AsyncIterator, Iterable
 
-    from fsspec import AbstractFileSystem
     from fsspec.asyn import AsyncFileSystem
     from fsspec.mapping import FSMap
 
@@ -43,9 +44,9 @@ def _make_async(fs: AbstractFileSystem) -> AsyncFileSystem:
     if fs.async_impl and fs.asynchronous:
         return fs
     if fs.async_impl:
-        raise NotImplementedError(
-            f"The filesystem '{fs}' is synchronous and wrapping synchronous filesystems using from_mapper has not been implemented. See https://github.com/zarr-developers/zarr-python/issues/2706 for more details."
-        )
+        fs_dict = fs.to_dict()
+        fs_dict["asynchronous"] = True
+        return AbstractFileSystem.from_dict(fs_dict)
     try:
         from fsspec.implementations.asyn_wrapper import AsyncFileSystemWrapper
 
@@ -187,7 +188,7 @@ def from_mapper(
         -------
         FsspecStore
         """
-        if not fs_map.fs.asynchronous:
+        if not fs_map.fs.async_impl or not fs_map.fs.asynchronous:
             fs_map.fs = _make_async(fs_map.fs)
         return cls(
             fs=fs_map.fs,

tests/test_store/test_fsspec.py

@@ -106,8 +106,11 @@ async def test_basic() -> None:
     assert out[0].to_bytes() == data[1:]
 
 
-def test_open_s3map() -> None:
-    s3_filesystem = s3fs.S3FileSystem(asynchronous=True, endpoint_url=endpoint_url, anon=False)
+@pytest.mark.parametrize("asynchronous", [True, False])
+def test_open_s3map(asynchronous: bool) -> None:
+    s3_filesystem = s3fs.S3FileSystem(
+        asynchronous=asynchronous, endpoint_url=endpoint_url, anon=False
+    )
     mapper = s3_filesystem.get_mapper(f"s3://{test_bucket_name}/map/foo/")
     arr = zarr.open(store=mapper, mode="w", shape=(3, 3))
     assert isinstance(arr, Array)