(fix): dtype encoding roundtrip

Author: ilan-gold

src/zarr/core/metadata/v2.py

@@ -193,7 +193,12 @@ def to_dict(self) -> dict[str, JSON]:
             zarray_dict["fill_value"] = fill_value
 
         _ = zarray_dict.pop("dtype")
-        zarray_dict["dtype"] = self.dtype.str
+        dtype_json: JSON
+        if self.dtype.kind == "V":
+            dtype_json = tuple(self.dtype.descr)
+        else:
+            dtype_json = self.dtype.str
+        zarray_dict["dtype"] = dtype_json
 
         return zarray_dict
 
@@ -220,6 +225,8 @@ def update_attributes(self, attributes: dict[str, JSON]) -> Self:
 
 
 def parse_dtype(data: npt.DTypeLike) -> np.dtype[Any]:
+    if isinstance(data, list):  # this is a valid _VoidDTypeLike check
+        data = [tuple(d) for d in data]
     return np.dtype(data)
 
 

tests/test_v2.py

@@ -246,15 +246,22 @@ def test_default_filters_and_compressor(dtype_expected: Any) -> None:
 
 
 @pytest.mark.parametrize("fill_value", [None, (b"", 0, 0.0)], ids=["no_fill", "fill"])
-def test_structured_dtype(fill_value, tmp_path) -> None:
+def test_structured_dtype_roundtrip(fill_value, tmp_path) -> None:
     a = np.array(
         [(b"aaa", 1, 4.2), (b"bbb", 2, 8.4), (b"ccc", 3, 12.6)],
         dtype=[("foo", "S3"), ("bar", "i4"), ("baz", "f8")],
     )
+    array_path = tmp_path / "data.zarr"
     za = zarr.create(
-        shape=(3,), path=tmp_path, chunks=(2,), fill_value=fill_value, zarr_format=2, dtype=a.dtype
+        shape=(3,),
+        store=array_path,
+        chunks=(2,),
+        fill_value=fill_value,
+        zarr_format=2,
+        dtype=a.dtype,
     )
     if fill_value is not None:
         assert (np.array([fill_value] * a.shape[0], dtype=a.dtype) == za[:]).all()
     za[...] = a
+    za = zarr.open_array(store=array_path)
     assert (a == za[:]).all()