Improve runtime type checking in from_flat()

src/pydantic_zarr/v2.py

@@ -983,10 +983,14 @@ def from_flat_group(data: dict[str, AnyArraySpec | AnyGroupSpec]) -> AnyGroupSpe
             # this is an array or group that belongs to the group we are ultimately returning
             if isinstance(value, ArraySpec):
                 member_arrays[subparent_name] = value
-            else:
+            elif isinstance(value, GroupSpec):
                 if subparent_name not in submember_by_parent_name:
                     submember_by_parent_name[subparent_name] = {}
                 submember_by_parent_name[subparent_name][root_name] = value
+            else:
+                raise ValueError(
+                    f"Value at '{key}' is not a v2 ArraySpec or GroupSpec (got {type(value)=})"
+                )
         else:
             # these are groups or arrays that belong to one of the member groups
             # not great that we repeat this conditional dict initialization

src/pydantic_zarr/v3.py

@@ -968,10 +968,14 @@ def from_flat_group(
             # this is an array or group that belongs to the group we are ultimately returning
             if isinstance(value, ArraySpec):
                 member_arrays[subparent_name] = value
-            else:
+            elif isinstance(value, GroupSpec):
                 if subparent_name not in submember_by_parent_name:
                     submember_by_parent_name[subparent_name] = {}
                 submember_by_parent_name[subparent_name][root_name] = value
+            else:
+                raise ValueError(
+                    f"Value at '{key}' is not a v3 ArraySpec or GroupSpec (got {type(value)=})"
+                )
         else:
             # these are groups or arrays that belong to one of the member groups
             # not great that we repeat this conditional dict initialization

tests/test_pydantic_zarr/test_v2.py

@@ -5,6 +5,7 @@
 from __future__ import annotations
 
 import json
+import re
 from typing import TYPE_CHECKING, Any
 
 import pytest
@@ -654,3 +655,16 @@ def test_arrayspec_from_zarr(dtype_example: DTypeExample) -> None:
         observed["dtype"] = list(observed["dtype"])
 
     assert arr_spec.model_dump() == observed
+
+
+def test_mix_v3_v2_fails() -> None:
+    from pydantic_zarr.v3 import ArraySpec as ArraySpecv3
+
+    members_flat = {"/a": ArraySpecv3.from_array(np.ones(1))}
+    with pytest.raises(
+        ValueError,
+        match=re.escape(
+            "Value at '/a' is not a v2 ArraySpec or GroupSpec (got type(value)=<class 'pydantic_zarr.v3.ArraySpec'>)"
+        ),
+    ):
+        GroupSpec.from_flat(members_flat)  # type: ignore[arg-type]

tests/test_pydantic_zarr/test_v3.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import json
+import re
 from dataclasses import asdict
 
 import numpy as np
@@ -236,3 +237,16 @@ def test_from_zarr_depth() -> None:
         assert group_in_3.attributes == tree[""].attributes  # type: ignore[attr-defined]
         assert group_in_3.members["1"].attributes == tree["/1"].attributes  # type: ignore[attr-defined]
         assert group_in_3.members["1"].members["2"].attributes == tree["/1/2"].attributes  # type: ignore[attr-defined]
+
+
+def test_mix_v3_v2_fails() -> None:
+    from pydantic_zarr.v2 import ArraySpec as ArraySpecv2
+
+    members_flat = {"/a": ArraySpecv2.from_array(np.ones(1))}
+    with pytest.raises(
+        ValueError,
+        match=re.escape(
+            "Value at '/a' is not a v3 ArraySpec or GroupSpec (got type(value)=<class 'pydantic_zarr.v2.ArraySpec'>)"
+        ),
+    ):
+        GroupSpec.from_flat(members_flat)  # type: ignore[arg-type]