From cbd759c61c947411a0b7c31725334a929aa7d803 Mon Sep 17 00:00:00 2001
From: nishantharkut <nhnishantharkut@gmail.com>
Date: Tue, 17 Mar 2026 13:58:42 +0530
Subject: [PATCH 1/2] fix: guard data_vars when no grid is recognized

Check self._grid before delegating in the accessor data_vars property so unsupported datasets return an empty set instead of calling through a missing grid implementation. Add a focused regression test for the no-grid path, and align nearby accessor return annotations with actual return types to clear return-type diagnostics.
---
 tests/test_accessor.py         | 17 +++++++++++++++++
 xarray_subset_grid/accessor.py | 11 +++++------
 2 files changed, 22 insertions(+), 6 deletions(-)
 create mode 100644 tests/test_accessor.py

diff --git a/tests/test_accessor.py b/tests/test_accessor.py
new file mode 100644
index 0000000..7ec84d6
--- /dev/null
+++ b/tests/test_accessor.py
@@ -0,0 +1,17 @@
+import pytest
+import xarray as xr
+
+import xarray_subset_grid.accessor  # noqa: F401
+
+
+def test_data_vars_returns_empty_set_when_grid_not_recognized():
+    ds = xr.Dataset(
+        data_vars={"foo": ("x", [1, 2, 3])},
+        coords={"x": [0, 1, 2]},
+    )
+
+    with pytest.warns(UserWarning, match="no grid type found in this dataset"):
+        accessor = ds.xsg
+
+    assert accessor.grid is None
+    assert accessor.data_vars == set()
diff --git a/xarray_subset_grid/accessor.py b/xarray_subset_grid/accessor.py
index 7a4ca7a..cba1637 100644
--- a/xarray_subset_grid/accessor.py
+++ b/xarray_subset_grid/accessor.py
@@ -3,6 +3,7 @@
 # from typing import Optional, Union
 import numpy as np
 import xarray as xr
+from xarray.core.coordinates import DatasetCoordinates
 
 from xarray_subset_grid.grid import Grid
 from xarray_subset_grid.grids import (
@@ -78,18 +79,16 @@ def data_vars(self) -> set[str]:
         data analysis. These can be discarded when subsetting the
         dataset when they are not needed.
         """
-        if self._ds:
+        if self._grid:
             return self._grid.data_vars(self._ds)
         return set()
 
     @property
-    def coords(self) -> set[str]:
-        if self._ds:
-            return self._ds.coords
-        return set()
+    def coords(self) -> DatasetCoordinates:
+        return self._ds.coords
 
     @property
-    def grid_vars(self) -> set[str]:
+    def grid_vars(self) -> set[str] | list[str]:
         """List of grid variables.
 
         These variables are used to define the grid and thus should be

From bbfb6abc1dc63bc441cd7490d07addb46990e3bb Mon Sep 17 00:00:00 2001
From: nishantharkut <nhnishantharkut@gmail.com>
Date: Tue, 17 Mar 2026 21:43:45 +0530
Subject: [PATCH 2/2] fix: address review feedback on accessor type annotations

- Move DatasetCoordinates import behind TYPE_CHECKING to avoid
  runtime dependency on private xarray.core module
- Revert grid_vars annotation to set[str] to match actual return types
---
 xarray_subset_grid/accessor.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/xarray_subset_grid/accessor.py b/xarray_subset_grid/accessor.py
index cba1637..1b127fd 100644
--- a/xarray_subset_grid/accessor.py
+++ b/xarray_subset_grid/accessor.py
@@ -1,9 +1,9 @@
 import warnings
+from typing import TYPE_CHECKING
 
 # from typing import Optional, Union
 import numpy as np
 import xarray as xr
-from xarray.core.coordinates import DatasetCoordinates
 
 from xarray_subset_grid.grid import Grid
 from xarray_subset_grid.grids import (
@@ -16,6 +16,9 @@
     UGrid,
 )
 
+if TYPE_CHECKING:
+    from xarray.core.coordinates import DatasetCoordinates
+
 _grid_impls = [
     FVCOMGrid,
     SELFEGrid,
@@ -84,11 +87,11 @@ def data_vars(self) -> set[str]:
         return set()
 
     @property
-    def coords(self) -> DatasetCoordinates:
+    def coords(self) -> "DatasetCoordinates":
         return self._ds.coords
 
     @property
-    def grid_vars(self) -> set[str] | list[str]:
+    def grid_vars(self) -> set[str]:
         """List of grid variables.
 
         These variables are used to define the grid and thus should be