Filtering when reading a Grid file, avoid time leaking into the Grid

uxarray/io/_ugrid.py

@@ -3,6 +3,7 @@
 
 import uxarray.conventions.ugrid as ugrid
 from uxarray.constants import INT_DTYPE, INT_FILL_VALUE
+from uxarray.conventions.descriptors import DESCRIPTOR_NAMES
 from uxarray.grid.connectivity import _replace_fill_values
 
 
@@ -82,9 +83,37 @@ def _read_ugrid(ds):
 
     ds = ds.swap_dims(dim_dict)
 
+    # Strip non-grid extras (e.g. a stray scalar `time` coordinate, or unrelated data variables
+    ds = _keep_only_grid_vars(ds)
+
     return ds, dim_dict
 
 
+def _keep_only_grid_vars(ds):
+    """Return ``ds`` with only recognized UGRID grid variables/coordinates.
+
+    Anything else on the dataset (a stray scalar ``time`` coordinate, unrelated
+    data variables, etc.) is dropped so it cannot leak onto ``grid._ds``.
+
+    Runs on the file-read path only
+    """
+    # uxarray's own canonical grid-variable names (the same lists Grid filters against)
+    keep = {"grid_topology"}
+    keep.update(ugrid.SPHERICAL_COORD_NAMES)  # node/edge/face lon-lat
+    keep.update(ugrid.CARTESIAN_COORD_NAMES)  # node/edge/face x-y-z
+    keep.update(
+        ugrid.CONNECTIVITY_NAMES
+    )  # face_node_connectivity, edge_node_connectivity, ...
+    keep.update(
+        DESCRIPTOR_NAMES
+    )  # n_nodes_per_face, face_areas, boundary_*_indices, ...
+
+    # drop_vars removes variables/coords by name (never bare dimensions), so grid
+    # dims survive with their variables; errors="ignore" tolerates absent names.
+    drop = [name for name in ds.variables if name not in keep]
+    return ds.drop_vars(drop, errors="ignore")
+
+
 def _encode_ugrid(ds):
     """Encodes an unstructured grid represented under a ``Grid`` object as a
     ``xr.Dataset`` with an updated grid topology variable."""