Check mesh equality on MeshToGridESMFRegridder call (SciTools#138)

* check mesh equality on call

* fix test

* attempt lenient equality

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* apply var_name leniency to grids

* temporary test fix

* fix tests

* fix tests

* fix tests

* fix tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

esmf_regrid/experimental/unstructured_scheme.py

@@ -432,9 +432,26 @@ def __call__(self, cube):
 
         """
         mesh = cube.mesh
-        # TODO: Ensure cube has the same mesh as that of the recorded mesh.
-        #  For the time being, we simply check that the mesh exists.
+        # TODO: replace temporary hack when iris issues are sorted.
         assert mesh is not None
+        # Ignore differences in var_name that might be caused by saving.
+        # TODO: uncomment this when iris issue with masked array comparison is sorted.
+        # self_mesh = copy.deepcopy(self.mesh)
+        # self_mesh.var_name = mesh.var_name
+        # for self_coord, other_coord in zip(self_mesh.all_coords, mesh.all_coords):
+        #     if self_coord is not None:
+        #         self_coord.var_name = other_coord.var_name
+        # for self_con, other_con in zip(
+        #     self_mesh.all_connectivities, mesh.all_connectivities
+        # ):
+        #     if self_con is not None:
+        #         self_con.var_name = other_con.var_name
+        # if self_mesh != mesh:
+        #     raise ValueError(
+        #         "The given cube is not defined on the same "
+        #         "source mesh as this regridder."
+        #     )
+
         mesh_dim = cube.mesh_dim()
 
         regrid_info = (mesh_dim, self.grid_x, self.grid_y, self.regridder)
@@ -691,7 +708,12 @@ def __call__(self, cube):
 
         """
         grid_x, grid_y = get_xy_dim_coords(cube)
-        if (grid_x != self.grid_x) or (grid_y != self.grid_y):
+        # Ignore differences in var_name that might be caused by saving.
+        self_grid_x = copy.deepcopy(self.grid_x)
+        self_grid_x.var_name = grid_x.var_name
+        self_grid_y = copy.deepcopy(self.grid_y)
+        self_grid_y.var_name = grid_y.var_name
+        if (grid_x != self_grid_x) or (grid_y != self_grid_y):
             raise ValueError(
                 "The given cube is not defined on the same "
                 "source grid as this regridder."

esmf_regrid/tests/unit/experimental/io/test_round_tripping.py

@@ -1,5 +1,7 @@
 """Unit tests for round tripping (saving then loading) with :mod:`esmf_regrid.experimental.io`."""
 
+from copy import deepcopy
+
 import numpy as np
 from numpy import ma
 
@@ -42,8 +44,6 @@ def _make_mesh_to_grid_regridder():
     lat_bounds = (-90, 90)
     # TODO check that circularity is preserved.
     tgt = _grid_cube(tgt_lons, tgt_lats, lon_bounds, lat_bounds, circular=True)
-    tgt.coord("longitude").var_name = "longitude"
-    tgt.coord("latitude").var_name = "latitude"
     src = _gridlike_mesh_cube(src_lons, src_lats)
 
     rg = MeshToGridESMFRegridder(src, tgt, mdtol=0.5)
@@ -94,8 +94,12 @@ def test_MeshToGridESMFRegridder_round_trip(tmp_path):
     loaded_rg = load_regridder(str(filename))
 
     assert original_rg.mdtol == loaded_rg.mdtol
-    assert original_rg.grid_x == loaded_rg.grid_x
-    assert original_rg.grid_y == loaded_rg.grid_y
+    loaded_grid_x = deepcopy(loaded_rg.grid_x)
+    loaded_grid_x.var_name = original_rg.grid_x.var_name
+    assert original_rg.grid_x == loaded_grid_x
+    loaded_grid_y = deepcopy(loaded_rg.grid_y)
+    loaded_grid_y.var_name = original_rg.grid_y.var_name
+    assert original_rg.grid_y == loaded_grid_y
     # TODO: uncomment when iris mesh comparison becomes available.
     # assert original_rg.mesh == loaded_rg.mesh
 
@@ -111,7 +115,17 @@ def test_MeshToGridESMFRegridder_round_trip(tmp_path):
     src_mask = np.zeros(src.data.shape)
     src_mask[0] = 1
     src.data = ma.array(src_data, mask=src_mask)
-    assert original_rg(src) == loaded_rg(src)
+    # Compare results, ignoring var_name changes due to saving.
+    original_result = original_rg(src)
+    loaded_result = loaded_rg(src)
+    original_result.var_name = loaded_result.var_name
+    original_result.coord("latitude").var_name = loaded_result.coord(
+        "latitude"
+    ).var_name
+    original_result.coord("longitude").var_name = loaded_result.coord(
+        "longitude"
+    ).var_name
+    assert original_result == loaded_result
 
     # Ensure version data is equal.
     assert original_rg.regridder.esmf_version == loaded_rg.regridder.esmf_version

esmf_regrid/tests/unit/experimental/unstructured_scheme/test_MeshToGridESMFRegridder.py

@@ -14,6 +14,7 @@
 )
 from esmf_regrid.tests.unit.experimental.unstructured_scheme.test__mesh_to_MeshInfo import (
     _gridlike_mesh,
+    _gridlike_mesh_cube,
 )
 from esmf_regrid.tests.unit.experimental.unstructured_scheme.test__regrid_unstructured_to_rectilinear__prepare import (
     _flat_mesh_cube,
@@ -136,6 +137,34 @@ def test_invalid_mdtol():
         _ = MeshToGridESMFRegridder(src, tgt, mdtol=-1)
 
 
+@pytest.mark.xfail
+def test_mistmatched_mesh():
+    """
+    Test the calling of :func:`esmf_regrid.experimental.unstructured_scheme.MeshToGridESMFRegridder`.
+
+    Checks that an error is raised when the regridder is called with a cube
+    whose mesh does not match the one used for initialisation.
+    """
+    src = _flat_mesh_cube()
+
+    n_lons = 6
+    n_lats = 5
+    lon_bounds = (-180, 180)
+    lat_bounds = (-90, 90)
+    tgt = _grid_cube(n_lons, n_lats, lon_bounds, lat_bounds, circular=True)
+
+    rg = MeshToGridESMFRegridder(src, tgt)
+
+    other_src = _gridlike_mesh_cube(n_lons, n_lats)
+
+    with pytest.raises(ValueError) as excinfo:
+        _ = rg(other_src)
+    expected_message = (
+        "The given cube is not defined on the same " "source mesh as this regridder."
+    )
+    assert expected_message in str(excinfo.value)
+
+
 def test_laziness():
     """Test that regridding is lazy when source data is lazy."""
     n_lons = 12