bug[next]: Fix codegen in gtfn for unused vertical offset provider (#…

…1746)

Providing an offest provider for a vertical dimension without using that
dimension in a program, e.g. no arguments are fields defined on K,
resulted in erroneous C++ code.

src/gt4py/next/program_processors/codegens/gtfn/itir_to_gtfn_ir.py

@@ -198,6 +198,9 @@ def _collect_offset_definitions(
                         "Mapping an offset to a horizontal dimension in unstructured is not allowed."
                     )
                 # create alias from vertical offset to vertical dimension
+                offset_definitions[dim.value] = TagDefinition(
+                    name=Sym(id=dim.value), alias=_vertical_dimension
+                )
                 offset_definitions[offset_name] = TagDefinition(
                     name=Sym(id=offset_name), alias=SymRef(id=dim.value)
                 )

tests/next_tests/integration_tests/cases.py

@@ -499,13 +499,21 @@ def unstructured_case(
             Vertex: mesh_descriptor.num_vertices,
             Edge: mesh_descriptor.num_edges,
             Cell: mesh_descriptor.num_cells,
-            KDim: 10,
         },
         grid_type=common.GridType.UNSTRUCTURED,
         allocator=exec_alloc_descriptor.allocator,
     )
 
 
+@pytest.fixture
+def unstructured_case_3d(unstructured_case):
+    return dataclasses.replace(
+        unstructured_case,
+        default_sizes={**unstructured_case.default_sizes, KDim: 10},
+        offset_provider={**unstructured_case.offset_provider, "KOff": KDim},
+    )
+
+
 def _allocate_from_type(
     case: Case,
     arg_type: ts.TypeSpec,

tests/next_tests/integration_tests/feature_tests/ffront_tests/test_execution.py

@@ -41,6 +41,7 @@
     Edge,
     cartesian_case,
     unstructured_case,
+    unstructured_case_3d,
 )
 from next_tests.integration_tests.feature_tests.ffront_tests.ffront_test_utils import (
     exec_alloc_descriptor,
@@ -93,6 +94,20 @@ def testee(a: cases.VField) -> cases.EField:
     )
 
 
+def test_horizontal_only_with_3d_mesh(unstructured_case_3d):
+    # test field operator operating only on horizontal fields while using an offset provider
+    # including a vertical dimension.
+    @gtx.field_operator
+    def testee(a: cases.VField) -> cases.VField:
+        return a
+
+    cases.verify_with_default_data(
+        unstructured_case_3d,
+        testee,
+        ref=lambda a: a,
+    )
+
+
 @pytest.mark.uses_unstructured_shift
 def test_composed_unstructured_shift(unstructured_case):
     @gtx.field_operator

tests/next_tests/integration_tests/feature_tests/ffront_tests/test_gt4py_builtins.py

@@ -29,6 +29,7 @@
     Vertex,
     cartesian_case,
     unstructured_case,
+    unstructured_case_3d,
 )
 from next_tests.integration_tests.feature_tests.ffront_tests.ffront_test_utils import (
     exec_alloc_descriptor,
@@ -105,10 +106,10 @@ def reduction_ke_field(
 @pytest.mark.parametrize(
     "fop", [reduction_e_field, reduction_ek_field, reduction_ke_field], ids=lambda fop: fop.__name__
 )
-def test_neighbor_sum(unstructured_case, fop):
-    v2e_table = unstructured_case.offset_provider["V2E"].ndarray
+def test_neighbor_sum(unstructured_case_3d, fop):
+    v2e_table = unstructured_case_3d.offset_provider["V2E"].ndarray
 
-    edge_f = cases.allocate(unstructured_case, fop, "edge_f")()
+    edge_f = cases.allocate(unstructured_case_3d, fop, "edge_f")()
 
     local_dim_idx = edge_f.domain.dims.index(Edge) + 1
     adv_indexing = tuple(
@@ -131,10 +132,10 @@ def test_neighbor_sum(unstructured_case, fop):
         where=broadcasted_table != common._DEFAULT_SKIP_VALUE,
     )
     cases.verify(
-        unstructured_case,
+        unstructured_case_3d,
         fop,
         edge_f,
-        out=cases.allocate(unstructured_case, fop, cases.RETURN)(),
+        out=cases.allocate(unstructured_case_3d, fop, cases.RETURN)(),
         ref=ref,
     )
 
@@ -463,11 +464,13 @@ def conditional_program(
     )
 
 
-def test_promotion(unstructured_case):
+def test_promotion(unstructured_case_3d):
     @gtx.field_operator
     def promotion(
         inp1: gtx.Field[[Edge, KDim], float64], inp2: gtx.Field[[KDim], float64]
     ) -> gtx.Field[[Edge, KDim], float64]:
         return inp1 / inp2
 
-    cases.verify_with_default_data(unstructured_case, promotion, ref=lambda inp1, inp2: inp1 / inp2)
+    cases.verify_with_default_data(
+        unstructured_case_3d, promotion, ref=lambda inp1, inp2: inp1 / inp2
+    )