fix[cartesian]: Support for data dims of size one in dace backends

src/gt4py/cartesian/gtc/dace/oir_to_tasklet.py

@@ -7,6 +7,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 import operator
+import warnings
 from dataclasses import dataclass
 from functools import reduce
 from typing import Any, Final
@@ -101,9 +102,26 @@ def visit_FieldAccess(self, node: oir.FieldAccess, ctx: Context, is_target: bool
         # Gather all parts of the variable name in this list
         name_parts = [tasklet_name]
 
+        # Domain sizes of data dimensions
+        data_domains: list[int] = (
+            ctx.tree.containers[node.name].shape[-len(node.data_index) :] if node.data_index else []
+        )
+
         # Data dimension subscript
         data_indices: list[str] = []
-        for index in node.data_index:
+        for dimension, index in enumerate(node.data_index):
+            # special case: domain size of this data dimension is one
+            if data_domains[dimension] == 1:
+                if not isinstance(index, oir.Literal):
+                    warnings.warn(
+                        f"Data dimension {dimension} of field {node.name} has static size one. Accessing without a Literal is suspicious.",
+                        stacklevel=2,
+                    )
+
+                # no need for data dimension subscript because that access
+                # is entirely captured in the memlet.
+                continue
+
             data_indices.append(self.visit(index, ctx=ctx, is_target=False))
 
         if isinstance(node.offset, oir.AbsoluteKIndex):
@@ -139,9 +157,6 @@ def visit_FieldAccess(self, node: oir.FieldAccess, ctx: Context, is_target: bool
             return "".join(filter(None, name_parts))
 
         # Build Memlet and add it to inputs/outputs
-        data_domains: list[int] = (
-            ctx.tree.containers[node.name].shape[-len(node.data_index) :] if node.data_index else []
-        )
         memlet = Memlet(
             data=node.name,
             subset=_memlet_subset(node, data_domains, ctx),

tests/cartesian_tests/integration_tests/feature_tests/test_call_interface.py

@@ -11,6 +11,7 @@
 import numpy as np
 import pytest
 
+from gt4py.cartesian.frontend.exceptions import GTScriptSyntaxError
 import gt4py.cartesian.gtscript as gtscript
 import gt4py.storage as gt_storage
 from gt4py.cartesian.gtscript import Field, K
@@ -404,6 +405,58 @@ def test_mismatch(self, sample_stencil):
                 )
             )
 
+    @pytest.mark.parametrize("backend", ALL_BACKENDS)
+    def test_data_dimension_1d(self, backend: str):
+        @gtscript.stencil(backend=backend)
+        def data_dimension_1d(field_out: gtscript.Field[gtscript.IJ, (np.float64, (1,))]):
+            with computation(FORWARD), interval(...):
+                field_out[0, 0][0] = 42.0
+
+        ones = gt_storage.ones(
+            shape=(2, 3),
+            dimensions=["I", "J"],
+            dtype=(np.float64, (1,)),
+            backend=backend,
+            aligned_index=(0, 0),
+        )
+        data_dimension_1d(ones)
+        assert ones[0, 0][0] == 42.0
+
+    @pytest.mark.requires_dace
+    def test_data_dimension_1d_warning(self):
+        backend = "dace:cpu"
+
+        # Expect parsing to emit a warning
+        with pytest.warns(UserWarning, match="Accessing without a Literal is suspicious."):
+
+            @gtscript.stencil(backend=backend)
+            def data_dimension_1d_warning(
+                field_out: gtscript.Field[gtscript.IJ, (np.float64, (1,))], index: int
+            ):
+                with computation(FORWARD), interval(...):
+                    # 1. warn about accessing an array of static size 1 with a variable index
+                    # 2. add a runtime check and error out in case index != 0
+                    field_out[0, 0][index] = 42.0
+
+        ones = gt_storage.ones(
+            shape=(2, 3),
+            dimensions=["I", "J"],
+            dtype=(np.float64, (1,)),
+            backend=backend,
+            aligned_index=(0, 0),
+        )
+        data_dimension_1d_warning(ones, index=0)
+        assert ones[0, 0][0] == 42.0
+
+    def test_data_dimensions_1d_error(self):
+        # Expect out of bounds write to be caught at stencil parse time
+        with pytest.raises(GTScriptSyntaxError, match="Data index out of bounds."):
+
+            @gtscript.stencil(backend=self.backend)
+            def data_dimension_1d_error(field_out: gtscript.Field[gtscript.IJ, (np.float64, (1,))]):
+                with computation(FORWARD), interval(...):
+                    field_out[0, 0][1] = 42.0
+
 
 @pytest.mark.parametrize("backend", ALL_BACKENDS)
 def test_origin_unchanged(backend):