feat[next]: Support for staggered fields

src/gt4py/next/common.py

@@ -1263,11 +1263,21 @@ class GridType(StrEnum):
     UNSTRUCTURED = "unstructured"
 
 
+def check_staggered(dim: Dimension) -> bool:
+    return dim.value.startswith(_STAGGERED_PREFIX)
+
+
 def order_dimensions(dims: Iterable[Dimension]) -> list[Dimension]:
     """Find the canonical ordering of the dimensions in `dims`."""
     if sum(1 for dim in dims if dim.kind == DimensionKind.LOCAL) > 1:
         raise ValueError("There are more than one dimension with DimensionKind 'LOCAL'.")
-    return sorted(dims, key=lambda dim: (_DIM_KIND_ORDER[dim.kind], dim.value))
+    return sorted(
+        dims,
+        key=lambda dim: (
+            _DIM_KIND_ORDER[dim.kind],
+            flip_staggered(dim).value if check_staggered(dim) else dim.value,
+        ),
+    )
 
 
 def check_dims(dims: Sequence[Dimension]) -> None:
@@ -1355,3 +1365,22 @@ def __gt_builtin_func__(cls, /, func: fbuiltins.BuiltInFunction[_R, _P]) -> Call
 #: Equivalent to the `_FillValue` attribute in the UGRID Conventions
 #: (see: http://ugrid-conventions.github.io/ugrid-conventions/).
 _DEFAULT_SKIP_VALUE: Final[int] = -1
+_STAGGERED_PREFIX = "_Staggered"
+
+
+def flip_staggered(dim: Dimension) -> Dimension:
+    if dim.value.startswith(_STAGGERED_PREFIX):
+        return Dimension(dim.value[len(_STAGGERED_PREFIX) :], dim.kind)
+    else:
+        return Dimension(f"{_STAGGERED_PREFIX}{dim.value}", dim.kind)
+
+
+def connectivity_for_cartesian_shift(dim: Dimension, offset: int | float) -> CartesianConnectivity:
+    if isinstance(offset, float):
+        integral_offset, half = divmod(offset, 1)
+        assert half == 0.5
+        if dim.value.startswith(_STAGGERED_PREFIX):
+            integral_offset += 1
+        return CartesianConnectivity(dim, int(integral_offset), codomain=flip_staggered(dim))
+    else:
+        return CartesianConnectivity(dim, offset, codomain=dim)

src/gt4py/next/config.py

@@ -64,7 +64,7 @@ def env_flag_to_int(name: str, default: int) -> int:
 #: Master debug flag
 #: Changes defaults for all the other options to be as helpful for debugging as possible.
 #: Does not override values set in environment variables.
-DEBUG: Final[bool] = env_flag_to_bool("GT4PY_DEBUG", default=False)
+DEBUG: Final[bool] = env_flag_to_bool("GT4PY_DEBUG", default=True)
 
 
 #: Verbose flag for DSL compilation errors

src/gt4py/next/ffront/foast_passes/type_deduction.py

@@ -10,7 +10,7 @@
 
 import gt4py.next.ffront.field_operator_ast as foast
 from gt4py.eve import NodeTranslator, NodeVisitor, traits
-from gt4py.next import errors, utils
+from gt4py.next import common, errors, utils
 from gt4py.next.common import DimensionKind, promote_dims
 from gt4py.next.ffront import (  # noqa
     dialect_ast_enums,
@@ -655,13 +655,20 @@ def _deduce_compare_type(
     def _deduce_binop_type(
         self, node: foast.BinOp, *, left: foast.Expr, right: foast.Expr, **kwargs: Any
     ) -> Optional[ts.TypeSpec]:
-        # e.g. `IDim+1`
+        # e.g. `IDim+1` or `IDim+0.5`
         if (
             isinstance(left.type, ts.DimensionType)
             and isinstance(right.type, ts.ScalarType)
-            and type_info.is_integral(right.type)
+            and type_info.is_arithmetic(right.type)
         ):
-            return ts.OffsetType(source=left.type.dim, target=(left.type.dim,))
+            if not isinstance(right, foast.Constant):
+                raise NotImplementedError()
+            offset_index = right.value
+            if node.op == dialect_ast_enums.BinaryOperator.SUB:
+                offset_index *= -1
+            conn = common.connectivity_for_cartesian_shift(left.type.dim, offset_index)
+            return ts.OffsetType(source=conn.codomain, target=(conn.domain_dim,))
+
         if isinstance(left.type, ts.OffsetType):
             raise errors.DSLError(
                 node.location, f"Type '{left.type}' can not be used in operator '{node.op}'."

src/gt4py/next/ffront/foast_to_gtir.py

@@ -305,17 +305,19 @@ def _visit_shift(self, node: foast.Call, **kwargs: Any) -> itir.Expr:
                 # `field(Dim + idx)`
                 case foast.BinOp(
                     op=dialect_ast_enums.BinaryOperator.ADD | dialect_ast_enums.BinaryOperator.SUB,
-                    left=foast.Name(id=dimension),  # TODO(tehrengruber): use type of lhs
+                    left=foast.Name(),  # TODO(tehrengruber): use type of lhs
                     right=foast.Constant(value=offset_index),
                 ):
                     if arg.op == dialect_ast_enums.BinaryOperator.SUB:
                         offset_index *= -1
-                    # TODO(havogt): we rely on the naming-convention for implicit offsets, see `dimension_to_implicit_offset`
+                    conn = common.connectivity_for_cartesian_shift(
+                        node.args[0].left.type.dim, offset_index
+                    )
                     current_expr = im.as_fieldop(
                         im.lambda_("__it")(
                             im.deref(
                                 im.shift(
-                                    common.dimension_to_implicit_offset(dimension), offset_index
+                                    im.cartesian_offset(conn.domain_dim, conn.codomain), conn.offset
                                 )("__it")
                             )
                         )

src/gt4py/next/iterator/ir.py

@@ -81,17 +81,23 @@ def __str__(self):
 InfinityLiteral.POSITIVE = InfinityLiteral(name="POSITIVE")
 
 
-class OffsetLiteral(Expr):
-    value: Union[int, str]
-
-
 class AxisLiteral(Expr):
     # TODO(havogt): Refactor to use declare Axis/Dimension at the Program level.
     # Now every use of the literal has to provide the kind, where usually we only care of the name.
     value: str
     kind: common.DimensionKind = common.DimensionKind.HORIZONTAL
 
 
+class CartesianOffset(Expr):
+    domain: AxisLiteral
+    codomain: AxisLiteral
+
+
+# TODO(tehrengruber): allow int only and create OffsetRef for str instead
+class OffsetLiteral(Expr):
+    value: Union[int, str]
+
+
 class SymRef(Expr):
     id: Coerced[SymbolRef]
 
@@ -150,8 +156,9 @@ class Program(Node, ValidatedSymbolTableTrait):
 Expr.__hash__ = Node.__hash__  # type: ignore[method-assign]
 Literal.__hash__ = Node.__hash__  # type: ignore[method-assign]
 NoneLiteral.__hash__ = Node.__hash__  # type: ignore[method-assign]
-OffsetLiteral.__hash__ = Node.__hash__  # type: ignore[method-assign]
 AxisLiteral.__hash__ = Node.__hash__  # type: ignore[method-assign]
+OffsetLiteral.__hash__ = Node.__hash__  # type: ignore[method-assign]
+CartesianOffset.__hash__ = Node.__hash__  # type: ignore[method-assign]
 SymRef.__hash__ = Node.__hash__  # type: ignore[method-assign]
 Lambda.__hash__ = Node.__hash__  # type: ignore[method-assign]
 FunCall.__hash__ = Node.__hash__  # type: ignore[method-assign]

src/gt4py/next/iterator/ir_utils/domain_utils.py

@@ -124,54 +124,62 @@ def translate(
             return self
         if len(shift) == 2:
             off, val = shift
-            assert isinstance(off, itir.OffsetLiteral) and isinstance(off.value, str)
-            connectivity_type = common.get_offset_type(offset_provider_type, off.value)
-
-            if isinstance(connectivity_type, common.Dimension):
-                if val is trace_shifts.Sentinel.VALUE:
-                    raise NotImplementedError("Dynamic offsets not supported.")
-                assert isinstance(val, itir.OffsetLiteral) and isinstance(val.value, int)
-                current_dim = connectivity_type
-                # cartesian offset
-                new_ranges[current_dim] = SymbolicRange.translate(
-                    self.ranges[current_dim], val.value
-                )
-            elif isinstance(connectivity_type, common.NeighborConnectivityType):
-                # unstructured shift
-                assert (
-                    isinstance(val, itir.OffsetLiteral) and isinstance(val.value, int)
-                ) or val in [
-                    trace_shifts.Sentinel.ALL_NEIGHBORS,
-                    trace_shifts.Sentinel.VALUE,
-                ]
-                horizontal_sizes: dict[str, itir.Expr]
-                if symbolic_domain_sizes is not None:
-                    horizontal_sizes = {
-                        k: im.ensure_expr(v) for k, v in symbolic_domain_sizes.items()
-                    }
-                else:
-                    # note: ugly but cheap re-computation, but should disappear
-                    assert common.is_offset_provider(offset_provider)
-                    horizontal_sizes = {
-                        k: im.literal(str(v), builtins.INTEGER_INDEX_BUILTIN)
-                        for k, v in _max_domain_sizes_by_location_type(offset_provider).items()
-                    }
-
-                old_dim = connectivity_type.source_dim
-                new_dim = connectivity_type.codomain
-
-                assert new_dim not in new_ranges or old_dim == new_dim
-
-                new_range = SymbolicRange(
-                    im.literal("0", builtins.INTEGER_INDEX_BUILTIN),
-                    horizontal_sizes[new_dim.value],
-                )
+            if isinstance(off, itir.CartesianOffset):
+                old_dim = common.Dimension(value=off.domain.value, kind=off.domain.kind)
+                new_dim = common.Dimension(value=off.codomain.value, kind=off.codomain.kind)
+                new_range = SymbolicRange.translate(self.ranges[old_dim], val.value)
                 new_ranges = dict(
                     (dim, range_) if dim != old_dim else (new_dim, new_range)
                     for dim, range_ in new_ranges.items()
                 )
             else:
-                raise AssertionError()
+                assert isinstance(off, itir.OffsetLiteral) and isinstance(off.value, str)
+                connectivity_type = common.get_offset_type(offset_provider_type, off.value)
+                if isinstance(connectivity_type, common.Dimension):
+                    if val is trace_shifts.Sentinel.VALUE:
+                        raise NotImplementedError("Dynamic offsets not supported.")
+                    assert isinstance(val, itir.OffsetLiteral) and isinstance(val.value, int)
+                    current_dim = connectivity_type
+                    # cartesian offset
+                    new_ranges[current_dim] = SymbolicRange.translate(
+                        self.ranges[current_dim], val.value
+                    )
+                elif isinstance(connectivity_type, common.NeighborConnectivityType):
+                    # unstructured shift
+                    assert (
+                        isinstance(val, itir.OffsetLiteral) and isinstance(val.value, int)
+                    ) or val in [
+                        trace_shifts.Sentinel.ALL_NEIGHBORS,
+                        trace_shifts.Sentinel.VALUE,
+                    ]
+                    horizontal_sizes: dict[str, itir.Expr]
+                    if symbolic_domain_sizes is not None:
+                        horizontal_sizes = {
+                            k: im.ensure_expr(v) for k, v in symbolic_domain_sizes.items()
+                        }
+                    else:
+                        # note: ugly but cheap re-computation, but should disappear
+                        assert common.is_offset_provider(offset_provider)
+                        horizontal_sizes = {
+                            k: im.literal(str(v), builtins.INTEGER_INDEX_BUILTIN)
+                            for k, v in _max_domain_sizes_by_location_type(offset_provider).items()
+                        }
+
+                    old_dim = connectivity_type.source_dim
+                    new_dim = connectivity_type.codomain
+
+                    assert new_dim not in new_ranges or old_dim == new_dim
+
+                    new_range = SymbolicRange(
+                        im.literal("0", builtins.INTEGER_INDEX_BUILTIN),
+                        horizontal_sizes[new_dim.value],
+                    )
+                    new_ranges = dict(
+                        (dim, range_) if dim != old_dim else (new_dim, new_range)
+                        for dim, range_ in new_ranges.items()
+                    )
+                else:
+                    raise AssertionError()
             return SymbolicDomain(self.grid_type, new_ranges)
         elif len(shift) > 2:
             return self.translate(shift[0:2], offset_provider, symbolic_domain_sizes).translate(

src/gt4py/next/iterator/ir_utils/ir_makers.py

@@ -578,6 +578,10 @@ def axis_literal(dim: common.Dimension) -> itir.AxisLiteral:
     return itir.AxisLiteral(value=dim.value, kind=dim.kind)
 
 
+def cartesian_offset(domain: common.Dimension, codomain: common.Dimension):
+    return itir.CartesianOffset(domain=axis_literal(domain), codomain=axis_literal(codomain))
+
+
 def cast_as_fieldop(type_: str, domain: Optional[itir.FunCall] = None):
     """
     Promotes the function `cast_` to a field_operator.

src/gt4py/next/iterator/pretty_printer.py

@@ -143,6 +143,11 @@ def visit_InfinityLiteral(self, node: ir.InfinityLiteral, *, prec: int) -> list[
     def visit_OffsetLiteral(self, node: ir.OffsetLiteral, *, prec: int) -> list[str]:
         return [str(node.value) + "ₒ"]
 
+    def visit_CartesianOffset(self, node: ir.CartesianOffset, *, prec: int) -> list[str]:
+        (domain,) = self.visit(node.domain, prec=0)
+        (codomain,) = self.visit(node.codomain, prec=0)
+        return [f"{domain}₂{codomain}"]
+
     def visit_AxisLiteral(self, node: ir.AxisLiteral, *, prec: int) -> list[str]:
         kind = ""
         if node.kind == ir.DimensionKind.HORIZONTAL:

src/gt4py/next/iterator/transforms/trace_shifts.py

@@ -137,7 +137,8 @@ def _can_deref(x):
 
 def _shift(*offsets):
     assert all(
-        isinstance(offset, ir.OffsetLiteral) or offset in [Sentinel.ALL_NEIGHBORS, Sentinel.VALUE]
+        isinstance(offset, (ir.OffsetLiteral, ir.CartesianOffset))
+        or offset in [Sentinel.ALL_NEIGHBORS, Sentinel.VALUE]
         for offset in offsets
     )
 

src/gt4py/next/iterator/type_system/inference.py

@@ -473,6 +473,15 @@ def visit_OffsetLiteral(self, node: itir.OffsetLiteral, **kwargs) -> it_ts.Offse
             assert isinstance(node.value, str)
             return it_ts.OffsetLiteralType(value=node.value)
 
+    def visit_CartesianOffset(
+        self, node: itir.CartesianOffset, *, ctx
+    ) -> it_ts.CartesianOffsetType:
+        self.visit(node.domain, ctx=ctx)
+        self.visit(node.codomain, ctx=ctx)
+        return it_ts.CartesianOffsetType(
+            domain=node.domain.type.dim, codomain=node.codomain.type.dim
+        )
+
     def visit_Literal(self, node: itir.Literal, **kwargs) -> ts.ScalarType:
         assert isinstance(node.type, ts.ScalarType)
         return node.type

src/gt4py/next/iterator/type_system/type_specifications.py

@@ -20,6 +20,11 @@ class OffsetLiteralType(ts.TypeSpec):
     value: ts.ScalarType | str
 
 
+class CartesianOffsetType(ts.TypeSpec):
+    domain: common.Dimension
+    codomain: common.Dimension
+
+
 class IteratorType(ts.DataType, ts.CallableType):
     position_dims: list[common.Dimension] | Literal["unknown"]
     defined_dims: list[common.Dimension]