feat[cartesian]: option to force annotated temporaries

src/gt4py/cartesian/definitions.py

@@ -10,6 +10,7 @@
 import functools
 import os
 import platform
+import warnings
 from dataclasses import dataclass
 from typing import Literal, Tuple, Union
 
@@ -42,6 +43,28 @@
 """Default literal precision used for unspecific `float` types and casts."""
 
 
+def _check_boolean_env_var(name: str, default: bool) -> bool:
+    envvar = os.environ.get(name, default=default)
+    if type(envvar) is bool:
+        return envvar
+
+    if type(envvar) is str:
+        if envvar.lower() in ["true", "1"]:
+            return True
+        if envvar in ["false", "0"]:
+            return False
+
+    warnings.warn(
+        f"Could not match `{name}={envvar}` into a boolean value. Falling back to the default `{default}`.",
+        stacklevel=2,
+    )
+    return default
+
+
+FORCE_ANNOTATED_TEMPORARIES = _check_boolean_env_var("GT4PY_FORCE_ANNOTATED_TEMPORARIES", False)
+"""If True, forces all temporaries in stencils to have type annotations."""
+
+
 @enum.unique
 class AccessKind(enum.IntFlag):
     NONE = 0
@@ -123,6 +146,8 @@ class BuildOptions(AttributeClassLike):
     "Literal precision for `int` types and casts. Defaults to architecture precision unless overwritten by the environment variable `GT4PY_LITERAL_INT_PRECISION`."
     literal_float_precision = attribute(of=int, default=LITERAL_FLOAT_PRECISION)
     "Literal precision for `float` types and casts. Defaults to architecture precision unless overwritten by the environment variable `GT4PY_LITERAL_FLOAT_PRECISION`."
+    force_annotated_temporaries = attribute(of=bool, default=FORCE_ANNOTATED_TEMPORARIES)
+    "If True, enforce all temporaries to have type annotations. Defaults to False unless overwritten by the environment variable `GT4PY_FORCE_ANNOTATED_TEMPORARIES`."
 
     @property
     def qualified_name(self):

src/gt4py/cartesian/frontend/gtscript_frontend.py

@@ -799,6 +799,7 @@ def __init__(
         self.domain = domain or nodes.Domain.LatLonGrid()
         self.literal_int_precision = options.literal_int_precision
         self.literal_float_precision = options.literal_float_precision
+        self.force_annotated_temporaries = options.force_annotated_temporaries
         self.temp_decls = temp_decls or {}
         self.parsing_context = None
         self.iteration_order = None
@@ -1705,6 +1706,11 @@ def _resolve_assign(
                             message="Temporaries with data dimensions need to be declared explicitly.",
                             loc=nodes.Location.from_ast_node(t, scope=self.stencil_name),
                         )
+                    if self.force_annotated_temporaries and target_annotation is None:
+                        raise GTScriptSyntaxError(
+                            message=f"Missing type hint for '{name}' in stencil '{self.stencil_name}'.",
+                            loc=nodes.Location.from_ast_node(t, scope=self.stencil_name),
+                        )
                     dtype = nodes.DataType.AUTO
                     axes = nodes.Domain.LatLonGrid().axes_names
                     if target_annotation is not None:

tests/cartesian_tests/unit_tests/frontend_tests/test_gtscript_frontend.py

@@ -57,6 +57,7 @@ def parse_definition(
     dtypes: Dict[Type, Type] = None,
     literal_int_precision: int | None = None,
     literal_float_precision: int | None = None,
+    force_annotated_temporaries: bool | None = None,
     rebuild=False,
     **kwargs,
 ) -> nodes.StencilDefinition:
@@ -73,6 +74,8 @@ def parse_definition(
         build_args["literal_int_precision"] = literal_int_precision
     if literal_float_precision is not None:
         build_args["literal_float_precision"] = literal_float_precision
+    if force_annotated_temporaries is not None:
+        build_args["force_annotated_temporaries"] = force_annotated_temporaries
 
     build_options = gt_definitions.BuildOptions(**build_args)
 
@@ -2222,3 +2225,35 @@ def stencil(in_field: gtscript.Field[float], out_field: gtscript.Field[float]):
                 name=inspect.stack()[0][3],
                 module=self.__class__.__name__,
             )
+
+
+class TestForceAnnotatedTemporaries:
+    def test_missing_annotation(self):
+        def good_case(in_field: gtscript.Field[float], out_field: gtscript.Field[float]):
+            with computation(PARALLEL), interval(...):
+                tmp: float = 2 * in_field
+                out_field = tmp
+
+        parsed = parse_definition(
+            good_case, name=inspect.stack()[0][3], module=self.__class__.__name__
+        )
+
+        declaration = parsed.computations[0].body.stmts[0]
+        assert isinstance(declaration, nodes.FieldDecl)
+        assert declaration.data_type == nodes.DataType.FLOAT64
+
+        def bad_case(in_field: gtscript.Field[float], out_field: gtscript.Field[float]):
+            with computation(PARALLEL), interval(...):
+                tmp = 2 * in_field
+                out_field = tmp
+
+        with pytest.raises(
+            gt_frontend.GTScriptSyntaxError,
+            match="Missing type hint for 'tmp' in stencil 'bad_case'.",
+        ):
+            parse_definition(
+                bad_case,
+                name=inspect.stack()[0][3],
+                module=self.__class__.__name__,
+                force_annotated_temporaries=True,
+            )