feat: Support duty parameters annotated as type unions, with both old…

… and modern syntax, even on Python 3.8 and 3.9

pyproject.toml

@@ -29,6 +29,7 @@ classifiers = [
     "Typing :: Typed",
 ]
 dependencies = [
+    "eval-type-backport; python_version < '3.10'",
     "failprint>=0.11,!=1.0.0",
 ]
 

src/duty/validation.py

@@ -9,9 +9,21 @@
 
 import sys
 import textwrap
+from contextlib import suppress
 from functools import cached_property
 from inspect import Parameter, Signature, signature
-from typing import Any, Callable, Sequence
+from typing import Any, Callable, ForwardRef, Sequence, Union, get_args, get_origin
+
+# TODO: Update once support for Python 3.9 is dropped.
+if sys.version_info < (3, 10):
+    from eval_type_backport import eval_type_backport as eval_type
+
+    union_types = (Union,)
+else:
+    from types import UnionType
+    from typing import _eval_type as eval_type  # type: ignore[attr-defined]
+
+    union_types = (Union, UnionType)
 
 
 def to_bool(value: str) -> bool:
@@ -40,6 +52,12 @@ def cast_arg(arg: Any, annotation: Any) -> Any:
         return arg
     if annotation is bool:
         annotation = to_bool
+    if get_origin(annotation) in union_types:
+        for sub_annotation in get_args(annotation):
+            if sub_annotation is type(None):
+                continue
+            with suppress(Exception):
+                return cast_arg(arg, sub_annotation)
     try:
         return annotation(arg)
     except Exception:  # noqa: BLE001
@@ -187,9 +205,10 @@ def _get_params_caster(func: Callable, *args: Any, **kwargs: Any) -> ParamsCaste
                 param.kind,
                 default=param.default,
                 annotation=(
-                    eval(  # noqa: PGH001,S307
-                        param.annotation,
+                    eval_type(
+                        ForwardRef(param.annotation) if isinstance(param.annotation, str) else param.annotation,
                         exec_globals,
+                        {},
                     )
                     if param.annotation is not Parameter.empty
                     else type(param.default)

tests/test_validation.py

@@ -145,3 +145,20 @@ def func(ctx, a=0):  # noqa: ANN202,ARG001,ANN001
     caster = _get_params_caster(func, a="1")
     _, kwargs = caster.cast(a="1")
     assert kwargs == {"a": 1}
+
+
+def test_validating_modern_annotations() -> None:
+    """Test modern type annotations in function signatures."""
+
+    def func(ctx, a: int | None = None):  # noqa: ANN202,ARG001,ANN001
+        ...
+
+    caster = _get_params_caster(func, a=1)
+    _, kwargs = caster.cast(a="1")
+    assert kwargs == {"a": 1}
+    caster = _get_params_caster(func, a=None)
+    _, kwargs = caster.cast(a=None)
+    assert kwargs == {"a": None}
+    caster = _get_params_caster(func)
+    _, kwargs = caster.cast()
+    assert kwargs == {}