argparse: Forbid invalid type and choices combinations

stdlib/@tests/test_cases/check_argparse.py

@@ -0,0 +1,18 @@
+from argparse import ArgumentParser, FileType
+
+parser = ArgumentParser()
+
+parser.add_argument("--foo")
+parser.add_argument("--foo", choices=[""])
+parser.add_argument("--foo", choices=[1, 2, 3])  # type: ignore
+
+parser.add_argument("--foo", type=int)
+parser.add_argument("--foo", type=int, choices=[1, 2, 3])
+parser.add_argument("--foo", type=int, choices=[""])  # type: ignore
+
+parser.add_argument("--foo", type="")
+parser.add_argument("--foo", type="", choices=[1, 2, 3])
+parser.add_argument("--foo", type="", choices=[""])
+
+parser.add_argument("--foo", type=FileType())
+parser.add_argument("--foo", type=FileType(), choices=[""])  # type: ignore

stdlib/argparse.pyi

@@ -3,7 +3,7 @@ from _typeshed import sentinel
 from collections.abc import Callable, Generator, Iterable, Sequence
 from re import Pattern
 from typing import IO, Any, Generic, Literal, NewType, NoReturn, Protocol, TypeVar, overload
-from typing_extensions import Self, TypeAlias, deprecated
+from typing_extensions import Never, Self, TypeAlias, deprecated
 
 __all__ = [
     "ArgumentParser",
@@ -83,14 +83,37 @@ class _ActionsContainer:
     def _registry_get(self, registry_name: str, value: Any, default: Any = None) -> Any: ...
     def set_defaults(self, **kwargs: Any) -> None: ...
     def get_default(self, dest: str) -> Any: ...
+    # If `type` is `FileType`, supplying `choices` makes no sense.
+    # (This overload is provided for documentation's sake, as the next overload
+    # will match if `type` is `FileType` and `choices` is provided, although
+    # the possible choices are `IO[Any]`.)
+    @overload
     def add_argument(
         self,
         *name_or_flags: str,
         action: _ActionStr | type[Action] = ...,
         nargs: int | _NArgsStr | _SUPPRESS_T | None = None,
         const: Any = ...,
         default: Any = ...,
-        type: _ActionType = ...,
+        type: FileType,
+        choices: None = ...,
+        required: bool = ...,
+        help: str | None = ...,
+        metavar: str | tuple[str, ...] | None = ...,
+        dest: str | None = ...,
+        version: str = ...,
+        **kwargs: Any,
+    ) -> Action: ...
+    # If `type` is a callable, its return type is supplied to `choices`.
+    @overload
+    def add_argument(
+        self,
+        *name_or_flags: str,
+        action: _ActionStr | type[Action] = ...,
+        nargs: int | _NArgsStr | _SUPPRESS_T | None = None,
+        const: Any = ...,
+        default: Any = ...,
+        type: Callable[[str], _T],
         choices: Iterable[_T] | None = ...,
         required: bool = ...,
         help: str | None = ...,
@@ -99,6 +122,42 @@ class _ActionsContainer:
         version: str = ...,
         **kwargs: Any,
     ) -> Action: ...
+    # If `type` is a string, the possible `choices` depend on `type`.
+    @overload
+    def add_argument(
+        self,
+        *name_or_flags: str,
+        action: _ActionStr | type[Action] = ...,
+        nargs: int | _NArgsStr | _SUPPRESS_T | None = None,
+        const: Any = ...,
+        default: Any = ...,
+        type: str,
+        choices: Iterable[Any] | None = ...,
+        required: bool = ...,
+        help: str | None = ...,
+        metavar: str | tuple[str, ...] | None = ...,
+        dest: str | None = ...,
+        version: str = ...,
+        **kwargs: Any,
+    ) -> Action: ...
+    # If `type` is not supplied, `choices` must be strings.
+    @overload
+    def add_argument(
+        self,
+        *name_or_flags: str,
+        action: _ActionStr | type[Action] = ...,
+        nargs: int | _NArgsStr | _SUPPRESS_T | None = None,
+        const: Any = ...,
+        default: Any = ...,
+        type: Never = ...,
+        choices: Iterable[str] | None = ...,
+        required: bool = ...,
+        help: str | None = ...,
+        metavar: str | tuple[str, ...] | None = ...,
+        dest: str | None = ...,
+        version: str = ...,
+        **kwargs: Any,
+    ) -> Action: ...
     def add_argument_group(
         self,
         title: str | None = None,