chore: preserve magicgui-decorated function parameter hints with Para…

…mSpec (#600)

* chore: better param typing for magicgui decorated functions

* mainfunc

src/magicgui/type_map/_magicgui.py

@@ -16,17 +16,22 @@
 from magicgui.widgets import FunctionGui, MainFunctionGui
 
 if TYPE_CHECKING:
+    from typing_extensions import ParamSpec
+
     from magicgui.application import AppRef
+
+    _P = ParamSpec("_P")
+
 __all__ = ["magicgui", "magic_factory", "MagicFactory"]
 
 
 _R = TypeVar("_R")
-_T = TypeVar("_T", bound=FunctionGui)
+_FGuiVar = TypeVar("_FGuiVar", bound=FunctionGui)
 
 
 @overload
 def magicgui(
-    function: Callable[..., _R],
+    function: Callable[_P, _R],
     *,
     layout: str = "horizontal",
     scrollable: bool = False,
@@ -40,7 +45,7 @@ def magicgui(
     persist: bool = False,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> FunctionGui[_R]:
+) -> FunctionGui[_P, _R]:
     ...
 
 
@@ -60,13 +65,13 @@ def magicgui(
     persist: bool = False,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> Callable[[Callable[..., _R]], FunctionGui[_R]]:
+) -> Callable[[Callable[_P, _R]], FunctionGui[_P, _R]]:
     ...
 
 
 @overload
 def magicgui(
-    function: Callable[..., _R],
+    function: Callable[_P, _R],
     *,
     layout: str = "horizontal",
     scrollable: bool = False,
@@ -80,7 +85,7 @@ def magicgui(
     persist: bool = False,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> MainFunctionGui[_R]:
+) -> MainFunctionGui[_P, _R]:
     ...
 
 
@@ -100,7 +105,7 @@ def magicgui(
     persist: bool = False,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> Callable[[Callable[..., _R]], MainFunctionGui[_R]]:
+) -> Callable[[Callable[_P, _R]], MainFunctionGui[_P, _R]]:
     ...
 
 
@@ -206,7 +211,7 @@ def magicgui(
 
 @overload
 def magic_factory(
-    function: Callable[..., _R],
+    function: Callable[_P, _R],
     *,
     layout: str = "horizontal",
     scrollable: bool = False,
@@ -221,7 +226,7 @@ def magic_factory(
     widget_init: Callable[[FunctionGui], None] | None = None,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> MagicFactory[_R, FunctionGui]:
+) -> MagicFactory[FunctionGui[_P, _R]]:
     ...
 
 
@@ -242,13 +247,13 @@ def magic_factory(
     widget_init: Callable[[FunctionGui], None] | None = None,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> Callable[[Callable[..., _R]], MagicFactory[_R, FunctionGui]]:
+) -> Callable[[Callable[_P, _R]], MagicFactory[FunctionGui[_P, _R]]]:
     ...
 
 
 @overload
 def magic_factory(
-    function: Callable[..., _R],
+    function: Callable[_P, _R],
     *,
     layout: str = "horizontal",
     scrollable: bool = False,
@@ -263,7 +268,7 @@ def magic_factory(
     widget_init: Callable[[FunctionGui], None] | None = None,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> MagicFactory[_R, MainFunctionGui]:
+) -> MagicFactory[MainFunctionGui[_P, _R]]:
     ...
 
 
@@ -284,7 +289,7 @@ def magic_factory(
     widget_init: Callable[[FunctionGui], None] | None = None,
     raise_on_unknown: bool = False,
     **param_options: dict,
-) -> Callable[[Callable[..., _R]], MagicFactory[_R, MainFunctionGui]]:
+) -> Callable[[Callable[_P, _R]], MagicFactory[MainFunctionGui[_P, _R]]]:
     ...
 
 
@@ -418,7 +423,7 @@ def magic_factory(
 
 # _R is the return type of the decorated function
 # _T is the type of the FunctionGui instance (FunctionGui or MainFunctionGui)
-class MagicFactory(partial, Generic[_R, _T]):
+class MagicFactory(partial, Generic[_FGuiVar]):
     """Factory function that returns a FunctionGui instance.
 
     While this can be used directly, (see example below) the preferred usage is
@@ -436,15 +441,17 @@ class MagicFactory(partial, Generic[_R, _T]):
     >>> widget2 = factory(auto_call=True, labels=True)
     """
 
-    _widget_init: Callable[[_T], None] | None = None
-    func: Callable[..., _T]
+    _widget_init: Callable[[_FGuiVar], None] | None = None
+    # func here is the function that will be called to create the widget
+    # i.e. it will be either the FunctionGui or MainFunctionGui class
+    func: Callable[..., _FGuiVar]
 
     def __new__(
         cls,
-        function: Callable[..., _R],
+        function: Callable,
         *args: Any,
-        magic_class: type[_T] = FunctionGui,  # type: ignore
-        widget_init: Callable[[_T], None] | None = None,
+        magic_class: type[_FGuiVar] = FunctionGui,  # type: ignore
+        widget_init: Callable[[_FGuiVar], None] | None = None,
         **keywords: Any,
     ) -> MagicFactory:
         """Create new MagicFactory."""
@@ -477,7 +484,9 @@ def __repr__(self) -> str:
         ]
         return f"MagicFactory({', '.join(args)})"
 
-    def __call__(self, *args: Any, **kwargs: Any) -> _T:
+    # TODO: annotate args and kwargs here so that
+    # calling a MagicFactory instance gives proper mypy hints
+    def __call__(self, *args: Any, **kwargs: Any) -> _FGuiVar:
         """Call the wrapped _magicgui and return a FunctionGui."""
         if args:
             raise ValueError("MagicFactory instance only accept keyword arguments")

src/magicgui/types.py

@@ -38,7 +38,7 @@ class ChoicesDict(TypedDict):
 #: be provided an instance of a
 #: [~magicgui.widgets.FunctionGui][magicgui.widgets.FunctionGui],
 #: the result of the function that was called, and the return annotation itself.
-ReturnCallback = Callable[["FunctionGui[Any]", Any, type], None]
+ReturnCallback = Callable[["FunctionGui", Any, type], None]
 #: A valid file path type
 PathLike = Union[Path, str, bytes]
 

src/magicgui/widgets/_function_gui.py

@@ -30,10 +30,16 @@
 if TYPE_CHECKING:
     from pathlib import Path
 
+    from typing_extensions import ParamSpec
+
     from magicgui.application import Application, AppRef  # noqa: F401
     from magicgui.widgets import TextEdit
     from magicgui.widgets.protocols import ContainerProtocol, MainWindowProtocol
 
+    _P = ParamSpec("_P")
+else:
+    _P = TypeVar("_P")  # easier runtime dependency than ParamSpec
+
 
 def _inject_tooltips_from_docstrings(
     docstring: str | None, sig: MagicSignature
@@ -70,7 +76,7 @@ def _inject_tooltips_from_docstrings(
 _VT = TypeVar("_VT")
 
 
-class FunctionGui(Container, Generic[_R]):
+class FunctionGui(Container, Generic[_P, _R]):
     """Wrapper for a container of widgets representing a callable object.
 
     Parameters
@@ -129,7 +135,7 @@ class FunctionGui(Container, Generic[_R]):
 
     def __init__(
         self,
-        function: Callable[..., _R],
+        function: Callable[_P, _R],
         call_button: bool | str | None = None,
         layout: str = "vertical",
         scrollable: bool = False,
@@ -276,9 +282,12 @@ def __signature__(self) -> MagicSignature:
         """Return a MagicSignature object representing the current state of the gui."""
         return super().__signature__.replace(return_annotation=self.return_annotation)
 
-    def __call__(self, *args: Any, update_widget: bool = False, **kwargs: Any) -> _R:
+    def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _R:
         """Call the original function with the current parameter values from the Gui.
 
+        You may pass a `update_widget=True` keyword argument to update the widget
+        values to match the current parameter values before calling the function.
+
         It is also possible to override the current parameter values from the GUI by
         providing args/kwargs to the function call.  Only those provided will override
         the ones from the gui.  A `called` signal will also be emitted with the results.
@@ -298,6 +307,8 @@ def __call__(self, *args: Any, update_widget: bool = False, **kwargs: Any) -> _R
         gui()  # calls the original function with the current parameters
         ```
         """
+        update_widget: bool = bool(kwargs.pop("update_widget", False))
+
         sig = self.__signature__
         try:
             bound = sig.bind(*args, **kwargs)
@@ -441,12 +452,12 @@ def _load(self, path: str | Path | None = None, quiet: bool = False) -> None:
         super()._load(path or self._dump_path, quiet=quiet)
 
 
-class MainFunctionGui(FunctionGui[_R], MainWindow):
+class MainFunctionGui(FunctionGui[_P, _R], MainWindow):
     """Container of widgets as a Main Application Window."""
 
     _widget: MainWindowProtocol
 
-    def __init__(self, function: Callable, *args: Any, **kwargs: Any) -> None:
+    def __init__(self, function: Callable[_P, _R], *args: Any, **kwargs: Any) -> None:
         super().__init__(function, *args, **kwargs)
         self.create_menu_item("Help", "Documentation", callback=self._show_docs)
         self._help_text_edit: TextEdit | None = None