add 'observer' type alias

Author: daniel.eades

stubs/docutils/docutils/statemachine.pyi

@@ -7,6 +7,7 @@ _T = TypeVar("_T")
 _Context = TypeVar("_Context")
 _TransitionResult: TypeAlias = tuple[_Context, str | None, list[str]]
 _TransitionMethod: TypeAlias = Callable[[Match[str], _Context, str], _TransitionResult[_Context]]
+_Observer: TypeAlias = Callable[[StateMachine[_Context]], None]
 
 class StateMachine(Generic[_Context]):
     input_lines: StringList | None
@@ -17,7 +18,7 @@ class StateMachine(Generic[_Context]):
     initial_state: str
     current_state: str
     states: dict[str, State[_Context]]
-    observers: list[Callable[[Self], None]]
+    observers: list[_Observer[_Context]]
     def __init__(self, state_classes: Iterable[type[State[_Context]]], initial_state: str, debug: bool = False) -> None: ...
     def unlink(self) -> None: ...
     def run(
@@ -48,8 +49,8 @@ class StateMachine(Generic[_Context]):
     def add_states(self, state_classes: Iterable[type[State[_Context]]]) -> None: ...
     def runtime_init(self) -> None: ...
     def error(self) -> None: ...
-    def attach_observer(self, observer) -> None: ...
-    def detach_observer(self, observer) -> None: ...
+    def attach_observer(self, observer: _Observer[_Context]) -> None: ...
+    def detach_observer(self, observer: _Observer[_Context]) -> None: ...
     def notify_observers(self) -> None: ...
 
 class State(Generic[_Context]):