fix(crons): Fix type hints for monitor decorator (#2944)

Fixes GH-2939

sentry_sdk/crons/_decorator.py

@@ -5,8 +5,11 @@
 
 if TYPE_CHECKING:
     from typing import (
+        Any,
         Awaitable,
         Callable,
+        cast,
+        overload,
         ParamSpec,
         TypeVar,
         Union,
@@ -17,22 +20,50 @@
 
 
 class MonitorMixin:
-    def __call__(self, fn):
-        # type: (Callable[P, R]) -> Callable[P, Union[R, Awaitable[R]]]
-        if iscoroutinefunction(fn):
+    if TYPE_CHECKING:
+
+        @overload
+        def __call__(self, fn):
+            # type: (Callable[P, Awaitable[Any]]) -> Callable[P, Awaitable[Any]]
+            # Unfortunately, mypy does not give us any reliable way to type check the
+            # return value of an Awaitable (i.e. async function) for this overload,
+            # since calling iscouroutinefunction narrows the type to Callable[P, Awaitable[Any]].
+            ...
 
-            @wraps(fn)
-            async def inner(*args: "P.args", **kwargs: "P.kwargs"):
-                # type: (...) -> R
-                with self:  # type: ignore[attr-defined]
-                    return await fn(*args, **kwargs)
+        @overload
+        def __call__(self, fn):
+            # type: (Callable[P, R]) -> Callable[P, R]
+            ...
+
+    def __call__(
+        self,
+        fn,  # type: Union[Callable[P, R], Callable[P, Awaitable[Any]]]
+    ):
+        # type: (...) -> Union[Callable[P, R], Callable[P, Awaitable[Any]]]
+        if iscoroutinefunction(fn):
+            return self._async_wrapper(fn)
 
         else:
+            if TYPE_CHECKING:
+                fn = cast("Callable[P, R]", fn)
+            return self._sync_wrapper(fn)
+
+    def _async_wrapper(self, fn):
+        # type: (Callable[P, Awaitable[Any]]) -> Callable[P, Awaitable[Any]]
+        @wraps(fn)
+        async def inner(*args: "P.args", **kwargs: "P.kwargs"):
+            # type: (...) -> R
+            with self:  # type: ignore[attr-defined]
+                return await fn(*args, **kwargs)
+
+        return inner
 
-            @wraps(fn)
-            def inner(*args: "P.args", **kwargs: "P.kwargs"):
-                # type: (...) -> R
-                with self:  # type: ignore[attr-defined]
-                    return fn(*args, **kwargs)
+    def _sync_wrapper(self, fn):
+        # type: (Callable[P, R]) -> Callable[P, R]
+        @wraps(fn)
+        def inner(*args: "P.args", **kwargs: "P.kwargs"):
+            # type: (...) -> R
+            with self:  # type: ignore[attr-defined]
+                return fn(*args, **kwargs)
 
         return inner