[solox3]

> I can't use my editor/IDE to "go to definition" of bar/baz

I use "Find Usages" on foo to see where it is used. Once you see where it is used, you know what the types can be. It's not great, but it's also something that can be progressively remedied.

In the event that the function is not as trivial as your example suggests, the author should have written a docstring to help you understand what it is trying to do, in addition to type annotations that will make it more readable.

In this example, bar can either be a function, a class, or any object with __call__(), so the type information is less important in this case, than actual docstrings that express intent.