Rule suggestion: unknown dict value is affected to a variable

[njourdane]

I'm interested for a rule that warns me when an unknown dict value is affected to a variable, like this:

def(self, my_dict: dict[str, Any]):
    my_var = my_dict["foo"] # bad: unknown variable type for "my_var"

def(self, my_dict: dict[str, Any]):
    my_var: str = my_dict["foo"] # good: my_var is typed

def(self, my_dict: MyDictType):
    my_var = my_dict["foo"] # good: dict is typed

Using dict[str, Any] is pretty common for me. For my experience, it usually doesn't mean that all the items of the dictionary have an unknown type, but it usually means that the dictionary is untyped (expect for the keys): in many cases, I known the type of the item.

A rule that warns me when I'm able to type a variable could help me to improve typing in my projects.

[ntBre]

This seems like a better fit for a type checker like ty or at least a future type-aware linter. I don't think ty has any existing rules to require a narrower type than Any in this case.

https://play.ty.dev/8f9be4df-c3cc-4f68-af87-24eb9451f08e