Make it possible to obtain non-type arguments in type analyze plugin hooks

Feature

It should be possible to obtain value expressions used as generic arguments in an AnalyzeTypeContext
For example, given typing.Annotated[builtins.int, "hello world"], I want to obtain "hello world", which is not a type, but a value.

Pitch

This feature would enable type checking of dependencies in FastAPI. FastAPI dependency injection allows specification of dependencies like this:

def my_dependency() -> SomeType:
    return ...


@app.get("/")
def route_handler(arg: Annotated[SomeType, Depends(my_dependency)]):
    return arg.do_something()

In this situation, MyPy should (with the help of a FastAPI specific plugin) be able to verify that the return type of my_dependency matches the type, which is the first generic argument of Annotated.

Currently, a plugin could theoretically obtain dependencies using get_type_analyze_hook. However, when inspecting the type arguments (ctx.type.args), any non-type argument to Annotated is not accessible within the scope of this hook.

Furthermore, this could potentially enable additional inspections relating to Pydantic fields.

Commencez par l’API get_type_analyze_hook et AnalyzeTypeContext, puis suivez la façon dont ctx.type.args traite les arguments de typing.Annotated. Le travail est terminé lorsqu’un plugin peut obtenir des expressions de valeurs qui ne sont pas des types, telles que "hello world" ou Depends(my_dependency), lors de l’analyse d’arguments génériques.