Misleading error message with `dict.get` like method. (polymorphic function with conflicting context)

Consider this example that emulates dict.get: (https://mypy-play.net/?mypy=latest&python=3.12)

from typing import Any, reveal_type

class Map[K, V]:
    def set(self, key: K, value: V) -> None: ...
    def get[T](self, key: Any, default: T, /) -> V | T: ...

d_any: Map[str, Any] = Map()

reveal_type(d_any.get("key", None))  # Any | None  ✅️

result: str = reveal_type(d_any.get("key", None))  # Any | str ❌️
# error: Argument 2 to "get" of "Map" has incompatible type "None"; expected "str" 

mypys error message is misleading. None is a perfectly reasonable argument for the default value of d_any.get. The problem is that the return type Any | None is not assignable to str. It would make more sense if either:

1. mypy reports that Any | None cannot be assigned to str.
   (e.g. by a two step approach: first try to solve with context and if that fails, use the return type that is inferred from the arguments alone)[^1]
2. mypy reports that it cannot find a solution for the type variable T.
   (e.g. single step that considers both constraints from arguments and context)

[^1]: In certain special cases like tuple/list/set/dict-comprehensions, the current behavior that inverts the priority seems fine

Inizia riproducendo l'esempio nel mypy playground collegato e confronta la diagnosi con i due risultati proposti. Traccia l'inferenza dei tipi generici di mypy e il comportamento del tipaggio contestuale per la chiamata polimorfica a get. Il lavoro è completo quando la diagnosi non attribuisce più erroneamente la colpa a None e un test di regressione copre questo esempio.