Keys and values could be narrower for closed TypedDicts

I was very excited to try out mypy 2.2 with the initial support for the TypedDict closed keyword.
But in our code base, where we often iterate over TypedDicts, it did not help much because the keys and values are still inferred as str and object, respectively.

from typing_extensions import TypedDict, reveal_type


class Closed(TypedDict, closed=True, total=False):
    a: int
    b: str

c = Closed(a=1, b='a')
reveal_type(c.items())

for key, val in c.items():
    c[key]

$ mypy --pretty test.py
test.py:9: note: Revealed type is "_collections_abc.dict_items[str, object]"
test.py:12: error: TypedDict key must be a string literal; expected one of ("a", "b")  [literal-required]
        c[key]
          ^~~
Found 1 error in 1 file (checked 1 source file)

ty narrows both keys and values here

$ ty check test.py
ty check test.py 
info[revealed-type]: Revealed type
 --> test.py:9:13
  |
9 | reveal_type(c.items())
  |             ^^^^^^^^^^ `dict_items[Literal["a", "b"], int | str]`
  |

Found 1 diagnostic

Inizia riproducendo l’esempio test.py dell’issue con mypy --pretty, concentrandoti su TypedDict.items() e sul successivo accesso c[key]. Traccia il percorso di controllo dei tipi TypedDict responsabile di questi tipi inferiti; il lavoro è completato quando l’iterazione su un TypedDict chiuso rivela un’unione letterale delle chiavi e i corrispondenti tipi di valore, e l’accesso tramite indice con la chiave iterata viene accettato.