MyPy should report error if variable imported in TYPE_CHECKING block?

Currently, MyPy doesn't report an error when a variable is imported in the if TYPE_CHECKING block and then used elsewhere.
For example, MyPy accepts this code:

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import NamedTuple

class C(NamedTuple):
    x: int
    y: int

even though, at runtime, it fails:

Traceback (most recent call last):
  File "type_checking_test.py", line 6, in <module>
    class C(NamedTuple):
NameError: name 'NamedTuple' is not defined

(I'm using MyPy version 0.650.)

Should this be fixed? I think this could be fixed by adding an is_type_checking_only variable to SymbolTableNode, which is True if the variable was imported or assigned within a TYPE_CHECKING block, and ensuring that this flag is false for any variables used in places other than type annotations in the actual code.

Inizia riproducendo il problema con l’esempio fornito che usa TYPE_CHECKING e NamedTuple, quindi traccia come vengono gestiti gli import e le voci della tabella dei simboli provenienti dai blocchi TYPE_CHECKING. Il lavoro è completato quando MyPy segnala l’uso non valido a runtime continuando al contempo a consentire i nomi usati solo nelle annotazioni di tipo, con una copertura del comportamento dell’esempio.