type checking in lambdas stops working when using `Iterable` instead of `list`

[Tinche]

Say we have a function like this:

from collections.abc import Callable, Iterable

def f[T](a: Callable[[T], Iterable[list[T]]]) -> None: ...

This generates no errors:

from typing import assert_never

f(lambda a: [assert_never(True)])

It would appear there's no checking in the lambda body.

However if I change the Iterable to list:

def f[T](a: Callable[[T], list[list[T]]]) -> None: ...

Then it works, and an error is shown as expected.

[A5rocks]

For some reason this fails:

from collections.abc import Callable, Iterable

def f[T](a: Callable[[T], Iterable[list[T]]]) -> None: ...

from typing import assert_never

f(lambda a: reveal_type([assert_never(True)]))

with:

main.py:7: note: Revealed type is "builtins.list[builtins.list[T`469]]"
main.py:7: error: Argument 1 to "assert_never" has incompatible type "bool"; expected "Never"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

Maybe there's something that's hiding the error messages (maybe we eagerly evaluate for type context and don't want possibly wrong output?) but then we're forgetting to actually show the error messages later?