(🐞) no error when can't able to infer type argument and becomes `Never`

# Some stub
from typing import TypeVar
 
T = TypeVar("T")

def something(x: T = ...) -> T: 
    """x, the parameter for everything (formally Twitter)"""

# some other file
f: object
f = something()
reveal_type(f)  # Never
if f:
    print("hi")  # unreachable
print("hi")  # unreachable

We have an interesting array of bugs on display here, but most importantly I think, is that the call to something doesn't report that T can't be inferred.

Seeing as f is object here, I would expect T to be inferred as object

Reproduce the reported example in mypy and inspect the type-inference and error-reporting paths used for a call with an unconstrained TypeVar default. Verify the intended result for f: object = something() and ensure the completed behavior no longer silently produces Never or marks the following code unreachable.