Hang on some type hints

[WiredBovine]

Bug Report
mypy hangs and appears to have entered an infinite loop on some function argument type hints.

To Reproduce

The following code hangs mypy version 1.15.0 on my machine:

def normal_dist_intersection(m1: float | np.ndarray, m2: float | np.ndarray, s1: float | np.ndarray, s2: float | np.ndarray):
    return (m2*s1*s1 - s2 * (m1*s2 + s1*np.sqrt((m1 - m2)**2 + 2*(s1*s1 - s2*s2) * np.log(s1/s2)))) / (s1*s1 - s2*s2)

The following code works as expected. Note that the only difference is the removal of the last float type hint.

def normal_dist_intersection(m1: float | np.ndarray, m2: float | np.ndarray, s1: float | np.ndarray, s2: np.ndarray):
    return (m2*s1*s1 - s2 * (m1*s2 + s1*np.sqrt((m1 - m2)**2 + 2*(s1*s1 - s2*s2) * np.log(s1/s2)))) / (s1*s1 - s2*s2)

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: python -m mypy some/path/to/file/under/test.py
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.11.11

[brianschubert]

Thanks! Looks similar to #14978

[sterliakov]

It's exactly #14978. For every overload signature of a numpy function (such as ndarray.__add__ with whopping 17 overloads of which 9 are relevant), we accept all arguments. Nest 6 such arguments, and we check simple operations $9^6 \approx 500,000$ times. Nest 10, and we'll be checking that forever.