IPv4Network.supernet skips new_prefix validation for /0 networks

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: Python ipaddress documentation, IPv4Network.supernet: "A ValueError is raised if new_prefix is larger than our prefix."

Expected: supernet(new_prefix=1) raises ValueError for IPv4Network('0.0.0.0/0').

Actual: Returns IPv4Network('0.0.0.0/0') without raising an exception.

import ipaddress

network, p = "0.0.0.0/0", 1
n = ipaddress.IPv4Network(network)
if not isinstance(p, int) or not 0 <= p <= 32:
    print("REFUTATION REJECTED: invalid IPv4 prefix")
else:
    expected = ("exception", "ValueError") if p > n.prefixlen else (
        "result", str(ipaddress.IPv4Network((int(n.network_address), p), strict=False))
    )
    try:
        actual = ("result", str(n.supernet(new_prefix=p)))
    except Exception as e:
        actual = ("exception", type(e).__name__)
    if actual != expected:
        print("REFUTATION CONFIRMED:", {"network": network, "new_prefix": p},
              "actual=", actual, "expected=", expected)
    else:
        print("REFUTATION REJECTED: actual matches documented expectation")

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library ipaddress:

REFUTATION CONFIRMED: {'network': '0.0.0.0/0', 'new_prefix': 1} actual= ('result', '0.0.0.0/0') expected= ('exception', 'ValueError')

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/ipaddress-c4

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).