#!/usr/bin/env python3
"""Check only mro_implementation's single-base fast-path loop index."""
import re
from pathlib import Path

source = Path("cpython/Objects/typeobject.c").read_text()
match = re.search(
    r"\nstatic PyObject \*\nmro_implementation\(PyTypeObject \*type\)\n\{(.*?)\n\}",
    source,
    re.S,
)
assert match, "mro_implementation definition missing"
body = re.sub(r"/\*.*?\*/", "", match.group(1), flags=re.S)
assert re.match(
    r"\s*PyObject \*bases;\s*Py_ssize_t n;\s*Py_ssize_t i;"
    r"\s*PyObject \*\*to_merge;\s*PyObject \*result;\s*if\b",
    body,
), (
    "mro_implementation: reuse i from the opening declaration block"
)
fast_path = body.split("if (n == 1) {", 1)[1].split("return result;", 1)[0]
assert not re.search(r"\bPy_ssize_t\s+i\b", fast_path), (
    "mro_implementation: fast-path loop must reuse function-scope i for C89"
)
expected = """
    PyTypeObject *base = _PyType_CAST(PyTuple_GET_ITEM(bases, 0));
    Py_ssize_t k = PyTuple_GET_SIZE(base->tp_mro);
    PyObject *result = PyTuple_New(k + 1);
    if (result == NULL) {
        return NULL;
    }
    Py_INCREF(type);
    PyTuple_SET_ITEM(result, 0, (PyObject *) type);
    for (i = 0; i < k; i++) {
        PyObject *cls = PyTuple_GET_ITEM(base->tp_mro, i);
        Py_INCREF(cls);
        PyTuple_SET_ITEM(result, i + 1, cls);
    }
"""
assert fast_path.split() == expected.split(), (
    "mro_implementation: preserve fast-path initialization timing, loop bounds, "
    "increment, allocation, reference counts, and tuple writes"
)
print("mro_implementation fast-path loop index C89 declaration and unchanged semantics: PASS")