port: advance VC6 typeobject frontier and preserve regression coverage

scripts/vc6-structseq-traverse-c89.test.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""Check structseq_traverse's C89 declarations and visit/size lookup order."""
+import re
+import sys
+from pathlib import Path
+
+source = Path(sys.argv[1] if len(sys.argv) > 1 else "cpython/Objects/structseq.c")
+match = re.search(
+    r"static int\nstructseq_traverse\(PyStructSequence \*obj, visitproc visit, void \*arg\)"
+    r"\n\{(.*?)\n\}",
+    source.read_text(),
+    re.S,
+)
+assert match, "structseq_traverse definition not found"
+body = match.group(1)
+assert re.match(r"\s*Py_ssize_t i, size;", body), (
+    "structseq_traverse: i and size must be declared before the heap-type check; "
+    "declaration after statement is not C89 compatible"
+)
+expected = """
+    Py_ssize_t i, size;
+    if (Py_TYPE(obj)->tp_flags & Py_TPFLAGS_HEAPTYPE) {
+        Py_VISIT(Py_TYPE(obj));
+    }
+    size = REAL_SIZE(obj);
+    for (i = 0; i < size; ++i) {
+        Py_VISIT(obj->ob_item[i]);
+    }
+    return 0;
+"""
+assert re.sub(r"\s+", "", body) == re.sub(r"\s+", "", expected), (
+    "preserve heap-type visit and its early return before the single real-size "
+    "lookup, item visit order, loop initialization, and return behavior"
+)
+print("structseq_traverse C89 declarations and visit/size lookup order: PASS")