port: advance VC6 typeobject frontier and preserve regression coverage

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

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+"""Check structseq_repr's loop declaration and unchanged iteration 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 PyObject \*\nstructseq_repr\(PyStructSequence \*obj\)\n\{(.*?)\n\}",
+    source.read_text(),
+    re.S,
+)
+assert match, "structseq_repr definition not found"
+body = match.group(1)
+assert not re.search(r"for\s*\(\s*Py_ssize_t\b", body), (
+    "structseq_repr: VC6 rejects the C99 loop initializer declaration; "
+    "declare i in the function declaration block"
+)
+assert re.match(
+    r"\s*PyTypeObject \*typ = Py_TYPE\(obj\);"
+    r"\s*_PyUnicodeWriter writer;\s*Py_ssize_t i;",
+    body,
+), "i must be declared without initialization in the function declaration block"
+assert len(re.findall(r"\bPy_ssize_t\s+i\s*;", body)) == 1, (
+    "declare i exactly once"
+)
+assert re.search(
+    r"if \(_PyUnicodeWriter_WriteChar\(&writer, '\('\) < 0\) "
+    r"\{\s*goto error;\s*\}\s*"
+    r"for \(i\s*=\s*0; i < VISIBLE_SIZE\(obj\); i\+\+\) \{",
+    body,
+), "preserve zero initialization after '(' output, per-iteration size lookup, and increment"
+assert len(re.findall(r"\bfor\s*\(", body)) == 1, "preserve the single item loop"
+assert "typ->tp_members[i].name" in body, "preserve member-name indexing"
+assert "PyStructSequence_GET_ITEM(obj, i)" in body, "preserve item indexing"
+print("structseq_repr C89 loop declaration and iteration order: PASS")