serializer.py
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| 1 | """Deterministic YAML serializer for freeze blocks (§K5.7).""" |
| 2 | |
| 3 | from __future__ import annotations |
| 4 | |
| 5 | from typing import Any |
| 6 | |
| 7 | import yaml |
| 8 | |
| 9 | |
| 10 | def _ordered_mapping_items(data: dict[str, Any]) -> list[tuple[str, Any]]: |
| 11 | """Preserve existing keys' relative order; place ``review_stamp`` per §K5.7. |
| 12 | |
| 13 | Contract: preserve existing keys' relative order; place ``review_stamp`` after |
| 14 | ``frozen_inputs`` if present, else after ``outputs``, else last. |
| 15 | """ |
| 16 | stamp_present = "review_stamp" in data |
| 17 | items: list[tuple[str, Any]] = [ |
| 18 | (key, value) for key, value in data.items() if key != "review_stamp" |
| 19 | ] |
| 20 | if not stamp_present: |
| 21 | return items |
| 22 | |
| 23 | keys = [key for key, _ in items] |
| 24 | if "frozen_inputs" in keys: |
| 25 | insert_at = keys.index("frozen_inputs") + 1 |
| 26 | elif "outputs" in keys: |
| 27 | insert_at = keys.index("outputs") + 1 |
| 28 | else: |
| 29 | insert_at = len(items) |
| 30 | items.insert(insert_at, ("review_stamp", data["review_stamp"])) |
| 31 | return items |
| 32 | |
| 33 | |
| 34 | def dump_freeze_mapping(data: dict[str, Any]) -> str: |
| 35 | """Serialize a freeze mapping deterministically (round-trip stable).""" |
| 36 | ordered = dict(_ordered_mapping_items(data)) |
| 37 | text = yaml.safe_dump( |
| 38 | ordered, |
| 39 | sort_keys=False, |
| 40 | allow_unicode=True, |
| 41 | default_flow_style=False, |
| 42 | width=10_000, |
| 43 | ) |
| 44 | if not text.endswith("\n"): |
| 45 | text += "\n" |
| 46 | return text |
| 47 | |
| 48 | |
| 49 | def parse_freeze_mapping(text: str) -> dict[str, Any]: |
| 50 | """Parse YAML mapping text for a freeze block.""" |
| 51 | parsed = yaml.safe_load(text) |
| 52 | if not isinstance(parsed, dict): |
| 53 | raise ValueError("freeze block must be a mapping") |
| 54 | return parsed |
| 55 | |
| 56 | |
| 57 | def round_trip_stable(data: dict[str, Any]) -> bool: |
| 58 | """Return True when serialize(parse(serialize(x))) is byte-stable.""" |
| 59 | once = dump_freeze_mapping(data) |
| 60 | twice = dump_freeze_mapping(parse_freeze_mapping(once)) |
| 61 | return once == twice |