Fix NamedTuple hash returning 0 on Python 3.14+#980
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worksbyfriday wants to merge 1 commit intojcrist:mainfrom
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Fix NamedTuple hash returning 0 on Python 3.14+#980worksbyfriday wants to merge 1 commit intojcrist:mainfrom
worksbyfriday wants to merge 1 commit intojcrist:mainfrom
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In Python 3.14, CPython added hash caching to tuples (gh-131525).
PyTupleObject gained an ob_hash field that is checked by tuple_hash()
before computing: if ob_hash != -1, the cached value is returned
immediately.
When msgspec allocates NamedTuples via tp_alloc (which zero-initializes
memory via calloc), ob_hash is set to 0 — a valid cached hash value.
This causes hash() to return 0 for all msgspec-deserialized NamedTuples,
breaking their use as dictionary keys and in sets.
The fix resets ob_hash to -1 ("not yet computed") immediately after
tp_alloc in all three NamedTuple construction sites: msgpack decoder,
JSON decoder, and convert. The reset is conditional on PY314_PLUS and
compiles to a no-op on earlier Python versions.
Fixes jcrist#967
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Summary
Fixes #967.
In Python 3.14, CPython added hash caching to tuples (gh-131525, PR #131529).
PyTupleObjectgained anob_hashfield initialized to-1("not yet computed"). Whentuple_hash()seesob_hash != -1, it returns the cached value immediately.msgspec allocates NamedTuples via
tp_alloc, which zero-initializes memory. This setsob_hashto0— a valid cached hash value — sohash()returns0for all msgspec-deserialized NamedTuples without ever computing the real hash. This breaks dictionary lookups and set membership when deserialized NamedTuples are used as keys.The fix adds
MS_TUPLE_RESET_HASH(op)— a macro that setsob_hash = -1on Python 3.14+ (no-op on earlier versions) — immediately aftertp_allocin all three NamedTuple construction sites:mpack_decode_namedtuple(msgpack decoder)json_decode_namedtuple(JSON decoder)convert_seq_to_namedtuple(convert)Test plan
test_namedtuple_hash_preserved_after_roundtripintest_common.py(covers msgpack + JSON)test_namedtuple_hash_preservedintest_convert.py(covers convert path)hash(original) == hash(decoded)and dict lookup with decoded keysob_hashexists inPyTupleObject