Support packing Python 3.15 frozentdict (PEP 814) (#738)

Support packing a Python 3.15 `frozendict`.

This PR doesn't support _unpacking_ into a `frozendict` other than with
the generic `object_pairs_hook=frozendict`.

---------

Signed-off-by: Edgar Ramírez Mondragón <edgarrm358@gmail.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: edgarrmondragon

msgpack/_packer.pyx

@@ -4,6 +4,7 @@ from cpython.datetime cimport (
     PyDateTime_CheckExact, PyDelta_CheckExact,
     datetime_tzinfo, timedelta_days, timedelta_seconds, timedelta_microseconds,
 )
+from cpython.frozendict cimport PyAnyDict_Check, PyAnyDict_CheckExact
 
 cdef ExtType
 cdef Timestamp
@@ -202,7 +203,7 @@ cdef class Packer:
                 rawval = o
             msgpack_pack_raw(&self.pk, L)
             msgpack_pack_raw_body(&self.pk, rawval, L)
-        elif PyDict_CheckExact(o) if strict else PyDict_Check(o):
+        elif PyAnyDict_CheckExact(o) if strict else PyAnyDict_Check(o):
             L = len(o)
             if L > ITEM_LIMIT:
                 raise ValueError("dict is too large")

msgpack/fallback.py

@@ -37,6 +37,17 @@ def newlist_hint(size):
         return []
 
 
+# frozendict is a builtin type added in Python 3.15 (PEP 814).
+if sys.version_info >= (3, 15):
+    import builtins
+
+    frozendict = builtins.frozendict
+else:
+
+    class frozendict:
+        pass
+
+
 from .exceptions import BufferFull, ExtraData, FormatError, OutOfData, StackError
 from .ext import ExtType, Timestamp
 
@@ -695,6 +706,7 @@ def _pack(
             list_types = list
         else:
             list_types = (list, tuple)
+        dict_types = (dict, frozendict)
         while True:
             if nest_limit < 0:
                 raise ValueError("recursion limit exceeded")
@@ -788,7 +800,7 @@ def _pack(
                 for i in range(n):
                     self._pack(obj[i], nest_limit - 1)
                 return
-            if check(obj, dict):
+            if check(obj, dict_types):
                 return self._pack_map_pairs(len(obj), obj.items(), nest_limit - 1)
 
             if self._datetime and check(obj, _DateTime) and obj.tzinfo is not None:

pyproject.toml

@@ -47,6 +47,6 @@ lint.select = [
 
 [dependency-groups]
 dev = [
-    "cython>=3.2.5",
+    "cython>=3.3.0",
     "pytest>=9.0.3",
 ]

requirements.txt

@@ -1,4 +1,4 @@
-cython==3.2.5
+cython==3.3.0
 setuptools==78.1.1
 pytest
 build

test/test_pack.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import struct
+import sys
 from collections import OrderedDict
 from io import BytesIO
 
@@ -162,6 +163,25 @@ def pair_hook(seq):
     assert unpackb(packb(od), object_pairs_hook=pair_hook, use_list=1) == seq
 
 
+@pytest.mark.skipif(sys.version_info < (3, 15), reason="frozendict requires Python 3.15+")
+def test_frozendict():
+    import builtins
+
+    fd = builtins.frozendict(a=1, b=[1, 2, 3])
+    unpacked = unpackb(packb(fd), use_list=1)
+    assert isinstance(unpacked, dict)
+    assert unpacked == fd
+
+    unpacked = unpackb(packb(fd), use_list=1, object_pairs_hook=builtins.frozendict)
+    assert isinstance(unpacked, builtins.frozendict)
+    assert unpacked == fd
+
+    packer = Packer(strict_types=True)
+    unpacked = unpackb(packer.pack(fd), use_list=1)
+    assert isinstance(unpacked, dict)
+    assert unpacked == fd
+
+
 def test_pairlist():
     pairlist = [(b"a", 1), (2, b"b"), (b"foo", b"bar")]
     packer = Packer()