gh-60074: add new stable API function PyType_FromMetaclass (GH-93012)

Added a new stable API function ``PyType_FromMetaclass``, which mirrors
the behavior of ``PyType_FromModuleAndSpec`` except that it takes an
additional metaclass argument. This is, e.g., useful for language
binding tools that need to store additional information in the type
object.

1 files changed, 13 insertions, 0 deletions

diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 49cd821..95930ba 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -605,6 +605,19 @@ class CAPITest(unittest.TestCase):
         del obj.value
         self.assertEqual(obj.pvalue, 0)
 
+    def test_heaptype_with_custom_metaclass(self):
+        self.assertTrue(issubclass(_testcapi.HeapCTypeMetaclass, type))
+        self.assertTrue(issubclass(_testcapi.HeapCTypeMetaclassCustomNew, type))
+
+        t = _testcapi.pytype_fromspec_meta(_testcapi.HeapCTypeMetaclass)
+        self.assertIsInstance(t, type)
+        self.assertEqual(t.__name__, "HeapCTypeViaMetaclass")
+        self.assertIs(type(t), _testcapi.HeapCTypeMetaclass)
+
+        msg = "Metaclasses with custom tp_new are not supported."
+        with self.assertRaisesRegex(TypeError, msg):
+            t = _testcapi.pytype_fromspec_meta(_testcapi.HeapCTypeMetaclassCustomNew)
+
     def test_pynumber_tobase(self):
         from _testcapi import pynumber_tobase
         self.assertEqual(pynumber_tobase(123, 2), '0b1111011')