gh-117398: Add multiphase support to _datetime (gh-119373)

This is minimal support.  Subinterpreters are not supported yet.  That will be addressed in a later change.

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

Lib/test/datetimetester.py

@@ -47,6 +47,26 @@
     pass
 #
 
+# This is copied from test_import/__init__.py.
+# XXX Move it to support/__init__.py.
+def no_rerun(reason):
+    """Skip rerunning for a particular test.
+
+    WARNING: Use this decorator with care; skipping rerunning makes it
+    impossible to find reference leaks. Provide a clear reason for skipping the
+    test using the 'reason' parameter.
+    """
+    def deco(func):
+        _has_run = False
+        def wrapper(self):
+            nonlocal _has_run
+            if _has_run:
+                self.skipTest(reason)
+            func(self)
+            _has_run = True
+        return wrapper
+    return deco
+
 pickle_loads = {pickle.loads, pickle._loads}
 
 pickle_choices = [(pickle, pickle, proto)
@@ -6383,6 +6403,7 @@ class IranTest(ZoneInfoTest):
 
 
 @unittest.skipIf(_testcapi is None, 'need _testcapi module')
+@no_rerun("the encapsulated datetime C API does not support reloading")
 class CapiTest(unittest.TestCase):
     def setUp(self):
         # Since the C API is not present in the _Pure tests, skip all tests

Modules/_datetimemodule.c

@@ -7040,30 +7040,26 @@ _datetime_exec(PyObject *module)
 }
 #undef DATETIME_ADD_MACRO
 
-static struct PyModuleDef datetimemodule = {
+static PyModuleDef_Slot module_slots[] = {
+    {Py_mod_exec, _datetime_exec},
+    {Py_mod_multiple_interpreters, Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED},
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {0, NULL},
+};
+
+static PyModuleDef datetimemodule = {
     .m_base = PyModuleDef_HEAD_INIT,
     .m_name = "_datetime",
     .m_doc = "Fast implementation of the datetime type.",
-    .m_size = -1,
+    .m_size = 0,
     .m_methods = module_methods,
+    .m_slots = module_slots,
 };
 
 PyMODINIT_FUNC
 PyInit__datetime(void)
 {
-    PyObject *mod = PyModule_Create(&datetimemodule);
-    if (mod == NULL)
-        return NULL;
-#ifdef Py_GIL_DISABLED
-    PyUnstable_Module_SetGIL(mod, Py_MOD_GIL_NOT_USED);
-#endif
-
-    if (_datetime_exec(mod) < 0) {
-        Py_DECREF(mod);
-        return NULL;
-    }
-
-    return mod;
+    return PyModuleDef_Init(&datetimemodule);
 }
 
 /* ---------------------------------------------------------------------------