gh-117398: Isolate _datetime (3.13.0a6 PoC)

Include/datetime.h

@@ -186,18 +186,31 @@ typedef struct {
 } PyDateTime_CAPI;
 
 #define PyDateTime_CAPSULE_NAME "datetime.datetime_CAPI"
-
+#define PyDateTime_INTERNAL_CAPSULE_NAME "datetime.datetime_CAPI_INTERNAL"
 
 /* This block is only used as part of the public API and should not be
  * included in _datetimemodule.c, which does not use the C API capsule.
  * See bpo-35081 for more details.
  * */
 #ifndef _PY_DATETIME_IMPL
-/* Define global variable for the C API and a macro for setting it. */
-static PyDateTime_CAPI *PyDateTimeAPI = NULL;
+static PyDateTime_CAPI *
+_PyDateTimeAPI_not_ready(void)
+{
+    return NULL;
+}
+static PyDateTime_CAPI *(*_PyDateTimeAPI_Get)(void) = _PyDateTimeAPI_not_ready;
+
+static inline void
+_PyDateTimeAPI_Import(void)
+{
+    void *(*func)(void) = PyCapsule_Import(PyDateTime_INTERNAL_CAPSULE_NAME, 0);
+    if (func) {
+        _PyDateTimeAPI_Get = func();
+    }
+}
 
-#define PyDateTime_IMPORT \
-    PyDateTimeAPI = (PyDateTime_CAPI *)PyCapsule_Import(PyDateTime_CAPSULE_NAME, 0)
+#define PyDateTimeAPI _PyDateTimeAPI_Get()
+#define PyDateTime_IMPORT _PyDateTimeAPI_Import()
 
 /* Macro for access to the UTC singleton */
 #define PyDateTime_TimeZone_UTC PyDateTimeAPI->TimeZone_UTC

Lib/test/datetimetester.py

@@ -91,7 +91,7 @@ def test_name_cleanup(self):
                     if not name.startswith('__') and not name.endswith('__'))
         allowed = set(['MAXYEAR', 'MINYEAR', 'date', 'datetime',
                        'datetime_CAPI', 'time', 'timedelta', 'timezone',
-                       'tzinfo', 'UTC', 'sys'])
+                       'tzinfo', 'UTC', 'sys', 'datetime_CAPI_INTERNAL'])
         self.assertEqual(names - allowed, set([]))
 
     def test_divide_and_round(self):

Lib/test/test_capi/test_misc.py

@@ -2282,6 +2282,23 @@ def test_module_state_shared_in_global(self):
         subinterp_attr_id = os.read(r, 100)
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
+    @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
+    def test_datetime_capi_client(self):
+        script = textwrap.dedent("""
+            import importlib.machinery
+            import importlib.util
+            fullname = '_test_datetime_capi_client'
+            origin = importlib.util.find_spec('_testmultiphase').origin
+            loader = importlib.machinery.ExtensionFileLoader(fullname, origin)
+            spec = importlib.util.spec_from_loader(fullname, loader)
+            module = importlib.util.module_from_spec(spec)
+            spec.loader.exec_module(module)
+        """)
+        exec(script)  # run main interp first
+        exec(script)  # run main interp twice
+        ret = support.run_in_subinterp(script)
+        self.assertEqual(ret, 0)
+
 
 @requires_subinterpreters
 class InterpreterConfigTests(unittest.TestCase):

Misc/NEWS.d/next/Library/2023-03-24-11-10-16.gh-issue-117398.q4ueXs.rst

@@ -0,0 +1 @@
+Apply :pep:`687` to :mod:`datetime`. Patch by Erlend Aasland.