pythongh-129405: Fix doc for Py_mod_multiple_interpreters default, and add test (pythonGH-129406)

(cherry picked from commit fc8d2cb)

Co-authored-by: Petr Viktorin <[email protected]>

Author: encukou

Doc/c-api/module.rst

@@ -415,7 +415,7 @@ The available slot types are:
    in one module definition.
 
    If ``Py_mod_multiple_interpreters`` is not specified, the import
-   machinery defaults to ``Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED``.
+   machinery defaults to ``Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED``.
 
    .. versionadded:: 3.12
 

Lib/test/test_import/__init__.py

@@ -2404,8 +2404,10 @@ def test_single_init_extension_compat(self):
 
     @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
     def test_multi_init_extension_compat(self):
+        # Module with Py_MOD_PER_INTERPRETER_GIL_SUPPORTED
         module = '_testmultiphase'
         require_extension(module)
+
         if not Py_GIL_DISABLED:
             with self.subTest(f'{module}: not strict'):
                 self.check_compatible_here(module, strict=False)
@@ -2416,6 +2418,8 @@ def test_multi_init_extension_compat(self):
 
     @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
     def test_multi_init_extension_non_isolated_compat(self):
+        # Module with Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED
+        # and Py_MOD_GIL_NOT_USED
         modname = '_test_non_isolated'
         filename = _testmultiphase.__file__
         module = import_extension_from_file(modname, filename)
@@ -2431,20 +2435,31 @@ def test_multi_init_extension_non_isolated_compat(self):
 
     @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
     def test_multi_init_extension_per_interpreter_gil_compat(self):
-        modname = '_test_shared_gil_only'
-        filename = _testmultiphase.__file__
-        module = import_extension_from_file(modname, filename)
 
-        require_extension(module)
-        with self.subTest(f'{modname}: isolated, strict'):
-            self.check_incompatible_here(modname, filename, isolated=True)
-        with self.subTest(f'{modname}: not isolated, strict'):
-            self.check_compatible_here(modname, filename,
-                                       strict=True, isolated=False)
-        if not Py_GIL_DISABLED:
-            with self.subTest(f'{modname}: not isolated, not strict'):
-                self.check_compatible_here(modname, filename,
-                                           strict=False, isolated=False)
+        # _test_shared_gil_only:
+        #   Explicit Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED (default)
+        #   and Py_MOD_GIL_NOT_USED
+        # _test_no_multiple_interpreter_slot:
+        #   No Py_mod_multiple_interpreters slot
+        #   and Py_MOD_GIL_NOT_USED
+        for modname in ('_test_shared_gil_only',
+                        '_test_no_multiple_interpreter_slot'):
+            with self.subTest(modname=modname):
+
+                filename = _testmultiphase.__file__
+                module = import_extension_from_file(modname, filename)
+
+                require_extension(module)
+                with self.subTest(f'{modname}: isolated, strict'):
+                    self.check_incompatible_here(modname, filename,
+                                                 isolated=True)
+                with self.subTest(f'{modname}: not isolated, strict'):
+                    self.check_compatible_here(modname, filename,
+                                               strict=True, isolated=False)
+                if not Py_GIL_DISABLED:
+                    with self.subTest(f'{modname}: not isolated, not strict'):
+                        self.check_compatible_here(
+                            modname, filename, strict=False, isolated=False)
 
     @unittest.skipIf(_testinternalcapi is None, "requires _testinternalcapi")
     def test_python_compat(self):

Modules/_testmultiphase.c

@@ -969,3 +969,21 @@ PyInit__test_shared_gil_only(void)
 {
     return PyModuleDef_Init(&shared_gil_only_def);
 }
+
+
+static PyModuleDef_Slot no_multiple_interpreter_slot_slots[] = {
+    {Py_mod_exec, execfunc},
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {0, NULL},
+};
+
+static PyModuleDef no_multiple_interpreter_slot_def = TEST_MODULE_DEF(
+    "_test_no_multiple_interpreter_slot",
+    no_multiple_interpreter_slot_slots,
+    testexport_methods);
+
+PyMODINIT_FUNC
+PyInit__test_no_multiple_interpreter_slot(void)
+{
+    return PyModuleDef_Init(&no_multiple_interpreter_slot_def);
+}