Issue #23014: Make importlib.abc.Loader.create_module() required when

importlib.abc.Loader.exec_module() is also defined.

Before this change, create_module() was optional **and** could return
None to trigger default semantics. This change now reduces the
options for choosing default semantics to one and in the most
backporting-friendly way (define create_module() to return None).

4 files changed, 19 insertions, 3 deletions

diff --git a/Lib/test/test_importlib/import_/test___loader__.py b/Lib/test/test_importlib/import_/test___loader__.py
index 9998cd6..4b18093 100644
--- a/Lib/test/test_importlib/import_/test___loader__.py
+++ b/Lib/test/test_importlib/import_/test___loader__.py
@@ -11,6 +11,9 @@ class SpecLoaderMock:
     def find_spec(self, fullname, path=None, target=None):
         return machinery.ModuleSpec(fullname, self)
 
+    def create_module(self, spec):
+        return None
+
     def exec_module(self, module):
         pass
 
diff --git a/Lib/test/test_importlib/import_/test_api.py b/Lib/test/test_importlib/import_/test_api.py
index 2c61b01..7069d9e 100644
--- a/Lib/test/test_importlib/import_/test_api.py
+++ b/Lib/test/test_importlib/import_/test_api.py
@@ -17,6 +17,10 @@ class BadSpecFinderLoader:
             return spec
 
     @staticmethod
+    def create_module(spec):
+        return None
+
+    @staticmethod
     def exec_module(module):
         if module.__name__ == SUBMOD_NAME:
             raise ImportError('I cannot be loaded!')
diff --git a/Lib/test/test_importlib/test_spec.py b/Lib/test/test_importlib/test_spec.py
index 418b4c0..8b333e8 100644
--- a/Lib/test/test_importlib/test_spec.py
+++ b/Lib/test/test_importlib/test_spec.py
@@ -34,6 +34,9 @@ class TestLoader:
     def _is_package(self, name):
         return self.package
 
+    def create_module(self, spec):
+        return None
+
 
 class NewLoader(TestLoader):
 
diff --git a/Lib/test/test_importlib/test_util.py b/Lib/test/test_importlib/test_util.py
index cd9344c..2493af7 100644
--- a/Lib/test/test_importlib/test_util.py
+++ b/Lib/test/test_importlib/test_util.py
@@ -41,10 +41,16 @@ class DecodeSourceBytesTests:
 class ModuleFromSpecTests:
 
     def test_no_create_module(self):
-        class Loader(self.abc.Loader):
-            pass
+        class Loader:
+            def exec_module(self, module):
+                pass
         spec = self.machinery.ModuleSpec('test', Loader())
-        module = self.util.module_from_spec(spec)
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter('always')
+            module = self.util.module_from_spec(spec)
+        self.assertEqual(1, len(w))
+        self.assertTrue(issubclass(w[0].category, DeprecationWarning))
+        self.assertIn('create_module', str(w[0].message))
         self.assertIsInstance(module, types.ModuleType)
         self.assertEqual(module.__name__, spec.name)