gh-65961: Do not rely solely on `__cached__` (GH-97990)

Make sure `__spec__.cached` (at minimum) can be used.

1 files changed, 71 insertions, 0 deletions

diff --git a/Lib/test/test_importlib/import_/test_helpers.py b/Lib/test/test_importlib/import_/test_helpers.py
new file mode 100644
index 0000000..90df56f
--- /dev/null
+++ b/Lib/test/test_importlib/import_/test_helpers.py
@@ -0,0 +1,71 @@
+"""Tests for helper functions used by import.c ."""
+
+from importlib import _bootstrap_external, machinery
+import os.path
+import unittest
+
+from .. import util
+
+
+class FixUpModuleTests:
+
+    def test_no_loader_but_spec(self):
+        loader = object()
+        name = "hello"
+        path = "hello.py"
+        spec = machinery.ModuleSpec(name, loader)
+        ns = {"__spec__": spec}
+        _bootstrap_external._fix_up_module(ns, name, path)
+
+        expected = {"__spec__": spec, "__loader__": loader, "__file__": path,
+                    "__cached__": None}
+        self.assertEqual(ns, expected)
+
+    def test_no_loader_no_spec_but_sourceless(self):
+        name = "hello"
+        path = "hello.py"
+        ns = {}
+        _bootstrap_external._fix_up_module(ns, name, path, path)
+
+        expected = {"__file__": path, "__cached__": path}
+
+        for key, val in expected.items():
+            with self.subTest(f"{key}: {val}"):
+                self.assertEqual(ns[key], val)
+
+        spec = ns["__spec__"]
+        self.assertIsInstance(spec, machinery.ModuleSpec)
+        self.assertEqual(spec.name, name)
+        self.assertEqual(spec.origin, os.path.abspath(path))
+        self.assertEqual(spec.cached, os.path.abspath(path))
+        self.assertIsInstance(spec.loader, machinery.SourcelessFileLoader)
+        self.assertEqual(spec.loader.name, name)
+        self.assertEqual(spec.loader.path, path)
+        self.assertEqual(spec.loader, ns["__loader__"])
+
+    def test_no_loader_no_spec_but_source(self):
+        name = "hello"
+        path = "hello.py"
+        ns = {}
+        _bootstrap_external._fix_up_module(ns, name, path)
+
+        expected = {"__file__": path, "__cached__": None}
+
+        for key, val in expected.items():
+            with self.subTest(f"{key}: {val}"):
+                self.assertEqual(ns[key], val)
+
+        spec = ns["__spec__"]
+        self.assertIsInstance(spec, machinery.ModuleSpec)
+        self.assertEqual(spec.name, name)
+        self.assertEqual(spec.origin, os.path.abspath(path))
+        self.assertIsInstance(spec.loader, machinery.SourceFileLoader)
+        self.assertEqual(spec.loader.name, name)
+        self.assertEqual(spec.loader.path, path)
+        self.assertEqual(spec.loader, ns["__loader__"])
+
+
+FrozenFixUpModuleTests, SourceFixUpModuleTests = util.test_both(FixUpModuleTests)
+
+if __name__ == "__main__":
+    unittest.main()