Close #15386: There was a loophole that meant importlib.machinery and imp would sometimes reference an uninitialised copy of importlib._bootstrap

2 files changed, 14 insertions, 1 deletions

diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 28655f0e65..3c8359aca1 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -165,6 +165,9 @@ example, to run all the tests except for the gui tests, give the
 option '-uall,-gui'.
 """
 
+# We import importlib *ASAP* in order to test #15386
+import importlib
+
 import builtins
 import faulthandler
 import getopt
diff --git a/Lib/test/test_import.py b/Lib/test/test_import.py
index 89ec8dcedc..51b52c7e0b 100644
--- a/Lib/test/test_import.py
+++ b/Lib/test/test_import.py
@@ -1,8 +1,9 @@
+# We import importlib *ASAP* in order to test #15386
+import importlib
 import builtins
 import imp
 from importlib.test.import_ import test_suite as importlib_import_test_suite
 from importlib.test.import_ import util as importlib_util
-import importlib
 import marshal
 import os
 import platform
@@ -777,6 +778,15 @@ class ImportlibBootstrapTests(unittest.TestCase):
         self.assertEqual(mod.__package__, 'importlib')
         self.assertTrue(mod.__file__.endswith('_bootstrap.py'), mod.__file__)
 
+    def test_there_can_be_only_one(self):
+        # Issue #15386 revealed a tricky loophole in the bootstrapping
+        # This test is technically redundant, since the bug caused importing
+        # this test module to crash completely, but it helps prove the point
+        from importlib import machinery
+        mod = sys.modules['_frozen_importlib']
+        self.assertIs(machinery.FileFinder, mod.FileFinder)
+        self.assertIs(imp.new_module, mod.new_module)
+
 
 class ImportTracebackTests(unittest.TestCase):