Issue #15001: fix segfault on "del sys.modules['__main__']"

Patch by Victor Stinner.

Lib/test/test_cmd_line.py

@@ -2,9 +2,12 @@
 # All tests are executed with environment variables ignored
 # See test_cmd_line_script.py for testing of script execution
 
-import test.test_support, unittest
+import test.test_support
 import sys
-from test.script_helper import spawn_python, kill_python, python_exit_code
+import unittest
+from test.script_helper import (
+    assert_python_ok, spawn_python, kill_python, python_exit_code
+)
 
 
 class CmdLineTest(unittest.TestCase):
@@ -101,6 +104,18 @@ class CmdLineTest(unittest.TestCase):
         data = self.start_python('-R', '-c', code)
         self.assertTrue('hash_randomization=1' in data)
 
+    def test_del___main__(self):
+        # Issue #15001: PyRun_SimpleFileExFlags() did crash because it kept a
+        # borrowed reference to the dict of __main__ module and later modify
+        # the dict whereas the module was destroyed
+        filename = test.test_support.TESTFN
+        self.addCleanup(test.test_support.unlink, filename)
+        with open(filename, "w") as script:
+            print >>script, "import sys"
+            print >>script, "del sys.modules['__main__']"
+        assert_python_ok(filename)
+
+
 def test_main():
     test.test_support.run_unittest(CmdLineTest)
     test.test_support.reap_children()