gh-135836: Fix IndexError in asyncio.create_connection() (#135875)

Lib/asyncio/base_events.py

@@ -1015,6 +1015,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         exceptions.append(my_exceptions)
         family, type_, proto, _, address = addr_info
         sock = None
+        try:
             try:
                 sock = socket.socket(family=family, type=type_, proto=proto)
                 sock.setblocking(False)
@@ -1042,12 +1043,16 @@ class BaseEventLoop(events.AbstractEventLoop):
                 return sock
             except OSError as exc:
                 my_exceptions.append(exc)
-            if sock is not None:
-                sock.close()
                 raise
         except:
             if sock is not None:
+                try:
                     sock.close()
+                except OSError:
+                    # An error when closing a newly created socket is
+                    # not important, but it can overwrite more important
+                    # non-OSError error. So ignore it.
+                    pass
             raise
         finally:
             exceptions = my_exceptions = None

Lib/test/test_asyncio/test_base_events.py

@@ -24,6 +24,10 @@ import warnings
 MOCK_ANY = mock.ANY
 
 
+class CustomError(Exception):
+    pass
+
+
 def tearDownModule():
     asyncio._set_event_loop_policy(None)
 
@@ -1326,6 +1330,31 @@ class BaseEventLoopWithSelectorTests(test_utils.TestCase):
         self.assertEqual(len(cm.exception.exceptions), 1)
         self.assertIsInstance(cm.exception.exceptions[0], OSError)
 
+    @patch_socket
+    def test_create_connection_connect_non_os_err_close_err(self, m_socket):
+        # Test the case when sock_connect() raises non-OSError exception
+        # and sock.close() raises OSError.
+        async def getaddrinfo(*args, **kw):
+            return [(2, 1, 6, '', ('107.6.106.82', 80))]
+
+        def getaddrinfo_task(*args, **kwds):
+            return self.loop.create_task(getaddrinfo(*args, **kwds))
+
+        self.loop.getaddrinfo = getaddrinfo_task
+        self.loop.sock_connect = mock.Mock()
+        self.loop.sock_connect.side_effect = CustomError
+        sock = mock.Mock()
+        m_socket.socket.return_value = sock
+        sock.close.side_effect = OSError
+
+        coro = self.loop.create_connection(MyProto, 'example.com', 80)
+        self.assertRaises(
+            CustomError, self.loop.run_until_complete, coro)
+
+        coro = self.loop.create_connection(MyProto, 'example.com', 80, all_errors=True)
+        self.assertRaises(
+            CustomError, self.loop.run_until_complete, coro)
+
     def test_create_connection_multiple(self):
         async def getaddrinfo(*args, **kw):
             return [(2, 1, 6, '', ('0.0.0.1', 80)),

Misc/NEWS.d/next/Library/2025-06-24-10-52-35.gh-issue-135836.s37351.rst

@@ -0,0 +1,3 @@
+Fix :exc:`IndexError` in :meth:`asyncio.loop.create_connection` that could
+occur when non-\ :exc:`OSError` exception is raised during connection and
+socket's ``close()`` raises :exc:`!OSError`.