Deal gracefully with passing None watchers to hub.cancel_wait, something that...

Deal gracefully with passing None watchers to hub.cancel_wait, something that may be more common now that we try to destroy watchers ASAP for GC reasons. Fixes #1089.

CHANGES.rst

@@ -35,6 +35,10 @@
 - Add the ``dnspython`` resolver as a lightweight alternative to
   c-ares. See :pr:`1088`.
 
+- Fix calling ``shutdown`` on a closed socket. It was raising
+  ``AttributeError``, now it once again raises the correct
+  ``socket.error``. Reported in :issue:`1089` by André Cimander.
+
 1.3a1 (2018-01-27)
 ==================
 

src/gevent/hub.py

@@ -679,8 +679,15 @@ class Hub(RawGreenlet):
 
         .. versionchanged:: 1.3a1
            Added the *close_watcher* parameter. If true, the watcher
-           will be closed after the exception is thrown.
+           will be closed after the exception is thrown. The watcher should then
+           be discarded. Closing the watcher is important to release native resources.
+        .. versionchanged:: 1.3a2
+           Allow the *watcher* to be ``None``. No action is taken in that case.
         """
+        if watcher is None:
+            # Presumably already closed.
+            # See https://github.com/gevent/gevent/issues/1089
+            return
         if watcher.callback is not None:
             self.loop.run_callback(self._cancel_wait, watcher, error, close_watcher)
         elif close_watcher:

src/greentest/test__socket.py

@@ -439,5 +439,15 @@ class TestFunctions(greentest.TestCase):
         self.assertMonkeyPatchedFuncSignatures('socket', exclude=exclude)
 
 
+class TestSocket(greentest.TestCase):
+
+    def test_shutdown_when_closed(self):
+        # https://github.com/gevent/gevent/issues/1089
+        # we once raised an AttributeError.
+        s = socket.socket()
+        s.close()
+        with self.assertRaises(socket.error):
+            s.shutdown(socket.SHUT_RDWR)
+
 if __name__ == '__main__':
     greentest.main()