Ignore stale renames defined for nonexistent commands

Closes #1619

Author: jlu5

plugins/Owner/test.py

@@ -157,6 +157,16 @@ def testRenameNested(self):
         self.assertRegexp('list Admin', 'capability remove')
         self.assertNotRegexp('list Admin', 'rmcap')
 
+    def testIgnoreStaleRenames(self):
+        """
+        Test that stale renames in the config don't cause loading a plugin
+        to fail, if a command ever gets removed.
+        https://github.com/progval/Limnoria/issues/1619
+        """
+        plugin.registerRename(
+            'Utilities', command='nonexistent', newName='test')
+        self.assertNotError('load Utilities')
+
     def testDefaultPluginErrorsWhenCommandNotInPlugin(self):
         self.assertError('defaultplugin foobar owner')
 

src/plugin.py

@@ -130,7 +130,11 @@ def renameCommand(cb, name, newName):
     assert newName == callbacks.canonicalName(newName), \
            'newName must already be normalized.'
     if name != newName:
-        method = getattr(cb.__class__, name)
+        method = getattr(cb.__class__, name, None)
+        if method is None:
+            log.debug('Ignoring rename of command %s.%s that no longer exists',
+                      cb.__class__.__name__, name)
+            return
         setattr(cb.__class__, newName, method)
         delattr(cb.__class__, name)