MessageParser: Fix crash (and unexpected behavior) when matching backslashes

Closes GH-1497.

plugins/MessageParser/plugin.py

@@ -183,7 +183,9 @@ class MessageParser(callbacks.Plugin, plugins.ChannelDBHandler):
                         self._updateRank(irc.network, channel, regexp)
                         for (i, j) in enumerate(match.groups()):
                             if match.group(i+1) is not None:
-                                thisaction = re.sub(r'\$' + str(i+1), match.group(i+1), thisaction)
+                                # Need a lambda to prevent re.sub from
+                                # interpreting backslashes in the replacement
+                                thisaction = re.sub(r'\$' + str(i+1), lambda _: match.group(i+1), thisaction)
                         actions.append(thisaction)
                         if max_triggers != 0 and max_triggers == len(actions):
                             break

plugins/MessageParser/test.py

@@ -91,6 +91,13 @@ class MessageParserTestCase(ChannelPluginTestCase):
         self.feedMsg('test')
         self.assertResponse(' ', 'Error: No closing quotation')
 
+    def testMatchedBackslashes(self):
+        # Makes sure backslashes in matched arguments are not interpreted
+        # (re.sub interprets them in the repl argument for some reason...)
+        self.assertNotError(r'messageparser add test(.*)test "echo $1"')
+        self.feedMsg(r'testhello\xhellotest')
+        self.assertResponse(' ', r'hello\xhello')
+
     def testShow(self):
         self.assertNotError('messageparser add "stuff" "echo i saw some stuff"')
         self.assertRegexp('messageparser show "nostuff"', 'there is no such regexp trigger')