Properly handle all ISUPPORT negations

upstream.go

@@ -634,22 +634,31 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 				delete(uc.isupport, parameter)
 			}
 
-			if !negate && hasValue {
-				// TODO: reset to defaults when the token is negated
+			var err error
 			switch parameter {
 			case "CHANMODES":
-					if err := uc.handleChanModes(value); err != nil {
-						return err
+				if !negate {
+					err = uc.handleChanModes(value)
+				} else {
+					uc.availableChannelModes = stdChannelModes
 				}
 			case "CHANTYPES":
+				if !negate {
 					uc.availableChannelTypes = value
+				} else {
+					uc.availableChannelTypes = stdChannelTypes
+				}
 			case "PREFIX":
-					if err := uc.handleMemberships(value); err != nil {
+				if !negate {
+					err = uc.handleMemberships(value)
+				} else {
+					uc.availableMemberships = stdMemberships
+				}
+			}
+			if err != nil {
 				return err
 			}
 		}
-			}
-		}
 	case "BATCH":
 		var tag string
 		if err := parseMessageParams(msg, &tag); err != nil {