@Override
    public ExpressionResult visitTrendOP(MQEParser.TrendOPContext ctx) {
        int trendRange = Integer.parseInt(ctx.INTEGER().getText());
        if (trendRange < 1) {
            ExpressionResult result = new ExpressionResult();
            result.setType(ExpressionResultType.UNKNOWN);
            result.setError("The trend range must be greater than 0.");
            return result;
        }
        setMaxTrendRange(trendRange);
        return super.visitTrendOP(ctx);
    }
Used for verify the alarm expression and get the metrics name when read the alarm rules.
oap-server/server-alarm-plugin/src/main/java/org/apache/skywalking/oap/server/core/alarm/provider/expr/rt/AlarmMQEVerifyVisitor.java