PHPStrom中使用数组短语法[]，出现红色破浪线

问题：用PHPStrom打开之前的项目，突然出现红色波浪线，这是为什么？

出现红色破浪线1 出现红色破浪线2

报错如下：

Short array syntax is allowed in PHP 5.4 only less... (Ctrl+F1)

Checks that language features used in the source code correspond the selected language level. (i.e. traits can be used only in PHP 5.4). Desired language level is set in the project configuration (Project Settings | PHP).

报错信息

解决办法：

File -> Settings... 将语法等级更改为5.4即可