升级到Xcode 8之后发现代码高亮（syntax highlighting）和代码自动补全(code completion)的功能没有了，试过重启Xcode，删除DeriveData，重启Mac都没用。Google以后还是在StackOverFlow找到了方法。

Fixed. Problem was related to the presence of target in project which is not compiled. So if you have targets e.g. A, B, C and C is not compiled this cause problems with syntax highlighting.

如图，当一个工程含有多个target的时候，需要对每一个target进行编译（Command+b），之后问题就解决了。