[Bug] exclamatory mark in chainWebpack

[meteorlxy]

Bug report

Version

0.10.0, 0.9.1, 0.9.0

(0.8.4 and before does not have this bug. So that could be something related to the introduction of cache-loader in 0.9.0)

Steps to reproduce

Reproduce repo https://github.com/meteorlxy/vuepress-bug-repro

In brief, add ANY exclamatory mark (!) in chainWebpack of config.js will cause an error.

E.g.

// .vuepress/config.js
module.exports = {
  chainWebpack: (config, isServer) => {
    // !exclamatory mark in comments or codes will both cause errors

    let test = true
    if (!test) {
      // ...
    }
  }
}

What is expected?

Works well

What is actually happening?

Error

Other relevant information

• Your OS: Windows 10 / Ubuntu 18.04
• Node.js version: 8.11.1
• Browser version: .
• Is this a global or local install? local
• Which package manager did you use for the install? yarn