Style in vue files is ignored when `sideEffects: false` is defined in package.json

Bug report

Version

0.14.0

Steps to reproduce

Create a vue component in .vuepress/components

<template>
  <p class="red">Should be red</p>
</template>

<style scoped>
.red {
  color: red
}
</style>

Add "sideEffects": false to package.json file

The scoped attribute doesn’t have an impact

What is expected?

When runnig the build, the css should be extracted in a CSS file

What is actually happening?

The CSS is dropped at some point, but it works correctly under dev

Other relevant information

• Your OS: latest osx
• Node.js version: 10
• Browser version: Chrome
• Is this a global or local install? local
• Which package manager did you use for the install? yarn

[ulivz]

I found a related issue: https://github.com/webpack/webpack/issues/6741.

CSS usually doesn’t produce an export, so it really should be excluded from tree shaking.

After change sideEffects: false to:

  "sideEffects": [
    "*.vue"
  ],

The style comes back.

[posva]

Finally found the problem: it’s adding sideEffects: false to package.json file (it’s a webpack thing for libraries). I created a pull request adding that to the package.json file: https://github.com/ulivz/vuepress-718/pull/1