Problem when use VuePress in an existing project

[tinchox5]

Step to reproduce:
Start a clean vue project using vue-cli@2.9.3, then install Vuepress@0.4.6 in the main project folder using "npm install -D vuepress".

What happens:

npm WARN mini-css-extract-plugin@0.4.0 requires a peer of webpack@^4.4.0 but none is installed. You must install peer dependencies yourself.
npm WARN webpack-serve@0.3.1 requires a peer of webpack@^4.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN time-fix-plugin@2.0.0 requires a peer of webpack@>=4.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN koa-webpack@3.0.2 requires a peer of webpack@^4.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN webpack-dev-middleware@3.1.2 requires a peer of webpack@^4.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN webpack-hot-client@2.2.2 requires a peer of webpack@^4.0.0 but none is installed. You must install peer dependencies yourself.

[yyx990803]

It's weird because yarn is able to produce a correct dep tree in this case but npm cannot...
I'd suggest using yarn for now.

[tinchox5]

Thank you!

[yyx990803]

Confirmed this is a known issue in npm. Will likely have to use Yarn for this specific case for now.