postcss8 support for nuxt 2.15+

Since nuxt@2.15 nuxt supports opting-in to use postcss@8 (via nuxt/nuxt.js#8546).

Upgrade is pending for csstools/postcss-preset-env#191 (see nuxt/nuxt.js#8087 and nuxt/nuxt.js#8408)

In the meantime, this module allows rapid migration:

- Ensures supported nuxt version is used (>= 2.15.3)
- Forces to use upgraded dependencies using __NUXT_PREPATHS__
- Will be updated accordingly to self-disable when a nuxt version with default postcss8 detected
- Use autoprefixer instead of postcss-preset-env

Usage

Install @nuxt/postcss8 as devDependency:

``sh
yarn add --dev @nuxt/postcss8


or


npm i -D @nuxt/postcss8
`

Add @nuxt/postcss8 to buildModules in nuxt.config:

`js
// nuxt.config
export default {
buildModules: [
'@nuxt/postcss8'
]
}
`

$3

If you have a nuxt module that requires postcss@8, install postcss@8 and @nuxt/postcss8 as dependency:

`sh
yarn add postcss@8 @nuxt/postcss8


or


npm i postcss@8 @nuxt/postcss8
`

Inside module:
`js
export default async function() {
await this.addModule(require('@nuxt/postcss8'))
}
``