feat: support style lang postcss

[zyy7259]

No description provided.

[Akryum]

Hum postcss is already applied to any style block. Not sure this is needed at all.

[zyy7259]

I need to specify the lang attribute of the style block to enable syntax highlight.

Without lang being specified, there will be syntax problem.

When I specify the lang with 'postcss', the syntax highlight works fine. But webpack won't able to recognize it.

here is a test project

git clone [email protected]:zyy7259/test-vue-cli-style-postcss.git
cd test-vue-cli-style-postcss
yarn
yarn build

[zyy7259]

or maybe change createCSSRule('css', /\.css$/) to createCSSRule('css', /\.(p(ost)?)?css$/)?

[hsxfjames]

A similar discussion is already in vuejs/vetur#506.
At last @blake-newman says:

The issue is solved with explicitness with vue-loader. <style lang="postcss/pcss/sugarcss/sss">

I think it is sensible to keep this feature. In the past, all we need is to install postcss-cssnext and add the custom config in .postcssrc.js.

[zyy7259]

Why did the CI fail :(

[octref]

Thanks again for supporting <style lang="postcss"> in vue-loader. As PostCSS allows plugins to extend the syntax, it's rather hard to support its syntax highlighting and give correct language features. Having at least a lang attribute allows Vetur to not apply CSS grammar / language features to it and cause frustration. In the future when we have better PostCSS support in VS Code or Vetur, I will gradually turn on more supports for PostCSS in Vetur.