No (separate) source maps for PostCSS

[dummdidumm]

Describe the bug
When preprocessing PostCSS, there is no source map returned although PostCSS supports it.

To Reproduce
Preprocess any file with postcss and see that map of the returned object is undefined.

Expected behavior
A map object is returned.

Reason / how to fix this
PostCSS's SourceMap options have an option inline which is true by default. The result is that the source maps are inlined in the output and not returned in the map object. Setting this to false will fix this. I suggest to make inline: false the default but also allow to override these options. Currently this is not possible.

Information about your project:

• Your browser and the version: -

• Your operating system: Windows

• svelte-preprocess version (Please check you can reproduce the issue with the latest release!): Latest

• Whether your project uses Webpack or Rollup: Rollup

Additional context

Would be great to have this so we can process the information in language-tools and show Svelte warnings at the correct positions.

[HelenDias]

Hi @kaisermann! Can you assignee me to this bug?
I would like to help 😄