[v4] Sourcemaps not enabled in postcss plugin

[wesbos]

The postcss plugin doesn't write soucemaps when doing the lightning CSS conversion.

I think this is where it needs to happen but trying to patch it with pnpm does not give me sourcemaps, so Im wondering if there is a larger issue

[wesbos]

Looks like you need to explicitly pass the sourcemap from lightning CSS to postcss. Here is a good example: https://github.com/onigoetz/postcss-lightningcss/blob/main/src/index.js#L23-L66

[thecrypticace]

Sourcemaps are still a WIP. We don't track them at all at the moment in v4 but we have a PR for it. I think PostCSS source map support is going to be rather complicated because we're not utilizing the PostCSS AST and will require further research.