Save className registrations to disk on build

[otaviomad]

Hey all,

We've been using VE extensively to build our design system library at our company. One issue we encountered is that if you have any vanilla extract .css.js files, you require the bundler to take over and build them on dev time and production build time. This isn't a huge deal, but sometimes we have customers who are either unable to customize their bundling setups or have bundling setups that are too customized and would require too much effort to implement vanilla extract bundling.

The easy solution for this would be to just pre-compile the .css.ts files into .vanilla.js and .css files. This is facilitated by the new bundle option. However, by itself this feature is incomplete. We also have customers using vanilla extract in the front end - and they sometimes import classNames for extensions or overrides, which strip out the "full" className to the singular "identifier" className. If we pre-bundle our VE files, we'd lose the list of registered classNames in the compiler, which will break overrides and other types of selectors.

My suggestion for this would be to have an option to save into memory a .vanilla.registrations.js file, which has all the information that VE would otherwise generate if it had access to the original source. Implementation could be as simple as looking into disk to see that there are adjacent registration files to vanilla.m?js files. This way if someone isn't using VE, they get to use the generated CSS but if they are, they get to use the robust type safety for CSS overrides as well.

I'd be happy to implement a draft for this. I'm already familiar with the Vanilla Extract codebase and have contributed to it in the past.

[otaviomad]

The new injectFilescopes feature flag (#1654) is kinda close to what we'd like but not quite.

The fact that VE information can be injected into the built file is pretty close to what I'd like, but I'd still compile the css, with the marked difference that it will also inject the className registrations. @askoufis sorry to ping you like this, but do you think that's a possibility? I reiterate that I'd be comfortable implementing this feature myself.