facebook
[postcss-plugin] Add @layer and polyfill support via @csstools/postcss-cascade-layers
What changed / motivation ?
This update refactors the useCSSLayers option to streamline the implementation of CSS layer polyfilling. We're replacing our custom, internally handled polyfill with the robust and well-maintained @csstools/postcss-cascade-layers library. This ensures a more compliant and robust solution for handling CSS layer specificity.
Linked PR/Issues
Fixes https://github.com/facebook/stylex/issues/1062
Additional Context
useCSSLayers Option Refactoring
The previously self-implemented polyfill logic has been removed:
// babal-plugin/src/index.js
if (!useLayers) {
ltrRule = addSpecificityLevel(ltrRule, index);
rtlRule = rtlRule && addSpecificityLevel(rtlRule, index);
}
The polyfill functionality is now powered by @csstools/postcss-cascade-layers, ensuring a more robust and compliant solution:
// babel-plugin/src/index.js
async function transformCollectedCSS(collectedCSS: string): Promise<string> {
return (await postcss([cascadeLayers()]).process(collectedCSS)).css;
}
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@necolas, I'm considering implementing the polyfill for @csstools/postcss-cascade-layers within the processStylexRules method, as per your review. However, this change would require processStylexRules to become an async function, which could lead to significant breaking changes across the codebase. Are these extensive changes what you intended?