Summary

This draft is a work in progress on exploring the integration of SWC in the Metro traspilation pipeline along with Babel to help OSS users with a faster overall bundling speeds.

Goal

• Improve bundling speed for OSS users
  • SWC is faster than Babel in benchmarks, and hypothesis is transpiling the majority of code using SWC will improves overall bundling speed in Metro. 

Non-Goal

• Remove Babal
  • There are many community packages that come with Babel transforms, and we need to support that for the foreseeable future.

Tasks

• Import the original POC.
• Setup the new npm package metro-swc-transformer.
• Use napi.rs to create a native Node.js addon.
• Add typescript support.
• Algin Module Configuration with Metro Preset
• Add lazy imports with SWC config
• Add support for require optional packages. 
• Create SWC opt-in transformer config to use SWC in metro-transform-worker. 
• Create a minimal Babel pass to strip flow types before SWC.
  • This should be config driven so we don't have to do this first pass for all files.
• Create config for fallback to current full Babel pipeline for selected files.
• Check for missing transforms that can cause compatibility issues.
  • This will be a breaking change, as we are not aiming for 1:1 mapping but documenting what has changed. Ideally, we need to use the same presets as SWC Web. But we still need to align on React Native specific transforms.
  • Risk of adoption gets harder for exiting apps.
  • Risk of apps using different transpilation pipeline which is not compatible with each other.
• Add Sourcemap support and check regressions in debugging experience.
• Add HMR support.
• Test and dogfood new SWC pipeline and bug fixes.
• NPM release with different packages for different architecture approach number 3 explained in Napi docs.

Test plan

TODO