New package

• @lavamoat/react-native-lockdown (beta)
• SES lockdown via Metro serializer
• Supports Hermes and legacy JSC (unsupported V8 untested)

React Native app init order

Metro

• resolution
• transformation
• serialization
  • getPolyfills
    • ses (jsc) or ses/hermes
    • repair
      • backup: Promise._<_onHandle/_onReject/_noop>
      • repairIntrinsics(rnOptions)
      • restore: Promise._<_onHandle/_onReject/_noop>
    • @react-native/js-polyfills
    • vetted shims (e.g. reflect-metadata)
• getRunModuleStatement
  • node_modules/react-native/Libraries/Core/InitializeCore.js
    • [metro] moduleId: 59/64/69/111/x
  • hardenIntrinsics()
  • index.js
    • [metro] moduleId: 0

(user ignores SES shim with babel)

Hermes https://github.com/facebook/hermes/blob/main/utils/promise/index.js
RN https://github.com/facebook/react-native/blob/main/packages/react-native/Libraries/Core/polyfillPromise.js
SES removes https://github.com/then/promise/blob/master/src/core.js#L68-L70
(https://github.com/then/promise/blob/master/src/es6-extensions.js requires)
so we add them back as vetted shims after repair

https://github.com/facebook/react-native/blob/main/packages/community-cli-plugin/src/utils/loadMetroConfig.js#L59-L76
https://github.com/facebook/react-native/blob/main/packages/metro-config/src/index.flow.js#L61-L73

Follow-up with e2e test

Follow-up ship type declarations

• tsconfig.json
• improve types
• repair.js -> repair.ts (cross-module linking)
• index.js -> index.js? etc

Follow-up extend assertPolyfills

Follow-up node/macOS CI failures (unrelated to this PR)

Follow-up update upstream template metro.config.js to modern TS @import

Follow-up maybe another refactor

Follow-up update all /packages LICENSE.md -> LICENSE and add one for laverna

• chore: rename all LICENSE.md to LICENSE #1700