[lazerg]

Summary:

@react-native/babel-preset runs the class features plugins (transform-private-methods and transform-private-property-in-object, plus transform-class-properties when classes are lowered) but not @babel/plugin-transform-class-static-block. Those plugins throw "Static class blocks are not enabled" on any class with a static { } block, so an app file or dependency using one fails to bundle. The preset now adds the static block plugin next to the private methods plugin, so it only runs when the class features plugins do. With unstable_preserveClassPrivate the block is still left as is, like before.

Fixes #59853

Changelog:

[GENERAL] [FIXED] - Babel preset no longer fails on class static blocks

Test Plan:

Added tests for a class with a static block under the hermes-stable and hermes-legacy profiles; both fail with "Static class blocks are not enabled" before the change. jest packages/react-native-babel-preset passes and the existing transform snapshots are unchanged. The plugin's ^7.26.0 range is already in yarn.lock, so the lockfile doesn't change.

[vzaidman]

I think this is needed, but the tests only cover a public static field. A static block touching a #private field or super is the ordering-sensitive case (static-block plugin runs before private-methods) worth one test, plus a test asserting the hermes-stable + preserveClassPrivate path leaves the block intact.

[lazerg]

Thanks, added both: one test with a #private field and super in a static block, and one checking that hermes-stable with preserveClassPrivate leaves the block alone. Both passed without touching the plugin order.