Babel preset: Add Hermes V1 native runtime workarounds for hermes#1761#56816
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## Summary: Three Babel plugins added to `@react-native/babel-preset` that work around runtime codegen bugs in the bundled Hermes V1 (250829098.0.13, branch cut 2025-08-29) by rewriting source patterns before they reach the engine. Each plugin papers over a different bug that has been fixed on Hermes `static_h` but has not been backported to the V1 stable branch. - `fix-hermes-v1-async-arrow-non-simple-params`: facebook/hermes#1761 (fixed in static_h by 68bfb3a48b31, 2025-09-11). Async arrow functions with destructured, defaulted, or rest parameters silently resolve `await` with `undefined` while the function body continues executing in the background. The plugin rewrites the params to a simple identifier with inline destructuring so Hermes never sees the buggy shape. Gated on `isHermesProfile && preserveAsync` since `plugin-transform-async-to-generator` rewrites the pattern away when `preserveAsync` is false. - `fix-hermes-v1-class-in-finally`: Fixed in static_h by 1e94fbe0ebb4 (2026-02-12). Class declarations inside a `finally` block trip Hermes V1's variable caching path. The plugin wraps them in an IIFE so the class lives in its own scope. - `fix-hermes-v1-super-in-object-accessor`: Fixed in static_h by 18a963465944 (2025-11-04). Object-literal getters and setters using `super.x` trip the `genFunctionExpression` home object path. The plugin marks the accessor as computed with a string key. All three gate on `isHermesProfile` and bail out fast on the common case. The plugins are a direct port of work by @kitten (Phil Pluckthun, Expo team) in `babel-preset-expo` (expo/expo#45601, MIT licensed). All plugin design and implementation credit belongs to him. This PR carries his work over to `@react-native/babel-preset` so bare React Native consumers benefit from the same fix. ## Changelog: [GENERAL] [FIXED] - Work around three Hermes V1 source-level codegen bugs in `@react-native/babel-preset` (async-arrow non-simple params, class-in-finally, super-in-object-accessor) ## Test Plan: - 18 new inline-snapshot test cases across three new test files verify both the transformed output and the fast-bail behavior on irrelevant patterns. - `yarn jest packages/react-native-babel-preset` clean (65 tests, 24 snapshots). - Full repo `yarn test` clean (279 suites, 5656 tests passed, 1816 snapshots). - `yarn lint`, `yarn format-check`, `yarn flow-check`, `yarn test-typescript`, `yarn featureflags --verify-unchanged`, `yarn build-types --validate` all clean. - Existing `transform-snapshot-test` passes byte-identical: the kitchen-sink fixture has none of the buggy patterns so the new plugins do not change its output for any profile. - Verified end-to-end downstream: `babel-preset-expo@56.0.7` (which carries the same plugins) applied to vanilla `@convex-dev/better-auth@0.12.2` fixes the `useConvexAuth.isAuthenticated` race that the destructured-param async-arrow shape produces on Hermes V1. - Public repro: https://github.com/ramonclaudio/convex-better-auth-368-repro ## Caveats: `fix-hermes-v1-class-in-finally` rewrites block-scoped `class` declarations inside `finally` blocks to function-scoped `var` initializers. Observable only when code references the class by name from outside the `finally` (rare pattern). The same plugin shape has run in `babel-preset-expo@56.0.6+` and Expo SDK 56 preview for a week without reported regressions, but flagging in case Meta's internal test fleet surfaces an edge case the OSS test suite does not catch. ## References: - facebook/hermes#1761 (root-cause issue, fixed in static_h) - expo/expo#45601 (source of the ported plugins, by @kitten) - expo/expo#45592 (user-facing bug report on SDK 56 preview) Co-authored-by: Phil Pluckthun <phil@kitten.sh>
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@CalixTang has imported this pull request. If you are a Meta employee, you can view this in D105609206. |
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Anything I can do to help push this forward @CalixTang? |
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Summary:
Three Babel plugins for
@react-native/babel-presetthat work around runtime bugs in the bundled Hermes V1 (250829098.0.13). Rewrites the code patterns at compile time so Hermes never sees them. Port of @kitten's plugins inbabel-preset-expo(expo/expo#45601).Changelog:
[GENERAL] [FIXED] - Work around three Hermes V1 source-level codegen bugs in
@react-native/babel-preset(async-arrow non-simple params, class-in-finally, super-in-object-accessor)Test Plan:
Test repro at ramonclaudio/hermes-1761-repro. 55/55 PASS on iPhone 17 Pro / iOS 26.5 in both Debug and Release builds.
Locally on
packages/react-native-babel-preset:yarn jest packages/react-native-babel-presetclean (65 tests, 24 snapshots).yarn testclean (279 suites, 5656 tests, 1816 snapshots).yarn lint,yarn format-check,yarn flow-check,yarn test-typescript,yarn featureflags --verify-unchanged,yarn build-types --validateall clean.transform-snapshot-testis unchanged: the kitchen-sink fixture has none of the bug patterns so the new plugins don't alter its output.