[iOS][SwiftPM] 0.87 Release app crashes because Hermes compiler emits bytecode 98 but runtime expects 99

[marandaneto]

Description

React Native 0.87's experimental full SwiftPM iOS integration selects incompatible Hermes compiler and runtime versions for Release builds.

npx react-native spm add --deintegrate --yes does two independent Hermes resolutions:

1. download-spm-artifacts.js defaults the SwiftPM runtime artifact to hermes-compiler/latest-v1. At reproduction time this resolves to 260318099.0.1, so the generated artifacts.json points at:

   hermes-ios/260318099.0.1/hermes-ios-260318099.0.1-hermes-ios-release.tar.gz

2. generate-spm-xcodeproj.js resolves hermes-compiler/package.json from the React Native npm dependency tree and injects that compiler as HERMES_CLI_PATH. React Native 0.87.0 pins hermes-compiler@250829098.0.16.

The selected compiler emits HBC bytecode version 98, while the downloaded SwiftPM runtime expects bytecode version 99. The Release build succeeds, but the app terminates immediately when launched:

Compiling JS failed: Wrong bytecode version. Expected 99 but got 98

This is reproducible in a stock bare React Native CLI app with no third-party native dependencies. CocoaPods is not used after spm add --deintegrate.

Expected behavior: the SwiftPM Hermes runtime artifact and HERMES_CLI_PATH compiler must be selected from the same Hermes version.

Relevant 0.87.0 code:

• Artifact download defaults to latest-v1: https://github.com/react/react-native/blob/v0.87.0/packages/react-native/scripts/spm/download-spm-artifacts.js#L397-L428
• Project generation resolves the npm compiler relative to React Native: https://github.com/react/react-native/blob/v0.87.0/packages/react-native/scripts/spm/generate-spm-xcodeproj.js#L1420-L1448

A temporary workaround is to install hermes-compiler@260318099.0.1 at the app level and point HERMES_CLI_PATH at that matching compiler.

Steps to reproduce

1. Clone https://github.com/marandaneto/react-native-087-swiftpm-hermes-bytecode-repro

2. Run npm run reproduce. This installs dependencies, converts the stock project using npx react-native spm add --deintegrate --yes, prints the selected compiler and runtime versions, and performs a Release simulator build.

3. Boot an iOS Simulator.

4. Install the generated app:

   xcrun simctl install booted ios/build/DerivedData/Build/Products/Release-iphonesimulator/HermesSwiftPMRepro.app

5. Launch it with console output:

   xcrun simctl launch --terminate-running-process --console-pty booted org.reactjs.native.example.HermesSwiftPMRepro

The process terminates with Wrong bytecode version. Expected 99 but got 98.

React Native Version

0.87.0

Affected Platforms

Runtime - iOS, Build - MacOS

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.6
  CPU: (14) arm64 Apple M4 Pro
  Memory: 4.18 GB / 48.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 26.7.0
    path: /opt/homebrew/bin/node
  Yarn:
    version: 1.22.22
    path: /opt/homebrew/bin/yarn
  npm:
    version: 11.19.0
    path: /opt/homebrew/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/lib/ruby/gems/4.0.0/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.5
      - iOS 26.5
      - macOS 26.5
      - tvOS 26.5
      - visionOS 26.5
      - watchOS 26.5
IDEs:
  Xcode:
    version: 26.6/17F113
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 21.0.11
  Ruby:
    version: 4.0.6
    path: /opt/homebrew/opt/ruby/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.2.0
    wanted: 20.2.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.87.0
    wanted: 0.87.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

Compiler selected by generated HERMES_CLI_PATH:
node_modules/hermes-compiler/hermesc/osx-bin/hermesc
Hermes release version: 250829098.0.16
HBC bytecode version: 98

SwiftPM release artifacts.json:
https://repo1.maven.org/maven2/com/facebook/hermes/hermes-ios/260318099.0.1/hermes-ios-260318099.0.1-hermes-ios-release.tar.gz

Runtime:
ReactInstance: evaluateJavaScript() with JS bundle
Js error message: getPropertyAsObject: property 'console' is undefined, expected an Object
Original js error message: Non-js exception: Compiling JS failed: Wrong bytecode version. Expected 99 but got 98, sourceURL: .../HermesSwiftPMRepro.app/main.jsbundle
*** Terminating app due to uncaught exception 'RCTFatalException: NSException: Unhandled JS Exception: [runtime not ready]: Error: Non-js exception: Compiling JS failed: Wrong bytecode version. Expected 99 but got 98'
libc++abi: terminating due to uncaught exception of type NSException

MANDATORY Reproducer

https://github.com/marandaneto/react-native-087-swiftpm-hermes-bytecode-repro

Screenshots and Videos

Not applicable; the Release app terminates immediately and the console output above contains the failure.