react / react/react-native

Codegen variable naming can result in incorrect code

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#53,839 4 comments 0 reactions 0 assignees View on GitHub

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Resolution: PR Submitted Stale Tech: Codegen Type: New Architecture
Dominant language
C++
Stars
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Avg merge
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Merged PRs (30d)
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Description

Description
type MyEventType = {
  type: string;
  payload: {
    message: string;
  }
};

export interface NativeProps extends ViewProps {
  onPressed?: CodegenTypes.BubblingEventHandler<MyEventType> | null;
}

codegen generates such a code not the payload variable gets shadowed. And the bug is in the line: payload.setProperty(runtime, "payload", payload);

void SimpleViewEventEmitter::onPressed(OnPressed event) const {
  dispatchEvent("pressed", [event=std::move(event)](jsi::Runtime &runtime) {
    auto payload = jsi::Object(runtime);
    payload.setProperty(runtime, "type", event.type);
{
  auto payload = jsi::Object(runtime);
  payload.setProperty(runtime, "message", event.payload.message);
  payload.setProperty(runtime, "payload", payload);
}
    return payload;
  });
}

See
https://github.com/mfazekas/codegen-variable-naming-bug

Steps to reproduce
check out https://github.com/mfazekas/codegen-variable-naming-bug
cd ReproducerApp/ios
pod install
cat build/generated/ios/react/renderer/components/AppSpec/EventEmitters.cpp
React Native Version

0.81.4

Affected Platforms

Other (please specify)

Areas

Codegen

Output of npx @react-native-community/cli info
info Fetching system and libraries information...
System:
  OS: macOS 15.6
  CPU: (12) arm64 Apple M2 Max
  Memory: 125.66 MB / 32.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.16.0
    path: ~/.nvm/versions/node/v22.16.0/bin/node
  Yarn:
    version: 1.22.21
    path: ~/.local/bin/yarn
  npm:
    version: 11.5.2
    path: ~/.nvm/versions/node/v22.16.0/bin/npm
  Watchman:
    version: 2025.06.30.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/boga/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.5
      - iOS 18.5
      - macOS 15.5
      - tvOS 18.5
      - visionOS 2.5
      - watchOS 11.5
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.1 AI-251.26094.121.2513.14007798
  Xcode:
    version: 16.4/16F6
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 20.0.1
    path: /usr/bin/javac
  Ruby:
    version: 2.7.8
    path: /Users/boga/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native: Not Found
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true
Stacktrace or Logs
n/a
MANDATORY Reproducer

https://github.com/mfazekas/codegen-variable-naming-bug

Screenshots and Videos

No response

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the mandatory reproducer, run pod install in ReproducerApp/ios, and inspect build/generated/ios/react/renderer/components/AppSpec/EventEmitters.cpp. Trace the generated event payload naming from the TypeScript example; done means the generated C++ no longer shadows the outer payload and preserves the nested event data.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp, react-native, typescript
Domain
mobile-dev, tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
68/100

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