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[Hermes] Remove legacy Hermes C++ code and HERMES_V1_ENABLED compile definition#56697

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[Hermes] Remove legacy Hermes C++ code and HERMES_V1_ENABLED compile definition#56697
cipolleschi wants to merge 1 commit intomainfrom
cipolleschi/remove-legacy-hermes-phase1

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@cipolleschi cipolleschi commented May 6, 2026

Summary

  • Remove all dead C++ code behind !defined(HERMES_V1_ENABLED) guards in HermesExecutorFactory.cpp and HermesInstance.cpp
  • Delete Registration.h, Registration.cpp, ConnectionDemux.h, ConnectionDemux.cpp, and ConnectionDemuxTests.cpp (entirely legacy code)
  • Remove HERMES_V1_ENABLED compile definition from react-native-flags.cmake
  • Remove HERMES_V1_ENABLED cache variable from Android CMakeLists.txt

This is Phase 1 of removing legacy Hermes support. Since Hermes V1 is already the default on all platforms and the 0.86 branch has been cut, all legacy Hermes code
is dead and can be safely removed.

Changelog:

[General][Breaking] - Remove Legacy Hermes from C++ code

Test plan

  • Android: ./gradlew :packages:rn-tester:android:app:assembleDebug — BUILD SUCCEEDED
  • iOS: xcodebuild rn-tester on iPhone 16 Pro simulator — BUILD SUCCEEDED

Legacy Hermes support is no longer needed since 0.86 branch has been cut.
This removes all dead code behind `!defined(HERMES_V1_ENABLED)` guards
and the CMake infrastructure that set the HERMES_V1_ENABLED compile
definition.
@meta-cla meta-cla Bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label May 6, 2026
@facebook-github-tools facebook-github-tools Bot added p: Facebook Partner: Facebook Partner labels May 6, 2026
@cipolleschi cipolleschi changed the title Remove legacy Hermes C++ code and HERMES_V1_ENABLED compile definition [Hermes] Remove legacy Hermes C++ code and HERMES_V1_ENABLED compile definition May 6, 2026
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