[Android] hermesV1Enabled flag ignored

[farwayer]

Description

hermesV1Enabled flag in the project's gradle.properties is ignored for Android builds.

I added debug prints to node_modules/react-native/settings.gradle.kts

buildscript {
  val properties = java.util.Properties()
  val propertiesToInherit = listOf("hermesV1Enabled", "react.hermesV1Enabled")

  try {
    file("../../android/gradle.properties").inputStream().use { properties.load(it) }

    gradle.rootProject {
      propertiesToInherit.forEach { property ->
        println(properties.getProperty(property)) // false
        if (properties.containsKey(property)) {
          gradle.rootProject.extra.set(property, properties.getProperty(property))
        }
      }
    }
  } catch (e: Exception) {
    // fail silently
  }
}

and apparently the properties (tried both hermesV1Enabled and react.hermesV1Enabled) are being read correctly. But in the hermes assembly file node_modules/react-native/ReactAndroid/hermes-engine/build.gradle.kts the value is read as true:

val hermesV1Enabled =
    rootProject.extensions.getByType(PrivateReactExtension::class.java).hermesV1Enabled.get()
println(hermesV1Enabled) // true

Hardcoding the value in this file to false results in a build of a regular (non-V1) Hermes.

Steps to reproduce

1. npx @react-native-community/cli@latest init test
2. "resolutions": {"hermes-compiler": "0.15.0"} => package.json
3. yarn
4. hermesV1Enabled=false => android/gradle.settings
5. add to android/settings.gradle

includeBuild('../node_modules/react-native') {
    dependencySubstitution {
        substitute(module("com.facebook.react:react-android")).using(project(":packages:react-native:ReactAndroid"))
        substitute(module("com.facebook.react:react-native")).using(project(":packages:react-native:ReactAndroid"))
        substitute(module("com.facebook.react:hermes-android")).using(project(":packages:react-native:ReactAndroid:hermes-engine"))
        substitute(module("com.facebook.react:hermes-engine")).using(project(":packages:react-native:ReactAndroid:hermes-engine"))
    }
}

6. yarn start & yarn android
7. open debugger
8. type HermesInternal.getRuntimeProperties()

Build:  "Release"
Builtins Frozen: false
Bytecode Version: 98
CommonJS Modules: "None"
Debugger Enabled: true
GC: "hades (concurrent)"
OSS Release Version: "for RN 0.84.0"
Static Hermes: true
VM Experiments:0

React Native Version

0.84.0

Affected Platforms

Runtime - Android, Build - Linux

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

System:
Binaries:
  Node:
    version: 25.6.1
    path: /usr/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/bin/yarn
  npm:
    version: 11.10.0
    path: /usr/bin/npm
  Watchman: Not Found
SDKs:
  Android SDK:
    Android NDK: 27.1.12297006
IDEs:
  Android Studio: Not Found
Languages:
  Java:
    version: 17.0.18
    path: /usr/bin/javac
  Ruby:
    version: 3.4.8
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.84.0
    wanted: 0.84.0
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

-

MANDATORY Reproducer

https://github.com/farwayer/rn-bug-disable-hermesv1

Screenshots and Videos

No response