From 42c1c4630cdc7a435a580b88b4913ba0c396cc7a Mon Sep 17 00:00:00 2001
From: Zeya Peng <zeyap@meta.com>
Date: Tue, 14 Jul 2026 17:11:07 +0100
Subject: [PATCH] [0.87] Bootstrap Metro from InitializeCore until setup-env is
 graph-reachable

Summary:
Fresh 0.87 projects redbox on launch with:

  Failed to call into JavaScript module method RCTDeviceEventEmitter.emit().
  Module has not been registered as callable.
  Registered callable JavaScript modules (n = 1): AppRegistry.

Core initialization never runs. Metro's `getModulesRunBeforeMainModule`
(see metro/src/lib/getAppendScripts.js) only emits the run-before `__r()`
call for a module that is *already present in the bundle graph*, and
silently skips it otherwise.

#57475 switched the run-before target from `Libraries/Core/InitializeCore`
to `src/setup-env.js`. `InitializeCore` is reachable in the graph (imported
by `Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js`), but
`src/setup-env.js` is imported by nothing, so Metro skips it and core init
never runs. The two modules are functionally identical (both call
`setUpDefaultReactNativeEnvironment().default()`).

Evidence (bundle tail):
- setup-env target:     `__r(0);`            (broken)
- InitializeCore target: `__r(110); __r(0);`  (fixed)

This is an INTERIM stopgap to unblock the 0.87 RC. It only changes the
internal Metro bootstrap target back to `InitializeCore`; the public
`react-native/setup-env` entry point and its deprecation of InitializeCore
are unchanged. The proper fix (make `setup-env` graph-reachable, or make
Metro treat `getModulesRunBeforeMainModule` entries as graph roots) should
land on main and supersede this.

Changelog:
[General][Fixed] - Fix apps failing to boot ("RCTDeviceEventEmitter not
registered as callable") due to core init not running.

Test Plan:
- `yarn test-release-local -t RNTestProject -p iOS`: app boots without redbox.
- Bundle tail now contains `__r(<InitializeCore>); __r(0);` instead of just `__r(0);`.
---
 .../src/utils/loadMetroConfig.js                    | 13 ++++++-------
 packages/metro-config/src/index.flow.js             |  2 +-
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/packages/community-cli-plugin/src/utils/loadMetroConfig.js b/packages/community-cli-plugin/src/utils/loadMetroConfig.js
index a41b028fa29a..43d9e4126af7 100644
--- a/packages/community-cli-plugin/src/utils/loadMetroConfig.js
+++ b/packages/community-cli-plugin/src/utils/loadMetroConfig.js
@@ -60,17 +60,16 @@ function getCommunityCliDefaultConfig(
   return {
     resolver,
     serializer: {
-      // We can include multiple copies of setup-env here because Metro will
+      // We can include multiple copies of InitializeCore here because metro will
       // only add ones that are already part of the bundle
       getModulesRunBeforeMainModule: () => [
-        // NOTE: ctx.reactNativePath is an absolute path, therefore we need to
-        // reference setup-env.js here by exact path specifier.
-        require.resolve(path.join(ctx.reactNativePath, 'src/setup-env.js'), {
-          paths: [ctx.root],
-        }),
+        require.resolve(
+          path.join(ctx.reactNativePath, 'Libraries/Core/InitializeCore'),
+          {paths: [ctx.root]},
+        ),
         ...outOfTreePlatforms.map(platform =>
           require.resolve(
-            `${ctx.platforms[platform].npmPackageName}/setup-env`,
+            `${ctx.platforms[platform].npmPackageName}/Libraries/Core/InitializeCore`,
             {paths: [ctx.root]},
           ),
         ),
diff --git a/packages/metro-config/src/index.flow.js b/packages/metro-config/src/index.flow.js
index dcac214b3978..03a9aed5ace4 100644
--- a/packages/metro-config/src/index.flow.js
+++ b/packages/metro-config/src/index.flow.js
@@ -61,7 +61,7 @@ export function getDefaultConfig(projectRoot: string): ConfigT {
     serializer: {
       // Note: This option is overridden in cli-plugin-metro (getOverrideConfig)
       getModulesRunBeforeMainModule: () => [
-        require.resolve('react-native/setup-env'),
+        require.resolve('react-native/Libraries/Core/InitializeCore'),
       ],
       getPolyfills: () => require('@react-native/js-polyfills')(),
       isThirdPartyModule({path: modulePath}: Readonly<{path: string, ...}>) {