From be8b598661e39a1f81881c269b1285dc60e1129f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kr=C3=A6n=20Hansen?= <mail@kraenhansen.dk>
Date: Sat, 31 Oct 2026 22:01:02 +0100
Subject: [PATCH] Report Hermes fatal errors on the New Architecture

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 .../runtime/hermes/jni/JHermesInstance.cpp     | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/packages/react-native/ReactAndroid/src/main/jni/react/runtime/hermes/jni/JHermesInstance.cpp b/packages/react-native/ReactAndroid/src/main/jni/react/runtime/hermes/jni/JHermesInstance.cpp
index c9d828ac2fd6..4ac660d40bac 100644
--- a/packages/react-native/ReactAndroid/src/main/jni/react/runtime/hermes/jni/JHermesInstance.cpp
+++ b/packages/react-native/ReactAndroid/src/main/jni/react/runtime/hermes/jni/JHermesInstance.cpp
@@ -7,13 +7,31 @@
 
 #include "JHermesInstance.h"
 
+#include <android/log.h>
 #include <fbjni/fbjni.h>
+#include <hermes/hermes.h>
+
+#include <mutex>
 
 namespace facebook::react {
 
+static void hermesFatalHandler(const std::string& reason) {
+  __android_log_assert(nullptr, "Hermes", "%s", reason.c_str());
+}
+
+static constinit std::once_flag flag;
+
 jni::local_ref<JHermesInstance::jhybriddata> JHermesInstance::initHybrid(
     jni::alias_ref<jclass> /* unused */,
     bool allocInOldGenBeforeTTI) {
+  std::call_once(flag, []() {
+    auto* fatalHandlerInterface =
+        jsi::castInterface<facebook::hermes::ISetFatalHandler>(
+            facebook::hermes::makeHermesRootAPI());
+    if (fatalHandlerInterface) {
+      fatalHandlerInterface->setFatalHandler(hermesFatalHandler);
+    }
+  });
   return makeCxxInstance(allocInOldGenBeforeTTI);
 }