[Worklets 0.11.0] WorkletRuntime.legacyModeInit crashes on debug-native + Metro dev bundle (jsi::Value::getObject assertion in installUnpacker)

[LeCiel]

Description

react-native-worklets@0.11.0 crashes on startup during WorkletRuntime.init on debug-native iOS builds with a Metro-served dev JS bundle. Release builds (EAS release native + release bundle) of the same code run cleanly.

Stack (SIGABRT on the JS thread)

__pthread_kill
pthread_kill
__abort
abort
__assert_rtn
facebook::jsi::Value::getObject(facebook::jsi::Runtime&) &&
worklets::UnpackerLoader::installUnpacker(facebook::jsi::Runtime&, worklets::CodeUnpacker const&)
worklets::UnpackerLoader::installUnpackers(facebook::jsi::Runtime&) const
worklets::WorkletRuntime::legacyModeInit(std::__1::shared_ptr<worklets::UnpackerLoader> const&)
worklets::WorkletRuntime::init(std::__1::shared_ptr<worklets::JSIWorkletsModuleProxy> const&)
worklets::WorkletsModuleProxy::start()
-[WorkletsModule start]

The getObject cast in installUnpacker fires the JSI assertion (in debug builds, __assert_rtn is fatal; in release builds NDEBUG strips it and the same undefined-behavior path silently continues, which is why release doesn't visibly crash).

Build matrix

Build	Native	JS bundle	Result
npx expo run:ios (Xcode debug scheme)	debug	Metro dev bundle	crash
EAS production profile (test)	release	release bundle	runs cleanly
EAS dev-personal profile	release	release bundle + dev OTA	runs cleanly

The last two use react-native-worklets@0.11.0 too — the crash is exclusive to the debug-native + dev-bundle combination.

Environment

react-native	0.85.3
react-native-reanimated	4.5.2
react-native-worklets	0.11.0
react	19.2
Architecture	New Architecture (Fabric + TurboModules)
JS engine	Hermes
Platform	iOS Simulator (iPhone, iOS 26) — also reproduces on device
Build type	Debug app + Metro dev bundle
Host	macOS 26.5.1, Xcode 16, Apple silicon
Expo	SDK 56

Reproduction

1. Fresh app with react-native-worklets@0.11.0 + react-native-reanimated@4.5.2 (the two are the same pair as our tree).
2. rm -rf ios node_modules ~/Library/Developer/Xcode/DerivedData/*
3. npm ci
4. npx expo prebuild --platform ios --clean
5. npx expo run:ios
6. App crashes on launch before any JS user code executes; SIGABRT on com.facebook.react.runtime.JavaScript thread with the stack above.

Metro is attached and shows no JS error — the abort happens in native WorkletsModule start before the JS runtime hands the bundle to any user module.

Known-good

Rolling back to react-native-worklets@0.10.2 + react-native-reanimated@4.5.1 (last peer combination) restores debug-build startup on the same tree.

Adjacent issues

• Debug native + release EAS Update bundle: loadUnpackers passes empty sourceMap, Hermes crashes at startup #9600 (closed) — installUnpackers sourceMap ?? '' in 0.9.1, but that case was debug-native + release-transformed OTA bundle. Ours is debug-native + Metro dev bundle, and the failure is a bare getObject assertion rather than the source-map JSON parse.
• [Worklets] evalWithSourceMap still crashes on empty source-map strings after #9607 (debug app + release OTA bundle) #9906 (open) — evalWithSourceMap empty-source-map crash after fix(Worklets): always expecting sourceMaps in unpackers #9607 in the same debug + release-OTA combination.
• Both are in the installUnpacker / UnpackerLoader neighbourhood; the 0.11.0 refactor around legacyModeInit may have introduced a new variant that hits any debug build with a dev-transform bundle.

Impact for us

Production users are unaffected (release builds work), but the entire team's local Xcode-based debug cycle is broken — this is what surfaced the report. We've pinned back to 0.10.2 / 4.5.1 as a workaround.

Happy to bisect against 0.11.0 nightlies or test a patch build if useful.

[github-actions]

Hey! 👋

It looks like you've omitted a few important sections from the issue template.

Please complete Steps to reproduce, Snack or a link to a repository, Reanimated version, React Native version and Platforms sections.

[github-actions]

Hey! 👋

The issue doesn't seem to contain a minimal reproduction.

Could you provide a snack or a link to a GitHub repository under your username that reproduces the problem?

[LeCiel]

Update: also reproduces on Android debug builds — same assertion, same worklets frames, libworklets.so instead of the iOS dylib:

Abort message: jsi.h:1709: Value::getObject(Runtime&): assertion "isObject()" failed
  #02 libworklets.so  facebook::jsi::Value::getObject
  #03 libworklets.so  worklets::UnpackerLoader::installUnpacker
  #04 libworklets.so  worklets::UnpackerLoader::installUnpackers

Same Metro-dev-bundle debug-native combination, no other tree changes. So this isn't iOS-specific — it's the whole WorkletRuntime.legacyModeInit → installUnpacker path failing the getObject invariant whenever the runtime is initialized in a debug context.

Updated build matrix:

Build	Native	JS bundle	iOS	Android
Local dev (expo run:ios / expo run:android)	debug	Metro dev	crash	crash
EAS release / TestFlight / internal-track	release	release	runs cleanly	runs cleanly

Since release strips __assert_rtn, the invariant violation is silent in production but still an undefined-behavior path.

[tjzel]

Hey @LeCiel, could you check if the following patch fixes your issue? (for worklets 0.11.0)

diff --git a/node_modules/react-native-worklets/Common/cpp/worklets/WorkletRuntime/WorkletHermesRuntime.cpp b/node_modules/react-native-worklets/Common/cpp/worklets/WorkletRuntime/WorkletHermesRuntime.cpp
index 1098911..2130b73 100644
--- a/node_modules/react-native-worklets/Common/cpp/worklets/WorkletRuntime/WorkletHermesRuntime.cpp
+++ b/node_modules/react-native-worklets/Common/cpp/worklets/WorkletRuntime/WorkletHermesRuntime.cpp
@@ -42,7 +42,10 @@ WorkletHermesRuntime::WorkletHermesRuntime(std::unique_ptr<facebook::hermes::Her
         }
         std::shared_ptr<const jsi::Buffer> sourceMap;
         if (count > 2 && args[2].isString()) {
-          sourceMap = std::make_shared<const jsi::StringBuffer>(args[2].asString(rt).utf8(rt));
+          auto sourceMapString = args[2].asString(rt).utf8(rt);
+          if (!sourceMapString.empty()) {
+            sourceMap = std::make_shared<const jsi::StringBuffer>(std::move(sourceMapString));
+          }
         }
         return wrappedRuntime->evaluateJavaScriptWithSourceMap(code, sourceMap, sourceURL);
       });
diff --git a/node_modules/react-native-worklets/lib/module/memory/valueUnpacker.native.js b/node_modules/react-native-worklets/lib/module/memory/valueUnpacker.native.js
index 92e2404..1ee622f 100644
--- a/node_modules/react-native-worklets/lib/module/memory/valueUnpacker.native.js
+++ b/node_modules/react-native-worklets/lib/module/memory/valueUnpacker.native.js
@@ -14,7 +14,7 @@ export function installValueUnpacker() {
         const initData = objectToUnpack.__initData;
         if (initData.bytecode !== undefined) {
           workletFun = globalThis.evalBytecode(initData.bytecode);
-        } else if (globalThis.evalWithSourceMap) {
+        } else if (globalThis.evalWithSourceMap && initData.sourceMap) {
           // if the runtime (hermes only for now) supports loading source maps
           // we want to use the proper filename for the location as it guarantees
           // that debugger understands and loads the source code of the file where
diff --git a/node_modules/react-native-worklets/plugin/index.js b/node_modules/react-native-worklets/plugin/index.js
index 1cd05b0..45a8f18 100644
--- a/node_modules/react-native-worklets/plugin/index.js
+++ b/node_modules/react-native-worklets/plugin/index.js
@@ -381,9 +381,19 @@ var require_utils = __commonJS({
     exports2.replaceWithFactoryCall = replaceWithFactoryCall;
     var types_12 = require("@babel/types");
     function isRelease(state) {
-      var _a, _b, _c;
-      const pattern = /(prod|release|stag[ei])/i;
-      return !!(((_a = state.file.opts.envName) === null || _a === void 0 ? void 0 : _a.match(pattern)) || ((_b = process.env.BABEL_ENV) === null || _b === void 0 ? void 0 : _b.match(pattern)) || ((_c = process.env.NODE_ENV) === null || _c === void 0 ? void 0 : _c.match(pattern)));
+      var _a, _b;
+      const releasePattern = /(prod|release|stag[ei])/i;
+      const developmentPattern = /dev/i;
+      const envName = state.file.opts.envName;
+      if (envName) {
+        if (envName.match(releasePattern)) {
+          return true;
+        }
+        if (envName.match(developmentPattern)) {
+          return false;
+        }
+      }
+      return !!(((_a = process.env.BABEL_ENV) === null || _a === void 0 ? void 0 : _a.match(releasePattern)) || ((_b = process.env.NODE_ENV) === null || _b === void 0 ? void 0 : _b.match(releasePattern)));
     }
     function replaceWithFactoryCall(toReplace, name, factoryCall) {
       if (!name || !needsDeclaration(toReplace)) {
diff --git a/node_modules/react-native-worklets/src/memory/valueUnpacker.native.ts b/node_modules/react-native-worklets/src/memory/valueUnpacker.native.ts
index 8bcfec4..fad70a0 100644
--- a/node_modules/react-native-worklets/src/memory/valueUnpacker.native.ts
+++ b/node_modules/react-native-worklets/src/memory/valueUnpacker.native.ts
@@ -26,7 +26,7 @@ export function installValueUnpacker() {
         const initData = objectToUnpack.__initData;
         if (initData!.bytecode !== undefined) {
           workletFun = globalThis.evalBytecode!(initData!.bytecode);
-        } else if (globalThis.evalWithSourceMap) {
+        } else if (globalThis.evalWithSourceMap && initData!.sourceMap) {
           // if the runtime (hermes only for now) supports loading source maps
           // we want to use the proper filename for the location as it guarantees
           // that debugger understands and loads the source code of the file where
@@ -34,7 +34,7 @@ export function installValueUnpacker() {
           workletFun = globalThis.evalWithSourceMap(
             initData!.code!,
             initData!.location!,
-            initData!.sourceMap!
+            initData!.sourceMap
           );
         } else if (globalThis.evalWithSourceUrl) {
           // if the runtime doesn't support loading source maps, in dev mode we

[LeCiel]

Confirmed — the 4-file patch applied via patch-package on top of react-native-worklets@0.11.0 + react-native-reanimated@4.5.2 fixes the crash for us on iOS debug builds (Metro dev bundle). App boots cleanly, worklets initialize past WorkletRuntime.legacyModeInit, and the assertion no longer fires. Xcode build log confirms WorkletHermesRuntime.cpp recompiled with the change:

› Compiling react-native-worklets Pods/RNWorklets » WorkletHermesRuntime.cpp

Will confirm Android debug next once we get a test build out, but I expect the same result since it's the same C++ path.

Thank you @tjzel! Any timeline you can share for the fix landing in a stable release?

[tjzel]

I'll release the fix this week