Fix LogBox parsing for cross-runtime jsi::JSErrors by Naim08 · Pull Request #55994 · react/react-native

Naim08 · 2026-03-08T17:31:14Z

Summary

When a jsi::JSError is thrown from a background Hermes runtime and caught in the RuntimeScheduler, the error's jsi::Value belongs to a different jsi::Runtime. Forwarding this cross-runtime value to onTaskError_ is undefined behavior and causes LogBox to display "Unknown" instead of the actual error message.

This PR introduces a reportError() helper in both RuntimeScheduler_Legacy and RuntimeScheduler_Modern that:

Re-creates the error as a proper Error instance in the current runtime using the safe C++ string accessors (getMessage() / getStack())
Preserves the original message and stack trace
Falls back to a simple jsi::JSError if reconstruction fails

Changelog:

[GENERAL] [FIXED] - Fix LogBox showing "Unknown" for errors originating from background Hermes runtimes

Test plan:

Added handlingCrossRuntimeError test: throws a jsi::JSError from a second Hermes runtime and verifies the error message is correctly forwarded
Added handlingErrorPreservesMessage test: verifies same-runtime errors still work correctly with the new code path
Updated StubErrorUtils to capture and expose the last reported error message for assertion

🤖 Generated with Claude Code

meta-cla · 2026-03-08T17:31:20Z

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Pull request overview

Fixes LogBox error display for tasks that throw jsi::JSError originating from a different Hermes runtime by avoiding cross-runtime jsi::Value usage and reconstructing an Error object in the current runtime before reporting.

Changes:

Add reportError() helper to Legacy/Modern RuntimeScheduler implementations to reconstruct and forward errors safely in the current runtime.
Update scheduler error handling call sites to use reportError() for jsi::JSError.
Extend test scaffolding and add new tests to validate cross-runtime error forwarding and message preservation.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
packages/react-native/ReactCommon/react/renderer/runtimescheduler/tests/StubErrorUtils.h	Capture last reported error message from `ErrorUtils.reportFatalError` for assertions.
packages/react-native/ReactCommon/react/renderer/runtimescheduler/tests/RuntimeSchedulerTest.cpp	Add tests covering cross-runtime `jsi::JSError` handling and message preservation.
packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Modern.h	Declare `reportError()` helper and document cross-runtime error rationale.
packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Modern.cpp	Implement `reportError()` and route `jsi::JSError` handling through it.
packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Legacy.{h,cpp}	Add/implement `reportError()` and route `jsi::JSError` handling through it.

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Copilot · 2026-03-08T17:34:48Z

  int reportFatalCallCount_;
+  std::string lastReportedMessage_;


StubErrorUtils leaves reportFatalCallCount_ uninitialized. Because the object is created with the implicit default constructor, the first reportFatalCallCount_++ is undefined behavior and can make the tests flaky. Initialize this member (and lastReportedMessage_) with in-class initializers or an explicit constructor.

Suggested change

int reportFatalCallCount_;

std::string lastReportedMessage_;

int reportFatalCallCount_{0};

std::string lastReportedMessage_{};

Copilot · 2026-03-08T17:34:48Z

          [this](
-              jsi::Runtime &runtime, const jsi::Value &, const jsi::Value *arguments, size_t) noexcept -> jsi::Value {
+              jsi::Runtime &runtime, const jsi::Value &, const jsi::Value *arguments, size_t count) noexcept -> jsi::Value {
            reportFatalCallCount_++;
+            if (count > 0 && arguments[0].isObject()) {
+              auto obj = arguments[0].getObject(runtime);
+              auto msgVal = obj.getProperty(runtime, "message");
+              if (msgVal.isString()) {
+                lastReportedMessage_ = msgVal.getString(runtime).utf8(runtime);


The host function lambda for reportFatalError is declared noexcept, but the newly added JSI operations (getObject, getProperty, getString) can throw jsi::JSIException. If any of those throw, the process will std::terminate(). Remove noexcept here or wrap the property access in a try/catch to keep the stub safe.

Copilot · 2026-03-08T17:34:49Z

            reportFatalCallCount_++;
+            if (count > 0 && arguments[0].isObject()) {
+              auto obj = arguments[0].getObject(runtime);
+              auto msgVal = obj.getProperty(runtime, "message");
+              if (msgVal.isString()) {
+                lastReportedMessage_ = msgVal.getString(runtime).utf8(runtime);
+              }
+            }


lastReportedMessage_ is only updated when a valid message string is found; otherwise it retains its previous value. Consider clearing it at the start of each reportFatalError call (or explicitly setting it to an empty string when parsing fails) to avoid stale assertions if multiple errors are reported.

Copilot · 2026-03-08T17:34:49Z

+        error.getStack());
+    onTaskError_(runtime, localError);
+  } catch (...) {
+    jsi::JSError fallbackError(runtime, error.getMessage());


In the fallback path you construct jsi::JSError with only error.getMessage(), which drops the original stack trace even though error.getStack() is available as a safe C++ string. Consider using the JSError(Runtime&, message, stack) constructor here so LogBox still gets a stack when reconstruction fails.

Suggested change

jsi::JSError fallbackError(runtime, error.getMessage());

jsi::JSError fallbackError(

runtime,

error.getMessage(),

error.getStack());

Copilot · 2026-03-08T17:34:49Z

+        error.getStack());
+    onTaskError_(runtime, localError);
+  } catch (...) {
+    jsi::JSError fallbackError(runtime, error.getMessage());


The fallback path reconstructs a jsi::JSError with only the message, which discards error.getStack() even though it is already available and safe. Consider using the JSError(Runtime&, message, stack) constructor in the fallback to preserve the original stack trace when Error reconstruction fails.

Suggested change

jsi::JSError fallbackError(runtime, error.getMessage());

jsi::JSError fallbackError(

runtime,

error.getMessage(),

error.getStack());

meta-cla · 2026-03-08T17:37:35Z

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Fix LogBox parsing for cross-runtime jsi::JSErrors

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Copilot AI review requested due to automatic review settings March 8, 2026 17:31

Copilot started reviewing on behalf of Naim08 March 8, 2026 17:31 View session

Copilot AI reviewed Mar 8, 2026

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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 Mar 8, 2026

facebook-github-bot added the Shared with Meta Applied via automation to indicate that an Issue or Pull Request has been shared with the team. label Mar 8, 2026

cortinico mentioned this pull request Jun 4, 2026

Fixes LogBox displaying "Unknown" when an exception is thrown from an… #56000

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Fix LogBox parsing for cross-runtime jsi::JSErrors - #55994

Fix LogBox parsing for cross-runtime jsi::JSErrors#55994
Naim08 wants to merge 1 commit into
react:mainfrom
Naim08:fix/jsi-error-forwarding

Naim08 commented Mar 8, 2026 •

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Summary

Changelog:

Test plan:

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Naim08 commented Mar 8, 2026 •

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