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Updated 7:05 PM PT - Sep 6th, 2026
❌ @robobun, your commit 7583b32 has 3 failures in
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WalkthroughChangesWorker error propagation
Merge Risk: 🟡 Moderate · up to Worker errors may be silently suppressed when a parent registers a logging-only error listener, preventing the expected unhandled-error report and process exit. This behavior should be explicitly resolved or accepted before merge. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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CI on 38e032f (build #81810):
The other annotations are |
… no error listener
An uncaught error or unhandled rejection inside a Web Worker (the global
Worker constructor) with no 'error' listener on the parent Worker object
was silent: nothing printed, the worker closed, the process exited 0.
postMessageErrorToWorkerObject fired an ErrorEvent and stopped; with no
listener the event was dropped.
For Kind::Web, structured-clone the thrown value on the worker side. On
the parent, when the Worker has no error listener and was not terminated,
deserialize it (or build an Error from the message) and hand it to
Bun__reportUnhandledError: process.on('uncaughtException') can observe it,
otherwise it is printed and the exit code becomes 1. A parent that is
itself a worker re-enters the same path one level up. With a listener the
event is dispatched as before. The parent ErrorEvent is now cancelable.
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Inline comments:
In `@src/jsc/bindings/webcore/WorkerMessagingProxy.cpp`:
- Line 459: Update the Web worker error dispatch in WorkerMessagingProxy so the
transferred thrown value is deserialized once, assigned to init.error, and
reused when generating the default error report. Preserve the existing message
handling and dispatch behavior while ensuring ErrorEvent::error() exposes the
original deserialized value.
- Around line 455-466: Update the error-event handling in WorkerMessagingProxy
so the default uncaught-error report is suppressed only when the dispatched
ErrorEvent is defaultPrevented(), rather than merely when an error listener
exists. Retain the existing Web-worker, termination, and parent-propagation
conditions, and use the dispatched event’s cancellation state after
dispatchEvent.
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src/jsc/bindings/webcore/WorkerMessagingProxy.cppsrc/jsc/bindings/webcore/WorkerMessagingProxy.htest/js/web/workers/worker.test.ts
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…ispatches; assert propagation via a listening and a non-listening parent instead
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Inline comments:
In `@test/js/web/workers/worker.test.ts`:
- Line 487: In the worker test immediately before the successful exit-code
assertion, conditionally assert that stderr is empty when exitCode is nonzero,
then retain the existing expect(exitCode).toBe(0) assertion.
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test/js/web/workers/worker.test.ts
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Status after the rebase onto current main (head 7583b32, CI #111884):
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Problem
Worker(the global constructor) whose parent has noerrorlistener is silent: nothing on stderr,closefires, and the process exits 0. The same throw throughnode:worker_threadsprintserror: ...and exits 1.WorkerMessagingProxy::postMessageErrorToWorkerObject(src/jsc/bindings/webcore/WorkerMessagingProxy.cpp) posts a task that dispatches anErrorEventon the parentWorkerand stops. With no listener the event is dropped. Thenode:worker_threadswrapper never hits this because it always registers anerrorlistener that re-emits on itsEventEmitter, whose no-listener path callsBun__reportUnhandledError.Fix
Kind::Web, structured-clone the thrown value on the worker thread and carry it with the message. On the parent, after dispatching the (nowcancelable)ErrorEvent, if theWorkerhad noerrorlistener and was not terminated, deserialize it (or build anErrorfrom the message) and pass it toBun__reportUnhandledError.process.on("uncaughtException")can observe it, otherwise it is printed and the exit code becomes 1. When the parent is itself a worker, this is an uncaught error in that worker, so the report repeats one level up.node:worker_threadscontract, and what the existing docs example and tests rely on). The HTML spec instead suppresses only onpreventDefault(). That stricter rule is a one-line change if wanted, see Notes.test/js/web/workers/worker.test.ts"error event" (9 new tests: four producers with no listener,uncaughtExceptioncapture, nested worker to main, listener present,terminate()race,worker_threadscontrol).Background
WorkerMessagingProxyis the one object shared between the parent-sideWorkerand the thread running its global scope. Worker-thread events reach the parent as tasks posted to the parent'sScriptExecutionContext.web_worker.rson_unhandled_rejectionis the worker VM's last-resort handler for both uncaught exceptions and unhandled rejections. It formats the error, callsWebWorker__dispatchError(which lands inpostErrorToWorkerObject), runs the worker'sexithandlers, and arms termination.Bun__reportUnhandledErrorroutes a value intoVirtualMachine::uncaught_exceptionon the calling thread:uncaughtExceptionlisteners first, then print and exit code 1.Notes
preventDefault()does not stop the report. This PR keys on listener presence instead, becauseworker.addEventListener("error", ...)withoutpreventDefault()is the documented way to handle a worker error indocs/runtime/workers.mdxand in existing tests, and flipping that would turn those into process-fatal errors. Switching to the spec rule ishadListener->event->defaultPrevented()in the posted task plus doc and test updates.closecode for a mid-life unhandled rejection is still 0 (the rejection path does not set the worker's exit code). That is independent of this change; the parent now prints the rejection and exits 1 either way.terminate()gate mirrorsWorker::dispatchEvent: an error task that lands afterterminate()or after the proxy is closing is neither dispatched nor reported.Worker::dispatchErrorWithMessage; Worker / worker_threads: WebCore-shaped lifetimes, joined threads, one ordered VM teardown #37075 moved that code intoWorkerMessagingProxy, so the branch was rebased and the change re-applied there.