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WebWorker::create pointed the transpiler log at a local Log and then moved that Log into a scopeguard. The resolver wrote its error into the moved-from slot. The guarded log stayed empty, so Log::to_js returned undefined and the Worker constructor threw TypeError: undefined. Point the transpiler at the log inside the guard. Report a preload failure as a plain string with the same wording as --preload on the CLI.
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Updated 2:27 AM PT - Sep 6th, 2026
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Included review availability: Your plan provides up to 10 included reviews per hour; 1 remains after this review. WalkthroughWorker specifier resolution now distinguishes entry points from preloads. Preload failures return formatted synchronous errors. Entry-point failures retain existing JavaScript-log handling. Temporary transpiler logging restoration is guarded, and tests cover preload options and termination stress rounds. ChangesWorker resolution
Suggested reviewers: Merge Risk: 🔵 Low · up to Worker preload failures now produce a targeted module-resolution error, but formatting compatibility with the established CLI preload error contract remains open and should be confirmed before release. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@src/jsc/web_worker.rs`:
- Line 1336: Update resolve_entry_point_specifier to format preload resolution
errors with err.name() and bun_core::fmt::format_json_string_latin1(str),
matching the existing CLI formatter behavior and preserving escaped quoted
specifiers. Add a regression case for a preload specifier containing a quote,
then run the worker test suite.
In `@test/js/web/workers/worker.test.ts`:
- Around line 61-66: Parameterize the duplicate preload-resolution tests using
describe.each(), supplying both array and string preload shapes as test cases
while preserving the shared Worker construction and expected ModuleNotFound
assertion.
- Around line 61-66: Update both Worker constructor assertions for the missing
preload path to verify the thrown error is a TypeError and retains the expected
message, rather than checking only the message string. Apply this consistently
to both the array and string forms of the preload option.
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src/jsc/web_worker.rstest/js/web/workers/worker.test.ts
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LGTM — both earlier nits are addressed (the change-narrating comment is gone, and the specifier is now quoted via bun_core::fmt::quote, with the new "quote" test case covering escaping).
Checked the reordered guard: the Log is owned by the scopeguard from construction, set_log(&raw mut *temp_log) installs a pointer into the guard's storage only after the guard is armed, and the drop closure restores prev_log before the guarded Log drops — no window where the transpiler holds a dangling log. Also verified quoted_writer routes the quote-containing specifier through write_json_string, so the test's JSON.stringify expectation lines up.
Extended reasoning...
Overview
The PR fixes new Worker(entry, { preload: ["./missing.js"] }) throwing TypeError: undefined by (1) reordering the temp-log setup in WebWorker::create so the bun_ast::Log lives inside the scopeguard from the start rather than being moved into it after set_log installed a pointer to the pre-move stack slot, and (2) adding a SpecifierRole enum so resolve_entry_point_specifier can produce a preload-specific message that names the specifier, matching the CLI --preload wording in jsc_hooks.rs. A describe.each in worker.test.ts covers string vs array preload and a specifier containing a double-quote.
Security risks
None. This is error-message plumbing on a resolve-failure path; no new parsing of untrusted data, no privilege boundaries, no allocation sizing driven by external input. The quoting helper is the existing repo primitive.
Level of scrutiny
Moderate for the unsafe scopeguard reorder, low for the rest. I traced the guard lifecycle: prev_log is captured, the guard is constructed owning a fresh Log, temp_log = &mut *restore borrows the guard's payload, and only then is set_log(&raw mut *temp_log) called — so the guard is armed before the pointer is published, satisfying REVIEW.md's "arm Drop/RAII guard before any fallible call". On drop, set_log(prev_log) runs before drop(log), so the transpiler never observes a freed log. The SpecifierRole::Preload arm builds an owned BunString via clone_utf8 and returns None, matching the existing Err(_) arm's contract.
Other factors
Both optional comments from my earlier pass were acted on in commits 99dbf72 and 80ff175: the narrating comment at the guard site was replaced with a SAFETY line stating the invariant, and the hand-rolled \"{}\" was swapped for bun_core::fmt::quote(str). I confirmed quoted_writer (fmt.rs:1460) dispatches to js_printer::write_json_string when the input contains a quote, so the test's JSON.stringify(specifier) expectation for './has a "quote".js' will match. The coderabbitai threads on this revision were resolved by a non-author. Exit reason was dry_streak. Small, focused, well-tested — approving.
On a debug ASAN build the fs.readFile churn test and the 96-worker resolve-failure test run at 3 to 6.5 seconds, against the 5 second default. Use the same isDebug timeout that the un-awaited import() test in the same block already has. Release builds are unchanged.
…g their timeout A worker takes about 150ms to start on a debug ASAN build. The 96-worker resolve-failure test and the 48-worker fs.readFile churn test ran at 3 to 6.5 seconds against the 5 second default. Run 4 rounds instead of 12 on debug builds. Release builds run the same workload as before.
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LGTM — all earlier feedback is addressed: the specifier is now quoted via bun_core::fmt::quote, the narrating comment is gone, and the two slow terminate() tests shrink their round count under debug builds instead of raising a per-test timeout.
What was reviewed:
- The scopeguard reorder in
WebWorker::create—set_lognow points at the guard's own slot after the guard is armed, and the drop closure restoresprev_logbefore the guardedLogdrops, so the raw pointer is never left dangling. bun_core::fmt::quoteroutes throughwrite_json_stringwhen the input contains a quote, so the test'sJSON.stringify(specifier)expectation matches for both fixture specifiers.isDebugwas already imported in worker.test.ts; the remainingisDebug ? 30_000 : 5_000at line 669 is pre-existing and untouched by this diff.
Extended reasoning...
Overview
The PR fixes new Worker(entry, { preload: [...] }) throwing TypeError: undefined when a preload specifier fails to resolve. Two changes in src/jsc/web_worker.rs: (1) the temporary bun_ast::Log is now constructed directly inside the scopeguard and the transpiler is pointed at that slot afterward, so the resolver writes to the same Log the error path reads (previously it wrote to a moved-from stack local); (2) a SpecifierRole enum lets resolve_entry_point_specifier emit "{err} resolving preload {quoted}" for preloads while leaving the entry-point path unchanged. test/js/web/workers/worker.test.ts gains a describe.each over both preload shapes (string and array) with two specifiers (one containing a "), asserting the exact TypeError message; two unrelated terminate()-race stress tests now scale rounds down under isDebug.
Security risks
None. No user-controlled input reaches a new trust boundary; the change only reorders existing raw-pointer log-swap code and formats an error string. The specifier echoed into the error message is quoted through the repo's JSON-escaping helper, so no injection into log output.
Level of scrutiny
Moderate. The unsafe block manipulating (*parent).transpiler.log was already present; this PR reorders it into a shape that is strictly more correct (guard armed before the pointer swap, set_log targets memory that outlives the pointer's use, drop closure restores prev_log before the guarded value drops). I traced bun_core::fmt::quote → quoted_writer → write_json_string to confirm the test's JSON.stringify expectation matches for both the plain and quote-containing fixture specifiers.
Other factors
This is the fifth review pass. Every earlier inline comment I left has a corresponding fix commit: 99dbf729 (quote helper), a906c193 (comment trim), and 39553746 (workload shrink replacing the timeout bump). No third-party CHANGES_REQUESTED remain; the coderabbitai threads were resolved by a non-author. Bug hunter exited on dry_streak with zero findings. The change is small, well-tested, and follows REVIEW.md's guidance on error wording, quoting, RAII ordering, and test workload scaling.
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Status: the diff is complete and reviewed. Three CI runs so far (110823, 110853, 110866) were each red only on tests this PR does not touch: quic-endpoint.test.ts (lsquic leak, x64-asan), spawn-stdin-destroy.test.ts (EPIPE, Windows x64), fetch-leak.test.ts (x64), and regression/issue/10887.test.ts (test runner worker stalled, alpine). Each is reported separately. test/js/web/workers/worker.test.ts passed on every lane in all three runs. Ready for a maintainer. |
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Problem
new Worker("./worker.ts", { preload: ["./missing.js"] })throwsTypeError: undefined. The message is the literal string "undefined". It names no specifier and no cause.WebWorker::create(src/jsc/web_worker.rs:310). It points the transpiler log at a localLog, then moves thatLoginto ascopeguard. The resolver writes theModuleNotFounderror into the moved-from slot. The guarded log stays empty,Log::to_jsreturnsundefinedfor an empty log, and the C++ side throws that as the message.Fix
Loginside the guard first. Point the transpiler at that slot. The resolver and the reader now share oneLog.TypeError: ModuleNotFound resolving preload "./missing.js". This is the same wording thatbun --preloaduses on the CLI (src/runtime/jsc_hooks.rs). A newSpecifierRoleargument tellsresolve_entry_point_specifierwhich message to produce. The entry point path is unchanged.test/js/web/workers/worker.test.ts(one new test in thepreloadblock, stock bun fails it with message "undefined"). The rest of that file passes.Background
Workerconstructor resolvespreloadspecifiers on the parent thread, insideWebWorker::create. The entry point itself resolves later, on the worker thread, inspin().Transpiler::resolve_entry_pointreports a failure by appending to the log thattranspiler.logpoints at. It returns only an error tag. So the caller must read that log to get the message.WebWorker::createswaps in a temporary log for the duration of the call so that a preload error does not land in the parent VM's log. Ascopeguardrestores the old pointer on every return path.Notes
Repro on 1.4.2 and 1.4.3:
The string form
preload: "./load-sentry.js"behaves the same both before and after.#32369 found the same root cause in June. It was never rebased and now conflicts with main. This PR replaces it. It also drops the
BuildMessage: ... (entry point)prefix that #32369 would have shown for a preload.Two tests in the same file,
terminate() while fs.readFile completions keep arrivingandterminate() while the entry point fails to resolve, run at 3 to 6.5 s on a debug ASAN build, against the 5 s default timeout. They time out with and without this change. Both now run 4 rounds instead of 12 on debug builds. Release builds run the same workload as before. #37374 reworks those tests more thoroughly.[human-review] gate passed · iteration 1 · 2 files touched
fails on main (without fix)
passes on PR (with fix)
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gate history · 1 passed · 1 rejected · iteration 1
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