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Updated 3:54 PM PT - Aug 16th, 2026
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Included review availability: Your plan includes up to 5 reviews per rolling hour; 1 remains after this review. WalkthroughChangesBun SQL lazy-property loaders no longer report pending exceptions in debug builds. Property and prototype inspection clears lookup exceptions and handles missing results. Regression tests cover throwing traps and lazy initializers. Inspection exception safety
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In `@test/js/bun/util/inspect.test.js`:
- Around line 933-941: Update the run function to consume proc.stderr
concurrently with proc.stdout and proc.exited, and include the drained stderr
result in the Promise.all handling so every piped child-process stream is read.
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Applied in eedb6d6: the fixture runner now reads stderr alongside stdout and the exit code, so a child that writes a lot to stderr cannot block on the pipe. The three tests still fail on the unfixed build (USE_SYSTEM_BUN=1) and pass with the fix. |
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I reviewed this and didn't find any bugs. Since it touches JSC exception handling in the Bun.inspect property-walk path and removes a debug-only error-reporting hook, a human look would still be worthwhile.
What was reviewed:
getPropertySlotreorder matches the existing pattern inforEachPropertyOrdered(bindings.cpp:5814-5817).getPrototypeempty-check +CLEAR_IF_EXCEPTIONmirrors the fast path a few lines up (bindings.cpp:5601-5611).- Removed
#if BUN_DEBUGblocks indefaultBunSQLObject/constructBunSQLObject— no other lazyBun.*callback reports load failures that way, andRETURN_IF_EXCEPTIONon the next line still propagates. - Tests spawn children, drain stdout/stderr/exit concurrently, assert exact stdout before exit code.
Extended reasoning...
Overview
Three files: src/jsc/bindings/bindings.cpp reorders CLEAR_IF_EXCEPTION to run before the continue when getPropertySlot returns false, and adds an empty-value check + exception clear after getPrototype in the slow-path prototype walk. src/jsc/bindings/BunObject.cpp drops two debug-only reportUncaughtExceptionAtEventLoop calls that ran user JS on top of a pending exception. test/js/bun/util/inspect.test.js adds three subprocess-based crash regressions.
Security risks
None identified. The change swallows exceptions from Proxy get/getPrototypeOf traps during formatting, which is the existing intent (the CLEAR_IF_EXCEPTION was already there, just ordered wrong) and matches how the fast path and forEachPropertyOrdered already behave. No new user-controlled input reaches native code.
Level of scrutiny
Moderate-to-high. This is C++ JSC bindings on the console.log/Bun.inspect hot path, in the exception-handling category the repo flags as most-blocked. The individual hunks are small and each mirrors an existing pattern in the same file, but the interaction between stale exceptions, lazy property reification, and the debug-only SQL hook is subtle enough (the PR description walks through two separate assertion trips) that a maintainer familiar with this loop should confirm the reasoning.
Other factors
The bug hunter found nothing. CodeRabbit's stderr-drain comment was addressed in eedb6d6. The PR description is thorough, cites BUN_JSC_validateExceptionChecks=1 passing, and explicitly calls out the one remaining sibling site (napi_get_all_property_names) as out of scope. Tests follow harness conventions (it.concurrent, bunEnv, await using, stdout asserted before exit code) and the third test's fragile assumption (Bun.$ being the first lazy property, Archive following it) is documented in a comment.
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Closing as a duplicate of #29642, which fixes the same stale-exception / getPrototype null dereference in forEachPropertyImpl (the same two hunks in bindings.cpp) and now also carries the BunObject.cpp debug-block removal and the consolidated regression tests. |
…p or getPrototypeOf throws during the property walk (#29642) ### Problem - `Bun.inspect()`, `console.log()` and `expect()` failure output crash with `Segmentation fault at address 0x5` (debug builds: UBSan "member call on null pointer of type 'JSC::JSCell'" in `JSCJSValueCell.h`) when a property lookup throws while an object is being formatted. Release repro: ```js const proto = new Proxy({ a: 1 }, { getPrototypeOf() { throw new Error("boom"); } }); console.log(Object.create(proto)); ``` and likewise with a Proxy whose `get` trap (or a getter reached through a Proxy) throws for one property. - The same happens with a lazily initialized property of the `Bun` object whose initializer throws (fuzzer sample: `globalThis.Symbol` replaced, then `Bun.inspect(Bun)`; the builtin behind `Bun.$` calls `Symbol("cwd")`). Release builds print `Bun` with most of its properties missing (72 of 115 on the shipped build); debug builds abort with `ASSERTION FAILED: Unexpected exception observed` / `Symbol is not a function. (In 'Symbol("cwd")' ...)` when the next lazy property is built. - Plain-JavaScript variant of the same leak: `console.log` of a module namespace during an import cycle, when one export is still in its temporal dead zone, throws `ReferenceError: Cannot access 'x' before initialization` out of `console.log` (the stale exception is picked up while the next export is formatted). `util.inspect` prints such an export as `<uninitialized>`. - Cause, in the slow path of `JSC__JSValue__forEachPropertyImpl` (`src/jsc/bindings/bindings.cpp`): - `object->getPropertySlot()` reports a throwing Proxy trap, a throwing lazy initializer or a TDZ namespace export as "not found" with the exception still pending, and the loop `continue`d before the `CLEAR_IF_EXCEPTION` below it. The following lookups and formatting callbacks then run with that exception pending (the dropped properties, the rethrown `ReferenceError`, the debug assertion). - When the walk moves to the next prototype, `iterating->getPrototype(globalObject).getObject()` runs `getObject()` on the empty `JSValue` that `getPrototype` returns when it threw (either because of the stale exception above or because the `getPrototypeOf` trap itself throws). The empty value passes `isCell()`, so this reads the type byte of a null cell: the fault at address 5. - `napi_get_all_property_names` (`src/jsc/bindings/napi.cpp`, descriptor filter loop) has the same `getPrototype().getObject()` chain after an unchecked `getOwnPropertyDescriptor`, so a Proxy trap throwing there returned `napi_ok` with an exception pending in own-only mode and segfaulted in include-prototypes mode. - `defaultBunSQLObject` / `constructBunSQLObject` (`src/jsc/bindings/BunObject.cpp`) had a debug-only block that handed a sql module load failure to `reportUncaughtExceptionAtEventLoop` while the exception was still pending on the VM, so `globalThis.Symbol = NaN; Bun.sql` (and the fuzzer sample above, once the walk gets past `Bun.$`) aborted debug builds with `ASSERTION FAILED: ... object->structure() == this` in `Structure::storedPrototype` instead of throwing. ### Fix - `bindings.cpp`: clear the exception after `getPropertySlot` regardless of its result, which is what the ordered variant `JSC__JSValue__forEachPropertyOrdered` already does; read the next prototype into a `JSValue`, clear the exception and stop the walk when it is empty. (An earlier revision also held the prototype being walked under an `EnsureStillAliveScope`; dropped, since the raw pointer is used after every call into JS in the loop body and so is live across them anyway.) - Behaviour change to note: a property whose lookup throws is now left out of the output instead of the whole `console.log` / `Bun.inspect` call throwing or crashing. For TDZ namespace exports this differs from `util.inspect`'s `<uninitialized>`; printing that marker would be a formatter feature on top of this fix and is not attempted here. - `napi.cpp`: check for an exception after `getOwnPropertyDescriptor` and after `getPrototype` and return `napi_pending_exception`, which is what Node returns for these cases. - `BunObject.cpp`: drop the debug-only report. The exception is propagated to the reader by the `RETURN_IF_EXCEPTION` right below it, so debug builds now behave like release builds (`Bun.sql` throws). - Why this is the right place: the formatter deliberately swallows errors thrown by individual properties (getters, traps) and prints the rest of the object; these two sites were the only ones in the walk that acted on a "not found" result or a prototype value before clearing the exception that produced it. Skipping just the property (or stopping at just the prototype) whose lookup threw is the existing behaviour for every other throw site in this function. - Verification: - `test/js/bun/util/inspect.test.js`, "Bun.inspect when a property lookup throws" (5 spawned cases): a Proxy `get` trap, a getter behind a Proxy, a `getPrototypeOf` trap, a throwing lazy `Bun` property, and a two-file import cycle with a TDZ export. Without the fix (shipped release build and an unfixed debug build) all five fail: the Proxy children segfault / fail UBSan, the `Bun` child prints `[false,false,...]` on release and aborts on debug, the cycle child exits 1 with the `ReferenceError`; with it each prints everything except the one property whose lookup threw. - `test/js/bun/util/BunObject.test.ts`, "a lazy property whose builtin fails to load throws from the read": `Bun.$` / `sql` / `SQL` / `postgres` with `Symbol` broken throw a `TypeError` on two consecutive reads. Aborts on an unfixed debug build (the `BunObject.cpp` hunk); passes on release either way, as the removed block is debug-only. The fixture builds `process.env` before breaking `Symbol` because the `$` builder reads it, and building it on Windows reifies another `Bun` property mid-lookup, which on a Windows debug build would hit the separate `storedPrototype` assertion that #37001 fixes (verified on Linux only). - `test/napi/napi.test.ts`: `getOwnPropertyDescriptor` trap throwing in own-only and include-prototypes mode (compared against Node), and a `getPrototypeOf` trap that throws on the second call so the check after `getPrototype` is the one that fires. - Repros above and the tests also run clean under `BUN_JSC_validateExceptionChecks=1`. ### Background - `forEachPropertyImpl` is the property walk behind Bun's native formatter. It collects the property names of the object and of up to five prototypes, looks each one up through the original object with `getPropertySlot`, and hands the value to a callback that formats it. Errors thrown by individual properties are swallowed on purpose so that one bad getter does not make `console.log` throw. - A JSC exception is "pending" state on the VM, not C++ unwinding. A function that throws returns a failure value (`false`, or the empty `JSValue`) and leaves the exception on the VM; until something clears or rethrows it, most JSC entry points return early as soon as they are called, and debug builds assert when a function that did not throw is observed returning with an exception pending. `CLEAR_IF_EXCEPTION` drops the pending exception. - The empty `JSValue` (`JSValue()`) is encoded as 0. `isCell()` is true for it, so `getObject()` on it dereferences a null cell pointer rather than returning null; callers have to test the value itself first. - Lazy properties of the `Bun` object are entries in a static property table whose value is produced by a builder the first time the property is read (`PropertyCallback`). Some builders evaluate built-in JavaScript modules (the shell for `Bun.$`, the sql module for `Bun.sql`), so they can throw when that module fails to evaluate, and JSC reports that to the reader as "property not found" plus a pending exception. ### Consolidated duplicates Found repeatedly by the fuzzer (fingerprint `d678cafe50a2ad6e`). Earlier round, folded in here in April: #29071 #28991 #28919 #28918 #28882 #28854 #28530 #28325. This round, closed in favour of this PR: #30099 #30245 #37160 #37175 #37213 #37256 #37428 #38700 #38921 #39363 #39365 #39380 #39412 #39413 (and #39411, closed earlier). The `BunObject.cpp` hunk and the `BunObject.test.ts` test come from #30245 / #37428; the same hunk is also part of #37001, which fixes the underlying `storedPrototype` assertion in JSC. Related fixes that are not part of this bug and stay open on their own: #39382 (a custom inspect function when `node:util` fails to load), #37202 (`util.isError` with a throwing `getPrototypeOf` trap), #37331 (`forEachPropertyOrdered` when the callback throws), #37001 (stale structure in `JSObject::getPropertySlot`), #32263 (additional checks in the same napi loop). <!-- robobun:evidence:begin --> --- **no test proof** · iteration 11 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/js/bun/util/inspect.test.js test/napi/napi.test.ts <!-- robobun:evidence:end --> --------- Co-authored-by: robobun <robobun@users.noreply.github.com>
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What does this PR do?
Fixes a crash in the object formatter used by
Bun.inspect/console.logwhen looking up a property throws.JSC__JSValue__forEachPropertyImpl(bindings.cpp) walks the property names it collected and callsgetPropertySlotfor each one. When that lookup throws (a Proxygettrap in the prototype chain, or a lazy property on a static table whose initializer throws),getPropertySlotreturnsfalsewith the exception still pending, and the loop hitcontinuebefore reaching theCLEAR_IF_EXCEPTIONon the next line. The next property was then looked up with a stale exception on the VM:Bun.Archivein the fuzzer case, right afterBun.$whose initializer fails) tripsto_js_host_call's "no exception" assertion, since it returned a value while an exception was pending. This is the Fuzzilli crash.Bun.inspect(Bun)silently drops most of the object.The fix is to clear the exception before checking the return value, which is what
JSC__JSValue__forEachPropertyOrderedalready does a few lines further down.The end of the same loop did
iterating->getPrototype(globalObject).getObject(). A Proxy in the chain whosegetPrototypeOftrap throws returns an emptyJSValuethere, andgetObject()on the empty value reads through a null cell pointer. This segfaults a release build today (Segmentation fault at address 0x5):The stale-exception variant of the
gettrap case reaches the same line and segfaults the same way, so both hunks are needed for the Proxy repros. The walk now clears the exception and stops at that point, like the fast path already does for prototype traps.With the loop fixed, the original repro (
globalThis.Symbol = {}; Bun.inspect(Bun)) got further and hit a second assertion:defaultBunSQLObject/constructBunSQLObjecthad a debug-only block that calledreportUncaughtExceptionAtEventLoopwhile the exception from loading thesqlmodule was still pending. That runsprocess._fatalExceptionlookups and listeners on top of a pending exception, which tripsStructure::storedPrototypeinsidegetPropertySlotin debug builds. The block is removed; the error is already thrown to whoever accessesBun.sql, and no other lazyBun.*property reports its load failure this way.Two related things this PR does not change, both being handled separately: the same
getPrototype(...).getObject()pattern innapi_get_all_property_names(needs a native addon to reach), and them_utilInspectFunctionlazy initializer in ZigGlobalObject.cpp, which returns without setting anything whennode:utilfails to load, soLazyPropertyaborts (RELEASE_ASSERT) the first time a value with a custom inspect function is formatted. The first CI run hit that second one on Windows, whereBun.envhas a custom inspect function: with the walk fixed,Bun.inspect(Bun)now reachesBun.env, andnode:utilcan no longer be loaded onceSymbolis gone. It reproduces on main on every platform withconst c = Symbol.for("nodejs.util.inspect.custom"); globalThis.Symbol = {}; Bun.inspect({ [c]() { return "x"; } }).How did you verify your code works?
Three new tests in
test/js/bun/util/inspect.test.js("property lookup throws while formatting"). Each spawns a child so a crash shows up as a failed assertion rather than taking the runner down:gettrap on a prototype Proxy throws: unfixed build segfaults (empty stdout), fixed build prints{}.getPrototypeOftrap on a prototype Proxy throws: unfixed build segfaults, fixed build printsa: 1and stops walking the chain there.globalThis.Symbol = {}thenBun.inspect(Bun)): unfixed release build printsfalse truebecauseArchiveis dropped, unfixed debug build asserts, fixed build printstrue true. The fixture loadsnode:utilbefore clobberingSymbolso it stays clear of the unrelated util.inspect abort described above; it still printsfalse trueon the unfixed build with that line in place (checked on Linux and Windows).All three fail with
USE_SYSTEM_BUN=1 bun testand pass withbun bd test, on Linux and on a Windows x64 debug build. The fuzzer script, the minimized repros above, and the existing inspect / console / util.inspect tests pass on the debug build, also withBUN_JSC_validateExceptionChecks=1.no test proof · iteration 1 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/js/bun/util/inspect.test.js