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console.log and Bun.inspect named functions, classes and class instances
from the executable (JSC's calculatedDisplayName / calculatedClassName),
so a class whose name was set with Object.defineProperty, as tsc's
__setFunctionName and the __name helper do for lowered decorated
classes, printed as its temporary binding: `[class _classThis]`,
`_classThis {}`. Node prints the defined name. Check for an own string
`name` data property first, on the function itself and on the
constructor an instance or prototype object is named after; a
`displayName` property keeps its precedence and accessors are not run.
WalkthroughChangesThe bindings now resolve explicitly defined own Explicit Name Resolution
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Updated 5:39 AM PT - Aug 15th, 2026
⏳ @robobun, your commit 70537f6 is still building in
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LGTM — focused inspect-output fix that reads an own name data property before falling back to JSC's calculated name.
What was reviewed:
explicitFunctionNameusesgetDirect+isJSString, so accessors and lazy reification are skipped;displayNameprecedence is preserved by the early-return guard.constructorForClassNameguards with!overridesGetPrototype()beforegetPrototypeDirect(), so no proxy traps or user code run.- String-lifetime handling (
toZigString/toStringRefon a localWTF::Stringbacked by the JSString's StringImpl) matches the adjacentcalculatedClassNamepath exactly. - Tests cover class/instance/nested/extends/subclass/prototype/function, plus negative guards for
displayNameprecedence and that anamegetter is not invoked.
Extended reasoning...
Overview
The PR modifies three name-lookup bindings in src/jsc/bindings/bindings.cpp (JSC__JSValue__getClassName, getNameProperty, getName) so that a name property set via Object.defineProperty is displayed by Bun.inspect/console.log, matching Node.js. Two static helpers are added: explicitFunctionName reads an own string data property named name off a JSFunction, and constructorForClassName locates the constructor for an instance the same way JSObject::calculatedClassName does. Five new test cases in inspect.test.js cover the variant matrix.
Security risks
None. This is display-only formatting for Bun.inspect output. All new lookups are side-effect-free: getDirect does not walk the prototype, invoke getters, or reify lazy properties; getPrototypeDirect is only called when overridesGetPrototype() is false, so proxy traps cannot fire; tryGetValue() is the non-throwing string accessor. The isJSString check filters out GetterSetter slot values, which is what getDirect returns for accessor properties — verified by the "a name accessor is not invoked" test.
Level of scrutiny
Medium. JSC bindings C++ is a memory-sensitive area, but this change is narrow (~30 lines), adds no allocation or exception-throwing calls, and mirrors the existing calculatedClassName path's string-handling pattern (Zig::toZigString on a local WTF::String whose StringImpl is kept alive by the JSString cell stored on the function). No new GC roots, no cross-thread state, no reentrancy into user JS.
Other factors
The tests are well-constructed per the repo's review guidelines: they cover the sibling entry points (class value, instance, nested instance, extends clause, subclass, prototype object, function), assert exact output strings, and include negative guards (displayName still wins; a name getter is not called and the fallback executable name is used instead). The PR description documents that 3/5 tests fail on bun 1.4.0, satisfying the "test fails for the right reason" requirement, and lists the broader test suites that were re-run. The motivating use case (tsc/esbuild decorator lowering via __setFunctionName/__name) is real and common.
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Reproduced on bun 1.4.0: a class whose This is the base of #38757 (decorator lowering), which is in turn the base of #38758; merge order is #38922, #38757, #38758. Builds so far failed only on unrelated lanes: the aarch64 verify-baseline step timing out on a toolchain download, a |
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Actionable comments posted: 1
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Inline comments:
In `@src/jsc/bindings/bindings.cpp`:
- Around line 4903-4914: Update explicitFunctionName and its three callers to
distinguish an absent name property from a present property whose string value
is empty, returning presence separately from the name value so empty names do
not trigger fallback naming. Preserve existing behavior for non-string or
missing names, and add a regression test covering an explicitly empty name.
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src/jsc/bindings/bindings.cpptest/js/bun/util/inspect.test.js
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LGTM — small, side-effect-free change to how inspect resolves function/class names, matching Node's behavior for Object.defineProperty-set names.
What was reviewed:
explicitFunctionName/constructorForClassNameuse onlygetDirect,getPrototypeDirect,displayName(vm),tryGetValue()— none throw, run user JS, or allocate GC objects, so no exception scope or rooting is needed.- The
overridesGetPrototype()guard beforegetPrototypeDirect()mirrors JSC's owncalculatedClassNameand keeps Proxy traps out of the lookup. Zig::toZigString/Bun::toStringRefon a localWTF::Stringfollows the identical pattern already used at each call site's fallback path.- Tests cover class, instance, nested,
extends, prototype, function,displayNameprecedence, and confirm anamegetter is not invoked.
Extended reasoning...
Overview
This PR adds two static helpers in src/jsc/bindings/bindings.cpp (explicitFunctionName, constructorForClassName) and applies them in the three name-lookup bindings the formatter uses (JSC__JSValue__getClassName, JSC__JSValue__getNameProperty, JSC__JSValue__getName). When a function or class has an own name string data property (as set by tsc's __setFunctionName / esbuild's __name for lowered decorated classes), that name is now printed instead of the executable's binding name. Five new tests in test/js/bun/util/inspect.test.js cover the class value, instance, nested instance, extends clause, subclass, prototype, function, displayName precedence, and the guarantee that a name accessor is not invoked.
Security risks
None. This is display-only (console/inspect output). The new code deliberately uses getDirect and getPrototypeDirect, which read own property storage without invoking getters, walking prototypes through traps, or reifying lazy properties. isJSString gates the asString cast, and an accessor name (a GetterSetter cell) fails isJSString and falls through to the existing path — verified by the "a name accessor is not invoked" test. No user code can run from these helpers.
Level of scrutiny
Medium: C++ JSC bindings are memory-safety-sensitive, so I checked each new call against the REVIEW.md native-code checklist. None of the added calls can throw (so no missing RETURN_IF_EXCEPTION), none allocate or hold pointers across a call that can GC or run JS, and there are no refcount or ownership changes. The output-string handoff (Zig::toZigString(localWTFString) in getClassName/getNameProperty, Bun::toStringRef(localWTFString) in getName) is byte-for-byte the same pattern the immediately following fallback lines already use, so any lifetime concern there is pre-existing, not introduced.
Other factors
The change is small (~50 lines), the fallback to the existing calculatedDisplayName/calculatedClassName path is preserved when the explicit name is absent or empty, and displayName precedence is explicitly kept. The PR description states 3 of the 5 new tests fail on 1.4.0 (the two guard tests already passed), and the CI run for 65ad881 was green on every inspect/console/bun:test formatting suite with only unrelated infra timeouts. This is the base of a small stack (#38757, #38758) but stands on its own.
Key the lookup on JSC's own record of the name property having been modified (FunctionRareData::hasModifiedNameForBoundOrNonHostFunction) instead of on the presence of the property: JSC creates the property lazily the first time .name is read, so reading it must not change how a getter or an export default prints. With presence no longer the signal, a name redefined as "" can be honored too and prints the way an anonymous function or class instance already does.
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I reviewed this PR and didn't find any bugs. The change is focused and well-tested, but since it touches JSC C++ bindings (FunctionRareData flags, prototype/constructor resolution) and sits at the base of a stacked series, a maintainer look would still be worthwhile.
What was reviewed:
redefinedFunctionNameuses only non-throwing, non-reentrant JSC calls (getDirect,rareData(),tryGetValue()) and gates onhasModifiedNameForBoundOrNonHostFunction()so a merely reified.namedoesn't change output — covered by the "reading .name does not change the output" test.constructorForClassNameguardsgetPrototypeDirect()behind!overridesGetPrototype(), so proxies/exotic objects fall through to the existingcalculatedClassNamepath.- Null vs. empty distinction (CodeRabbit's comment) is addressed in 5727b0f:
isNull()gates presence, empty falls back to the anonymous rendering, with a dedicated test. Zig::toZigStringon the localWTF::Stringmatches the existingcalculatedClassNamepattern in the same function; the underlyingStringImplis still held by the JSString reached viagetDirect.
Extended reasoning...
Overview
This PR adds two static helpers in src/jsc/bindings/bindings.cpp — redefinedFunctionName and constructorForClassName — and wires them into the three name-lookup bindings the formatter uses (JSC__JSValue__getClassName, JSC__JSValue__getNameProperty, JSC__JSValue__getName). The effect is that Bun.inspect / console.log display a class or function's redefined name property (the shape tsc/esbuild decorator lowerings produce via __setFunctionName/__name) instead of the executable's original binding name. Seven new tests in test/js/bun/util/inspect.test.js cover the class, instance, nested-instance, extends, prototype, function, displayName-precedence, accessor-not-invoked, empty-name, and reified-name-idempotence cases.
Security risks
None identified. This is display-only formatting; no user input reaches an allocation size, syscall, or privilege boundary. All new JSC calls are the non-observable variants (getDirect, getPrototypeDirect, dynamicDowncast, tryGetValue) — no getters or proxy traps are invoked, which the "a name accessor is not invoked" test verifies.
Level of scrutiny
Medium. The change is small (~50 lines) and behavior is confined to inspect output, but it lives in C++ JSC bindings and relies on JSC internals: the FunctionRareData::hasModifiedNameForBoundOrNonHostFunction() flag semantics, the overridesGetPrototype() guard, and the assumption that constructorForClassName mirrors JSObject::calculatedClassName's lookup order. Those are the kind of details a maintainer who knows JSC should confirm. It's also the base of a three-PR stack (#38757, #38758), so a wrong assumption here would propagate.
Other factors
- CodeRabbit's one substantive comment (distinguish empty
namefrom absent) was addressed in commit 5727b0f; the helper now returns null-vs-empty and each caller branches accordingly, with a regression test. - CI on 65ad881 passed all inspect/console/bun:test formatting suites; the reported failures (aarch64 toolchain download timeout,
setInterval.test.jsASAN timeout,bake/deinitialization.test.tsWindows segfault) are unrelated to this diff. - The
Zig::toZigString(redefinedName)lifetime pattern matches the pre-existingZig::toZigString(calculated)a few lines below, so no new lifetime hazard is introduced. - No prior automated review from this bot on the PR.
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Problem
namewas set withObject.definePropertyis displayed under the name of the binding it was created in:Item.nameis"Item"in both. The same applies toBun.inspect, to theextendsclause ([class Child extends _classThis]), to bun:test output and snapshots, and to[Function: ...].__setFunctionName(_classThis, "Item")for standard decorators, and esbuild's--keep-namesand Bun's own lowering (js_parser: keep the inferred name of lowered anonymous decorated class expressions #38757) use the__namehelper, so tsc-compiled decorated classes already display like this in Bun today.JSC__JSValue__getName,JSC__JSValue__getNamePropertyandJSC__JSValue__getClassNameinsrc/jsc/bindings/bindings.cpptake the name from JSC'scalculatedDisplayName()/calculatedClassName(), which consult thedisplayNameproperty and then the executable's name, never thenameproperty.Fix
redefinedFunctionName: when JSC records that the program touched the function'snameproperty (FunctionRareData::hasModifiedNameForBoundOrNonHostFunction, set bydefineProperty, assignment anddelete), read the ownnamestring data property withgetDirect(accessors are not invoked) and display it; adisplayNameproperty still wins, as before. Applied in all three lookups; for instances and prototype objects,constructorForClassNamefinds the constructor the wayJSObject::calculatedClassNamedoes (ownconstructor, else the prototype's) and applies the same rule to it. A name redefined as""is honored too and takes the path an anonymous class already takes ([class (anonymous)],{}); everything else falls through to the existing code.Item.name) and the name node'sutil.inspectprints. Keying on the modified flag rather than on the property existing matters because JSC creates thenameproperty lazily the first time.nameis read (JSFunction::reifyName): keyed on presence, reading.namewould change how a getter (xvsget x) or an anonymousexport defaultprints; keyed on the flag, an untouched function prints exactly as today whether or not its name was reified, and only names the program redefined change output. The lookup has no side effects, which is also why anameaccessor is ignored (node would call it).test/js/bun/util/inspect.test.js, new blocka name defined with Object.defineProperty is displayed: class, instance, nested instance,extendsclause, subclass of the renamed class, prototype object, function, a name redefined as empty, plus guards thatdisplayNamekeeps precedence, that anamegetter is not called, and that reading.nameon a getter, a class, an instance and a property-initialized function leaves their output unchanged. 4 of the 7 fail on bun 1.4.0.inspect.test.js,node/util/util.test.js,custom-inspect,bun-inspect,console-table,console-iterator,expect.test.js,jest-extended, the snapshot tests anderror-name-preservationpass with the debug build (inspect-error.test.jshas two minified-file failures locally that are identical without this change).export default(starDefault); this change adds a check before those fallbacks and composes with them. js_parser: keep the inferred name of lowered anonymous decorated class expressions #38757 (decorator lowering switching to__name) is stacked on this branch so its output displays correctly from the start.Background
_classThisabove), and thenameproperty, which JSC creates lazily from the executable name and whichObject.definePropertycan replace.calculatedDisplayName()is JSC's debugger-oriented helper and reads the executable side;displayNameis a non-standard property JSC and Bun already honor for display.src/jsc/ConsoleObject.rs, andpretty_format.rsfor bun:test) asks these three bindings for the text it prints:get_namefor a function or class value and for the class in anextendsclause,get_class_namefor an instance (Item {}), andget_name_propertyfor JSX tags and some bun:test paths.getDirectreads a property straight out of the object's own property storage: no prototype walk, no getters. JSC materializes a function'snameproperty lazily on first access and, separately, flags in the function'sFunctionRareDatawhen the program has modified it;JSFunction::canAssumeNameAndLengthAreOriginalis JSC's own use of that flag, and this change uses it the same way.