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Updated 9:16 AM PT - Jun 27th, 2026
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WalkthroughRestrict matcher registration to own enumerable string-keyed properties (skip symbol keys), add tests for plain-object and symbol/prototype edge cases, expose String.isSymbol, add WTFStringImpl.isSymbol, and avoid treating empty symbol-backed WTF strings as Empty in Bun string wrapping. Changes
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Actionable comments posted: 1
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@test/js/bun/test/expect-extend.test.js`:
- Around line 375-383: The test titled "works on classes" no longer uses a class
(it defines a plain object `matchers`) so update the test to match intent:
either rename the test title to reflect that it uses a plain object (e.g.,
"works on plain objects") or change the test body to actually use a class
instance that has an own enumerable matcher (for example create a class and
assign `_toBeBar2` as an own property on the instance) before calling
`expect.extend(matchers)` and `expect(123)._toBeBar2();` so the test and the
code paths (`matchers`, `expect.extend`, `_toBeBar2`) are consistent.
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src/bun.js/test/expect.zigtest/js/bun/test/expect-extend.test.js
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Found 2 issues this PR may fix:
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⚠️ Outside diff range comments (1)
test/js/bun/test/expect-extend.test.js (1)
358-372: 🧹 Nitpick | 🔵 TrivialConsider adding negative assertion for inherited matchers.
The test verifies that own property
_toBeBazis registered, but doesn't assert that inherited_toBeBaris not available. Adding a negative check would strengthen coverage of the own-properties-only behavior:expect(() => expect(123)._toBeBar()).toThrow();🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@test/js/bun/test/expect-extend.test.js` around lines 358 - 372, Add a negative assertion to ensure inherited matcher _toBeBar is not registered: after calling expect.extend(Foo) and the positive check for _toBeBaz, verify that invoking _toBeBar on an expectation for 123 throws; update the test using the existing symbols (Bar, Foo, expect.extend, _toBeBaz, _toBeBar) so it asserts that only own properties are registered.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Outside diff comments:
In `@test/js/bun/test/expect-extend.test.js`:
- Around line 358-372: Add a negative assertion to ensure inherited matcher
_toBeBar is not registered: after calling expect.extend(Foo) and the positive
check for _toBeBaz, verify that invoking _toBeBar on an expectation for 123
throws; update the test using the existing symbols (Bar, Foo, expect.extend,
_toBeBaz, _toBeBar) so it asserts that only own properties are registered.
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test/js/bun/test/expect-extend.test.js
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LGTM — one-line fix with clear rationale, matching Jest behavior, and a regression test.
Extended reasoning...
Overview
This PR modifies src/bun.js/test/expect.zig (one line: own_properties_only = false → true) and updates test/js/bun/test/expect-extend.test.js to reflect the behavior change and add a regression test.
Security risks
None. This is a property iteration scope fix in the test framework, not touching auth, crypto, or permissions.
Level of scrutiny
Low. The change is minimal and mechanical — flipping a boolean flag to match the documented Jest behavior (Object.keys() iterates only own enumerable properties). The root cause (crash from releaseAssertNoException triggered by inherited non-function properties) is well-explained and the fix is the obvious correct solution.
Other factors
The test updates correctly adjust two existing tests that previously relied on the (incorrect) inherited-property behavior, and a new regression test directly exercises the crash scenario. No CODEOWNER-sensitive paths are touched.
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LGTM — both prior concerns (own symbol-keyed property handling and missing negative assertion) are fully addressed.
Extended reasoning...
Overview
This PR fixes a crash in expect.extend by switching JSPropertyIterator from own_properties_only: false to true, then additionally skips symbol-keyed own properties with an explicit continue guard. Supporting isSymbol() is added to WTFStringImplStruct and String. Zig cast syntax is also corrected for compilation correctness.
Security risks
None. This is a test-framework runtime fix with no auth, crypto, or privilege changes.
Level of scrutiny
Low-to-medium. The change is small and focused. The own_properties_only toggle and the symbol-skip guard are both necessary and correct to match Jest Object.keys() semantics. The isSymbol() implementation mirrors the existing is8Bit() pattern using the same m_hashAndFlags bitmask from WTFStringImpl.h.
Other factors
Both prior blocking comments are resolved: the symbol-keyed own property case has an explicit guard and regression test, and the works on prototypes test now includes the negative assertion. CI failures in bundler_compile.test.ts appear to be pre-existing flaky/infra issues unrelated to this PR.
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Addressed claude review: fixed edge case where |
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LGTM — all previously raised issues have been addressed.
Extended reasoning...
Overview
This PR fixes expect.extend to iterate only own enumerable properties (own_properties_only: true), matching Jest's Object.keys() behavior. It touches expect.zig, BunString.cpp, string.zig, wtf.zig, and the test file.
Issues addressed
Three rounds of review feedback have been fully resolved:
- Core fix —
own_properties_onlyflipped totrue, stopping inherited-property iteration that caused crashes viareleaseAssertNoException. - Symbol-keyed own properties —
if (matcher_name.isSymbol()) continue;added in the Zig loop, matching Jest'sObject.keys()(string-keys-only) behavior. - Empty-description symbol edge case —
BunString.cppnow checkswtfString->isEmpty() && !wtfString->isSymbol()before returningBunStringTag::Empty, preserving the symbol flag forSymbol()andSymbol("")whose description hasm_length == 0. Without this, theisSymbol()guard in Zig would silently miss those symbols.
Test coverage
Tests now cover: own-property registration, negative assertion that inherited matchers are excluded, Symbol.toStringTag on prototype, and own symbol-keyed properties including Symbol() and Symbol("") edge cases.
Security risks
None — this is test-framework code with no auth, crypto, or permission-sensitive paths.
Level of scrutiny
Moderate. The change is small and targeted, but it touches C++/Zig interop around WTF string internals. The BunString.cpp change is a one-liner guard that is straightforward and consistent with how the rest of the codebase treats symbols (e.g., isCrossThreadShareable already calls impl->isSymbol()). The Zig @as syntax fixes are mechanical correctness improvements.
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Actionable comments posted: 2
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@src/bun.js/bindings/BunString.cpp`:
- Around line 257-262: The toString(WTF::StringImpl*) overload preserves empty
Symbol() as BunStringTag::WTFStringImpl while toStringRef(WTF::StringImpl*)
still maps the same input to BunStringTag::Empty, causing inconsistent BunString
states; make toStringRef mirror toString (return BunStringTag::WTFStringImpl for
empty-symbol StringImpl*) and update any WTF-backed JS/zero-copy helpers and
assertions in this file that assume BunStringTag::WTFStringImpl is never empty
(relax those asserts or handle the empty-symbol case) so both helpers and
assertions treat empty-symbol StringImpl* consistently.
In `@src/bun.js/test/expect.zig`:
- Around line 939-948: The iterator is materializing values for symbol keys
because .include_value = true causes iter.next() to fetch values before the code
checks matcher_name.isSymbol(); change the logic to avoid prefetching by setting
.include_value = false in the JSPropertyIterator initializer and then, inside
the loop, call iter.next(), check if matcher_name.isSymbol() and continue for
symbols, and only for non-symbol names fetch the matcher function value from the
object (e.g., by reading the property from globalThis / using the appropriate
getProperty/getPropertySlot API) before assigning to matcher_fn; update
references to jsc.JSPropertyIterator, .include_value, iter.next(),
matcher_name.isSymbol(), and iter.value accordingly.
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src/bun.js/bindings/BunString.cppsrc/bun.js/test/expect.zigsrc/string.zigsrc/string/wtf.zigtest/js/bun/test/expect-extend.test.js
| BunString toString(WTF::StringImpl* wtfString) | ||
| { | ||
| if (wtfString->isEmpty()) | ||
| if (wtfString->isEmpty() && !wtfString->isSymbol()) | ||
| return { BunStringTag::Empty }; | ||
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| return { BunStringTag::WTFStringImpl, { .wtf = wtfString } }; |
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Don't preserve empty symbols in only one toString overload.
toString(WTF::StringImpl*) now keeps Symbol() / Symbol("") as BunStringTag::WTFStringImpl, but toStringRef(WTF::StringImpl*) still maps the same input back to .Empty, and the WTF-backed JS/zero-copy helpers in this file still assert that .WTFStringImpl is never empty. So the same empty-symbol StringImpl* now has two incompatible BunString states depending on which helper is used, and one path still loses the symbol bit entirely.
Consistency fix sketch
BunString toStringRef(WTF::StringImpl* wtfString)
{
- if (wtfString->isEmpty())
+ if (wtfString->isEmpty() && !wtfString->isSymbol())
return { BunStringTag::Empty };
wtfString->ref();
return { BunStringTag::WTFStringImpl, { .wtf = wtfString } };
}- ASSERT(refCount > 0 && !bunString->impl.wtf->isEmpty());
+ ASSERT(refCount > 0 && (!bunString->impl.wtf->isEmpty() || bunString->impl.wtf->isSymbol()));Apply the same invariant relaxation to the other WTF-backed assert sites in this file.
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@src/bun.js/bindings/BunString.cpp` around lines 257 - 262, The
toString(WTF::StringImpl*) overload preserves empty Symbol() as
BunStringTag::WTFStringImpl while toStringRef(WTF::StringImpl*) still maps the
same input to BunStringTag::Empty, causing inconsistent BunString states; make
toStringRef mirror toString (return BunStringTag::WTFStringImpl for empty-symbol
StringImpl*) and update any WTF-backed JS/zero-copy helpers and assertions in
this file that assume BunStringTag::WTFStringImpl is never empty (relax those
asserts or handle the empty-symbol case) so both helpers and assertions treat
empty-symbol StringImpl* consistently.
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LGTM — all previously raised concerns have been addressed.
Extended reasoning...
Overview
This PR fixes a crash in expect.extend caused by iterating inherited prototype properties (own_properties_only: false). The fix switches to own_properties_only: true (matching Jest's Object.keys() behavior), adds an isSymbol() guard to skip own symbol-keyed properties, and fixes an edge case in BunString.cpp where Symbol() / Symbol("") (zero-length descriptions) would lose their symbol identity via the isEmpty() short-circuit.
Security risks
No security-sensitive code paths are touched. The change is limited to the test runner's matcher registration logic and string utility helpers.
Level of scrutiny
Moderate — the fix touches expect.zig (test runner internals) and BunString.cpp (shared string binding). However, the changes are narrow and well-targeted: a one-line behavioral fix, supporting isSymbol() accessor in Zig/C++, and the BunString.cpp guard for empty-description symbols.
Other factors
All three concerns I raised in prior reviews have been resolved: (1) own symbol-keyed properties are now skipped via the isSymbol() guard, (2) the "works on prototypes" test has a negative assertion confirming inherited matchers are excluded, and (3) Symbol() / Symbol("") edge cases are covered by the BunString.cpp fix and the expanded test. Tests comprehensively exercise the regression paths.
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♻️ Duplicate comments (2)
src/bun.js/test/expect.zig (1)
939-948:⚠️ Potential issue | 🟠 MajorSkip symbol keys before
JSPropertyIteratorfetches their values.Line 947 skips symbol names too late. With
.include_value = true,iter.next()eagerly resolves the property value, so own symbol-keyed getters still execute/throw even though symbol keys are supposed to be ignored to matchObject.keys/Jest.Run this to confirm the eager-value path:
#!/bin/bash set -euo pipefail echo "=== expect.extend iterator configuration ===" sed -n '937,949p' src/bun.js/test/expect.zig | nl -ba echo echo "=== JSPropertyIterator eager value path ===" rg -n -C3 'include_value|getNameAndValue|getPropertySlot|next\(' \ src/bun.js/bindings/JSPropertyIterator.zig \ src/bun.js/bindings/JSPropertyIterator.cppExpected result:
next()routes through theinclude_value/getNameAndValue()path that calls into property lookup before the caller seesmatcher_name, which proves symbol getters can still run before Line 947.🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@src/bun.js/test/expect.zig` around lines 939 - 948, The iterator currently sets .include_value = true which makes iter.next() eagerly resolve property values (causing symbol-keyed getters to run before we check matcher_name); change the initialization of JSPropertyIterator (the iter variable) to use .include_value = false, then after confirming matcher_name is not a symbol (the if (matcher_name.isSymbol()) continue check), explicitly fetch the property value for non-symbol keys using the same lookup used by JSPropertyIterator (i.e., the getNameAndValue/getPropertySlot path) before assigning matcher_fn so symbol-keyed getters are never invoked.src/bun.js/bindings/BunString.cpp (1)
257-260:⚠️ Potential issue | 🟠 MajorMirror the empty-symbol exception in the ref path and WTF asserts.
Line 259 fixes only
toString(WTF::StringImpl*). Line 283 still maps the sameSymbol()/Symbol("")input toEmpty, and the WTF-backed asserts later in this file still reject emptyWTFStringImpls. That leaves two incompatibleBunStringstates for the sameStringImpl*and will still assert in debug/ASAN if one of these values later flows throughtoJS()ortransferToWTFString().Consistency fix sketch
BunString toStringRef(WTF::StringImpl* wtfString) { - if (wtfString->isEmpty()) + if (wtfString->isEmpty() && !wtfString->isSymbol()) return { BunStringTag::Empty }; wtfString->ref(); return { BunStringTag::WTFStringImpl, { .wtf = wtfString } }; }- ASSERT(refCount > 0 && !bunString->impl.wtf->isEmpty()); + ASSERT(refCount > 0 && (!bunString->impl.wtf->isEmpty() || bunString->impl.wtf->isSymbol()));Apply the same invariant relaxation to the other WTF-backed assert sites in this file.
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@src/bun.js/bindings/BunString.cpp` around lines 257 - 260, The toString(WTF::StringImpl*) change that treats an empty-but-symbol StringImpl as non-empty must be mirrored across the other WTF-backed code paths: update the other mapping that currently maps Symbol()/Symbol("") to BunStringTag::Empty and relax the WTF-backed asserts so they accept symbol-backed empty StringImpls; specifically, make the same invariant change in the code that constructs BunString from a WTF::StringImpl (the other branch that currently returns Empty), and adjust the assertions checked in transferToWTFString() and toJS() (and any WTF assert sites in this file) to allow symbol-empty StringImpls rather than asserting, so the same StringImpl* cannot produce two incompatible BunString states.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Duplicate comments:
In `@src/bun.js/bindings/BunString.cpp`:
- Around line 257-260: The toString(WTF::StringImpl*) change that treats an
empty-but-symbol StringImpl as non-empty must be mirrored across the other
WTF-backed code paths: update the other mapping that currently maps
Symbol()/Symbol("") to BunStringTag::Empty and relax the WTF-backed asserts so
they accept symbol-backed empty StringImpls; specifically, make the same
invariant change in the code that constructs BunString from a WTF::StringImpl
(the other branch that currently returns Empty), and adjust the assertions
checked in transferToWTFString() and toJS() (and any WTF assert sites in this
file) to allow symbol-empty StringImpls rather than asserting, so the same
StringImpl* cannot produce two incompatible BunString states.
In `@src/bun.js/test/expect.zig`:
- Around line 939-948: The iterator currently sets .include_value = true which
makes iter.next() eagerly resolve property values (causing symbol-keyed getters
to run before we check matcher_name); change the initialization of
JSPropertyIterator (the iter variable) to use .include_value = false, then after
confirming matcher_name is not a symbol (the if (matcher_name.isSymbol())
continue check), explicitly fetch the property value for non-symbol keys using
the same lookup used by JSPropertyIterator (i.e., the
getNameAndValue/getPropertySlot path) before assigning matcher_fn so
symbol-keyed getters are never invoked.
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♻️ Duplicate comments (1)
src/bun.js/bindings/BunString.cpp (1)
259-260:⚠️ Potential issue | 🟠 MajorKeep empty-symbol handling consistent across
toString*/toStringRef*overloads.Line 259 now preserves empty symbols for
toString(WTF::StringImpl*), buttoStringRef(WTF::StringImpl*)still collapses empty symbols toBunStringTag::Empty, and WTF-backed assert sites still assume non-empty. This reintroduces state divergence and can trip debug assertions downstream.Proposed consistency fix
BunString toStringRef(WTF::StringImpl* wtfString) { - if (wtfString->isEmpty()) + if (wtfString->isEmpty() && !wtfString->isSymbol()) return { BunStringTag::Empty }; wtfString->ref(); return { BunStringTag::WTFStringImpl, { .wtf = wtfString } }; }-ASSERT(refCount > 0 && !bunString->impl.wtf->isEmpty()); +ASSERT(refCount > 0 && (!bunString->impl.wtf->isEmpty() || bunString->impl.wtf->isSymbol()));Apply the same invariant relaxation to the other WTF-backed
!isEmpty()asserts in this file.🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@src/bun.js/bindings/BunString.cpp` around lines 259 - 260, The toString(WTF::StringImpl*) change preserves empty symbols but toStringRef(WTF::StringImpl*) and other WTF-backed paths still collapse empty symbols to BunStringTag::Empty, causing divergent state and broken asserts; update toStringRef(WTF::StringImpl*), and any other functions that assert !isEmpty() for WTF-backed strings in this file to treat isSymbol() as preserving symbols (i.e., do not convert empty && isSymbol() into BunStringTag::Empty), adjust the return/tagging logic to match toString(WTF::StringImpl*), and relax the WTF-backed !isEmpty() asserts accordingly so empty symbols remain distinct (reference: toString(WTF::StringImpl*), toStringRef(WTF::StringImpl*), BunStringTag::Empty).
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Duplicate comments:
In `@src/bun.js/bindings/BunString.cpp`:
- Around line 259-260: The toString(WTF::StringImpl*) change preserves empty
symbols but toStringRef(WTF::StringImpl*) and other WTF-backed paths still
collapse empty symbols to BunStringTag::Empty, causing divergent state and
broken asserts; update toStringRef(WTF::StringImpl*), and any other functions
that assert !isEmpty() for WTF-backed strings in this file to treat isSymbol()
as preserving symbols (i.e., do not convert empty && isSymbol() into
BunStringTag::Empty), adjust the return/tagging logic to match
toString(WTF::StringImpl*), and relax the WTF-backed !isEmpty() asserts
accordingly so empty symbols remain distinct (reference:
toString(WTF::StringImpl*), toStringRef(WTF::StringImpl*), BunStringTag::Empty).
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LGTM — the strings_only = true approach is the right fix, excluding symbols at the C++ PropertyNameMode::Strings level rather than filtering in Zig, which cleanly resolves all the edge cases I raised in prior reviews.
Extended reasoning...
Overview
The PR fixes a crash in expect.extend caused by iterating inherited properties (own_properties_only = false). The final implementation adds a strings_only parameter to JSPropertyIterator that selects PropertyNameMode::Strings in C++, excluding symbol-keyed properties at the enumeration source rather than filtering them after the fact.
Why Previous Concerns Are Addressed
My prior reviews raised concerns about: (1) own symbol keys still being iterated and causing throws, (2) Symbol()/Symbol("")\ edge cases where empty descriptions would bypass isSymbol()checks, and (3) getter side effects for symbol keys before skip. All three are resolved by usingPropertyNameMode::Strings` — symbols are never populated into the property name array, so none of these paths can trigger.
Test Coverage
The updated tests cover all regression paths: negative assertion confirming inherited matchers are excluded, own symbol-key skipping (including Symbol() and Symbol("") edge cases), and the original crash scenario with Symbol.toStringTag on the prototype.
Security / Risk
No security-sensitive code paths touched. The change is localized to expect.extend behavior and the JSPropertyIterator C++/Zig interface. The strings_only flag defaults to false, so existing callers are unaffected.
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| var iter = try jsc.JSPropertyIterator(.{ | ||
| .skip_empty_name = false, | ||
| .include_value = true, | ||
| .own_properties_only = false, | ||
| .own_properties_only = true, | ||
| }).init(globalThis, matchers_to_register); | ||
| defer iter.deinit(); | ||
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🔴 When expect.extend receives a matchers object with an own symbol-keyed property whose value is a function and whose symbol has a non-empty description (e.g., [Symbol.iterator]: fn), the function is silently registered under the symbol's description text as a plain string key (e.g., 'Symbol.iterator') instead of being skipped. This diverges from Jest's behavior — Jest uses Object.keys() and never sees symbol keys, so expect(x)['Symbol.iterator'] becomes an unexpectedly callable function while expect(x)[Symbol.iterator]() throws a TypeError.
Extended reasoning...
The fix in this PR changes own_properties_only from false to true at expect.zig:943, which correctly excludes inherited properties. However, JSPropertyIterator.cpp:48 initializes the property name array with PropertyNameMode::StringsAndSymbols — not PropertyNameMode::Strings — so own symbol-keyed enumerable properties are still yielded by the iterator even with own_properties_only = true.
For a symbol with a non-empty description like Symbol.iterator (description length 14), Bun::toString(prop.impl()) at JSPropertyIterator.cpp:152 returns {BunStringTag::WTFStringImpl, symbolImpl} because symbolImpl->isEmpty() is false (m_length > 0). In JSPropertyIterator.zig:next(), the name has tag .WTFStringImpl (not .Dead), and skip_empty_name = false (set at expect.zig:940), so the symbol key passes through to the loop body unchanged.
The final merged commit (ccc583e) does NOT include an isSymbol() check in the loop at expect.zig:946-962. When the value is a function, matcher_fn.jsType().isFunction() returns true, and putMayBeIndex is called with matcher_name = {WTFStringImpl, symbolImpl}. In JSC__JSValue__putMayBeIndex (bindings.cpp:3933-3934), key->toWTFString() extracts the description text from the SymbolImpl (returning WTF::String(symbolImpl) = 'Symbol.iterator'), and JSC::Identifier::fromString(vm, keyStr) creates a plain STRING identifier — not a symbol identifier. The function is silently registered under the string key 'Symbol.iterator', not under the actual symbol.
The observable impact: expect(x)['Symbol.iterator'] becomes a function (incorrectly accessible), while expect(x)[Symbol.iterator]() throws a TypeError (the expected usage is broken). No error is thrown during expect.extend; the failure is entirely silent. Jest uses Object.keys() which never yields symbol keys, so neither access would produce a function there — a silent behavioral divergence.
Step-by-step proof — given expect.extend({ [Symbol.iterator]: function(actual) { return {pass: true}; } }):
JSPropertyIteratorwithown_properties_only=trueenumerates own enumerable properties inStringsAndSymbolsmode —Symbol.iteratorkey is included.Bun::toString(prop.impl())atJSPropertyIterator.cpp:152: description'Symbol.iterator'hasm_length=14, soisEmpty()is false → returns{BunStringTag::WTFStringImpl, symbolImpl}.JSPropertyIterator.zig:next(): tag is.WTFStringImpl, not.Dead→ not filtered out.expect.zigloop (lines 946-962in merged code): noisSymbol()check present → proceeds to function check.- The function value passes
matcher_fn.jsType().isFunction()→putMayBeIndexis called. bindings.cpp:3933:key->toWTFString()on theSymbolImplreturns the description text'Symbol.iterator'.Identifier::fromString(vm, 'Symbol.iterator')creates a plain string identifier.- Result: the function is registered under the string key
'Symbol.iterator'on the Expect prototype.expect(x)['Symbol.iterator']returns the function;expect(x)[Symbol.iterator]()throws TypeError. - In Jest:
Object.keys()never yieldsSymbol.iterator→ the function is never registered → no accidental string-key registration occurs.
The PR description notes that intermediate review commits (599ae4b to e15885e) added an isSymbol() check to address this, but those commits were not included in the final merge (ccc583e). The fix would be to add an isSymbol() guard before the function validation check in the loop, or to switch JSPropertyIterator.cpp:48 to PropertyNameMode::Strings.
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| @@ -939,7 +939,7 @@ pub const Expect = struct { | |||
| var iter = try jsc.JSPropertyIterator(.{ | |||
| .skip_empty_name = false, | |||
| .include_value = true, | |||
| .own_properties_only = false, | |||
| .own_properties_only = true, | |||
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🔴 The PR description and several resolved review threads claim fixes that are not in this diff: the Verification section says "negative assertion added, isSymbol skip added… @as syntax fixes in wtf.zig", and the CodeRabbit walkthrough lists 5 changed files (BunString.cpp, string.zig, wtf.zig, expect.zig, test) — but the actual diff touches only 2 files and contains none of those fixes (no matcher_name.isSymbol() skip in the loop, no negative assertion that _toBeInherited is excluded, no BunString.cpp/string.zig/wtf.zig changes). The intermediate commits 599ae4b–e15885e referenced by the resolved threads (#2969260706, #2969260707, #2989815748, #2989961741, #2991495853) appear to have been dropped when expect.zig moved from src/bun.js/test/ to src/test_runner/ during the e643d7b restructure rebase — please either re-apply those commits or correct the description and re-open the resolved threads so reviewers don't approve based on stale state.
Extended reasoning...
What the issue is
This is a PR-state integrity problem: the description, the CodeRabbit walkthrough, and five review threads marked resolved all describe changes that do not exist in the diff being reviewed. A reviewer who trusts the "✅ Addressed in commits 599ae4b to e15885e" markers and the Verification section would reasonably conclude the symbol-handling work is done and approve — but the only functional change actually present is the one-line own_properties_only: false → true flip.
What the diff actually contains vs. what is claimed
Actual diff (2 files):
src/test_runner/expect.zig— single line:.own_properties_only = truetest/js/bun/test/expect-extend.test.js— three updated/added tests
Claimed but absent:
| Claim (source) | Where it should be | Present? |
|---|---|---|
| "isSymbol skip added" (PR description Verification) | expect.zig loop body, before the isFunction() check |
❌ — lines 946–963 have no matcher_name.isSymbol() check |
| "negative assertion added" (PR description Verification) | "works on prototypes" test | ❌ — test only calls expect(123)._toBeOwned(); never asserts _toBeInherited throws |
| "@as syntax fixes in wtf.zig" (PR description Verification) | src/string/wtf.zig |
❌ — file not in diff |
String.isSymbol / WTFStringImpl.isSymbol (CodeRabbit walkthrough) |
src/string.zig, src/string/wtf.zig |
❌ — files not in diff |
Empty-symbol guard in Bun::toString (CodeRabbit walkthrough, robobun comment 2026-03-25) |
src/bun.js/bindings/BunString.cpp |
❌ — file not in diff |
How the commits were lost — step-by-step
- The branch originally modified
src/bun.js/test/expect.zig(note the old path in resolved threads #2989815748, #2989961741, #2991495853). - Review rounds produced commits 599ae4b–e15885e adding the
isSymbol()skip, the negative assertion, theString.isSymbol/WTFStringImpl.isSymbolhelpers, and theBunString.cppempty-symbol guard. Threads were marked "✅ Addressed in commits 599ae4b to e15885e". - Base branch landed e643d7b "restructure src/", which moved
expect.zigfromsrc/bun.js/test/→src/test_runner/. - The PR was rebased onto the restructured tree. The current branch history (
git log) shows only one PR commit (b81462e) on top of e643d7b — commits 599ae4b–e15885e are gone. The single surviving hunk is theown_properties_onlyflip, re-applied at the new path. - GitHub kept the threads in the "resolved" state and the description was never updated, so the PR now advertises work it no longer contains.
Why existing signals don't catch this
- The resolved markers are sticky across force-pushes; GitHub does not re-open them when the referenced commits disappear.
- The CodeRabbit walkthrough was generated against the pre-rebase diff and was not regenerated ("Reviews paused").
- CI on the current head (b81462e) only fails on an unrelated 🍎 x64 build-cpp step, so there is no red signal pointing at the regression.
- The remaining tests in the diff still pass with only the
own_properties_onlyflip, because none of them exercise own symbol-keyed properties or assert exclusion of inherited matchers.
Relationship to other open comments (addressing the duplicate concern)
The unresolved inline comment #3110417798 and earlier threads do flag the technical consequences (own symbol keys still iterated; missing negative assertion) individually. This finding is the root cause that ties them together: those issues were already fixed once, in commits that were then lost during rebase. The actionable remedy here is different — rather than re-deriving each fix from scratch, the author should recover and re-apply 599ae4b–e15885e (or cherry-pick their content onto src/test_runner/expect.zig), which simultaneously closes all of the re-opened technical threads. If the author instead decides to descope (e.g. land only the own_properties_only flip now), the description must be corrected and the falsely-resolved threads re-opened so the review record matches reality.
Impact
Merging as-is would (a) ship a PR whose description materially misstates what it does, (b) leave the own-symbol-key Jest divergence unfixed despite resolved threads saying otherwise, and (c) leave the regression test without the negative assertion that guards the core behavioral change. The integrity risk is that a future reader of the PR will believe the symbol handling was completed here when it was not.
Fix
Either:
- Re-apply the dropped commits — cherry-pick 599ae4b–e15885e onto the current branch, retargeting
src/bun.js/test/expect.zigedits tosrc/test_runner/expect.zig; or - Descope — remove the stale Verification paragraph and CodeRabbit walkthrough claims from the description, and re-open threads #2969260706, #2969260707, #2989815748, #2989961741, #2991495853 so they accurately reflect the current diff.
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| it("works on prototypes", () => { | ||
| const Bar = { | ||
| _toBeBar() { | ||
| _toBeInherited() { | ||
| return { pass: true }; | ||
| }, | ||
| }; | ||
| const Foo = Object.create(Bar); | ||
| Foo._toBeOwned = function () { | ||
| return { pass: true }; | ||
| }; | ||
|
|
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| // Only own properties are registered (matches Jest's Object.keys behavior) | ||
| expect.extend(Foo); | ||
| expect(123)._toBeBar(); | ||
| expect(123)._toBeOwned(); |
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🟡 The test title "works on prototypes" is now misleading: the body (and its inline comment "Only own properties are registered") demonstrates that prototype-inherited matchers are ignored, which is the opposite of what the title implies. This is the same drift CodeRabbit flagged for the sibling "works on classes" test (renamed to "works on plain objects" in b767744), but this one was overlooked — consider renaming to something like "only registers own properties (ignores prototype)".
Extended reasoning...
What the issue is
Before this PR, the test at line 358 verified that a matcher inherited via the prototype chain (_toBeBar on Bar, inherited by Foo = Object.create(Bar)) was registered by expect.extend(Foo) — hence the title "works on prototypes". This PR inverts that behavior (own_properties_only: true), and the test body was rewritten to match: it now adds an own _toBeOwned to Foo, calls expect.extend(Foo), and asserts only _toBeOwned is callable. The inline comment explicitly states "Only own properties are registered (matches Jest's Object.keys behavior)". The title, however, still says "works on prototypes", which a reader will naturally parse as "prototype-inherited matchers work" — the exact behavior this PR removes.
Parallel to an already-fixed sibling
CodeRabbit raised this same class of issue for the adjacent test "works on classes" (inline comment #2969244502), and the author renamed it to "works on plain objects" in commit b767744. The "works on prototypes" test has the identical title-vs-body drift but was not renamed in that commit.
Why nothing else catches this
This is purely a naming/documentation concern. The test passes, lint passes, and CI does not check that test titles describe their bodies. The only signal a future maintainer gets is reading the title in a failure report — at which point "works on prototypes" actively misleads them about what broke.
Impact
No functional impact. The risk is maintainer confusion: a failure of this test would be reported as "works on prototypes" failing, suggesting Bun stopped supporting prototype-inherited matchers, when in fact the test is asserting they are not supported. It also weakens the test suite's self-documentation of the Jest-compat contract this PR establishes.
Step-by-step proof
- Read the title at
expect-extend.test.js:358:it("works on prototypes", ...)— implies prototype-inherited matchers work. - Read line 360-363:
Bardefines_toBeInherited;Foo = Object.create(Bar)inherits it. - Read line 365-367:
Foo._toBeOwnedis added as an own property. - Read line 369: comment says "Only own properties are registered" — directly contradicts the title.
- Read line 371: only
expect(123)._toBeOwned()is asserted;_toBeInheritedis never shown to work. - Conclusion: the body demonstrates prototype matchers are ignored, not that they work.
Fix
Rename the test, e.g.:
-it("works on prototypes", () => {
+it("only registers own properties (ignores prototype)", () => {or "skips inherited matchers", mirroring the rename applied to the sibling test in b767744.
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Rebased onto main. The conflict was in |
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Addressed the review feedback on this rebased (Rust) version:
On the older threads about own symbol-keyed properties and the |
expect.extend iterated inherited properties via own_properties_only: false, which caused it to encounter non-function properties like Symbol.toStringTag from the prototype chain. When throwing the validation error for these, a pending exception from the prototype chain property access could trigger releaseAssertNoException. Change to own_properties_only: true to match Jest's Object.keys() behavior where only own enumerable properties are registered as matchers.
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Stale PR review: closing. No human has commented on or reviewed this PR since it opened on 2026-03-21. It reverses a deliberate choice. #16437 (54eb823) set Reopen if this evidence is wrong. |
1 participant
expect.extendwas iterating inherited properties (own_properties_only = false), which caused it to encounter non-function properties likeSymbol.toStringTagfrom prototypes. When throwing the validation error for these inherited non-function properties, a pending exception from the prototype chain property access could triggerreleaseAssertNoException, crashing the process.Changed to
own_properties_only = true, matching Jest'sObject.keys()behavior where only own enumerable properties are registered as matchers.Updated the existing
works on prototypesandworks on classestests to reflect the corrected behavior, and added a regression test that passes an object whose prototype containsSymbol.toStringTagand other non-function properties.Verification (robobun): CI partially complete — Lint JavaScript passed, Buildkite pipeline passed, main Buildkite build #40576 still running. Single-line fix in expect.zig flips
own_properties_only: false→true. Three regression tests: (1) "works on prototypes" asserts own property registers AND inherited property throws (negative assertion guards against revert), (2) "works on plain objects" covers simple case, (3) "does not crash when prototype has non-function properties like Symbol.toStringTag" exercises the exact crash scenario. No TODO/FIXME/HACK in diff. CodeRabbit nits (test rename + negative assertion) were addressed in subsequent commits. No unrelated changes.Verification: CI Build #40655 in progress; prior Build #40624 failures were unrelated (bundler_compile.test.ts timeouts, Windows agent failures). Lint JavaScript passed. Diff has no TODO/FIXME/HACK markers. Tests exercise the exact regression paths: negative assertion confirms inherited matchers are excluded, own symbol-keyed properties are skipped (matching Jest Object.keys behavior). All CodeRabbit and Claude review comments addressed (test renamed, negative assertion added, isSymbol skip added). The @as syntax fixes in wtf.zig are correct Zig syntax.