bun:test: cover the isArray() exception checks for Proxy values in expect matchers

[robobun]

Problem

• Add missing exception checks in expect matchers, mock functions and error construction #40068 (3ee9801) added exception checks after JSC::isArray() at three call sites in src/jsc/bindings/bindings.cpp: expect.any(Array) (matchAsymmetricMatcherAndGetFlags), toMatchObject (Bun__deepMatch), and toHaveProperty with an array path (JSC__JSValue__getIfPropertyExistsFromPath).
• That PR added a test only for mockResolvedValue. Nothing in the tree runs these three matchers with a Proxy under BUN_JSC_validateExceptionChecks=1. A future edit can drop one of the checks and no test fails.
• Without a check, a debug build aborts with ERROR: Unchecked JS exception: This scope can throw a JS exception: isArraySlowInline @ JavaScriptCore/runtime/ArrayConstructor.cpp ... ASSERTION FAILED: exception check validation failed.

Fix

• Test only. It carries the test from bun:test: check exception after isArray() in expect.any(Array), toMatchObject, toHaveProperty #34753 into test/js/bun/test/expect.test.js. bun:test: check exception after isArray() in expect.any(Array), toMatchObject, toHaveProperty #34753 fixed the same three sites and is closed as superseded by Add missing exception checks in expect matchers, mock functions and error construction #40068.
• The test spawns a child with BUN_JSC_validateExceptionChecks=1. The child runs each matcher with transparent and revoked Proxy values and prints ok. The test asserts stdout, exitCode 0, and no signal. On a release build the option is a no-op and the child exits 0.
• Verified: bun bd test test/js/bun/test/expect.test.js -t isArray passes on main. With the three checks removed from bindings.cpp and rebuilt, the same test fails with exitCode: 134, signalCode: SIGABRT and the abort message above. The full file passes (416 pass, 2 todo).

Background

• JSC::isArray() follows the Array.isArray spec. For a Proxy it walks to the target and throws a TypeError if the Proxy is revoked. So it declares a throw scope, and the caller must check for an exception before the next JSC call.
• BUN_JSC_validateExceptionChecks=1 makes a debug JSC assert when a throw scope is left unchecked. It is the tool that finds these sites. Release builds ignore it.
• The test lives inside the if (isBun) block and reads harness with require inside the test body. This file also runs under Jest and Vitest, and the existing test("()") uses the same pattern for that reason.

Notes

Fail-before run on main with the three RETURN_IF_EXCEPTION lines after isArray() removed from bindings.cpp:

error: expect(received).toMatchObject(expected)
+   "exitCode": 134,
+   "signalCode": "SIGABRT",
+   "stderr":
+ "ERROR: Unchecked JS exception:
+     This scope can throw a JS exception: isArraySlowInline @ vendor/WebKit/Source/JavaScriptCore/runtime/ArrayConstructor.cpp:130
+     But the exception was unchecked as of this scope: hasInstance @ vendor/WebKit/Source/JavaScriptCore/runtime/JSObject.cpp:2686
+ ASSERTION FAILED: exception check validation failed

Pass-after on main as is: 1 pass, 417 filtered out.

The three repro snippets from #34753 also run without the abort on main under BUN_JSC_validateExceptionChecks=1 BUN_JSC_dumpSimulatedThrows=1:

expect(new Proxy({}, {})).toEqual(expect.any(Array));
expect(new Proxy([], {})).toMatchObject([]);
expect({ a: 1 }).toHaveProperty(new Proxy(new Set(["a"]), {}));

Each throws the normal matcher failure and the process exits 0.

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[stamp-90s] gate passed · iteration 2 · 1 files touched

passes on PR (with fix)

Test-only change.

Debug/ASAN (expected pass):
$ bun bd test 'test/js/bun/test/expect.test.js'
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test test/js/bun/test/expect.test.js
bun test v1.4.1 (d578a8c70)

test/js/bun/test/expect.test.js:
(pass) expect() > () [302.05ms]
(pass) expect() > toBe() > expect(0).toBe(0) == true [1.56ms]
(pass) expect() > toBe() > expect(0).toBe(0) == true [0.44ms]
(pass) expect() > toBe() > expect(0).toBe(0) == true [0.26ms]
(pass) expect() > toBe() > expect(-0).toBe(-0) == true [0.23ms]
(pass) expect() > toBe() > expect(1).toBe(1) == true [0.23ms]
(pass) expect() > toBe() > expect(1).toBe(1) == true [0.24ms]
(pass) expect() > toBe() > expect(NaN).toBe(NaN) == true [0.23ms]
(pass) expect() > toBe() > expect(Infinity).toBe(Infinity) == true [0.23ms]
(pass) expect() > toBe() > expect({}).toBe({}) == true [0.23ms]
(pass) expect() > toBe() > expect(Symbol(a)).toBe(Symbol(a)) == true [0.27ms]
(pass) expect() > toBe() > expect(0).toBe(false) == false [2.35ms]
(pass) expect() > toBe() > expect(0).toBe("") == false [0.50ms]
(pass) expect() > toBe() > expect(0).toBe(-0) == false [0.30ms]
(pass) expect() > toBe() > expect(0).toBe(-0) == false [0.29ms]
(pass) expect() > toBe() > expect(1).toBe(2) == false [0.32ms]
(pass) expect() > toBe() > expect(1).toBe(true) == false [0.30ms]
(pass) expect() > toBe() > expect(1).toBe("1") == false [0.45ms]
(pass) expect() > toBe() > expect(Infinity).toBe(-Infinity) == false [0.31ms]
(pass) expect() > toBe() > expect("foo").toBe("Foo") == false [0.30ms]
(pass) expect() > toBe() > expect("foo").toBe("bar") == false [0.29ms]
(pass) expect() > toBe() > expect("").toBe(" ") == false [0.33ms]
(pass) expect() > toBe() > expect("").toBe(" ") == false [0.29ms]
(pass) expect() > toBe() > expect("").toBe(true) == false [0.29ms]
(pass) expect() > toBe() > expect({}).toBe({}) == false [0.31ms]
(pass) expect() > toBe() > expect(Set {}).toBe(Set {}) == false [0.29ms]
(pass) expect() > toBe() > expect([Function: a]).toBe([Function: a]) == false [0.31ms]
(pass) expect() > toBe() > e
... (truncated)
Exit: 0

diff hotspot

test/js/bun/test/expect.test.js | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

gate history · 2 passed · 0 rejected · iteration 2

evidence per changed file

file                             reads  edits  tests
test/js/bun/test/expect.test.js      1      1      0

[robobun]

^{Updated 12:34 PM PT - Aug 30th, 2026}

✅ @robobun, your commit f97221a332f54aadde44ec98f52919ed2705c0f3 passed in Build #108597! 🎉

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🧪   To try this PR locally:

bunx bun-pr 40981

That installs a local version of the PR into your bun-40981 executable, so you can run:

bun-40981 --bun

[robobun]

Status: test-only follow-up to #40068. The isArray() exception checks it covers are already on main (3ee9801).

Verified on main with a debug build:

• bun bd test test/js/bun/test/expect.test.js -t isArray: 1 pass.
• With the three RETURN_IF_EXCEPTION lines after isArray() removed from bindings.cpp and rebuilt: the test fails with exit code 134 (SIGABRT) and Unchecked JS exception: isArraySlowInline.
• The full file passes: 416 pass, 2 todo.

#34753 proposed the same three checks and is closed as superseded.

[coderabbitai]

Walkthrough

This change adds a Bun regression test. The test runs assertion checks against normal, trapping, and revoked Proxies with exception validation enabled. It verifies successful output and exit status.

Changes

Proxy assertion regression

Layer / File(s)	Summary
Proxy assertion subprocess coverage test/js/bun/test/expect.test.js	A Bun subprocess exercises expect.any(Array), toMatchObject, and toHaveProperty with normal, trapping, and revoked Proxy values. The test checks ok output and exit code 0.

Possibly related PRs

• oven-sh/bun#34753: Adds the implementation fixes covered by this regression test.

Suggested reviewers: dylan-conway

Merge Risk: ⚪ Minimal · up to c5747

This PR adds focused coverage for Proxy exception handling without changing production behavior, so users should see no runtime impact. No actionable merge-blocking risk remains beyond a trivial import-style cleanup.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the test coverage for JSC::isArray() exception checks in Bun expect matchers. It is specific and related to the main change.
Description check	✅ Passed	The description explains the problem, fix, test scope, implementation context, and verification results. It does not use the exact template headings, but it provides the required information and is su…

Full details: Description check

Explanation

The description explains the problem, fix, test scope, implementation context, and verification results. It does not use the exact template headings, but it provides the required information and is substantially complete.

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@test/js/bun/test/expect.test.js`:
- Line 686: Move bunEnv and bunExe from the test body’s require("harness") call
to a module-scope harness import, and remove the local require while preserving
the test’s existing usage.

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Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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• test/js/bun/test/expect.test.js

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[claude]

LGTM — test-only addition that follows the file's existing patterns.

What was reviewed:

• Confirmed the new test sits inside the if (isBun) block (opened at line 570, closes at 713), so the inline require("harness") matches the file's Jest/Vitest-interop convention rather than violating the module-scope-import rule.
• Checked the assertion shape: positive signal (stdout: "ok\n", exitCode: 0, signalCode: null) via a combined toMatchObject, pipes drained concurrently, bunEnv spread, await using on the spawn — all per REVIEW.md subprocess guidance; stderr is captured into the received object so it surfaces in the diff on failure without being asserted on.
• Considered the USE_SYSTEM_BUN=1 rule: this test cannot fail on a release build by design (validateExceptionChecks is debug-only), but the PR demonstrates fail-before by reverting the three RETURN_IF_EXCEPTION sites and rebuilding, which is the correct load-bearing proof for this test class.

Extended reasoning...

Overview

This PR adds a single test case to test/js/bun/test/expect.test.js covering three JSC::isArray() call sites in src/jsc/bindings/bindings.cpp (expect.any(Array), toMatchObject, toHaveProperty with an array path) that were given RETURN_IF_EXCEPTION checks in a prior PR but had no test coverage. The test spawns a child with BUN_JSC_validateExceptionChecks=1, exercises each matcher against transparent and revoked Proxy values, and asserts the child prints ok and exits cleanly. No native code is touched.

Security risks

None. This is a test-only change that spawns bunExe() with an inline -e script and a single env var. No network, no filesystem writes, no untrusted input parsing.

Level of scrutiny

Low. The diff is 33 lines of test code added to an existing test file, placed in the correct location (the if (isBun) block alongside the existing Proxy toEqual/toStrictEqual tests). It follows the harness conventions REVIEW.md enforces: Promise.all on stdout/stderr/exited, combined-object assertion, {...bunEnv, ...} spread, await using on the spawn, and -e for a single-file fixture. The inline require("harness") is the established pattern in this file (see line 25) because the file is also run under Jest and Vitest where a top-level harness import would fail.

Other factors

The one CLAUDE.md rule this test nominally brushes against — "test must fail under USE_SYSTEM_BUN=1" — does not apply cleanly here: BUN_JSC_validateExceptionChecks is a debug-JSC-only knob (also referenced in the root CLAUDE.md build section), so a release system Bun will always pass. The PR description compensates with an explicit fail-before run (removing the three checks and rebuilding produces exitCode: 134, signalCode: SIGABRT with the expected assertion message), which is the correct proof that the test is load-bearing. The assertion is a positive one (stdout ok, exit 0, no signal) rather than grepping for the absence of a panic string, satisfying the "never check for no panic in output" rule. The bug hunt ran to dry_streak with no findings and no ruled-out candidates.