[robobun]

Problem

• No test on main fails when fs.cpSync stops rejecting an existing destination directory. The options are { recursive: true, force: false, errorOnExist: true }.
• The guard in onDir (src/js/internal/fs/cp-sync.ts:455) gives the rejection. With the guard removed, the 77 vendored test-fs-cp-* files and test/js/node/fs/cp.test.ts still pass. node:fs: apply cpSync errorOnExist per entry, not to the destination directory #33416 (closed) proposed that removal.

Fix

• Add Node's test/parallel/test-fs-cp-sync-dir-exists-error-on-exist.mjs, unmodified. The git blob is bcc95476a9f6, the same as at nodejs/node tag v26.10.0.
• The test copies a directory onto an existing directory that holds no colliding file. It expects ERR_FS_CP_EEXIST.
• This PR changes nothing under src/. The test passes on main. It fails with AssertionError: Missing expected exception. when the guard is removed.
• Verified: the new file on a debug build, through scripts/runner.node.ts. Also all 78 test-fs-cp-* files and test/js/node/fs/cp.test.ts.

Background

• With force: false and errorOnExist: true, cp throws when the destination exists. fs: throw on existing dir in cpSync with errorOnExist nodejs/node#64124 made cpSync do this for an existing directory (first release: v26.10.0). fs: port Node.js v26.3.0 fs tests and fix the gaps they surface — cp error semantics, watcher event delivery, watch ignore+AbortSignal, FileHandle pull/writer, glob port, opendir/Dir, mkdtempDisposable, rmdir-recursive end-of-life, mock.fn (+119 tests) #31830 added the same guard to Bun.
• test-fs-cp-sync-error-on-exist.mjs copies one tree twice, so files collide. mayCopyFile throws the same code for each colliding file. That test passes without the directory guard.
• test/js/node/test/parallel/ holds copies of Node's own tests. CI runs each file as a script with bun run.
• Considered a new case in cp.test.ts. The upstream file won because the same file runs under Node.

Notes

Results for the new file, all on linux-x64:

Runtime	Result
Node v26.10.0 (tarball sha256 checked against SHASUMS256.txt)	exit 0
Node v26.3.0 (before nodejs/node#64124)	AssertionError [ERR_ASSERTION]: Missing expected exception.
bun 1.4.3-canary.1+367d939d9 (release)	exit 0
bun debug build of this branch	exit 0
bun debug build, guard at cp-sync.ts:455-463 removed	AssertionError: Missing expected exception., exit 1

• bun run node:test:cp fetches from the main branch of nodejs/node, not from a tag. The file on main was identical to the file at v26.10.0 at fetch time. The file does not exist at v26.9.0.
• cpSync takes the native fast path only when errorOnExist is false and force is true (src/js/node/fs.ts:973). This test always runs the JavaScript walker, on every platform.
• In the tracked test tree, errorOnExist occurs in cp.test.ts, in 5 vendored test-fs-cp-* files (the new file included), and in one helper under test/js/node/test/common/. All of these ran against the build without the guard.
• test/js/node/fs/cp.test.ts on the debug build: 47 pass, 5 skip (Windows only), 0 fail, with and without the guard.
• fs.cp: take the native recursive copy again when it gives the walker's result #42906 (open) changes when cpSync takes the native path. Its diff keeps the rejection of an existing destination directory.

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no test proof · iteration 0 · no src or test change; test-proof not applicable

[robobun]

Status: ready for review. This PR adds one test file and changes nothing under src/.

How to check it:

1. Run bun bd run test/js/node/test/parallel/test-fs-cp-sync-dir-exists-error-on-exist.mjs. It exits 0.
2. Remove the guard at src/js/internal/fs/cp-sync.ts:455-463 and run the same command. It fails with AssertionError: Missing expected exception.

The same file exits 0 on Node v26.10.0 and fails on Node v26.3.0, which does not have nodejs/node#64124.

[coderabbitai]

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• test/js/node/test/parallel/test-fs-cp-sync-dir-exists-error-on-exist.mjs

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Walkthrough

Adds a test that checks cpSync throws ERR_FS_CP_EEXIST when it copies a directory into an existing destination directory with recursive: true, errorOnExist: true, and force: false.

Changes

cpSync existing-directory error test

Layer / File(s)	Summary
Assert error for an existing destination directory test/js/node/test/parallel/test-fs-cp-sync-dir-exists-error-on-exist.mjs	Creates source and destination directories with different files. Checks that cpSync throws ERR_FS_CP_EEXIST with the specified options.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 04c95

The added test covers the intended error case; no issue identified here prevents merging after normal checks.

🚥 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.
Description check	✅ Passed	The description clearly explains the problem, the test change, expected behavior, and verification results. It does not use the exact template headings, but it provides the required information in equ…
Title check	✅ Passed	The title clearly identifies the main change: adding a Node.js test for cpSync errorOnExist behavior on an existing directory.

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[claude]

LGTM — a single ported Node test file, no runtime changes.

What was reviewed:

• The new file matches the sibling async test (test-fs-cp-async-dir-exists-error-on-exist.mjs) line-for-line apart from cpSync/assert.throws, and the diff header's new-blob hash (bcc95476) is consistent with the claimed upstream blob.
• Traced the asserted path: with errorOnExist true the src/js/node/fs.ts:973 native fast path is skipped, so the JS walker's onDir guard at src/js/internal/fs/cp-sync.ts:455 fires and decorateSystemError leaves .code as ERR_FS_CP_EEXIST.
• Ruled out the mixed-separator path concern on Windows: the identical construction already runs in the async sibling, and fs helpers accept it.

Extended reasoning...

The PR adds one 32-line file under test/js/node/test/parallel, a directory of vendored Node.js tests that Bun runs as scripts, and touches nothing under src/. It exercises fs.cpSync with { recursive: true, errorOnExist: true, force: false } against an existing destination directory with non-colliding contents and expects ERR_FS_CP_EEXIST. No security-sensitive surface is involved. The existing onDir guard in cp-sync.ts already produces this error and the fast-path condition in fs.ts excludes errorOnExist, so the test should pass on main while covering a guard that previously had no dedicated test; the file is structurally identical to the already-vendored async sibling, and no CODEOWNER covers the path.