[robobun]

Problem

• On Linux, fs.watch() on a symlink reports the link target's basename as filename. For link.txt -> target.txt, bun 1.3.14 to 1.4.3 report target.txt. Node v26.3.0 and bun 1.3.13 report link.txt. fs.watch: decouple from bun.Watcher, own inotify/FSEvents/kqueue directly #29952 introduced the regression.
• After a log rotation, tail@2.2.6 on a current.log symlink watches the deleted dated file and emits ENOENT.
• Cause: the inotify dispatch names an event about the watched path itself (a self-event) after PathWatcher.path, which is the realpath (src/runtime/node/path_watcher.rs:1080, :1088, :986). libuv uses the path the caller gave.

Fix

• Each handler on a PathWatcher keeps the basename of the path its caller gave. The new emit_self and emit_self_unsuppressed report it for a self-event. Names of directory entries do not change.
• Deliberate difference from Node: libuv keeps one path per inotify watch, so two Node watchers on one inode in one thread both report the first one's name. Across Workers, Node reports each watcher's own name. Only a per-handler name matches that.
• Verified: test/js/node/watch/fs.watch.test.ts runs one fixture under bun and under node. The bun half fails on 1.4.3. Also test/js/node/watch/ and the 43 vendored test-fs-watch* node tests.

Background

• An inotify event for a watched file, or for the watched directory itself, carries no name. libuv fills in the basename of the watched path.
• A PathWatcher is one OS watch. Every fs.watch() call that resolves to the same realpath shares it, across Workers too. It has one handlers entry per call.
• macOS and FreeBSD do not change. libuv reports the resolved name there, as bun does.

Notes

Versions (Linux x64, the repro below, event:filename)

runtime	result
bun 1.2.0, bun 1.3.13, node v26.3.0	change:link.txt
bun 1.3.14, bun 1.4.3	change:real-target.txt
this branch	change:link.txt

#29952 (6228e35) is in bun-v1.3.14 and not in bun-v1.3.13. It made watch() store the get_fd_path() realpath as the dedup key and as PathWatcher.path, and the self-event name followed.

import * as fs from "node:fs";
import * as os from "node:os";
import * as path from "node:path";

const base = fs.mkdtempSync(path.join(os.tmpdir(), "fwsl-"));
fs.mkdirSync(path.join(base, "tdir"));
fs.mkdirSync(path.join(base, "ldir"));
fs.writeFileSync(path.join(base, "tdir", "real-target.txt"), "0");
fs.symlinkSync(path.join(base, "tdir", "real-target.txt"), path.join(base, "ldir", "link.txt"));
const sleep = ms => new Promise(r => setTimeout(r, ms));

const names = new Set();
const w = fs.watch(path.join(base, "ldir", "link.txt"), (e, f) => names.add(`${e}:${f}`));
await sleep(50);
fs.appendFileSync(path.join(base, "tdir", "real-target.txt"), "x");
await sleep(150);
w.close();
console.log("events:", [...names].join(", "));
fs.rmSync(base, { recursive: true, force: true });

Matrix (node v26.3.0 / bun 1.4.3 / this branch)

scenario	node	1.4.3	branch
link, append to target	change:link.txt	change:real-target.txt	change:link.txt
link, unlink target	change, rename, rename as link.txt	same, as real-target.txt	same as node
link, rename target	rename:link.txt	rename:real-target.txt	rename:link.txt
link-dir, rmdir target dir	rename:link-dir x2	rename:real-dir x2	rename:link-dir x2
link-dir, create child	rename:child.txt, change:child.txt	same	same
relative link.txt from its directory	change:link.txt	change:real-target.txt	change:link.txt
encoding: "hex"	hex of link.txt	hex of real-target.txt	hex of link.txt
target first, then link, append	both real-target.txt	both real-target.txt	real-target.txt / link.txt
link first, then target, append	both link.txt	both real-target.txt	link.txt / real-target.txt
main thread on target, Worker on link	real-target.txt / link.txt	both real-target.txt	real-target.txt / link.txt

Why the name is per handler. PathWatcher is process-wide and keyed by realpath, so a watcher on the link and a watcher on the target are two handlers on one PathWatcher. In libuv the name lives on the watcher_list, one per (loop, wd), and it is the path of the first uv_fs_event_start on that wd (linux.c#L2706-L2714). That is why two Node watchers in one thread share the first name, and why a Node Worker (own loop, own inotify fd) reports its own. A first-wins name stored on the PathWatcher would copy the same-thread case and break the Worker case. To copy both, bun would need name state per (wd, VM) that outlives the first watcher. No code can depend on receiving the name another watcher passed, so each handler reports its own.

macOS and FreeBSD. libuv watches a file with kqueue there and reports basename(F_GETPATH(fd)) or basename(F_KINFO kf_path), both resolved (kqueue.c#L493-L519). Its FSEvents path (directories) matches by realpath. fs_events.rs and the kqueue backend already name self-events after the realpath, so Handler.name exists only on Linux and Android. I could not run macOS. cargo check -p bun_runtime passes for x86_64-unknown-freebsd, aarch64-apple-darwin and aarch64-linux-android.

Consumers that break on 1.4.3 (both match Node on this branch)

• tail@2.2.6, new Tail("current.log", { follow: true }) with current.log -> app-<date>.log. On a rename event it sets this.filename = path.join(dir, filename) and watches that again. After a rotation that deletes the old dated file, 1.4.3 gives it the dated name: ENOENT: no such file or directory, watch '.../app-2026-01-01.log', and no line from the new file. Node and this branch give current.log and tail follows the new file.
• TypeScript 6.0.2 ts.sys.watchFile(link) with default options, target replaced by write-temp-then-rename three times. Node and this branch: Changed, Created for each save. 1.4.3: Changed, Created, Created for the first save, then nothing.

Not covered here (all behave the same before and after this PR)

• fs.watch on Linux: an event about the watched directory itself differs from Node (event type, filename for a trailing slash, recursive root) #43066: chmod/utimes of a watched directory reports change. Node reports rename, because libuv maps every mask bit outside IN_ATTRIB|IN_MODIFY to UV_RENAME and the kernel sets IN_ISDIR.
• fs.watch on Linux: an event about the watched directory itself differs from Node (event type, filename for a trailing slash, recursive root) #43066: a watched path with a trailing slash or a last segment of .. Node reports "" or "." for a self-event (uv__basename_r of the string as given). Bun takes the basename after FSWatcher::init joined and normalized the path, so it reports the directory name. node:fs: hand fs.watch and fs.watchFile paths to the OS as given on POSIX #41986 changes what path reaches watch().
• fs.watch on Linux: an event about the watched directory itself differs from Node (event type, filename for a trailing slash, recursive root) #43066: the root of a recursive watch. Bun reports change with undefined for a chmod of the root, Node reports nothing.
• fs.watch recursive on Linux: no event for a change behind a symlink entry that points outside the tree (regression in 1.3.14) #43065: a recursive watch does not report a change behind a symlink entry that points outside the tree. Node and bun 1.3.13 do. This is a second regression from fs.watch: decouple from bun.Watcher, own inotify/FSEvents/kqueue directly #29952.
• Windows is a separate backend. It hands libuv the link target (fs.watch(windows): resolve symlinks with realpath instead of passing the readlink target to libuv #39474 keeps that), and Node on Windows does not report changes to the target of a file symlink at all, so there is no Node name to match.

Related open PRs. #40200 rewrites this file and also adds a struct Handler { id, change, sink } at the same place, so the two conflict textually. On top of #40200 this fix is a cfg(linux/android) name field on its Handler, the watched path passed into Handlers::push, and the two emit_self methods on Handlers. It still uses basename(w.path) at the three Linux sites. #33396 adds a branch right after the emit call in the same loop. #38365 swaps get_fd_path for realpath in watch(). #42819 and #39827 touch the Windows side.

Self-review. A review before the push confirmed the 1.3.14 regression on the release binaries. It asked for the Node-run fixture, for a code comment that does not claim exact libuv parity, and for the not-covered list above. All are in this PR.

Suites run on the debug build: test/js/node/watch/*.test.ts, test/regression/issue/3657.test.ts, all 42 test/js/node/test/parallel/test-fs-watch* and test-fs-promises-watch* files plus sequential/test-fs-watch.js. cargo clippy -p bun_runtime and cargo fmt --check are clean.

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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/node/watch/fs.watch.test.ts

[robobun]

Status

Reproduced on Linux x64 with bun 1.4.3 against node v26.3.0:

// links/link.txt is a symlink to real/target.txt
fs.watch("links/link.txt", (event, filename) => console.log(event, filename));
fs.appendFileSync("real/target.txt", "x");
// node v26.3.0, bun 1.2.0, bun 1.3.13: change link.txt
// bun 1.3.14, bun 1.4.3:               change target.txt

• Tests: test/js/node/watch/fs.watch.test.ts, describe "a watched symlink is reported under its own name". It runs fixtures/symlink-filename-fixture.mjs under bun and under node. The bun test fails with USE_SYSTEM_BUN=1 and passes with bun bd test.
• Self-reviewed before the push. The review confirmed the regression from fs.watch: decouple from bun.Watcher, own inotify/FSEvents/kqueue directly #29952 on the release binaries. It asked for the fixture run under node, for a code comment that does not claim exact libuv parity, and for the list of cases this PR does not cover. All are in the PR.
• All review threads are resolved.

CI. The diff is green. Each of the two builds has one red test, a different one each time, and neither test touches fs.watch:

build	sha	red test	lane
#117008	0a0ad4d	test/bake/deinitialization.test.ts (segmentation fault)	Windows 2019 x64
#117016	527a643	test/js/bun/spawn/spawn.test.ts ("an idle reader stopped at the highwater ...")	Debian 13 x64-asan

• 527a643 changes only comments on top of 0a0ad4d. Each red test passed in the other build.
• src/runtime/node/path_watcher.rs is not compiled on Windows, and the new tests run on Linux only.
• test/js/node/watch/fs.watch.test.ts ran and passed on every Linux lane in both builds (glibc, musl, aarch64, ASAN).

The next step is a maintainer review. I will not start CI again for these two tests.

[coderabbitai]

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Walkthrough

PathWatcher now preserves each callback’s watched basename on Linux and Android. Linux self-events use handler-specific names and separate suppression paths. New fixtures and tests validate symlink changes, removals, directory-entry creation, and watcher ordering.

Changes

Symlink watcher name handling

Layer / File(s)	Summary
Per-handler watched-name storage src/runtime/node/path_watcher.rs	Handler records now store duplicate-suppression state and the original watched basename. Watch creation stores one handler for each callback context.
Linux self-event dispatch src/runtime/node/path_watcher.rs	Linux dispatch distinguishes self-events from relative paths. File and non-recursive root watchers use handler-specific names, while inode-retirement events bypass duplicate suppression.
Symlink behavior validation test/js/node/watch/fixtures/symlink-filename-fixture.mjs, test/js/node/watch/fs.watch.test.ts	The fixture and Linux tests cover symlink changes, removals, directory-entry creation, and Bun-versus-Node watcher naming.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 527a6

A missing watcher event can make this test wait for the broader test timeout rather than fail and clean up promptly. This is bounded by the outer runner timeout but should be addressed.

🚥 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 and concisely states the main Linux fs.watch symlink behavior fix.
Description check	✅ Passed	The description provides detailed problem, cause, fix, scope, verification results, test coverage, and known limitations. It does not use the template headings exactly, but it contains the required in…

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@test/js/node/watch/fixtures/symlink-filename-fixture.mjs`:
- Line 38: Update collect so its Promise.all(all) wait has a bounded timeout and
rejects when fewer than count events arrive; preserve the existing finally
cleanup so watchers close after rejection.

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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

[robobun]

^{Updated 6:00 AM PT - Sep 17th, 2026}

❌ @robobun, your commit 527a643 has 1 failures in Build #117016 (All Failures):

• test/js/bun/spawn/spawn.test.ts - code 1: stdout reader of an unref'd child and process lifetime > an idle reader stopped at the highwater … on 🐧 13 x64-asan

---

🧪   To try this PR locally:

bunx bun-pr 43064

That installs a local version of the PR into your bun-43064 executable, so you can run:

bun-43064 --bun

[claude]

Code review completed

Nothing new to post: everything this review found is already covered by existing comments on this pull request or didn't merit a separate one.