## Summary
Fixes a race condition on macOS where editing the entrypoint with vim's
atomic save causes "Module not found" errors during hot reload.
## Root Cause
On macOS, kqueue watches file descriptors/inodes, not paths. Vim's
atomic save sequence:
1. Rename `a.js` to `a.js~` → kqueue reports `NOTE_RENAME` on watched fd
2. Hot reloader immediately triggers reload
3. New file hasn't been created yet → `ENOENT` error
4. Vim re-creates `a.js`, and writes file contents into it
5. Directory gets `NOTE_WRITE` but file already removed from watchlist
```
rename("a.js", "a.js~") = 0
openat(AT_FDCWD, "a.js", O_WRONLY|O_CREAT, 0664) = 3
ftruncate(3, 0) = 0
write(3, "foobar\n", 7) = 7
close(3) = 0
```
This is macOS-specific because:
- **kqueue**: watches inodes, fd becomes stale when inode deleted
- **inotify (Linux)**: watches paths, gets `IN.MOVED_TO` (not
`IN.MOVE_SELF`), so files stay in watchlist
## Solution
When the entrypoint receives `NOTE_RENAME` on macOS:
1. Set `is_waiting_for_dir_change` flag
2. Skip immediate reload
3. Wait for parent directory `NOTE_WRITE` event
4. Use `faccessat()` to verify file exists
5. Trigger reload
This only applies to the entrypoint because dependencies have buffering
time during import graph traversal.
## Test Plan
Manual testing with vim on macOS:
1. Run `bun --hot entrypoint.js`
2. Edit entrypoint with vim (`:w`)
3. Verify no "Module not found" errors
4. Verify hot reload succeeds
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: taylor.fish <contact@taylor.fish>
## Summary
Adds `BUN_WATCHER_TRACE` environment variable that logs all file watcher
events to a JSON file for debugging. When set, the watcher appends
detailed event information to the specified file path.
## Motivation
Debugging watch-related issues (especially with `bun --watch` and `bun
--hot`) can be difficult without visibility into what the watcher is
actually seeing. This feature provides detailed trace logs showing
exactly which files are being watched and what events are triggered.
## Implementation
- **Isolated module** (`src/watcher/WatcherTrace.zig`) - All trace logic
in separate file
- **No locking needed** - Watcher runs on its own thread, no mutex
required
- **Append-only mode** - Traces persist across multiple runs for easier
debugging
- **Silent errors** - Won't break functionality if trace file can't be
created
- **JSON format** - Easy to parse and analyze
## Usage
```bash
BUN_WATCHER_TRACE=/tmp/watch.log bun --watch script.js
BUN_WATCHER_TRACE=/tmp/hot.log bun --hot server.ts
```
## JSON Output Format
Each line is a JSON object with:
```json
{
"timestamp": 1760280923269,
"index": 0,
"path": "/path/to/watched/file.js",
"delete": false,
"write": true,
"rename": false,
"metadata": false,
"move_to": false,
"changed_files": ["script.js"]
}
```
## Testing
All tests use stdout streaming to wait for actual reloads (no
sleeps/timeouts):
- Tests with `--watch` flag
- Tests with `fs.watch` API
- Tests that trace file appends across multiple runs
- Tests validation of JSON format and event details
```
✅ 4 pass
❌ 0 fail
📊 52 expect() calls
```
## Files Changed
- `src/Watcher.zig` - Minimal integration with WatcherTrace module
- `src/watcher/WatcherTrace.zig` - New isolated trace implementation
- `src/watcher/KEventWatcher.zig` - Calls writeTraceEvents before
onFileUpdate
- `src/watcher/INotifyWatcher.zig` - Calls writeTraceEvents before
onFileUpdate
- `src/watcher/WindowsWatcher.zig` - Calls writeTraceEvents before
onFileUpdate
- `test/cli/watch/watcher-trace.test.ts` - Comprehensive tests
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Replace `catch bun.outOfMemory()`, which can accidentally catch
non-OOM-related errors, with either `bun.handleOom` or a manual `catch
|err| switch (err)`.
(For internal tracking: fixes STAB-1070)
---------
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
* Move `DebugThreadLock` to `bun.safety`
* Enable in `ci_assert` builds, but store stack traces only in debug
builds
* Reduce size of struct by making optional field non-optional
* Add `initLockedIfNonComptime` as a workaround for not being able to
call `initLocked` in comptime contexts
* Add `lockOrAssert` method to acquire the lock if unlocked, or else
assert that the current thread acquired the lock
* Add stack traces to `CriticalSection` and `AllocPtr` in debug builds
* Make `MimallocArena.init` infallible
* Make `MimallocArena.heap` non-nullable
* Rename `RefCount.active_counts` to `raw_count` and provide read-only
`get` method
* Add `bun.safety.alloc.assertEq` to assert that two allocators are
equal (avoiding comparison of undefined `ptr`s)
(For internal tracking: fixes STAB-917, STAB-918, STAB-962, STAB-963,
STAB-964, STAB-965)
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
