<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/143637>143637</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang-Unit:: DirectoryWatcherTest.AddFiles flaky on MacOS
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          mizvekov
      </td>
    </tr>
</table>

<pre>
    On a MacOS machine, every so often `Clang-Unit::DirectoryWatcherTest.AddFiles` fails like so:
```
[ RUN      ] DirectoryWatcherTest.AddFiles
Unknown FSEvent type.
UNREACHABLE executed at /Users/mizvekov/Repos/llvm/2/clang/lib/DirectoryWatcher/mac/DirectoryWatcher-mac.cpp:152!
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0 AllClangUnitTests        0x0000000105c75570 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 56
1 AllClangUnitTests        0x0000000105c73bf0 llvm::sys::RunSignalHandlers() + 64
2  AllClangUnitTests        0x0000000105c75d54 SignalHandler(int, __siginfo*, void*) + 312
3  libsystem_platform.dylib 0x000000018f6d4624 _sigtramp + 56
4  libsystem_pthread.dylib  0x000000018f69a88c pthread_kill + 296
5  libsystem_c.dylib        0x000000018f5a3c60 abort + 124
6 AllClangUnitTests        0x0000000105c09b0c llvm::install_fatal_error_handler(void (*)(void*, char const*, bool), void*) (.cold.1) + 0
7  AllClangUnitTests        0x0000000107892d20 eventStreamCallback(__FSEventStream const*, void*, unsigned long, void*, unsigned int const*, unsigned long long const*) + 1604
8  FSEvents 0x0000000198ebe9f8 implementation_callback_rpc + 3256
9  FSEvents 0x0000000198ebdcb8 _Xcallback_rpc + 220
10 FSEvents 0x0000000198ebdbac FSEventsD2F_server + 68
11 FSEvents 0x0000000198ec15bc receive_and_dispatch_rcv_msg + 340
12 libdispatch.dylib 0x000000018f4fc85c _dispatch_client_callout + 16
13 libdispatch.dylib 0x000000018f4e75e0 _dispatch_continuation_pop + 596
14 libdispatch.dylib        0x000000018f4fa620 _dispatch_source_latch_and_call + 396
15 libdispatch.dylib        0x000000018f4f92f8 _dispatch_source_invoke + 844
16 libdispatch.dylib        0x000000018f4eb1b8 _dispatch_lane_serial_drain + 332
17 libdispatch.dylib 0x000000018f4ebe2c _dispatch_lane_invoke + 388
18 libdispatch.dylib 0x000000018f4f6264 _dispatch_root_queue_drain_deferred_wlh + 292
19 libdispatch.dylib        0x000000018f4f5ae8 _dispatch_workloop_worker_thread + 540
20 libsystem_pthread.dylib  0x000000018f696e64 _pthread_wqthread + 292
21 libsystem_pthread.dylib  0x000000018f695b74 start_wqthread + 8
```
</pre>
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