$ ./dune.exe build @install -w     
Internal error, please report upstream including the contents of _build/log.
Description:
  ("Fsevents.start: dispatch queue stopped", {})
Raised at Stdune__Code_error.raise in file
  "otherlibs/stdune/src/code_error.ml", line 10, characters 30-62
Called from Stdlib__Fun.protect in file "fun.ml", line 33, characters 8-15
Re-raised at Stdlib__Fun.protect in file "fun.ml", line 38, characters 6-52
Called from Stdlib__Fun.protect in file "fun.ml", line 33, characters 8-15
Re-raised at Stdlib__Fun.protect in file "fun.ml", line 38, characters 6-52
Called from Dune_file_watcher.add_watch in file
  "src/dune_file_watcher/dune_file_watcher.ml", line 729, characters 13-50
Called from Dune_engine__Fs_memo.Watcher.watch_path in file
  "src/dune_engine/fs_memo.ml", line 69, characters 10-50
Called from Dune_engine__Fs_memo.Watcher.memo_for_watching_via_parent.(fun)
  in file "src/dune_engine/fs_memo.ml", line 130, characters 8-58
Called from Fiber__Scheduler.exec in file "vendor/fiber/src/scheduler.ml",
  line 76, characters 8-11
-> required by
   ("fs_memo_for_watching_via_parent",
   External "/Library/TeX/texbin/latexmk/hg")
-> required by ("which", <opaque>)
-> required by ("which", <opaque>)
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by
   ("load-dir", In_build_dir "default/test/blackbox-tests/test-cases/cram")
-> required by ("toplevel", ())

I must not crash.  Uncertainty is the mind-killer. Exceptions are the
little-death that brings total obliteration.  I will fully express my cases. 
Execution will pass over me and through me.  And when it has gone past, I
will unwind the stack along its path.  Where the cases are handled there will
be nothing.  Only I will remain.