dune 3.0 crashes badly when doing dune build -w, and dune clean in same repo

[Alizter]

In my workflow I have dune building in the background with a watch. If I do a dune clean it crashes badly.

Expected Behavior

For dune clean to work, and dune build -w not to crash.

Actual Behavior

It crashes.

Reproduction

Doing the following

dune init proj foo
cd foo
dune build -w &
dune clean

crashes badly and gives:

This error backtrace

Internal error, please report upstream including the contents of _build/log.
Description:
  ("Fs_memo.Event.create called on a build path", {})
Raised at Stdune__code_error.raise in file "otherlibs/stdune/code_error.ml",
  line 11, characters 30-62
Called from Dune_file_watcher.Fs_memo_event.create in file
  "src/dune_file_watcher/dune_file_watcher.ml", line 30, characters 6-71
Called from
  Dune_file_watcher.process_inotify_event.create_event_unless_excluded in
  file "src/dune_file_watcher/dune_file_watcher.ml", line 179, characters
  28-62
Called from Stdune__list.concat_map.aux in file "otherlibs/stdune/list.ml",
  line 41, characters 15-18
Called from Dune_engine__scheduler.Run_once.iter in file
  "src/dune_engine/scheduler.ml", line 1031, characters 19-25
Called from Fiber.run.loop in file "src/fiber/fiber.ml", line 1008,
  characters 51-60
Called from Fiber.run.(fun) in file "src/fiber/fiber.ml" (inlined), line
  1010, characters 17-47
Called from Dune_engine__scheduler.Run_once.run in file
  "src/dune_engine/scheduler.ml", line 1101, characters 10-50
Re-raised at Stdune__exn.raise_with_backtrace in file
  "otherlibs/stdune/exn.ml" (inlined), line 36, characters 27-56
Called from Dune_engine__scheduler.Run.go.(fun) in file
  "src/dune_engine/scheduler.ml", line 1333, characters 30-61
Called from Cmdliner_term.app.(fun) in file
  "vendor/cmdliner/src/cmdliner_term.ml", line 25, characters 19-24
Called from Cmdliner.Term.run in file "vendor/cmdliner/src/cmdliner.ml", line
  117, characters 32-39
Called from Cmdliner.Term.term_eval in file
  "vendor/cmdliner/src/cmdliner.ml", line 147, characters 18-36
Called from Cmdliner.Term.Group.eval in file
  "vendor/cmdliner/src/cmdliner.ml", line 367, characters 22-48
Called from Main in file "bin/main.ml", line 90, characters 10-50

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.

Specifications

• Version of dune (output of dune --version): says n/a but is 3.0.0
• Version of ocaml (output of ocamlc --version) 4.13.1
• Operating system (distribution and version): Ubuntu 20.04.3 LTS

[Alizter]

@rgrinberg Do you want to add this to the watch project?

[ElectreAAS]

Just ran into this one too, with dune 3.3.1

[Alizter]

@ElectreAAS later versions of Dune should be more resilient to this, but I haven't tested this issue again.

---

I've tested it and it still appears to be an issue.

[emillon]

Is this done in #6360?

[Alizter]

Yes.