Failure in promote mode for directory targets with subdirectories

[panglesd]

Expected Behavior

When promoting a directory, the directory should be promoted

Actual Behavior

When there are deep enough subdirectories, an error like this one is raised:

  File "dune", lines 1-7, characters 0-121:
  1 | (rule
  2 |  (deps
  3 |   (source_tree deep))
  4 |  (targets (dir deep_copied))
  5 |  (mode promote)
  6 |  (action
  7 |   (run cp -r deep deep_copied)))
  Error: Cannot promote files to "deep_copied/a/b".
  Reason: opendir(deep_copied/a/b): No such file or directory
  -> required by _build/default/deep_copied
  [1]

Reproduction

• PR with a reproducing test: test: exhibit a bug when promoting directories #11213

Specifications

• Version of dune (output of dune --version): master
• Version of ocaml (output of ocamlc --version): 5.2.0 but I don't think it matters!
• Operating system (distribution and version): Archlinux but I don't think it matters!

Additional information

Running with verbose mode does not show any useful output:

  Dune context:
   { name = "default"
   ; kind = "default"
   ; profile = Dev
   ; merlin = true
   ; fdo_target_exe = None
   ; build_dir = In_build_dir "default"
   ; instrument_with = []
   }
  Actual targets:
  - _build/default/deep_copied
  Running[1]: (cd _build/default && /usr/bin/cp -r deep deep_copied)
  Promoting "_build/default/deep_copied/a/b/deep_file" to
  "deep_copied/a/b/deep_file"
  File "dune", lines 1-7, characters 0-121:
  1 | (rule
  2 |  (deps
  3 |   (source_tree deep))
  4 |  (targets (dir deep_copied))
  5 |  (mode promote)
  6 |  (action
  7 |   (run cp -r deep deep_copied)))
  Error: Cannot promote files to "deep_copied/a/b".
  Reason: opendir(deep_copied/a/b): No such file or directory
  -> required by _build/default/deep_copied
  [1]