$ echo "(lang dune 2.8)" > dune-project
$ mkdir lib
$ touch lib.opam file lib/lib.ml
$ cat >lib/dune <<EOF
> (library (name lib) (public_name lib))
> (copy_files (files ../file))
> EOF

$ dune build
Internal error, please report upstream including the contents of _build/log.
Description:
  ("dependency cycle that does not involve any files",
  { frames =
      [ ("eval-pred",
        { dir = In_build_dir "default"; predicate = { id = Glob "file" } })
      ; ("dir-contents-get0", ("default", "default/lib"))
      ; ("stanzas-to-entries", "default")
      ; ("<unnamed>", ())
      ; ("<unnamed>", ())
      ; ("<unnamed>", ())
      ; ("<unnamed>", ())
      ; ("load-dir", In_build_dir "default")
      ; ("eval-pred",
        { dir = In_build_dir "default"; predicate = { id = Glob "file" } })
      ]
  })
Raised at Stdune__code_error.raise in file "src/stdune/code_error.ml", line
  9, characters 30-62
Called from Dune_engine__dep_path.map in file "src/dune_engine/dep_path.ml",
  line 90, characters 10-15
Called from Stdune__exn_with_backtrace.map in file
  "src/stdune/exn_with_backtrace.ml", line 20, characters 40-45
Called from Stdune__exn_with_backtrace.map_and_reraise in file
  "src/stdune/exn_with_backtrace.ml" (inlined), line 22, characters 35-45
Called from Dune_engine__build_system.process_exn_and_reraise in file
  "src/dune_engine/build_system.ml", line 1915, characters 2-162
Called from Fiber.Execution_context.forward_exn_with_bt in file
  "src/fiber/fiber.ml", line 136, characters 10-17

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.