$ touch e.ml stubs.c
$ cat > dune << EOF
> (executable
>  (name e)
>  (modes exe)
>  (foreign_stubs
>   (language c)
>   (names stubs)))
> EOF

$ dune build

$ sed -e s/executable/test/ -i dune

$ dune build
Internal error, please report upstream including the contents of _build/log.
Description:
  ("Map.find_exn: failed to find key", { key = "e"; keys = [] })
Raised at Stdune__Code_error.raise in file
  "otherlibs/stdune-unstable/code_error.ml", line 11, characters 30-62
Called from Fiber.O.(>>|).(fun) in file "src/fiber/fiber.ml", line 288,
  characters 36-41
Called from Fiber.Execution_context.apply in file "src/fiber/fiber.ml", line
  182, characters 9-14
Re-raised at Stdune__Exn.raise_with_backtrace in file
  "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
  line 204, characters 8-13
Re-raised at Stdune__Exn.raise_with_backtrace in file
  "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
  line 204, characters 8-13
Re-raised at Stdune__Exn.raise_with_backtrace in file
  "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
  line 204, characters 8-13
-> required by ("load-dir", In_build_dir "default")
-> required by ("build-alias", { dir = "default"; name = "default" })

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.
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