Internal error: link_many: unable to find module

[afdw]

Expected Behavior

Dune should not crash.

Actual Behavior

Dune crashes with the following message:

Internal error, please report upstream including the contents of _build/log.
Description:
  ("link_many: unable to find module",
  { main_module_name = "Libzstd__type_gen"
  ; modules =
      Singleton
        { source =
            { path = [ "Zstd_stubs" ]
            ; files =
                { impl =
                    Some
                      { path = In_build_dir "default/src/zstd_stubs.ml"
                      ; dialect = "ocaml"
                      }
                ; intf = None
                }
            }
        ; obj_name = "zstd_stubs"
        ; pp = None
        ; visibility = "public"
        ; kind = Impl
        ; install_as = None
        }
  })
Raised at Stdune__Code_error.raise in file
  "otherlibs/stdune/src/code_error.ml", line 10, characters 30-62
Called from Dune_rules__Exe.link_many.(fun) in file "src/dune_rules/exe.ml",
  line 284, characters 12-215
Called from Fiber__Scheduler.exec in file "vendor/fiber/src/scheduler.ml",
  line 76, characters 8-11
-> required by ("<unnamed>", ())
-> required by ("load-dir", In_build_dir "default/src")
-> required by ("<unnamed>", ())
-> required by
   ("build-alias", { dir = In_build_dir "default"; name = "default" })
-> 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.

Reproduction

1. Download and unpack ocaml-zstd.zip.
2. Run opam switch create ..
3. Run dune build.

Specifications

• Version of dune (output of dune --version): 3.14.2

• Version of ocaml (output of ocamlc --version): 5.1.1

• Operating system (distribution and version): Arch Linux

• Link to gist with verbose output (run dune with the --verbose flag): https://pastebin.com/raw/ZTxqy70Y

[emillon]

Hi! I confirmed the problem; also this is not a regression (happens in 3.7.0 too). From a quick glance, this might be related to using (modules). Normally you don't need to manually split your library in 2 when using (ctypes), you just add it and dune will take care of the rest.

For example the whole dune file might just be:

(library
  (public_name zstd)
 (wrapped false)
 (ctypes
  (external_library_name libzstd)
  (headers (include "zstd.h"))
  (type_description
   (instance Types)
   (functor Type_description))
  (function_description
   (concurrency unlocked)
   (instance Functions)
   (functor Function_description))
  (generated_types Types_generated)
  (generated_entry_point C)))

But that being said, this error message needs to be fixed.