Regression: new error with jsoo and module_without_implementation

[dlesbre]

Expected Behavior

I have a simple js_of_ocaml executable which uses a (module_without_implementation interface). This compiled fine with dune 3.19.1 (on OCaml 4.14.1 and 5.2.0).

Actual Behavior

After updating to dune 3.20.0, I now have a compilation error:

File "bin/.main.eobjs/jsoo/_unknown_", line 1, characters 0-0:
Error: No rule found for bin/.main.eobjs/jsoo/dune__exe__Interface.cmo.js

Reproduction

I have a minimal example with the following setup (also as a ZIP Archive):

.
├── bin
│   ├── dune
│   ├── interface.mli
│   └── main.ml
└── dune-project

• dune file:

  (executable
   (modes js)
   (modules_without_implementation interface)
   (name main))

• interface.mli

  type t = Foo

• main.ml

  let _ = Interface.Foo

• dune-project

  (lang dune 3.19)
  (name minjs)
  (package
   (name minjs)
   (depends ocaml dune js_of_ocaml)
   (allow_empty))

To reproduce the bug, attempt to build in a switch with ocaml 4.14.1 (or 5.2.0). It fails with dune 3.20.0 but passes with 3.19.1:

opam switch create test ocaml-base-compiler.4.14.1
eval $(opam env --switch=test)
opam install dune.3.20.0 js_of_ocaml
dune build # error

opam install dune.3.19.1
eval $(opam env)
dune clean
dune build # no error

Specifications

• Version of dune (output of dune --version): 3.20.0
• Version of ocaml (output of ocamlc --version): 4.14.1 (also tested on 5.2.0)
• Operating system (distribution and version): Kubuntu 25.04 x86_64
• js_of_ocaml version 6.2.0

Additional information

dune build --verbose output:

Shared cache: enabled-except-user-rules
Shared cache location: /home/dorian/.cache/dune/db
Workspace root: /home/dorian/Documents/Github/minjs
Auto-detected concurrency: 20
Dune context:
 { name = "default"
 ; kind = "default"
 ; profile = Dev
 ; merlin = true
 ; fdo_target_exe = None
 ; build_dir = In_build_dir "default"
 ; instrument_with = []
 }
Actual targets:
- alias @@default
File "bin/.main.eobjs/jsoo/_unknown_", line 1, characters 0-0:
Error: No rule found for bin/.main.eobjs/jsoo/dune__exe__Interface.cmo.js

[Alizter]

Here is a reproduction case:

  $ cat > dune-project <<EOF
  > (lang dune 3.21)
  > EOF

  $ cat > dune <<EOF
  > (executable
  >  (name main)
  >  (modes js)
  >  (modules_without_implementation interface))
  > EOF

  $ cat > main.ml <<EOF
  > let _ = Interface.Foo
  > EOF

  $ cat > interface.mli <<EOF
  > type t = Foo
  > EOF

  $ dune build
  File ".main.eobjs/jsoo/_unknown_", line 1, characters 0-0:
  Error: No rule found for .main.eobjs/jsoo/dune__exe__Interface.cmo.js
  [1]

[Alizter]

I've bisected it to 0153f76. cc @vouillon @hhugo

[hhugo]

fixed in #12320

[hhugo]

#12320 has been merged.