Include mly files nested in subdirectories when compiling with dune

Say I have the following directory:

.
├── dune-project
├── myproj.opam
└── src
    ├── dune
    ├── module1.ml
    ├── parser1
    │   └── file1.ml
    └── parser2
        └── file2.ml

Since I want everything to be in the same library, I have the following:

src/dune:

(include_subdirs  unqualified)

(library
 (name myproj)
 (modules module1 file1 file2)
  )

And it compiles perfectly well.

Now, the thing is, my file1 and file2 are actually mly files so I have this:

.
├── dune-project
├── myproj.opam
└── src
    ├── dune
    ├── module1.ml
    ├── parser1
    │   └── parser1.mly
    └── parser2
        └── parser2.mly

If I try to compile (by changing file(1|2) by parser(1|2) in the dune file), I have the following error:

❯ dune build
File "src/dune", line 5, characters 26-33:
5 |  (modules module1 parser1 parser2 )
                              ^^^^^^^
Error: Module Parser2 doesn't exist.

I edit my dune file:

(include_subdirs  unqualified)

(menhir
 (modules parser1 parser2)
)

(library
 (name myproj)
 (modules module1 parser1 parser2 )
  )

Two errors now:

❯ dune build
File "src/dune", line 3, characters 0-36:
3 | (menhir
4 |  (modules parser1 parser2)
5 | )
Error: No rule found for src/parser1.mly
File "src/dune", line 3, characters 0-36:
3 | (menhir
4 |  (modules parser1 parser2)
5 | )
Error: No rule found for src/parser2.mly

Ok, I then add two dune files in parser(1|2) directories:

(menhir
 (modules parser(1|2))
)

[EDIT] Looks like I missed something but this was actually working pretty well

And I now have the same error as before:

❯ dune build
File "src/dune", line 5, characters 26-33:
5 |  (modules module1 parser1 parser2 )
                              ^^^^^^^
Error: Module Parser2 doesn't exist.

Am I missing something to please dune? (I have the same problem if I have .mll files)

The menhir stanza doesn't work with subdirs. It is a bug that is not yet fixed¹. There are a couple of workarounds, like adding the dune file to the folder where you have the parser (didn't check it myself). But I would suggest splitting the parsers into separate libraries or moving them to the src folder. The former is preferred, especially since then you won't need to write the modules stanza.

¹⁾As of January 2022