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Expected Behavior

dune build should succeed

Actual Behavior

dune build fails with

dune build --profile release --root . ./dist
File "dune.build", line 17, characters 3-23:
17 |    mirage-bootvar.solo5 mirage-crypto-rng-mirage mirage-kv-mem mirage-logs
        ^^^^^^^^^^^^^^^^^^^^
Error: Library "mirage-bootvar.solo5" in
_build/solo5/duniverse/mirage-bootvar/solo5 is hidden (optional with
unavailable dependencies).

Reproduction

Environment:

• OCaml 4.14.2
• dune 3.20.2
• mirage 4.10.4

Once you have an opam switch with the above, run:

• git clone https://github.com/mirage/mirage-skeleton.git
• cd mirage-skeleton/tutorial/hello
• mirage configure -t hvt
• make

You will observe the above error.

Looking deeper, this issue only appeared once lwt 6.0.0 came into the universe. Its src/core/dune file contains:

 (libraries
 (select lwt_rte.ml from
  (lwt_runtime_events -> lwt_rte.with.ml)
  (-> lwt_rte.without.ml))))

Now, mirage uses opam-monorepo to construct kind of a monorepo -- and here lwt (together with lwt_runtime_events) is present. I suspect dune attempts to use the first select case, and fails. Why on earth the error is about mirage-bootvar.solo5, I have no clue about.

Workarounds include:

• use lwt 5.9.2 (e.g. via opam pin)
• modify the src/core/dune by removing the line lwt_runtime_events -> lwt_rte.with.ml

If you have any further questions, please don't hesitate from asking.

Affected are all MirageOS unikernels (since they use lwt), with a fresh enough opam-repository (where lwt 6.0.0 is around).