How to opam install a package that uses ocaml-rs

[mimoo]

Hey!

I'm trying to publish an opam package that wraps a rust library. So far I've tried the following:

• run cargo vendor
• copy output of cargo vendor in .cargo/config
• add vendor in (dirs :standard \ "target" "vendor") of dune file to avoid errors if dune files are present there (which is my case)
• add all of that to the deps field in the dune rule

  deps
    (source_tree .)
    (source_tree .cargo)
    (source_tree vendor))
  

with all of that opam install . still attempts to make a connection to github. Any idea of what else I might be missing?

[zshipko]

I don’t have any experience with ocaml-rs + opam, but I believe this project is released on opam: https://github.com/c-cube/batsat-ocaml - maybe there are some hints in that repo? I can try to take a quick look at this later in the week if you’re still having issues.

Once you get something working I would be happy to add the steps to the readme!

[mimoo]

Thanks for the pointer!

Interestingly this does a few things I didn't list or do:

• creates the ./cargo/config as part of the dune action (this and this and this). My guess is that I'm stuck here because dune doesn't want to copy dot folders in the _build folder. BTW this should also mean that the .cargo/config is not used in https://github.com/zshipko/ocaml-rust-starter/
• ignores the vendor/ folder with the (ignored_subdirs command, and not the (dirs one (see this). According to the docs this seems like the right way of doing it (except that one should use the new data_only_dirs instead)
  • "The dirs stanza allows specifying the sub-directories dune will include in a build" (doc)
  • "One may also specify data only directories using the ignored_subdirs stanza" (doc)
• it commits Cargo.lock files. I didn't do it, and I had issues as cargo vendor seems to sometimes produce some (for example with cc)

[mimoo]

OK so I got it working with https://github.com/mimoo/randoml

Basically:

1. don't add Cargo.lock to your .gitignore
2. run cargo vendor and follow instructions (which will have you add stuff to your .cargo/config file
3. move the content of your .cargo/config file to a cargo-config file (this is a necessary hack due to a limitation of dune)
4. use the following dune file:

   ; forbid dune from building things in `target/` and `vendor/`
   
   (data_only_dirs "target" "vendor")
   
   ; creates the rust library if any rust file changes
   
   (rule
   (targets libXXX.a dllXXX.so)
   (deps
   (source_tree .)
   (source_tree vendor))
   (action
   (progn
       ; this is to circumvent a dumb limitation of dune
       ; which prevents us from copying any .folder to _build
       (run mkdir -p .cargo)
       (run cp cargo-config.toml .cargo/config.toml)
       ; cargo build
       (run cargo build --release --offline)
       ; extract the produced static library
       ; the .so fluff is here to remove errors that we sometimes get from dune
       (run
           sh
           -c
           "mv target/release/libXXX.so ./dllXXX.so 2> /dev/null || mv target/release/libXXX.dylib ./dllXXX.so 2> /dev/null || touch dllXXX.so")
       (run cp target/release/libXXX.a .))))
   
   ; the FFI OCaml lib
   
   (library
   (name YYY)
   (public_name YYY)
   (foreign_archives XXX))
   

note the fluff with the .so which I had to write. It looks a bit different than the one you have on https://github.com/zshipko/ocaml-rust-starter/blob/master/src/dune because in my case there's never any .so produced (macOS) so I need to produce a dumb one with touch

[mimoo]

(btw this seems to mostly work, on some distributions it doesn't: https://github.com/ocaml/opam-repository/pull/19057). I'm wondering if we could create a package like conf-rust-2018 that either contains a rust-toolchain file or that uses a specific version when building with cargo, to see if the version is installed on the system.

[mimoo]

which links to more discussion here: https://discuss.ocaml.org/t/cargo-opam-packaging-of-a-rust-ocaml-project/5743