OCaml Interop Dune Builder

This crate provides a helper utility, DuneBuilder, for Rust build scripts (build.rs) that need to compile OCaml code using Dune and link the resulting object files.

It simplifies the process of:

• Locating the Dune project.
• Determining relative build paths.
• Invoking Dune to build a specific target.
• Collecting the generated object (.o) files.

Usage

Add this crate as a build dependency in your Cargo.toml:

[build-dependencies]
ocaml-interop-dune-builder = "*"

Then, in your build.rs script:

use ocaml_interop_dune_builder::{DuneBuilder, DuneInvocation};

fn main() {
    let ocaml_source_dir = "ocaml_lib"; // Directory containing your OCaml sources relative to Cargo.toml

    // Instruct cargo to re-run the build script if OCaml files change.
    // Adjust paths and filenames as necessary.
    println!("cargo:rerun-if-changed={}/my_ocaml_lib.ml", ocaml_source_dir);
    println!("cargo:rerun-if-changed={}/dune", ocaml_source_dir); // Or specific dune files

    let objects = DuneBuilder::new(ocaml_source_dir)
        .with_profile("release") // Optional: set a build profile (default is "default")
        .with_dune_args(vec!["--display=quiet".to_string()]) // Optional: add custom dune arguments
        .with_dune_invocation(DuneInvocation::System) // Optional: invoke dune directly (default is OpamExec)
        .build("my_ocaml_lib.exe.o"); // Or other .o target

    // Use a C/C++ build tool like `cc` to link the OCaml objects.
    let mut build = cc::Build::new();
    for object_path in objects {
        build.object(object_path);
    }
    build.compile("name_of_your_static_library"); // e.g., "libocaml_callable"
}

This DuneBuilder handles finding the dune project, constructing paths, and running the dune build command. The collected object files can then be passed to a tool like the cc crate to compile and link them into your Rust project.

Configuration

The DuneBuilder can be configured using a fluent interface:

• new(ocaml_source_dir: P): Creates a new builder. ocaml_source_dir is the path to your OCaml sources, relative to the Cargo.toml of the crate being built.
• with_profile(profile_name: &str): Sets the Dune build profile (e.g., "release", "dev"). The default is "default".
• with_dune_args(extra_args: Vec<String>): Appends custom arguments to the dune build command.
• with_dune_invocation(invocation: DuneInvocation): Specifies how to call dune:
  • DuneInvocation::OpamExec (default): Uses opam exec -- dune ....
  • DuneInvocation::System: Uses dune ... directly from the system path.
• build(target: T): Executes the dune build command for the specified target (e.g., my_lib.a, my_exe.exe.o) and returns a Vec<PathBuf> of the compiled object files found in the build directory.