Call Rust from Haskell with cargo-cabal and hs-bindgen

See https://sraka.xyz/posts/hs-bindgen-introduction.html.

For now, this is a shell-based workflow, rather than using Nix to build everything, i.e. `nix develop` works but `nix build` doesn't. And `cargo build` has to be called manually to create the C library, rather than `cabal` being clever enough to invoke it itself.

We ran `cargo cabal init` from the `rust` directory (`nix shell github:yvan-sraka/cargo-cabal`), which generated `hsbindgen.toml` (which we use), and `Setup.lhs` (which just added `extra-lib-dirs`, and with the wrong paths, so we dspecify those statically instead in `garnet.cabal`). We also follow its advice to use `staticlib`.

Also, after we ran the first `cargo build` (requiring a `mkdir rust/src` before it would run), we took the generated the Haskell file, and moved the main contents in to `Main.hs` manually.

flake.nix

@@ -63,10 +63,6 @@
           rust-analyzer
         ];
       };
-      packages = {
-        haskell = haskell.packages."garnet:exe:garnet";
-        rust = rust.buildPackage { src = rust.cleanCargoSource ./rust; };
-      };
     }
     );
 }

haskell/Main.hs

@@ -1,5 +1,8 @@
 module Main (main) where
 
+import Foreign.C.String (CString, withCString)
+
+foreign import ccall safe "__c_hello" hello :: CString -> IO ()
+
 main :: IO ()
-main = do
+main = withCString "Haskell" hello
-    putStrLn "Hello from Haskell"

haskell/garnet.cabal

@@ -33,5 +33,11 @@ executable garnet
         -threaded
         -rtsopts
         -with-rtsopts=-N
+    extra-lib-dirs:
+        -- TODO referring to parent triggers warning - maybe put Rust stuff in subdir
+        -- TODO bit weird to have both of these, but it's what the `cargo-cabal` setup script did
+        ../rust/target/release
+        ../rust/target/debug
+    extra-bundled-libraries: garnet_rs
     build-depends:
         base >= 4.14,

rust/Cargo.lock

@@ -3,5 +3,217 @@
 version = 4
 
 [[package]]
-name = "garnet"
+name = "antlion"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd743dc9b5cf465db1be79d28b4bfd7fa143d289546afeea5dc933551883e1f6"
+dependencies = [
+ "proc-macro2",
+ "quote",
+]
+
+[[package]]
+name = "displaydoc"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97369cbbc041bc366949bc74d34658d6cda5621039731c6310521892a3a20ae0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.116",
+]
+
+[[package]]
+name = "garnet-rs"
 version = "0.1.0"
+dependencies = [
+ "hs-bindgen",
+]
+
+[[package]]
+name = "hs-bindgen"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3e9723a81f9f23c3e52b01ce72db20c7ab384c8618b1032eea04985260d10fc7"
+dependencies = [
+ "hs-bindgen-attribute",
+ "hs-bindgen-traits",
+]
+
+[[package]]
+name = "hs-bindgen-attribute"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e57fc3cb0491f749fc50e7cf186c189b64af557edb9f78e36eb78bb9021d6624"
+dependencies = [
+ "antlion",
+ "displaydoc",
+ "hs-bindgen-types",
+ "lazy_static",
+ "quote",
+ "rustc_version",
+ "semver 1.0.27",
+ "serde",
+ "syn 1.0.109",
+ "thiserror",
+ "toml",
+]
+
+[[package]]
+name = "hs-bindgen-traits"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e92e839254ee5975299f64183e8346548c4ba5e4ee0253a05426891a6f135a6a"
+
+[[package]]
+name = "hs-bindgen-types"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2d986de5641ea4aa8025589d7243e403961fb0f5572c4dd4764a1bb4a01768c"
+dependencies = [
+ "displaydoc",
+ "proc-macro2",
+ "quote",
+ "thiserror",
+]
+
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.106"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "21b2ebcf727b7760c461f091f9f0f539b77b8e87f2fd88131e7f1b433b3cece4"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
+dependencies = [
+ "semver 0.9.0",
+]
+
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+dependencies = [
+ "semver-parser",
+]
+
+[[package]]
+name = "semver"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d767eb0aabc880b29956c35734170f26ed551a859dbd361d140cdbeca61ab1e2"
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+
+[[package]]
+name = "serde"
+version = "1.0.228"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a8e94ea7f378bd32cbbd37198a4a91436180c5bb472411e48b5ec2e2124ae9e"
+dependencies = [
+ "serde_core",
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_core"
+version = "1.0.228"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41d385c7d4ca58e59fc732af25c3983b67ac852c1a25000afe1175de458b67ad"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.228"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d540f220d3187173da220f885ab66608367b6574e925011a9353e4badda91d79"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.116",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.109"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.116"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3df424c70518695237746f84cede799c9c58fcb37450d7b23716568cc8bc69cb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.69"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6aaf5339b578ea85b50e080feb250a3e8ae8cfcdff9a461c9ec2904bc923f52"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.69"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4fee6c4efc90059e10f81e6d42c60a18f76588c3d74cb83a0b242a2b6c7504c1"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.116",
+]
+
+[[package]]
+name = "toml"
+version = "0.5.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f4f7f0dd8d50a853a531c426359045b1998f04219d88799810762cd4ad314234"
+dependencies = [
+ "serde",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"

rust/Cargo.toml

@@ -1,8 +1,11 @@
 [package]
-name = "garnet"
+name = "garnet-rs"
 version = "0.1.0"
 edition = "2024"
 
-[[bin]]
+[lib]
-path = "main.rs"
+path = "lib.rs"
-name = "garnet"
+crate-type = ["staticlib"]
+
+[dependencies]
+hs-bindgen = { version = "0.8", features = ["full"] }

rust/hsbindgen.toml

@@ -0,0 +1,13 @@
+# Since the only `.cabal` format parser implementation and specification live
+# in Cabal itself ... this deadly simple config file is used by `hs-bindgen`
+# Rust crate to get needed data (like default exposed module name).
+
+default = "GarnetRs"
+
+# There is an unlikely future where instead we have a Rust `.cabal` parser,
+# that most likely would rely under the hood on a Haskell static lib wrapper
+# of `Cabal.Parse` or https://hackage.haskell.org/package/Cabal-syntax library.
+# But even in this case, it would be nice to know the `cargo-cabal` version that
+# generated the `.cabal` file used.
+
+version = "0.8.0"

rust/lib.rs

@@ -0,0 +1,6 @@
+use hs_bindgen::*;
+
+#[hs_bindgen(hello :: CString -> IO (()))]
+fn hello(name: &str) {
+    println!("Hello from Rust, {name}!");
+}

rust/main.rs

@@ -1,3 +0,0 @@
-fn main() {
-    println!("Hello from Rust");
-}