Build circuits in build.rs

Cargo.toml

@@ -64,6 +64,9 @@ tempfile = "3.0"
 tiny-keccak = "2.0.2"
 tracing-test = "0.2"
 
+[build-dependencies]
+wasmer = { version = "2.0", features = [ "dylib" ] }
+color-eyre = "0.5"
 wasmer-engine-dylib = "2.2.1"
 wasmer-compiler-cranelift = "2.2.1"
 

build.rs

@@ -0,0 +1,67 @@
+// TODO: Use ExitCode::exit_ok() when stable.
+
+use std::{process::Command, fs::canonicalize, path::{Path, PathBuf, Component}};
+use color_eyre::eyre::{Result, eyre};
+
+const ZKEY_FILE: &str = "./semaphore/build/snark/semaphore_final.zkey";
+const WASM_FILE: &str = "./semaphore/build/snark/semaphore.wasm";
+const DYLIB_FILE: &str = "./semaphore/build/snark/semaphore.dylib";
+
+// See <https://internals.rust-lang.org/t/path-to-lexical-absolute/14940>
+fn absolute(path: &str) -> Result<PathBuf> {
+    let path = Path::new(path);
+    let mut absolute = if path.is_absolute() {
+        PathBuf::new()
+    } else {
+        std::env::current_dir()?
+    };
+    for component in path.components() {
+        match component {
+            Component::CurDir => {},
+            Component::ParentDir => { absolute.pop(); },
+            component @ _ => absolute.push(component.as_os_str()),
+        }
+    }
+    Ok(absolute)
+}
+
+fn build_circuit() -> Result<()> {
+    println!("cargo:rerun-if-changed=./semaphore");
+    let run = |cmd: &[&str]| -> Result<()> {
+        Command::new(cmd[0])
+            .args(cmd[1..].iter())
+            .current_dir("./semaphore")
+            .status()?
+            .success()
+            .then(|| ())
+            .ok_or(eyre!("procees returned failure"))?;
+            Ok(())
+    };
+
+    // Compute absolute paths
+    let zkey_file = absolute(ZKEY_FILE)?;
+    let wasm_file = absolute(WASM_FILE)?;
+
+    // Build circuits if not exists
+    // TODO: This does not rebuild if the semaphore submodule is changed. 
+    // NOTE: This requires npm / nodejs to be installed.
+    if !(zkey_file.exists() && wasm_file.exists()) {
+        run(&["npm", "install"])?;
+        run(&["npm", "exec", "ts-node", "./scripts/compile-circuits.ts"])?;
+    }
+    assert!(zkey_file.exists());
+    assert!(wasm_file.exists());
+
+    // Export generated paths
+    println!("cargo:rustc-env=ZKEY_FILE={}", zkey_file.display());
+    println!("cargo:rustc-env=WASM_FILE={}", wasm_file.display());
+    
+    Ok(())
+}
+
+fn main() -> Result<()> {
+    build_circuit()?;
+
+
+    Ok(())
+}