Single source of truth for rapidsnark version in RAPIDSNARK_VERSION.

RAPIDSNARK_VERSION

@@ -0,0 +1 @@
+0.0.8

crates/build.rs

@@ -4,40 +4,30 @@ use std::path::Path;
 use std::process::Command;
 
 const RAPIDSNARK_DOWNLOAD_SCRIPT: &str = include_str!("./download_rapidsnark.sh");
+const RAPIDSNARK_LIB_DIR_ENV_VAR: &str = "RAPIDSNARK_LIB_DIR";
+const RAPIDSNARK_VERSION_FILE: &str = "../RAPIDSNARK_VERSION";
 
 fn main() {
     let target = env::var("TARGET").unwrap();
-    let out_dir = env::var("OUT_DIR").expect("OUT_DIR not set");
+    let out_dir = env::var("OUT_DIR").unwrap();
     let arch = target.split('-').next().unwrap();
 
     // See: https://github.com/zkmopro/chkstk_stub
     chkstk_stub::build();
 
-    // Try to list contents of the target directory
-    let rapidsnark_path = Path::new(&out_dir).join(Path::new("rapidsnark"));
-    // If the rapidsnark repo is not downloaded, download it
-    if !rapidsnark_path.exists() {
-        let rapidsnark_script_path = Path::new(&out_dir).join(Path::new("download_rapidsnark.sh"));
-        fs::write(&rapidsnark_script_path, RAPIDSNARK_DOWNLOAD_SCRIPT)
-            .expect("Failed to write build script");
-        let child_process = Command::new("sh")
-            .arg(rapidsnark_script_path.to_str().unwrap())
-            .spawn();
-        if let Err(e) = child_process {
-            panic!("Failed to spawn rapidsnark download: {e}");
-        }
-        let status = child_process.unwrap().wait();
-        if let Err(e) = status {
-            panic!("Failed to wait for rapidsnark download: {e}");
-        } else if !status.unwrap().success() {
-            panic!("Failed to wait for rapidsnark download");
-        }
-    }
-    let absolute_lib_path = if rapidsnark_path.join(&target).exists() {
-        rapidsnark_path.join(&target)
+    println!("cargo:rerun-if-changed={RAPIDSNARK_VERSION_FILE}");
+    println!("cargo:rerun-if-env-changed={RAPIDSNARK_LIB_DIR_ENV_VAR}");
+
+    let rapidsnark_lib_dir = if let Ok(lib_dir) = env::var(RAPIDSNARK_LIB_DIR_ENV_VAR) {
+        println!("cargo:warning=rapidsnark: using pre-supplied libs from {RAPIDSNARK_LIB_DIR_ENV_VAR}={lib_dir}");
+        Path::new(&lib_dir).to_path_buf()
     } else {
-        rapidsnark_path.join(arch)
-    };
+        println!("cargo:warning=rapidsnark: {RAPIDSNARK_LIB_DIR_ENV_VAR} not set, downloading...");
+        provide_rapidsnark(&out_dir, arch)
+    }
+    .canonicalize()
+    .unwrap_or_else(|error| panic!("{RAPIDSNARK_LIB_DIR_ENV_VAR} is not a valid path: {error}"));
+
     let compiler = cc::Build::new().get_compiler();
     let cpp_stdlib = if compiler.is_like_clang() {
         "c++"
@@ -47,7 +37,7 @@ fn main() {
 
     println!(
         "cargo:rustc-link-search=native={}",
-        absolute_lib_path.display()
+        rapidsnark_lib_dir.display()
     );
 
     // The shared rapidsnark artifact is already linked with its fr/fq/gmp implementation.
@@ -73,6 +63,52 @@ fn main() {
     println!("cargo:rustc-link-lib={thread_lib}");
 }
 
+fn rapidsnark_version() -> String {
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set");
+    let version_file = Path::new(&manifest_dir).join(RAPIDSNARK_VERSION_FILE);
+    fs::read_to_string(&version_file)
+        .unwrap_or_else(|e| panic!("Failed to read {}: {e}", version_file.display()))
+        .trim()
+        .to_string()
+}
+
+fn provide_rapidsnark(out_dir: &str, arch: &str) -> std::path::PathBuf {
+    let rapidsnark_path = Path::new(out_dir).join("rapidsnark");
+    if !is_rapidsnark_downloaded(&rapidsnark_path, arch) {
+        let version = rapidsnark_version();
+        let rapidsnark_script_path = Path::new(out_dir).join("download_rapidsnark.sh");
+        fs::write(&rapidsnark_script_path, RAPIDSNARK_DOWNLOAD_SCRIPT)
+            .expect("Failed to write build script");
+        let child_process = Command::new("sh")
+            .arg(rapidsnark_script_path.to_str().unwrap())
+            .env("RAPIDSNARK_VERSION", &version)
+            .spawn();
+        if let Err(e) = child_process {
+            panic!("Failed to spawn rapidsnark download: {e}");
+        }
+        let status = child_process.unwrap().wait();
+        if let Err(e) = status {
+            panic!("Failed to wait for rapidsnark download: {e}");
+        } else if !status.unwrap().success() {
+            panic!("Failed to wait for rapidsnark download");
+        }
+    }
+    rapidsnark_path.join(arch)
+}
+
+/// Checks whether the arch-specific subdirectory exists, not just the parent directory.
+///
+/// The download script creates the parent via `mkdir -p` before fetching, so checking the parent
+/// would silently skip re-downloads after a previously interrupted build.
+///
+/// The `arch` subdirectory (e.g. `x86_64/`) is itself unnecessary for isolation: `OUT_DIR` is
+/// already scoped to the full target triple by Cargo. A cleaner future refactor (option B) would
+/// have the script copy libs directly into `$OUT_DIR/rapidsnark/lib/` and sentinel on the presence
+/// of `librapidsnark.a` — eliminating the extra directory level.
+fn is_rapidsnark_downloaded(rapidsnark_path: &Path, arch: &str) -> bool {
+    rapidsnark_path.join(arch).exists()
+}
+
 fn is_static_rapidsnark() -> bool {
     env::var_os("CARGO_FEATURE_STATIC_RAPIDSNARK").is_some()
 }

crates/download_rapidsnark.sh

@@ -14,8 +14,12 @@ if [ -z "$TARGET" ]; then
     exit 1
 fi
 
-# Pinned rapidsnark release. Bump this to update the prebuilt artifacts.
-VERSION="v0.0.8"
+# Passed by build.rs from RAPIDSNARK_VERSION at the repo root. See CONTRIBUTING.md for bump instructions.
+if [ -z "$RAPIDSNARK_VERSION" ]; then
+    echo "RAPIDSNARK_VERSION not specified"
+    exit 1
+fi
+VERSION="v${RAPIDSNARK_VERSION}"
 # Upstream iden3 prebuilt archives (used for macOS / iOS / Android).
 IDEN3_BASE="https://github.com/iden3/rapidsnark/releases/download/$VERSION"
 # The iden3 Linux archives are non-PIC and built against a newer glibc, so they