feat(nix): Switch to which clang (#88)

Co-authored-by: Koby <[email protected]>

barretenberg-sys/build.rs

@@ -129,8 +129,20 @@ fn link_lib_omp(os: &OS) {
     // We are using clang, so we need to tell the linker where to search for lomp
     match os {
         OS::Linux => {
-            let llvm_dir = find_llvm_linux_path();
-            println!("cargo:rustc-link-search={llvm_dir}/lib")
+            let clang_path_string =
+                which_clang("clang").expect("Err: Expected to find clang installation on $PATH");
+            let clang_path = std::path::Path::new(clang_path_string.as_str());
+            let llvm_path = clang_path
+                .parent()
+                .expect("Expected to find parent directory of {clang_path_string}");
+            let llvm_lib_path = llvm_path.join("lib");
+            llvm_path
+                .try_exists()
+                .expect("Err: Clang lib path does not exist.");
+            println!(
+                "cargo:rustc-link-search={}",
+                llvm_lib_path.to_str().unwrap()
+            );
         }
         OS::Apple => {
             if let Some(brew_prefix) = find_brew_prefix() {
@@ -141,19 +153,19 @@ fn link_lib_omp(os: &OS) {
     println!("cargo:rustc-link-lib=omp");
 }
 
-fn find_llvm_linux_path() -> String {
-    // Most linux systems will have the `find` application
-    //
-    // This assumes that there is a single llvm-X folder in /usr/lib
-    let output = std::process::Command::new("sh")
-        .arg("-c")
-        .arg("find /usr/lib -type d -name \"*llvm-*\" -print -quit")
-        .stdout(std::process::Stdio::piped())
+fn which_clang(clang_command: &'static str) -> Option<String> {
+    let which_clang_command = std::process::Command::new("which")
+        .arg(clang_command)
         .output()
-        .expect("Failed to execute command to run `find`");
-    // This should be the path to llvm
-    let path_to_llvm = String::from_utf8(output.stdout).unwrap();
-    path_to_llvm.trim().to_owned()
+        .expect("Failed to execute which clang command");
+
+    if which_clang_command.status.success() {
+        let path =
+            String::from_utf8(which_clang_command.stdout).expect("Invalid UTF-8 output from which");
+        Some(path.trim().to_owned())
+    } else {
+        None
+    }
 }
 
 fn find_brew_prefix() -> Option<String> {

flake.nix

@@ -129,11 +129,24 @@
 
         packages.default = barretenberg-backend;
 
-        devShells.default = pkgs.mkShell ({
+        # llvmPackages should be aligned to selection from libbarretenberg
+        # better if we get rid of llvm targets and override them from input
+        devShells.default = pkgs.mkShell.override { stdenv = pkgs.llvmPackages.stdenv; } ({
           inputsFrom = builtins.attrValues self.checks;
 
           buildInputs = packages.default.buildInputs;
-          nativeBuildInputs = packages.default.nativeBuildInputs;
+          nativeBuildInputs = with pkgs; packages.default.nativeBuildInputs ++ [
+            which
+            starship
+            git
+            cargo
+            rustc
+          ];
+
+          shellHook = ''
+            eval "$(starship init bash)"
+          '';
+
         } // environment);
       });
 }