Patched build.rs to run on systems without rustup. Added flake for ni…

.envrc

@@ -0,0 +1 @@
+use flake;

build.rs

@@ -133,10 +133,20 @@ fn build_wasm_test_program(name: &'static str, root: &'static str) {
 }
 
 fn has_wasm32_wasi_target() -> bool {
-    let output = run(vec!["rustup", "target", "list", "--installed"], None, None);
-    let output = std::str::from_utf8(&output.stdout).unwrap();
+    // Using rustc here for systems that don't have rustup
+    let output = run(
+        vec!["rustc", "--print=target-libdir", "--target=wasm32-wasi"],
+        None,
+        None,
+    );
+    let Ok(output) = std::str::from_utf8(&output.stdout) else {
+        return false;
+    };
+    // If it returns regular output on stdout, then the compiler understands
+    // If the path exists, then we know the target is installed
+    // If the path doesn't exist, it must be installed with rustup or something
     for line in output.lines() {
-        if line == "wasm32-wasi" {
+        if !line.is_empty() && std::path::Path::new(line).exists() {
             return true;
         }
     }

flake.nix

@@ -0,0 +1,39 @@
+
+{
+  description = "Nix Devshell for Spin";
+
+  inputs = {
+    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    flake-utils.url  = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, rust-overlay, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+        };
+        rustTarget = pkgs.rust-bin.stable.latest.default.override {
+              extensions= [ "rust-src" "rust-analyzer" ];
+              targets = [ "wasm32-wasi" "wasm32-unknown-unknown" ];
+            };
+      in
+      with pkgs;
+      {
+        devShells.default = mkShell {
+          buildInputs = [
+            openssl
+            pkg-config
+            rustTarget
+          ];
+
+          shellHook = ''
+            '';
+        RUST_SRC_PATH = "${rustTarget}/lib/rustlib/src/rust/library";
+
+        };
+      }
+    );
+}