feat: nix-c-raw: Generate value api bindings

(cherry picked from commit 3c75dea63233670863f30547f90dd71498d547b0)

flake.nix

@@ -49,6 +49,8 @@
             buildInputs = [
               config.packages.nix
             ];
+            # Workaround: the gcc in the devshell doesn't find libc headers
+            RUST_NIX_C_RAW_EXTRA_CFLAGS = "-I${pkgs.stdenv.cc.libc.dev}/include";
             nativeBuildInputs = [
               pkgs.rust-analyzer
               pkgs.nixpkgs-fmt

rust/nix-c-raw/build.rs

@@ -36,6 +36,13 @@ fn c_headers() -> Vec<String> {
     {
         args.push(format!("-I{}", path.to_str().unwrap()));
     }
+
+    if let Ok(cflags) = std::env::var("RUST_NIX_C_RAW_EXTRA_CFLAGS") {
+        for flag in cflags.split_whitespace() {
+            args.push(flag.to_string());
+        }
+    }
+
     // write to stderr for debugging
     eprintln!("c_headers: {:?}", args);
     args

rust/nix-c-raw/include/nix-c-raw.h

@@ -1,3 +1,4 @@
 #include <nix_api_util.h>
 #include <nix_api_store.h>
 #include <nix_api_expr.h>
+#include <nix_api_value.h>