Optional cbindgen dependency

Cargo.toml

@@ -16,13 +16,13 @@ num-traits = "0.2.8"
 thiserror = "1.0.4"
 
 [build-dependencies]
-cbindgen = "0.22.0"
+cbindgen = { version = "0.22.0", default-features=false, optional = true}
 
 [dev-dependencies]
 criterion = "0.3.0"
 
 [features]
-headers = []
+headers = ["cbindgen"]
 
 [lib]
 name = "polylabel"

build.rs

@@ -1,19 +1,14 @@
-extern crate cbindgen;
-
-use std::env;
+#[cfg(feature = "cbindgen")]
+fn main() {
+    use std::env;
 
-fn write_headers() {
-    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
     let config = cbindgen::Config::from_file("cbindgen.toml").unwrap();
 
+    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
     cbindgen::generate_with_config(&crate_dir, config)
         .expect("Unable to generate bindings")
         .write_to_file("include/header.h");
 }
 
-fn main() {
-    let headers_enabled = env::var_os("CARGO_FEATURE_HEADERS").is_some();
-    if headers_enabled {
-        write_headers();
-    }
-}
+#[cfg(not(feature = "cbindgen"))]
+fn main() { }

include/header.h

@@ -1,4 +1,4 @@
-/* Generated with cbindgen:0.19.0 */
+/* Generated with cbindgen:0.22.0 */
 
 /* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */