Build molten inside the build script

Cargo.toml

@@ -11,3 +11,6 @@ documentation = "https://docs.rs/ash-molten"
 
 [dependencies]
 ash = "0.29"
+
+[features]
+external = []

build.rs

@@ -1,7 +1,27 @@
 use std::path::PathBuf;
+// Features are not used inside build scripts, so we have to explicitly query them from the
+// enviroment
+fn is_external_enabled() -> bool {
+    std::env::vars()
+        .filter_map(|(flag, _)| {
+            const NAME: &'static str = "CARGO_FEATURE_";
+            if flag.starts_with(NAME) {
+                let feature = flag.split(NAME).nth(1).expect("").to_string();
+                println!("{:?}", feature);
+                return Some(feature);
+            }
+            None
+        })
+        .find(|f| f == "EXTERNAL")
+        .is_some()
+}
 fn main() {
-    let project_dir = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap()).join("external");
+    // The 'external' feature was not enabled. Molten will be built automaticaly.
+    if !is_external_enabled() {
+        std::process::Command::new("bash").arg("build_molten.sh").status().expect("Unable to build molten");
+        let project_dir = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap()).join("native");
         println!("cargo:rustc-link-search=native={}", project_dir.display());
+    }
     println!("cargo:rustc-link-lib=framework=Metal");
     println!("cargo:rustc-link-lib=framework=AppKit");
     println!("cargo:rustc-link-lib=framework=QuartzCore");

build_molten.sh

@@ -2,4 +2,4 @@ git submodule update --init
 cd MoltenVK
 sh fetchDependencies
 make macos
-cp Package/Release/MoltenVK/macOS/static/libMoltenVK.a ../external
+cp Package/Release/MoltenVK/macOS/static/libMoltenVK.a ../native