Move bindgen generation from build.rs to api_gen binary

Replace the `generate-bindings` feature + build.rs approach with a
dedicated `api_gen` workspace member binary, following the pattern
used by fidelityfx-rs. Bindings are generated by running
`cargo r -p api_gen` instead of `cargo b -Fgenerate-bindings`.

This pins bindgen to =0.72.1 for reproducible output and removes the
build-dependency from the published crate.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MarijnS95

.github/workflows/ci.yml

@@ -54,12 +54,12 @@ jobs:
           src/xess/vk.rs
           src/xess/xess.rs
       - name: Generate
-        run: cargo b -Fgenerate-bindings
+        run: cargo r -p api_gen
       - name: Upload crate source
         uses: actions/upload-artifact@v6
         with:
           name: crate-source
           path: src/
       - name: Diff generated Rust code
         shell: bash
-        run: test -z "$(git status --porcelain)" || (echo "::error::Generated files are different, please regenerate with cargo b -Fgenerate-bindings!"; git status; false)
+        run: test -z "$(git status --porcelain)" || (echo "::error::Generated files are different, please regenerate with 'cargo r -p api_gen'!"; git status; false)

Cargo.toml

@@ -1,3 +1,6 @@
+[workspace]
+members = ["api_gen"]
+
 [package]
 name = "xess-sys"
 version = "0.1.0"
@@ -12,7 +15,7 @@ categories = ["external-ffi-bindings", "graphics", "rendering"]
 keywords = ["Intel", "XeSS", "XeLL", "frame generation", "upscaling"]
 rust-version = "1.74"
 
-# Headers contain a sequence of characters which are incorrectly interpreted as a doctest, these obviously fail 
+# Headers contain a sequence of characters which are incorrectly interpreted as a doctest, these obviously fail
 [lib]
 doctest = false
 
@@ -23,12 +26,8 @@ libloading = { version = "0.8", default-features = false }
 [target.'cfg(windows)'.dependencies]
 windows = { version = "0.62", default-features = false, optional = true }
 
-[build-dependencies]
-bindgen = { version = "0.72", optional = true }
-
 [features]
 default = ["vk", "dx12", "xess"]
-generate-bindings = ["dep:bindgen"]
 dx11 = []
 dx12 = []
 vk = ["dep:ash"]

api_gen/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "api_gen"
+edition = "2024"
+publish = false
+
+[dependencies]
+# Pin version to have control over how everything is generated (there is a CI
+# check that validates that all files are generated as currently checked in):
+bindgen = "=0.72.1"

build.rs api_gen/src/main.rsbuild.rs renamed to api_gen/src/main.rs

@@ -1,7 +1,7 @@
-#[cfg(feature = "generate-bindings")]
+use std::path::Path;
+
 fn vulkan_sdk_include_directory() -> Option<std::path::PathBuf> {
-    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();
-    let is_windows = target_os.as_str() == "windows";
+    let is_windows = cfg!(target_os = "windows");
 
     // Mostly on Windows, the Vulkan headers don't exist in a common location but can be found based
     // on VULKAN_SDK, set by the Vulkan SDK installer.
@@ -22,9 +22,8 @@ fn vulkan_sdk_include_directory() -> Option<std::path::PathBuf> {
     }
 }
 
-#[cfg(feature = "generate-bindings")]
 fn generate_bindings() {
-    let compile = |input_file, output_file, allowlist_function, allowlist_type| {
+    let compile = |input_file: &str, output_file: &str, allowlist_function, allowlist_type| {
         let mut bindings = bindgen::Builder::default()
             .header(input_file)
             .allowlist_recursively(false)
@@ -33,12 +32,15 @@ fn generate_bindings() {
             .allowlist_var(".*xess.*")
             .bitfield_enum(".*(flags|bits).*")
             .newtype_enum(".*result_t.*")
+            .newtype_enum(".*logging_level_t.*")
             .default_enum_style(bindgen::EnumVariation::Rust {
                 non_exhaustive: false,
             })
             .parse_callbacks(Box::new(RenameCallback))
             .derive_default(true)
-            .clang_args(["-x", "c++"])
+            // XeSS headers are Windows-only (D3D12, DXGI, etc.), so clang must
+            // always target MSVC even when api_gen itself runs on Linux.
+            .clang_args(["-x", "c++", "--target=x86_64-pc-windows-msvc"])
             .prepend_enum_name(false)
             .layout_tests(false)
             .dynamic_link_require_all(true)
@@ -47,11 +49,20 @@ fn generate_bindings() {
             assert!(vulkan_sdk_include_dir.is_dir());
             bindings = bindings.clang_arg(format!("-I{}", vulkan_sdk_include_dir.display()))
         }
+
+        let output_path = Path::new(output_file);
+        assert!(
+            output_path.parent().unwrap().is_dir(),
+            "Output directory does not exist for {output_file}"
+        );
+
         bindings
             .generate()
             .expect("Unable to generate bindings")
-            .write_to_file(output_file)
+            .write_to_file(output_path)
             .expect("Couldn't write bindings");
+
+        println!("Generated {output_file}");
     };
 
     compile(
@@ -114,11 +125,9 @@ fn generate_bindings() {
     );
 }
 
-#[cfg(feature = "generate-bindings")]
 #[derive(Debug)]
 struct RenameCallback;
 
-#[cfg(feature = "generate-bindings")]
 impl bindgen::callbacks::ParseCallbacks for RenameCallback {
     fn enum_variant_name(
         &self,
@@ -168,6 +177,5 @@ impl bindgen::callbacks::ParseCallbacks for RenameCallback {
 }
 
 fn main() {
-    #[cfg(feature = "generate-bindings")]
     generate_bindings();
 }

src/xell/xell.rs

@@ -49,7 +49,11 @@ where
             index % 8
         };
         let mask = 1 << bit_index;
-        if val { byte | mask } else { byte & !mask }
+        if val {
+            byte | mask
+        } else {
+            byte & !mask
+        }
     }
     #[inline]
     pub fn set_bit(&mut self, index: usize, val: bool) {