Rename nix-bindings-bindgen-raw to nix-bindings-util-sys

Adopt idiomatic Rust `-sys` crate naming convention, aligning with
the direction in PR #37 without adopting the full crate splitting.

nix-bindings-util-sys/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "nix-bindings-util-sys"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+license = "LGPL-2.1"
+
+[lib]
+path = "src/lib.rs"
+
+[build-dependencies]
+bindgen = "0.69"
+pkg-config = "0.3"

nix-bindings-util-sys/README.md

@@ -0,0 +1,12 @@
+# nix-bindings-util-sys
+
+This crate contains generated bindings for the Nix C API.
+**You should not have to use this crate directly,** and so you should probably not add it to your dependencies.
+Instead, use the `nix-bindings-util`, `nix-bindings-store` and `nix-bindings-expr` crates, which _should_ be sufficient.
+
+## Design
+
+Rust bindgen currently does not allow "layered" libraries to be split into separate crates.
+For example, the expr crate would have all-new types that are distinct and incompatible with the store crate.
+
+Ideally bindgen will support reusing already generated modules, and we could move the code generation into the appropriate crates, so that the system dependencies of each crate become accurate.

nix-bindings-util-sys/build.rs

@@ -0,0 +1,60 @@
+use std::env;
+use std::path::PathBuf;
+
+#[derive(Debug)]
+struct StripNixPrefix {}
+impl bindgen::callbacks::ParseCallbacks for StripNixPrefix {
+    fn item_name(&self, name: &str) -> Option<String> {
+        name.strip_prefix("nix_").map(String::from)
+    }
+}
+
+fn main() {
+    // Tell cargo to invalidate the built crate whenever the wrapper changes
+    println!("cargo:rerun-if-changed=include/nix-c-raw.h");
+    println!("cargo:rustc-link-lib=nixflake");
+
+    // https://rust-lang.github.io/rust-bindgen/library-usage.html
+    let bindings = bindgen::Builder::default()
+        .header("include/nix-c-raw.h")
+        // Find the includes
+        .clang_args(c_headers())
+        // Tell cargo to invalidate the built crate whenever any of the
+        // included header files changed.
+        .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
+        .parse_callbacks(Box::new(StripNixPrefix {}))
+        // Finish the builder and generate the bindings.
+        .generate()
+        // Unwrap the Result and panic on failure.
+        .expect("Unable to generate bindings");
+
+    // Write the bindings to the $OUT_DIR/bindings.rs file.
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("bindings.rs"))
+        .expect("Couldn't write bindings!");
+}
+
+fn c_headers() -> Vec<String> {
+    let mut args = Vec::new();
+    // args.push("-isystem".to_string());
+    for path in pkg_config::probe_library("nix-flake-c")
+        .unwrap()
+        .include_paths
+        .iter()
+    {
+        args.push(format!("-I{}", path.to_str().unwrap()));
+    }
+
+    for path in pkg_config::probe_library("bdw-gc")
+        .unwrap()
+        .include_paths
+        .iter()
+    {
+        args.push(format!("-I{}", path.to_str().unwrap()));
+    }
+
+    // write to stderr for debugging
+    eprintln!("c_headers: {:?}", args);
+    args
+}

nix-bindings-util-sys/include/nix-c-raw.h

@@ -0,0 +1,7 @@
+#include <nix_api_util.h>
+#include <nix_api_store.h>
+#define GC_THREADS
+#include <gc/gc.h>
+#include <nix_api_expr.h>
+#include <nix_api_value.h>
+#include <nix_api_flake.h>

nix-bindings-util-sys/src/lib.rs

@@ -0,0 +1,31 @@
+//! Raw bindings to Nix C API
+//!
+//! This crate contains automatically generated bindings from the Nix C headers.
+//! The bindings are generated by bindgen and include C-style naming conventions
+//! and documentation comments that don't always conform to Rust standards.
+//!
+//! Normally you don't have to use this crate directly.
+//! Instead use `nix-store` and `nix-expr`.
+
+// This file must only contain generated code, so that the module-level
+// #![allow(...)] attributes don't suppress warnings in hand-written code.
+// If you need to add hand-written code, use a submodule to isolate the
+// generated code. See:
+// https://github.com/nixops4/nixops4/pull/138/commits/330c3881be3d3cf3e59adebbe0ab1c0f15f6d2c9
+
+// Standard bindgen suppressions for C naming conventions
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+// Clippy suppressions for generated C bindings
+// bindgen doesn't generate safety docs
+#![allow(clippy::missing_safety_doc)]
+// Rustdoc suppressions for generated C documentation
+// The C headers contain Doxygen-style documentation that doesn't translate
+// well to Rust's rustdoc format, causing various warnings:
+#![allow(rustdoc::broken_intra_doc_links)] // @param[in]/[out] references don't resolve
+#![allow(rustdoc::bare_urls)] // C docs may contain unescaped URLs
+#![allow(rustdoc::invalid_html_tags)] // Doxygen HTML tags like <setting>
+#![allow(rustdoc::invalid_codeblock_attributes)] // C code examples may use unsupported attributes
+
+include!(concat!(env!("OUT_DIR"), "/bindings.rs"));