INTERNAL: Generate engine bindings from the arcus-memcached headers

Cargo.toml

@@ -52,3 +52,6 @@ todo = "warn"
 unimplemented = "warn"
 use_self = "warn"
 or_fun_call = "warn"
+
+[build-dependencies]
+bindgen = "0.73.2"

build.rs

@@ -0,0 +1,37 @@
+//! Generates `engine_api.rs` from the arcus-memcached headers at the crate root.
+
+use std::env;
+use std::error::Error;
+use std::path::{Path, PathBuf};
+
+const ENGINE_HEADER: &str = "include/memcached/engine.h";
+const CONFIG_FILES: [&str; 2] = ["config.h", "config_static.h"];
+const COPY_HINT: &str = "Copy config.h, config_static.h and include/memcached/*.h from a \
+                         configured arcus-memcached tree to the crate root.";
+
+fn main() -> Result<(), Box<dyn Error>> {
+    println!("cargo:rerun-if-changed=include");
+    for name in CONFIG_FILES {
+        println!("cargo:rerun-if-changed={name}");
+    }
+
+    for path in [ENGINE_HEADER].iter().chain(&CONFIG_FILES) {
+        if !Path::new(path).is_file() {
+            return Err(format!("{path} is missing. {COPY_HINT}").into());
+        }
+    }
+
+    let out = PathBuf::from(env::var("OUT_DIR")?).join("engine_api.rs");
+
+    bindgen::Builder::default()
+        .header(ENGINE_HEADER)
+        .clang_arg("-Iinclude")
+        .clang_arg("-I.")
+        .clang_args(["-include", "config.h"])
+        .allowlist_file(".*memcached/.*\\.h")
+        .generate()
+        .map_err(|e| format!("{}. {COPY_HINT}", e.to_string().trim_end()))?
+        .write_to_file(out)?;
+
+    Ok(())
+}

src/lib.rs

@@ -1,3 +1,5 @@
+mod memcached;
+
 pub fn add(left: u64, right: u64) -> u64 {
     left + right
 }

src/memcached.rs

@@ -0,0 +1,3 @@
+//! The interface memcached gives an extension and its engine.
+
+pub mod ffi;

src/memcached/ffi.rs

@@ -0,0 +1,19 @@
+//! Raw bindings to the arcus-memcached headers, generated by `build.rs`.
+
+// Generated code: which of these fire depends on the headers, so `expect` would turn a header
+// update into an "unfulfilled expectation" warning.
+#![allow(
+    dead_code,
+    non_camel_case_types,
+    non_snake_case,
+    non_upper_case_globals,
+    unused_qualifications,
+    clippy::all,
+    clippy::nursery,
+    clippy::pedantic,
+    clippy::restriction,
+    reason = "bindgen output: it keeps the C names, emits every declaration whether used or \
+              not, and carries its own `#[allow]`s"
+)]
+
+include!(concat!(env!("OUT_DIR"), "/engine_api.rs"));