Add ChatGPT generated build.rs

platform/rust-cxx/Cargo.toml → platform/rust/Cargo.toml

@@ -8,3 +8,4 @@ cxx = "1.0"
 
 [build-dependencies]
 cxx-build = "1.0"
+cmake = "0.1"

platform/rust/build.rs

@@ -0,0 +1,33 @@
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+    let project_root = PathBuf::from(manifest_dir)
+        .parent().unwrap() // "platform/"
+        .parent().unwrap() // "maplibre-native/"
+        .to_path_buf();
+
+    let mut cmake_cfg = cmake::Config::new(&project_root);
+    cmake_cfg
+        .define("MLN_WITH_CORE_ONLY", "ON")
+        .generator("Ninja")
+        .build_target("mbgl-core");
+
+    let build_output = cmake_cfg.build();
+
+    // The library is in build_output/build/libmbgl-core.a
+    let lib_dir = build_output.join("build");
+    println!("cargo:rustc-link-search=native={}", lib_dir.display());
+    println!("cargo:rustc-link-lib=static=mbgl-core");
+
+    // If on macOS/Clang:
+    println!("cargo:rustc-link-lib=c++");
+    // If on Linux/GCC:
+    // println!("cargo:rustc-link-lib=stdc++");
+
+    let mut cxx = cxx_build::bridge("src/lib.rs");
+    cxx.include(project_root.join("include"))
+        .flag_if_supported("-std=c++20")
+        .compile("maplibre_rust_bindings");
+}

platform/rust/src/lib.rs

@@ -0,0 +1,38 @@
+// platform/rust/src/lib.rs
+
+#[cxx::bridge(namespace = "mbgl::util")]
+mod ffi {
+    // cxx allows including C++ headers directly:
+    unsafe extern "C++" {
+        include!("mbgl/math/log2.hpp");
+
+        // We specify the C++ namespace and the free function name exactly.
+        // cxx can bind free functions directly if they have a compatible signature.
+            // The signature must match what's in log2.hpp:
+            //   "uint32_t ceil_log2(uint64_t x);"
+            //
+            // We'll express that to Rust as (u64 -> u32).
+            pub fn ceil_log2(x: u64) -> u32;
+    }
+}
+
+/// A safe Rust wrapper so you can call `ceil_log2` from your code:
+pub fn ceil_log2(x: u64) -> u32 {
+    ffi::ceil_log2(x)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_log2() {
+        let result = ceil_log2(1);
+        assert_eq!(result, 0, "log2(1) = 0 bits needed");
+
+        let result = ceil_log2(2);
+        assert_eq!(result, 1, "log2(2) = 1 bit needed");
+
+        let result = ceil_log2(3);
+        assert_eq!(result, 2, "log2(3) -> 2 bits needed");
+    }
+}