fix(rust): fix SIMDe configuration on aarch64 platforms when not installed yet (#63)

(In order to fix build on aarch64 platfroms, #62 is still needed in
addition to this change)

I was wondering why [the FastPFOR-rs
repository](https://github.com/fast-pack/FastPFOR) tests macOS runner
without installing SIMDe; FastPFOR fetches and build SIMDe
automatically. However, it seems the include path and define are not
configured correctly when with `cxx_build::bridge()`. So, this pull
request attempts to fix it by manually doing the equivalent to this part
of `cmake_modules/simde.cmake`.

```cmake
target_include_directories(simde INTERFACE "${simde_SOURCE_DIR}")

# Enables native aliases. Not ideal but makes it easier to convert old code.
target_compile_definitions(simde INTERFACE SIMDE_ENABLE_NATIVE_ALIASES)
```

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Yuri Astrakhan <yuriastrakhan@gmail.com>

Author: 3 people

.gitignore

@@ -2,12 +2,12 @@
 *.pdb
 .idea/
 .vscode/
+Cargo.lock
 codecov*
 debug/
 target/
 temp/
 tmp/
 venv/
 
-# This is a library, no lock
-Cargo.lock
+!codecov.yml

README.md

@@ -88,20 +88,24 @@ For local development, you may need to install the following packages:
 
 ```bash
 # This list may be incomplete
-sudo apt-get install build-essential libsimde-dev
+sudo apt-get install build-essential
 ```
 
+`libsimde-dev` is optional. On ARM/aarch64, the C++ build fetches `SIMDe` via `CMake`,
+and the Rust CXX bridge now reuses that fetched include path automatically.
+Install `libsimde-dev` only if you prefer a system package fallback.
+
 ### macOS
-To build `FastPFor` on macOS, you'll need to install `SIMDe`.
-Since Homebrew installs packages in `/opt/homebrew` (for Apple Silicon), you'll also need to explicitly set the include paths.
+On Apple Silicon, manual `SIMDe` installation is usually not required.
+The C++ build fetches `SIMDe` via `CMake`, and the Rust CXX bridge reuses that path.
+
+If you prefer a system package fallback, install `SIMDe` with Homebrew and set include flags.
 
 ```bash
-# install SIMDe via Homebrew
+# optional: install SIMDe via Homebrew
 brew install simde
-```
 
-```bash
-# Ensure the compiler can find the required headers before building
+# optional fallback: ensure the compiler can find Homebrew headers
 export CXXFLAGS="-I/opt/homebrew/include"
 export CFLAGS="-I/opt/homebrew/include"
 ```

build.rs

@@ -3,7 +3,7 @@
 /// Builds the C++ `FastPFOR` library and bridge when the `cpp` feature is enabled.
 #[cfg(feature = "cpp")]
 fn build_fastpfor() {
-    use std::path::Path;
+    use std::{env, path::Path};
 
     assert!(
         Path::new("cpp/CMakeLists.txt").exists(),
@@ -12,20 +12,42 @@ fn build_fastpfor() {
 
     // Compile FastPFOR using CMake
     println!("cargo:rerun-if-changed=cpp");
-    let lib_path = cmake::Config::new("cpp")
-        .define("WITH_TEST", "OFF")
-        .build()
-        .join("lib");
+    let cmake_out = cmake::Config::new("cpp").define("WITH_TEST", "OFF").build();
+    let lib_path = cmake_out.join("lib");
     let lib_path = lib_path.to_str().unwrap();
 
     // Compile the bridge
     println!("cargo:rerun-if-changed=src/cpp/fastpfor_bridge.h");
     println!("cargo:rerun-if-changed=src/cpp/mod.rs");
-    cxx_build::bridge("src/cpp/mod.rs")
+    let mut bridge = cxx_build::bridge("src/cpp/mod.rs");
+    bridge
         .include("cpp/headers")
         .include("src/cpp")
-        .std("c++14")
-        .compile("fastpfor_bridge");
+        .std("c++14");
+
+    // On ARM/aarch64, FastPFOR headers include SIMDe shims for SSE intrinsics.
+    // CMake fetches SIMDe to build FastPFOR itself, but the Rust/CXX bridge is a
+    // separate compilation unit and needs the same compile definition, plus an
+    // include path if CMake fetched SIMDe into the build tree.
+    if env::var("CARGO_CFG_TARGET_ARCH").is_ok_and(|arch| arch == "aarch64") {
+        // Mirror `cpp/cmake_modules/simde.cmake` for the bridge TU:
+        // FastPFOR headers use SSE names directly (e.g. __m128i, _mm_*),
+        // so we need SIMDe's native aliases enabled here as well, regardless of
+        // where the SIMDe headers are provided from.
+        bridge.define("SIMDE_ENABLE_NATIVE_ALIASES", None);
+
+        let simde_include = cmake_out.join("build").join("_deps").join("simde-src");
+        if simde_include.exists() {
+            bridge.include(simde_include);
+        } else {
+            println!(
+                "cargo:warning=SIMDe headers were not found in CMake build output; \
+                 ensure SIMDe is available on the include path if bridge compilation fails."
+            );
+        }
+    }
+
+    bridge.compile("fastpfor_bridge");
 
     // Link the FastPFOR library - must be done after the bridge is compiled
     println!("cargo:rustc-link-search=native={lib_path}");

codecov.yml

@@ -0,0 +1,6 @@
+codecov:
+  require_ci_to_pass: false
+
+coverage:
+  status:
+    patch: off