ffi: update build script

Signed-off-by: Yuki Kishimoto <[email protected]>

bindings/nostr-sdk-ffi/build.rs

@@ -3,11 +3,9 @@
 // Distributed under the MIT software license
 
 use std::env;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
-const DEFAULT_CLANG_VERSION: &str = "17";
-
 fn main() {
     if let Ok(output) = Command::new("git").args(["rev-parse", "HEAD"]).output() {
         if let Ok(git_hash) = String::from_utf8(output.stdout) {
@@ -22,30 +20,59 @@ fn main() {
 /// Adds a temporary workaround for an issue with the Rust compiler and Android
 /// in x86_64 devices: https://github.com/rust-lang/rust/issues/109717.
 /// The workaround comes from: https://github.com/mozilla/application-services/pull/5442
+/// This below code is inspired by: https://github.com/matrix-org/matrix-rust-sdk/blob/f18e0b18a1ea757921bcae07c29600a9839fdc97/bindings/matrix-sdk-ffi/build.rs
 fn setup_x86_64_android_workaround() {
-    let target_os = env::var("CARGO_CFG_TARGET_OS").expect("CARGO_CFG_TARGET_OS not set");
-    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH not set");
+    // Get target OS and arch
+    let target_os: String = env::var("CARGO_CFG_TARGET_OS").expect("CARGO_CFG_TARGET_OS not set");
+    let target_arch: String =
+        env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH not set");
+
+    // Check if match x86_64-android
     if target_arch == "x86_64" && target_os == "android" {
-        let android_ndk_home = env::var("ANDROID_NDK_HOME").expect("ANDROID_NDK_HOME not set");
-        let build_os = match env::consts::OS {
-            "linux" => "linux",
-            "macos" => "darwin",
-            "windows" => "windows",
-            _ => panic!(
-                "Unsupported OS. You must use either Linux, MacOS or Windows to build the crate."
-            ),
-        };
-        let clang_version =
-            env::var("NDK_CLANG_VERSION").unwrap_or_else(|_| DEFAULT_CLANG_VERSION.to_owned());
-        let linux_x86_64_lib_dir = format!(
-            "toolchains/llvm/prebuilt/{build_os}-x86_64/lib/clang/{clang_version}/lib/linux/"
+        // Configure rust to statically link against the `libclang_rt.builtins` supplied
+        // with clang.
+
+        // cargo-ndk sets CC_x86_64-linux-android to the path to `clang`, within the
+        // Android NDK.
+        let clang_path = PathBuf::from(
+            env::var("CC_x86_64-linux-android").expect("CC_x86_64-linux-android not set"),
         );
-        let linkpath = format!("{android_ndk_home}/{linux_x86_64_lib_dir}");
-        if Path::new(&linkpath).exists() {
-            println!("cargo:rustc-link-search={android_ndk_home}/{linux_x86_64_lib_dir}");
-            println!("cargo:rustc-link-lib=static=clang_rt.builtins-x86_64-android");
-        } else {
-            panic!("Path {linkpath} not exists");
-        }
+
+        // clang_path should now look something like
+        // `.../sdk/ndk/28.0.12674087/toolchains/llvm/prebuilt/linux-x86_64/bin/clang`.
+        // We strip `/bin/clang` from the end to get the toolchain path.
+        let toolchain_path = clang_path
+            .ancestors()
+            .nth(2)
+            .expect("could not find NDK toolchain path")
+            .to_str()
+            .expect("NDK toolchain path is not valid UTF-8");
+
+        let clang_version = get_clang_major_version(&clang_path);
+
+        println!("cargo:rustc-link-search={toolchain_path}/lib/clang/{clang_version}/lib/linux/");
+        println!("cargo:rustc-link-lib=static=clang_rt.builtins-x86_64-android");
     }
 }
+
+/// Run the clang binary at `clang_path`, and return its major version number
+fn get_clang_major_version(clang_path: &Path) -> String {
+    let clang_output = Command::new(clang_path)
+        .arg("-dumpversion")
+        .output()
+        .expect("failed to start clang");
+
+    if !clang_output.status.success() {
+        panic!(
+            "failed to run clang: {}",
+            String::from_utf8_lossy(&clang_output.stderr)
+        );
+    }
+
+    let clang_version = String::from_utf8(clang_output.stdout).expect("clang output is not utf8");
+    clang_version
+        .split('.')
+        .next()
+        .expect("could not parse clang output")
+        .to_owned()
+}