symblib-capi: fix static linking with musl (open-telemetry#438)

Signed-off-by: Florian Lehner <[email protected]>

Author: florianl

Cargo.lock

@@ -13,3 +13,6 @@ symblib.path = "../symblib"
 
 fallible-iterator.workspace = true
 thiserror.workspace = true
+
+[build-dependencies]
+serde_json = "1.0.140"

rust-crates/symblib-capi/Cargo.toml

@@ -0,0 +1,72 @@
+use std::{env, path::PathBuf, process::Command};
+
+fn main() {
+    // Fetch the cargo build manifest.
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+    let output = Command::new("cargo")
+        .args(&["metadata", "--format-version=1", "--no-deps"])
+        .current_dir(&manifest_dir)
+        .output()
+        .expect("Failed to execute cargo metadata");
+
+    if !output.status.success() {
+        println!("cargo:warning=Failed to get cargo metadata");
+        return;
+    }
+
+    let metadata: serde_json::Value =
+        serde_json::from_slice(&output.stdout).expect("Failed to parse cargo metadata");
+
+    let pkg_name = env::var("CARGO_PKG_NAME").unwrap();
+    let packages = metadata["packages"].as_array().unwrap();
+    let current_package = packages
+        .iter()
+        .find(|p| p["name"].as_str().unwrap() == pkg_name)
+        .expect("Could not find current package in metadata");
+
+    let targets = current_package["targets"].as_array().unwrap();
+    let has_staticlib_target = targets.iter().any(|t| {
+        let kinds = t["kind"].as_array().unwrap();
+        kinds.iter().any(|k| k.as_str().unwrap() == "staticlib")
+    });
+
+    if !has_staticlib_target {
+        return;
+    }
+
+    let target = match env::var("TARGET") {
+        Ok(t) => t,
+        Err(_) => return,
+    };
+
+    if !target.contains("-linux-musl") {
+        return;
+    }
+
+    let out_dir = env::var("OUT_DIR").unwrap();
+
+    // Get the target-libdir for the specified target
+    // $(shell rustc --target $(RUST_TARGET) --print target-libdir)/self-contained/libunwind.a
+    let output = Command::new("rustc")
+        .args(&["--target", &target, "--print", "target-libdir"])
+        .output()
+        .expect("failed to execute rustc");
+
+    if output.status.success() {
+        let target_libdir_str = String::from_utf8_lossy(&output.stdout).trim().to_string();
+        let libunwind_path = PathBuf::from(target_libdir_str)
+            .join("self-contained")
+            .join("libunwind.a");
+
+        if libunwind_path.exists() {
+            std::fs::copy(libunwind_path, format!("{}/libunwind.a", out_dir)).unwrap();
+
+            println!("cargo:rustc-link-search=native={}", out_dir);
+            println!("cargo:rustc-link-lib=static=unwind");
+        } else {
+            println!("cargo:warning={:?} does not exist", libunwind_path);
+        }
+    } else {
+        println!("cargo:warning=failed to identify target-libdir for libunwind.a");
+    }
+}