build(uci): restrict UCI dependency and feature to Linux targets

Ensure the UCI integration is only compiled on Linux, as the underlying native dependency is platform-specific. Added a build script to warn users when the feature is enabled on unsupported platforms.

Cargo.toml

@@ -25,7 +25,6 @@ netlink-bindings = { git = "https://github.com/one-d-wide/netlink-bindings.git",
 netlink-socket2 = { git = "https://github.com/one-d-wide/netlink-bindings.git", rev = "0b609e9380610e7da73f8c43cdf804a1d1bf5474" }
 fastrand = "2"
 rustix = { version = "1.1", features = ["fs", "system", "thread", "time"] }
-rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "3e7b6153b6df92b45428c32bb6461756563deecb", optional = true }
 thiserror = "2.0"
 libc = "0.2"
 flume = { version = "0.12.0",  default-features = false, features = ["eventual-fairness", "select"] }
@@ -34,5 +33,8 @@ flume = { version = "0.12.0",  default-features = false, features = ["eventual-f
 features = ["std"]
 version = "0.4"
 
+[target.'cfg(target_os = "linux")'.dependencies]
+rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "3e7b6153b6df92b45428c32bb6461756563deecb", optional = true }
+
 [features]
 uci = ["dep:rust-uci"]

build.rs

@@ -0,0 +1,16 @@
+use std::env;
+
+fn main() {
+    let uci_enabled = env::var_os("CARGO_FEATURE_UCI").is_some();
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+    let target = env::var("TARGET").unwrap_or_else(|_| "unknown".into());
+
+    if uci_enabled && target_os != "linux" {
+        println!(
+            "cargo::warning=feature `uci` is unsupported for target `{target}`; \
+             UCI integration will not be compiled"
+        );
+    }
+
+    println!("cargo::rerun-if-changed=build.rs");
+}

src/config.rs

@@ -7,9 +7,9 @@
 
 use anyhow::Result;
 use log::Level;
-#[cfg(feature = "uci")]
+#[cfg(all(target_os = "linux", feature = "uci"))]
 use log::warn;
-#[cfg(feature = "uci")]
+#[cfg(all(target_os = "linux", feature = "uci"))]
 use rust_uci::Uci;
 use std::fmt;
 use std::fmt::Display;
@@ -391,7 +391,7 @@ impl Config {
         None
     }
 
-    #[cfg(feature = "uci")]
+    #[cfg(all(target_os = "linux", feature = "uci"))]
     fn get_from_uci(key: &str) -> Option<String> {
         let mut uci = match Uci::new() {
             Ok(val) => val,
@@ -410,7 +410,7 @@ impl Config {
         };
     }
 
-    #[cfg(not(feature = "uci"))]
+    #[cfg(not(all(target_os = "linux", feature = "uci")))]
     fn get_from_uci(_: &str) -> Option<String> {
         None
     }