Make cross-compilation possible

README.md

@@ -13,7 +13,9 @@ installed on the system.
 The build script of crate will attempt to find the lib path of libpq using the
 following methods:
 
-* First, if the environment variable `PQ_LIB_DIR` is set, it will use its value
+* First it will look for an environment variable in the format of `PQ_LIB_DIR_{TARGET}`
+where `{TARGET}` gets replaced by the Target environment variable set for cross-compilation
+* Second, if the environment variable `PQ_LIB_DIR` is set, it will use its value
 * If the environment variable isn't set, it tries to use pkg-config to locate it.
 All the config options, such as `PKG_CONFIG_ALLOW_CROSS`, `PKG_CONFIG_ALL_STATIC`
 etc., of the crate [pkg-config](http://alexcrichton.com/pkg-config-rs/pkg_config/index.html)

build.rs

@@ -77,11 +77,19 @@ impl Display for LinkingOptions {
 }
 
 fn main() {
-    println!("cargo:rerun-if-env-changed=PQ_LIB_DIR");
     println!("cargo:rerun-if-env-changed=PQ_LIB_STATIC");
     println!("cargo:rerun-if-env-changed=TARGET");
 
-    if let Ok(lib_dir) = env::var("PQ_LIB_DIR") {
+    // if target is specified the more concrete pq_lib_dir overwrites a more general one
+    let lib_dir = if let Ok(target) = env::var("TARGET") {
+        let pq_lib_dir_for_target = format!("PQ_LIB_DIR_{}", target.to_ascii_uppercase().replace("-", "_"));
+        check_and_use_lib_dir(&pq_lib_dir_for_target).or_else(|_| check_and_use_lib_dir("PQ_LIB_DIR"))
+    }
+    else{
+        check_and_use_lib_dir("PQ_LIB_DIR")
+    };
+
+    if let Ok(lib_dir) = lib_dir {
         println!("cargo:rustc-link-search=native={}", lib_dir);
     } else if configured_by_pkg_config() {
         return // pkg_config does everything for us, including output for cargo
@@ -127,6 +135,20 @@ fn configured_by_vcpkg() -> bool {
     false
 }
 
+fn check_and_use_lib_dir(var_name: &str) -> Result<String, VarError>{
+    println!("cargo:rerun-if-env-changed={:?}", var_name);
+    println!("{:?} = {:?}", var_name , env::var(var_name));
+
+    let pq_lib_dir = env::var(var_name);
+    if let Ok(pg_lib_path) = pq_lib_dir.clone() {
+        let path =  PathBuf::from(&pg_lib_path);
+        if !path.exists() {
+            panic!("Folder {:?} doesn't exist in the configured path: {:?}", var_name, path);
+        }
+    }
+    pq_lib_dir
+}
+
 fn pg_config_path() -> PathBuf {
     if let Ok(target) = env::var("TARGET") {
         let pg_config_for_target = &format!("PG_CONFIG_{}", target.to_ascii_uppercase().replace("-", "_"));