Allow pkg-config to omit include paths if they equals to standard.

See #114

build/find_normal.rs

@@ -10,7 +10,7 @@ fn get_env_var(name: &str) -> String {
     }
 }
 
-pub fn probe_lua() -> PathBuf {
+pub fn probe_lua() -> Option<PathBuf> {
     let include_dir = get_env_var("LUA_INC");
     let lib_dir = get_env_var("LUA_LIB");
     let lua_lib = get_env_var("LUA_LIB_NAME");
@@ -38,7 +38,7 @@ pub fn probe_lua() -> PathBuf {
             println!("cargo:rustc-link-search=native={}", lib_dir);
             println!("cargo:rustc-link-lib={}{}", link_lib, lua_lib);
         }
-        return PathBuf::from(include_dir);
+        return Some(PathBuf::from(include_dir));
     }
 
     // Find using `pkg-config`
@@ -73,11 +73,7 @@ pub fn probe_lua() -> PathBuf {
         lua.expect(&format!("cannot find Lua {} using `pkg-config`", ver))
             .include_paths
             .get(0)
-            .expect(&format!(
-                "cannot find Lua {} include paths using `pkg-config`",
-                ver
-            ))
-            .clone()
+            .cloned()
     }
 
     #[cfg(feature = "luajit")]
@@ -90,7 +86,6 @@ pub fn probe_lua() -> PathBuf {
         lua.expect("cannot find LuaJIT using `pkg-config`")
             .include_paths
             .get(0)
-            .expect("cannot find LuaJIT include paths using `pkg-config`")
-            .clone()
+            .cloned()
     }
 }

build/find_vendored.rs

@@ -1,6 +1,6 @@
 use std::path::PathBuf;
 
-pub fn probe_lua() -> PathBuf {
+pub fn probe_lua() -> Option<PathBuf> {
     #[cfg(feature = "lua54")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua54);
     #[cfg(feature = "lua53")]
@@ -21,5 +21,5 @@ pub fn probe_lua() -> PathBuf {
     #[cfg(not(feature = "module"))]
     artifacts.print_cargo_metadata();
 
-    artifacts.include_dir().to_owned()
+    Some(artifacts.include_dir().to_owned())
 }

build/main.rs

@@ -68,11 +68,14 @@ impl CommandExt for Command {
     }
 }
 
-fn build_glue<P: AsRef<Path> + std::fmt::Debug>(include_path: &P) {
+// `include_path` is optional as Lua headers can be also found in compiler standard paths
+fn build_glue(include_path: Option<impl AsRef<Path>>) {
     let build_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
 
     let mut config = cc::Build::new();
-    config.include(include_path);
+    if let Some(include_path) = include_path {
+        config.include(include_path.as_ref());
+    }
 
     // Compile and run glue.c
     let glue = build_dir.join("glue");
@@ -243,11 +246,11 @@ fn main() {
             + "Please, use `pkg-config` or custom mode to link to a Lua dll."
     );
 
-    let include_dir = find::probe_lua();
     if env::var("TARGET").unwrap() != env::var("HOST").unwrap() {
         generate_glue().unwrap();
     } else {
-        build_glue(&include_dir);
+        let include_dir = find::probe_lua();
+        build_glue(include_dir);
         println!("cargo:rerun-if-changed=src/ffi/glue/glue.c");
     }