reorganized build script a bit

build.rs

@@ -7,39 +7,50 @@ fn main() -> Result<()> {
     build_phinit()?;
     run_simple_make("sommelier")?;
     run_simple_make("kernel")?;
+    // Rerun build.rs upon making or pulling in new commits
+    println!("cargo:rerun-if-changed=.git/refs/heads/master");
     Ok(())
 }
 
 fn build_phinit() -> Result<()> {
-    run_command_in_directory(
-        "ph-init",
-        "cargo",
-        &["build", "--release"]
-    )?;
-    run_command_in_directory(
-        "ph-init",
-        "strip",
-        &["target/release/ph-init"]
-    )?;
+    let _dir = ChdirTo::path("ph-init");
+
+    Command::new("cargo")
+        .arg("build")
+        .arg("--release")
+        .status()?;
+
+    Command::new("strip")
+        .arg("target/release/ph-init")
+        .status()?;
+
     Ok(())
 }
 
 fn run_simple_make<P: AsRef<Path>>(directory: P) -> Result<()> {
-    run_command_in_directory(directory, "make", &[])
+    let _dir = ChdirTo::path(directory);
+    Command::new("make").status()?;
+    Ok(())
 }
 
-fn run_command_in_directory<P: AsRef<Path>>(directory: P, cmd: &str, args: &[&str]) -> Result<()> {
-    let saved = push_directory(directory)?;
-    Command::new(cmd).args(args).status()?;
-    env::set_current_dir(saved)
+struct ChdirTo {
+    saved: PathBuf,
 }
 
-fn push_directory<P: AsRef<Path>>(directory: P) -> Result<PathBuf> {
-    let current = env::current_dir()?;
-    env::set_current_dir(directory.as_ref())?;
-    Ok(current)
+impl ChdirTo {
+    fn path<P: AsRef<Path>>(directory: P) -> ChdirTo {
+        let saved = env::current_dir()
+            .expect("current_dir()");
+        env::set_current_dir(directory.as_ref())
+            .expect("set_current_dir()");
+        ChdirTo { saved }
+    }
 }
 
-
-
+impl Drop for ChdirTo {
+    fn drop(&mut self) {
+        env::set_current_dir(&self.saved)
+            .expect("restore current dir");
+    }
+}