build.rs: factor out getting git command output into helper fn

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

build.rs

@@ -2,22 +2,19 @@
 use std::env;
 use std::process::Command;
 
+fn git_command(args: &[&str]) -> String {
+    match Command::new("git").args(args).output() {
+        Ok(output) => String::from_utf8(output.stdout).unwrap().trim_end().to_string(),
+        Err(err) => {
+            panic!("git {:?} failed: {}", args, err);
+        }
+    }
+}
+
 fn main() {
     let repoid = match env::var("REPOID") {
         Ok(repoid) => repoid,
-        Err(_) => {
+        Err(_) => git_command(&["rev-parse", "HEAD"]),
-            match Command::new("git")
-                .args(&["rev-parse", "HEAD"])
-                .output()
-            {
-                Ok(output) => {
-                    String::from_utf8(output.stdout).unwrap()
-                }
-                Err(err) => {
-                    panic!("git rev-parse failed: {}", err);
-                }
-            }
-        }
     };
 
     println!("cargo:rustc-env=REPOID={}", repoid);