version-helper: copy git.rs from gtk-rs/gir

Bare copy from https://github.com/gtk-rs/gir/blob/master/src/git.rs

gst-plugin-version-helper/src/git.rs

@@ -0,0 +1,36 @@
+use std::path::Path;
+use std::process::Command;
+
+pub fn repo_hash<P: AsRef<Path>>(path: P) -> Option<String> {
+    let git_path = path.as_ref().to_str();
+    let mut args = match git_path {
+        Some(path) => vec!["-C", path],
+        None => vec![],
+    };
+    args.extend(&["rev-parse", "--short", "HEAD"]);
+    let output = Command::new("git").args(&args).output().ok()?;
+    if !output.status.success() {
+        return None;
+    }
+    let hash = String::from_utf8(output.stdout).ok()?;
+    let hash = hash.trim_end_matches('\n');
+
+    if dirty(path) {
+        Some(format!("{}+", hash))
+    } else {
+        Some(hash.into())
+    }
+}
+
+fn dirty<P: AsRef<Path>>(path: P) -> bool {
+    let path = path.as_ref().to_str();
+    let mut args = match path {
+        Some(path) => vec!["-C", path],
+        None => vec![],
+    };
+    args.extend(&["ls-files", "-m"]);
+    match Command::new("git").args(&args).output() {
+        Ok(modified_files) => !modified_files.stdout.is_empty(),
+        Err(_) => false,
+    }
+}