feat: add experimental header method

src/main.rs

@@ -73,6 +73,10 @@ struct Cli {
     ///
     /// - counter will append an increasing number to the commit message for
     ///   each attempt
+    ///
+    /// - header will add an invalid git header line to the commit with an
+    ///   incrementing counter (git ignores additional headers, but this may not
+    ///   be compatible with future header changes)
     #[arg(short, long, value_enum, default_value_t = Method::Counter)]
     method: Method,
 
@@ -91,6 +95,7 @@ enum Method {
     Increment,
     Random,
     Counter,
+    Header,
 }
 
 fn main() -> Result<()> {
@@ -264,6 +269,7 @@ fn main() -> Result<()> {
 
             let mut sha1 = Sha1::default();
             let mut buffer = itoa::Buffer::new();
+            let mut first = true;
             loop {
                 if found.load(Ordering::SeqCst) {
                     break;
@@ -296,11 +302,25 @@ fn main() -> Result<()> {
                     }
                 };
 
-                author_parts[author_len - 2] = buffer.format(timestamp).to_owned();
-                committer_parts[committer_len - 2] = buffer.format(timestamp).to_owned();
+                if matches!(method, Method::Increment | Method::Decrement) {
+                    author_parts[author_len - 2] = buffer.format(timestamp).to_owned();
+                    committer_parts[committer_len - 2] = buffer.format(timestamp).to_owned();
 
-                header_lines[author_idx] = author_parts.join(" ");
-                header_lines[committer_idx] = committer_parts.join(" ");
+                    header_lines[author_idx] = author_parts.join(" ");
+                    header_lines[committer_idx] = committer_parts.join(" ");
+                }
+
+                if method == Method::Header {
+                    let count = counter.fetch_add(1, Ordering::SeqCst) + 1;
+                    let line = format!("xvain {}", buffer.format(count));
+                    if first {
+                        header_lines.insert(committer_idx + 1, line);
+                    } else {
+                        header_lines[committer_idx + 1] = line;
+                    }
+
+                    first = false;
+                }
 
                 let mut header = header_lines.join("\n");