feat: support comments in ordinary source buffers

src/repository.rs

@@ -1093,6 +1093,24 @@ pub fn discover_root(path: &Path) -> Result<PathBuf, String> {
     discover_root_with_cancellation(path, &AtomicBool::new(false))
 }
 
+/// Identify the exact source bytes without writing objects or snapshotting the checkout.
+pub(crate) fn source_snapshot_revision(root: &Path, content: &str) -> Result<String, String> {
+    let mut command = if root.join(".jj").exists() {
+        git_command(&store_for_jj(root)?)
+    } else {
+        let mut command = Command::new("git");
+        command.arg("-C").arg(root);
+        command
+    };
+    command.args(["hash-object", "--no-filters", "--stdin"]);
+    let id = text(checked(run(
+        command,
+        content.as_bytes().to_vec(),
+        &AtomicBool::new(false),
+    )?)?)?;
+    Ok(format!("working:{}", id.trim()))
+}
+
 fn discover_root_with_cancellation(path: &Path, cancelled: &AtomicBool) -> Result<PathBuf, String> {
     let path = fs::canonicalize(path).map_err(|error| error.to_string())?;
     let root = path