Add shortcut when oid is identical to parent's

Author: cruessler

gix-blame/src/lib.rs

@@ -824,9 +824,33 @@ pub fn blame_file<E>(
             break;
         }
 
+        let mut buffer = Vec::new();
+        let commit_id = odb.find_commit(&suspect, &mut buffer).unwrap().tree();
+        let tree = odb.find_tree(&commit_id, &mut buffer).unwrap();
+
+        let Some(entry) = tree.bisect_entry(file_path, false) else {
+            continue;
+        };
+
         if parent_ids.len() == 1 {
             let parent_id: ObjectId = *parent_ids.last().unwrap();
 
+            let mut buffer = Vec::new();
+            let parent_commit_id = odb.find_commit(&parent_id, &mut buffer).unwrap().tree();
+            let parent_tree = odb.find_tree(&parent_commit_id, &mut buffer).unwrap();
+
+            if let Some(parent_entry) = parent_tree.bisect_entry(file_path, false) {
+                if entry.oid == parent_entry.oid {
+                    // The blobs storing the blamed file in `entry` and `parent_entry` are identical
+                    // which is why we can pass blame to the parent without further checks.
+                    hunks_to_blame
+                        .iter_mut()
+                        .for_each(|unblamed_hunk| unblamed_hunk.pass_blame(suspect, parent_id));
+
+                    continue;
+                }
+            }
+
             let changes_for_file_path = get_changes_for_file_path(&odb, file_path, item.id, parent_id);
 
             let [ref modification]: [gix_diff::tree::recorder::Change] = changes_for_file_path[..] else {