rewrite: avoid abandoned commit parent lookup in `rebase_commit_with_…

…options`

This is an optimization to avoid fetching the parent commit of an
abandoned commit after rebasing, given that it might not even be used.

lib/src/repo.rs

@@ -1305,11 +1305,11 @@ impl MutableRepo {
                 let old_commit_id = rewriter.old_commit().id().clone();
                 let rebased_commit: RebasedCommit =
                     rebase_commit_with_options(settings, rewriter, &options)?;
-                let new_commit = match rebased_commit {
-                    RebasedCommit::Rewritten(new_commit) => new_commit,
-                    RebasedCommit::Abandoned { parent } => parent,
+                let new_commit_id = match rebased_commit {
+                    RebasedCommit::Rewritten(new_commit) => new_commit.id().clone(),
+                    RebasedCommit::Abandoned { parent_id } => parent_id,
                 };
-                rebased.insert(old_commit_id, new_commit.id().clone());
+                rebased.insert(old_commit_id, new_commit_id);
             }
             Ok(())
         })?;

lib/src/rewrite.rs

@@ -305,7 +305,7 @@ impl<'repo> CommitRewriter<'repo> {
 
 pub enum RebasedCommit {
     Rewritten(Commit),
-    Abandoned { parent: Commit },
+    Abandoned { parent_id: CommitId },
 }
 
 pub fn rebase_commit_with_options(
@@ -318,11 +318,8 @@ pub fn rebase_commit_with_options(
         rewriter.simplify_ancestor_merge();
     }
 
-    // TODO: avoid this lookup by not returning the old parent for
-    // RebasedCommit::Abandoned
-    let store = rewriter.mut_repo().store().clone();
     let single_parent = match &rewriter.new_parents[..] {
-        [parent] => Some(store.get_commit(parent)?),
+        [parent_id] => Some(parent_id.clone()),
         _ => None,
     };
     let new_parents = rewriter.new_parents.clone();
@@ -332,7 +329,7 @@ pub fn rebase_commit_with_options(
     } else {
         assert_eq!(new_parents.len(), 1);
         Ok(RebasedCommit::Abandoned {
-            parent: single_parent.unwrap(),
+            parent_id: single_parent.unwrap(),
         })
     }
 }