rewrite: add CommitRewriter::record_abandoned_commit()

We already have two uses for this function and I think we're soon
going to have more.

The function record the old commit as abandoned with the new parents,
which is typically what you want. We could record it as abandoned with
the old parents instead but then we'd have to do an extra iteration to
find the parents when rebasing any children. It would also be
confusing if
`rewriter.set_parents(new_parents).record_abandoned_commit()` didn't
respect the new parents.

lib/src/rewrite.rs

@@ -184,6 +184,13 @@ impl<'repo> CommitRewriter<'repo> {
         self.new_parents.retain(|parent| head_set.contains(parent));
     }
 
+    /// Records the old commit as abandoned with the new parents.
+    pub fn record_abandoned_commit(self) {
+        let old_commit_id =self.old_commit.id().clone();
+        let new_parents = self.new_parents;
+        self.mut_repo.record_abandoned_commit_with_parents(old_commit_id, new_parents);
+    }
+
     /// Rebase the old commit onto the new parents. Returns a `CommitBuilder`
     /// for the new commit. Returns `None` if the commit was abandoned.
     pub fn rebase_with_empty_behavior(
@@ -235,10 +242,7 @@ impl<'repo> CommitRewriter<'repo> {
                 EmptyBehaviour::AbandonAllEmpty => *parent.tree_id() == new_tree_id,
             };
             if should_abandon {
-                self.mut_repo.record_abandoned_commit_with_parents(
-                    self.old_commit.id().clone(),
-                    std::iter::once(parent.id().clone()),
-                );
+                self.record_abandoned_commit();
                 return Ok(None);
             }
         }

lib/tests/test_rewrite_transform.rs

@@ -50,11 +50,7 @@ fn test_transform_descendants_sync() {
         .transform_descendants(&settings, vec![commit_b.id().clone()], |mut rewriter| {
             rewriter.replace_parent(commit_a.id(), [commit_g.id()]);
             if *rewriter.old_commit() == commit_c {
-                let old_id = rewriter.old_commit().id().clone();
-                let new_parent_ids = rewriter.new_parents().to_vec();
-                rewriter
-                    .mut_repo()
-                    .record_abandoned_commit_with_parents(old_id, new_parent_ids);
+                rewriter.record_abandoned_commit();
             } else {
                 let old_commit_id = rewriter.old_commit().id().clone();
                 let new_commit = rewriter.rebase(&settings)?.write()?;