absorb: wrap absorb_hunks() result in struct

This patch also renames rewritten_commits as I'm going to add rewritten_source
field.

cli/src/commands/absorb.rs

@@ -91,27 +91,33 @@ pub(crate) fn cmd_absorb(
     workspace_command.check_rewritable(selected_trees.target_commits.keys())?;
 
     let mut tx = workspace_command.start_transaction();
-    let (rewritten_commits, num_rebased) =
-        absorb_hunks(tx.repo_mut(), &source, selected_trees.target_commits)?;
+    let stats = absorb_hunks(tx.repo_mut(), &source, selected_trees.target_commits)?;
 
     if let Some(mut formatter) = ui.status_formatter() {
-        if !rewritten_commits.is_empty() {
+        if !stats.rewritten_destinations.is_empty() {
             writeln!(formatter, "Absorbed changes into these revisions:")?;
             let template = tx.commit_summary_template();
-            for commit in rewritten_commits.iter().rev() {
+            for commit in stats.rewritten_destinations.iter().rev() {
                 write!(formatter, "  ")?;
                 template.format(commit, formatter.as_mut())?;
                 writeln!(formatter)?;
             }
         }
-        if num_rebased > 0 {
-            writeln!(formatter, "Rebased {num_rebased} descendant commits.")?;
+        if stats.num_rebased > 0 {
+            writeln!(
+                formatter,
+                "Rebased {} descendant commits.",
+                stats.num_rebased
+            )?;
         }
     }
 
     tx.finish(
         ui,
-        format!("absorb changes into {} commits", rewritten_commits.len()),
+        format!(
+            "absorb changes into {} commits",
+            stats.rewritten_destinations.len()
+        ),
     )?;
     Ok(())
 }

lib/src/absorb.rs

@@ -268,15 +268,26 @@ fn combine_texts(text1: &[u8], text2: &[u8], selected_ranges: &[SelectedRange])
     .collect()
 }
 
+/// Describes changes made by [`absorb_hunks()`].
+#[derive(Clone, Debug)]
+pub struct AbsorbStats {
+    /// Rewritten commits which the source hunks were absorbed into, in forward
+    /// topological order.
+    pub rewritten_destinations: Vec<Commit>,
+    /// Number of descendant commits which were rebased. The number of rewritten
+    /// destination commits are not included.
+    pub num_rebased: usize,
+}
+
 /// Merges selected trees into the specified commits. Abandons the source commit
 /// if it becomes discardable.
 pub fn absorb_hunks(
     repo: &mut MutableRepo,
     source: &AbsorbSource,
     mut selected_trees: HashMap<CommitId, MergedTreeBuilder>,
-) -> BackendResult<(Vec<Commit>, usize)> {
+) -> BackendResult<AbsorbStats> {
     let store = repo.store().clone();
-    let mut rewritten_commits = Vec::new();
+    let mut rewritten_destinations = Vec::new();
     let mut num_rebased = 0;
     // Rewrite commits in topological order so that descendant commits wouldn't
     // be rewritten multiple times.
@@ -309,10 +320,13 @@ pub fn absorb_hunks(
             .set_tree_id(new_tree.id())
             .set_predecessors(predecessors)
             .write()?;
-        rewritten_commits.push(new_commit);
+        rewritten_destinations.push(new_commit);
         Ok(())
     })?;
-    Ok((rewritten_commits, num_rebased))
+    Ok(AbsorbStats {
+        rewritten_destinations,
+        num_rebased,
+    })
 }
 
 struct FileValue {