Prevent churn calculation from returning an error on partial clones (#1736)

Co-authored-by: lawrence3699 <lawrence3699@users.noreply.github.com>
Co-authored-by: Spenser Black <spenserblack01@gmail.com>

Author: lawrence3699

src/info/git/mod.rs

@@ -130,8 +130,9 @@ fn get_churn_channel(
                 if is_bot_commit(&commit, &mailmap, bot_regex_pattern.as_ref())? {
                     continue;
                 }
-                compute_diff_with_parent(&mut number_of_commits_by_file_path, &commit, &repo)?;
-                diffs_computed += 1;
+                if compute_diff_with_parent(&mut number_of_commits_by_file_path, &commit, &repo)? {
+                    diffs_computed += 1;
+                }
                 if should_break(
                     is_traversal_complete.load(Ordering::Relaxed),
                     total_number_of_commits.load(Ordering::Relaxed),
@@ -179,11 +180,16 @@ fn update_signature_counts(
     Ok(())
 }
 
+
+/// This will get the trees for a commit and its parent and compute the diff. On success, this
+/// returns `Ok(true)`. If the trees are not available due to a partial clone, this will return
+/// `Ok(false)`. Essentially, this function will have successfully determined that there is no diff
+/// to compute. Other issues that prevent calculation will return `Err`. 
 fn compute_diff_with_parent(
     change_map: &mut HashMap<BString, usize>,
     commit: &Commit,
     repo: &gix::Repository,
-) -> Result<()> {
+) -> Result<bool> {
     let mut parents = commit.parent_ids();
     let parents = (
         parents
@@ -194,8 +200,12 @@ fn compute_diff_with_parent(
     );
 
     if let (parent_tree_id, None) = parents {
-        let old_tree = parent_tree_id.object()?.into_tree();
-        let new_tree = commit.tree()?;
+        let Some(old_tree) = parent_tree_id.try_object()?.map(|tree| tree.into_tree()) else {
+            return Ok(false);
+        };
+        let Some(new_tree) = commit.tree_id()?.try_object()?.map(|tree| tree.into_tree()) else {
+            return Ok(false);
+        };
         let changes =
             repo.diff_tree_to_tree(&old_tree, &new_tree, Options::default().with_rewrites(None))?;
         for change in &changes {
@@ -212,7 +222,7 @@ fn compute_diff_with_parent(
         }
     }
 
-    Ok(())
+    Ok(true)
 }
 
 fn is_bot_commit(

tests/fixtures/make_partial_repo.sh

@@ -28,3 +28,8 @@ git clone --filter=blob:none file://$PWD/base partial
 (cd partial
     git config diff.renames true
 )
+
+git clone --filter=tree:0 file://$PWD/base partial_treeless
+(cd partial_treeless
+    git config diff.renames true
+)

tests/repo.rs

@@ -84,6 +84,17 @@ fn test_partial_repo() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_treeless_partial_repo() -> Result<()> {
+    let repo = named_repo("make_partial_repo.sh", "partial_treeless")?;
+    let config: CliOptions = CliOptions {
+        input: repo.path().to_path_buf(),
+        ..Default::default()
+    };
+    let _info = build_info(&config).expect("no error");
+    Ok(())
+}
+
 #[test]
 fn test_repo_with_pre_epoch_dates() -> Result<()> {
     let repo = repo("make_pre_epoch_repo.sh")?;