merge-ort: expand only for out-of-cone conflicts

Merge conflicts happen often enough to want to avoid expanding a sparse
index when they happen, as long as those conflicts are within the
sparse-checkout cone. If a conflict exists outside of the
sparse-checkout cone, then we still need to expand before iterating over
the index entries. This is critical to do in advance because of how the
original_cache_nr is tracked to allow inserting and replacing cache
entries.

Iterate over the conflicted files and check if any paths are outside of
the sparse-checkout cone. If so, then expand the full index.

Add a test that demonstrates that we do not expand the index, even when
we hit a conflict within the sparse-checkout cone.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/merge-ort.c b/merge-ort.c
index 1531b4c94c..805f7c4139 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -4060,11 +4060,18 @@ static int record_conflicted_index_entries(struct merge_options *opt)
 
 	/*
 	 * We are in a conflicted state. These conflicts might be inside
-	 * sparse-directory entries, so expand the index preemptively.
-	 * Also, we set original_cache_nr below, but that might change if
+	 * sparse-directory entries, so check if any entries are outside
+	 * of the sparse-checkout cone preemptively.
+	 *
+	 * We set original_cache_nr below, but that might change if
 	 * index_name_pos() calls ask for paths within sparse directories.
 	 */
-	ensure_full_index(index);
+	strmap_for_each_entry(&opt->priv->conflicted, &iter, e) {
+		if (!path_in_sparse_checkout(e->key, index)) {
+			ensure_full_index(index);
+			break;
+		}
+	}
 
 	/* If any entries have skip_worktree set, we'll have to check 'em out */
 	state.force = 1;