Re: [PATCH v3 5/6] stash: apply stash using 'merge_ort_nonrecursive()'

diff --git a/builtin/stash.c b/builtin/stash.c
index 1bfba532044..3fe549f7d3c 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c

@@ -492,13 +493,13 @@ static void unstage_changes_unless_new(struct object_id *orig_tree)
 static int do_apply_stash(const char *prefix, struct stash_info *info,
 			  int index, int quiet)
 {
-	int ret;
+	int clean, ret;
 	int has_index = index;
 	struct merge_options o;
 	struct object_id c_tree;
 	struct object_id index_tree;
-	struct commit *result;
-	const struct object_id *bases[1];
+	struct tree *head, *merge, *merge_base;
+	struct lock_file lock = LOCK_INIT;
 
 	read_cache_preload(NULL);
 	if (refresh_and_write_cache(REFRESH_QUIET, 0, 0))

@@ -541,6 +542,7 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 
 	o.branch1 = "Updated upstream";
 	o.branch2 = "Stashed changes";
+	o.ancestor = "Stash base";
 
 	if (oideq(&info->b_tree, &c_tree))
 		o.branch1 = "Version stash was based on";

@@ -551,10 +553,26 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
 	if (o.verbosity >= 3)
 		printf_ln(_("Merging %s with %s"), o.branch1, o.branch2);
 
-	bases[0] = &info->b_tree;
+	head = lookup_tree(o.repo, &c_tree);
+	merge = lookup_tree(o.repo, &info->w_tree);
+	merge_base = lookup_tree(o.repo, &info->b_tree);
+
+	repo_hold_locked_index(o.repo, &lock, LOCK_DIE_ON_ERROR);
+	clean = merge_ort_nonrecursive(&o, head, merge, merge_base);
+
+	/*
+	 * If 'clean' >= 0, reverse the value for 'ret' so 'ret' is 0 when the
+	 * merge was clean, and nonzero if the merge was unclean or encountered
+	 * an error.
+	 */
+	ret = clean >= 0 ? !clean : clean;
+
+	if (ret < 0)
+		rollback_lock_file(&lock);
+	else if (write_locked_index(o.repo->index, &lock,
+				      COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		ret = error(_("could not write index"));
 
-	ret = merge_recursive_generic(&o, &c_tree, &info->w_tree, 1, bases,
-				      &result);

diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 85c6a56f1b7..aaf4d880dbc 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh

@@ -1385,7 +1385,7 @@ test_expect_success 'sparse-index is not expanded: stash' '
 	ensure_not_expanded stash &&
 	ensure_not_expanded stash list &&
 	ensure_not_expanded stash show stash@{0} &&
-	! ensure_not_expanded stash apply stash@{0} &&
+	ensure_not_expanded stash apply stash@{0} &&
 	ensure_not_expanded stash drop stash@{0} &&
 
 	echo >>sparse-index/deep/new &&

@@ -1399,7 +1399,7 @@ test_expect_success 'sparse-index is not expanded: stash' '
 	oid=$(git -C sparse-index stash create) &&
 	ensure_not_expanded stash store -m "test" $oid &&
 	ensure_not_expanded reset --hard &&
-	! ensure_not_expanded stash pop
+	ensure_not_expanded stash pop
 '
 
 test_expect_success 'sparse index is not expanded: diff' '