status: bugfix directory diff in sparse index

Adding the `recursive` flag for `wt_status_collect_changes_index` allows the
diff function to recurse into sparse directories when differences occur within
them. This corrects the issue observed in the `read-tree` sparse compatibility
test in which particular merges resulted in a directory appearing as "modified"
for sparse index repositories, rather than showing only the modified file
within the directory.

The `recursive` flag, even with a non-sparse index, does not substantially
change the performance of `status`. From the `p2000` performance suite:

Test                             before            after
------------------------------------------------------------------------
2000.2: git status (full-v3)     0.68(0.27+0.34)   0.64(0.26+0.33) -5.9%
2000.3: git status (full-v4)     0.68(0.27+0.35)   0.67(0.26+0.34) -1.5%
2000.4: git status (sparse-v3)   0.45(0.09+0.63)   0.45(0.10+0.74) +0.0%
2000.5: git status (sparse-v4)   0.45(0.09+0.62)   0.45(0.10+0.73) +0.0%

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

t/t1092-sparse-checkout-compatibility.sh

@@ -866,12 +866,7 @@ test_expect_success 'read-tree --prefix outside sparse definition' '
 	test_cmp sparse-checkout/folder2/0/a full-checkout/folder2/0/a
 '
 
-# TODO: predating any sparse index compatibility changes to `read-tree`, this
-# merge fails due to a status difference between the sparse index and non-sparse
-# index checkouts. Specifically, `folder2/0` (a directory) appears modified in
-# the sparse index, but `folder2/0/a` (correctly?) appears instead as a
-# modified entry in the non-sparse index checkouts.
-test_expect_failure 'read-tree --merge with directory-file conflicts' '
+test_expect_success 'read-tree --merge with directory-file conflicts' '
 	init_repos &&
 
 	test_all_match git checkout -b test-branch rename-base &&

wt-status.c

@@ -651,6 +651,13 @@ static void wt_status_collect_changes_index(struct wt_status *s)
 	rev.diffopt.detect_rename = s->detect_rename >= 0 ? s->detect_rename : rev.diffopt.detect_rename;
 	rev.diffopt.rename_limit = s->rename_limit >= 0 ? s->rename_limit : rev.diffopt.rename_limit;
 	rev.diffopt.rename_score = s->rename_score >= 0 ? s->rename_score : rev.diffopt.rename_score;
+
+	/*
+	 * The `recursive` flag must be set to properly perform a diff on sparse
+	 * directory entries, if they exist
+	 */
+	rev.diffopt.flags.recursive = 1;
+
 	copy_pathspec(&rev.prune_data, &s->pathspec);
 	run_diff_index(&rev, 1);
 	object_array_clear(&rev.pending);