[PATCH 2/4] oneway_diff: handle removed sparse directories

["Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>]

From: Victoria Dye <vdye@github.com>

Update 'do_oneway_diff()' to perform a 'diff_tree_oid()' on removed sparse
directories, as it does for added or modified sparse directories (see
9eb00af562 (diff-lib: handle index diffs with sparse dirs, 2021-07-14)).

At the moment, this update is unreachable code because 'unpack_trees()'
(currently the only way 'oneway_diff()' can be called, via 'diff_cache()')
will always traverse trees down to the individual removed files of a deleted
sparse directory. A subsequent patch will change this to better preserve a
sparse index in other uses of 'unpack_tree()', e.g. 'git reset --hard'.
However, making that change without this patch would result in (among other
issues) 'git status' printing only the name of a deleted sparse directory,
not its contents. To avoid introducing that bug, 'do_oneway_diff()' is
updated before modifying 'unpack_trees()'.

Signed-off-by: Victoria Dye <vdye@github.com>
---
 diff-lib.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/diff-lib.c b/diff-lib.c
index 7eb66a417aa..2edea41a234 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -466,6 +466,11 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 	 * Something removed from the tree?
 	 */
 	if (!idx) {
+		if (S_ISSPARSEDIR(tree->ce_mode)) {
+			diff_tree_oid(&tree->oid, NULL, tree->name, &revs->diffopt);
+			return;
+		}
+
 		diff_index_show_file(revs, "-", tree, &tree->oid, 1,
 				     tree->ce_mode, 0);
 		return;
-- 
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