[PATCH 4/4] unpack-trees: take care to propagate the split-index flag

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

When copying the `split_index` structure from one index structure to
another, we need to propagate the `SPLIT_INDEX_ORDERED` flag, too, if it
is set, otherwise Git might forget to write the shared index when that
is actually needed.

It just so _happens_ that in many instances when `unpack_trees()` is
called, the result causes the shared index to be written anyway, but
there are edge cases when that is not so.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 unpack-trees.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/unpack-trees.c b/unpack-trees.c
index 90b92114be8..ca5e47c77c0 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1916,6 +1916,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		 * create a new one.
 		 */
 		o->result.split_index = o->src_index->split_index;
+		if (o->src_index->cache_changed & SPLIT_INDEX_ORDERED)
+			o->result.cache_changed |= SPLIT_INDEX_ORDERED;
 		o->result.split_index->refcount++;
 	} else {
 		o->result.split_index = init_split_index(&o->result);
-- 
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