[PATCH 11/27] unpack-trees: allow sparse directories

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

The index_pos_by_traverse_info() currently throws a BUG() when a
directory entry exists exactly in the index. We need to consider that it
is possible to have a directory in a sparse index as long as that entry
is itself marked with the skip-worktree bit.

The negation of the 'pos' variable must be conditioned to only when it
starts as negative. This is identical behavior as before when the index
is full.

The starts_with() condition matches because our name.buf terminates with
a directory separator, just like our sparse directory entries.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 unpack-trees.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 4dd99219073..b324eec2a5d 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -746,9 +746,12 @@ static int index_pos_by_traverse_info(struct name_entry *names,
 	strbuf_make_traverse_path(&name, info, names->path, names->pathlen);
 	strbuf_addch(&name, '/');
 	pos = index_name_pos(o->src_index, name.buf, name.len);
-	if (pos >= 0)
-		BUG("This is a directory and should not exist in index");
-	pos = -pos - 1;
+	if (pos >= 0) {
+		if (!o->src_index->sparse_index ||
+		    !(o->src_index->cache[pos]->ce_flags & CE_SKIP_WORKTREE))
+			BUG("This is a directory and should not exist in index");
+	} else
+		pos = -pos - 1;
 	if (pos >= o->src_index->cache_nr ||
 	    !starts_with(o->src_index->cache[pos]->name, name.buf) ||
 	    (pos > 0 && starts_with(o->src_index->cache[pos-1]->name, name.buf)))
-- 
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