unpack-trees: allow sparse directories

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 'pos' variable is assigned a negative value if an exact match is not
found. Since a directory name can be an exact match, it is no longer an
error to have a nonnegative 'pos' value.

Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

unpack-trees.c

@@ -746,9 +746,13 @@ 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)))