[PATCH v3 4/8] unpack-trees: fix nested sparse-dir search

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

From: Derrick Stolee <dstolee@microsoft.com>

The iterated search in find_cache_entry() was recently modified to
include a loop that searches backwards for a sparse directory entry that
matches the given traverse_info and name_entry. However, the string
comparison failed to actually concatenate those two strings, so this
failed to find a sparse directory when it was not a top-level directory.

This caused some errors in rare cases where a 'git checkout' spanned a
diff that modified files within the sparse directory entry, but we could
not correctly find the entry.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 unpack-trees.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/unpack-trees.c b/unpack-trees.c
index 5786645f315..df1f4437723 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1255,9 +1255,10 @@ static int sparse_dir_matches_path(const struct cache_entry *ce,
 static struct cache_entry *find_cache_entry(struct traverse_info *info,
 					    const struct name_entry *p)
 {
-	struct cache_entry *ce;
+	struct cache_entry *ce = NULL;
 	int pos = find_cache_pos(info, p->path, p->pathlen);
 	struct unpack_trees_options *o = info->data;
+	struct strbuf full_path = STRBUF_INIT;
 
 	if (0 <= pos)
 		return o->src_index->cache[pos];
@@ -1273,6 +1274,10 @@ static struct cache_entry *find_cache_entry(struct traverse_info *info,
 	if (pos < 0 || pos >= o->src_index->cache_nr)
 		return NULL;
 
+	strbuf_addstr(&full_path, info->traverse_path);
+	strbuf_add(&full_path, p->path, p->pathlen);
+	strbuf_addch(&full_path, '/');
+
 	/*
 	 * Due to lexicographic sorting and sparse directory
 	 * entries ending with a trailing slash, our path as a
@@ -1283,17 +1288,20 @@ static struct cache_entry *find_cache_entry(struct traverse_info *info,
 	while (pos >= 0) {
 		ce = o->src_index->cache[pos];
 
-		if (strncmp(ce->name, p->path, p->pathlen))
-			return NULL;
+		if (strncmp(ce->name, full_path.buf, full_path.len)) {
+			ce = NULL;
+			break;
+		}
 
 		if (S_ISSPARSEDIR(ce->ce_mode) &&
 		    sparse_dir_matches_path(ce, info, p))
-			return ce;
+			break;
 
 		pos--;
 	}
 
-	return NULL;
+	strbuf_release(&full_path);
+	return ce;
 }
 
 static void debug_path(struct traverse_info *info)
-- 
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