[PATCH v2 2/2] cache-tree: do not generate empty trees as a result of all i-t-a subentries

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

If a subdirectory contains nothing but i-t-a entries, we generate an
empty tree object and add it to its parent tree. Which is wrong. Such
a subdirectory should not be added. We ignore i-t-a files _and_
directories.

Note that this has a cascading effect. If subdir 'a/b/c' contains
nothing but i-t-a entries, we ignore it. But then if 'a/b' contains
only (the non-existing) 'a/b/c', then we should ignore 'a/b' while
building 'a' too. And it goes all the way up to top directory.

Noticed-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 cache-tree.c          | 16 ++++++++++++++++
 t/t2203-add-intent.sh | 12 ++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/cache-tree.c b/cache-tree.c
index c2676e8..75e73d7 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -380,6 +380,13 @@ static int update_one(struct cache_tree *it,
 			continue;
 		}
 
+		/*
+		 * "sub" can be an empty tree if all subentries are i-t-a.
+		 */
+		if (sub && sub->cache_tree->entry_count < 0 &&
+		    !hashcmp(sha1, EMPTY_TREE_SHA1_BIN))
+			continue;
+
 		strbuf_grow(&buffer, entlen + 100);
 		strbuf_addf(&buffer, "%o %.*s%c", mode, entlen, path + baselen, '\0');
 		strbuf_add(&buffer, sha1, 20);
@@ -426,6 +433,15 @@ int cache_tree_update(struct index_state *istate, int flags)
 	i = update_one(it, cache, entries, "", 0, &skip, flags);
 	if (i < 0)
 		return i;
+	/*
+	 * Top dir can become empty if all entries are i-t-a (even
+	 * from subdirs). Note that we do allow to create an empty
+	 * tree from an empty index. Only error when an empty tree is
+	 * a result of the i-t-a thing.
+	 */
+	if (it->entry_count < 0 &&
+	    !hashcmp(it->sha1, EMPTY_TREE_SHA1_BIN))
+		return error(_("cannot build a tree from just intent-to-add entries"));
 	istate->cache_changed |= CACHE_TREE_CHANGED;
 	return 0;
 }
diff --git a/t/t2203-add-intent.sh b/t/t2203-add-intent.sh
index 24aed2e..a19f06b 100755
--- a/t/t2203-add-intent.sh
+++ b/t/t2203-add-intent.sh
@@ -99,5 +99,17 @@ test_expect_success 'cache-tree does not ignore dir that has i-t-a entries' '
 	)
 '
 
+test_expect_success 'cache-tree does skip dir that becomes empty' '
+	rm -fr ita-in-dir &&
+	git init ita-in-dir &&
+	(
+		cd ita-in-dir &&
+		mkdir -p 1/2/3 &&
+		echo 4 >1/2/3/4 &&
+		git add -N 1/2/3/4 &&
+		test_must_fail git commit -m committed
+	)
+'
+
 test_done
 
-- 
2.8.2.537.g0965dd9