[PATCH v3 1/2] cache-tree: invalidate i-t-a paths after generating trees

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

Intent-to-add entries used to forbid writing trees so it was not a
problem. After commit 3f6d56d (commit: ignore intent-to-add entries
instead of refusing - 2012-02-07), we can generate trees from an index
with i-t-a entries.

However, the commit forgets to invalidate all paths leading to i-t-a
entries. With fully valid cache-tree (e.g. after commit or
write-tree), diff operations may prefer cache-tree to index and not
see i-t-a entries in the index, because cache-tree does not have them.

Reported-by: Jonathon Mah <me@JonathonMah.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 This version ensures that entry_count can only be >= -1 after
 update_one returns. Not ideal but good enough.

 cache-tree.c          | 40 ++++++++++++++++++++++++++++++++++++----
 t/t2203-add-intent.sh | 20 ++++++++++++++++++++
 2 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/cache-tree.c b/cache-tree.c
index 28ed657..1fbc81a 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -248,6 +248,7 @@ static int update_one(struct cache_tree *it,
 	int missing_ok = flags & WRITE_TREE_MISSING_OK;
 	int dryrun = flags & WRITE_TREE_DRY_RUN;
 	int i;
+	int to_invalidate = 0;
 
 	if (0 <= it->entry_count && has_sha1_file(it->sha1))
 		return it->entry_count;
@@ -324,7 +325,14 @@ static int update_one(struct cache_tree *it,
 			if (!sub)
 				die("cache-tree.c: '%.*s' in '%s' not found",
 				    entlen, path + baselen, path);
-			i += sub->cache_tree->entry_count - 1;
+			i--; /* this entry is already counted in "sub" */
+			if (sub->cache_tree->entry_count < 0) {
+				i -= sub->cache_tree->entry_count;
+				sub->cache_tree->entry_count = -1;
+				to_invalidate = 1;
+			}
+			else
+				i += sub->cache_tree->entry_count;
 			sha1 = sub->cache_tree->sha1;
 			mode = S_IFDIR;
 		}
@@ -339,8 +347,23 @@ static int update_one(struct cache_tree *it,
 				mode, sha1_to_hex(sha1), entlen+baselen, path);
 		}
 
-		if (ce->ce_flags & (CE_REMOVE | CE_INTENT_TO_ADD))
-			continue; /* entry being removed or placeholder */
+		/*
+		 * CE_REMOVE entries are removed before the index is
+		 * written to disk. Skip them to remain consistent
+		 * with the future on-disk index.
+		 */
+		if (ce->ce_flags & CE_REMOVE)
+			continue;
+
+		/*
+		 * CE_INTENT_TO_ADD entries exist on on-disk index but
+		 * they are not part of generated trees. Invalidate up
+		 * to root to force cache-tree users to read elsewhere.
+		 */
+		if (ce->ce_flags & CE_INTENT_TO_ADD) {
+			to_invalidate = 1;
+			continue;
+		}
 
 		strbuf_grow(&buffer, entlen + 100);
 		strbuf_addf(&buffer, "%o %.*s%c", mode, entlen, path + baselen, '\0');
@@ -360,7 +383,7 @@ static int update_one(struct cache_tree *it,
 	}
 
 	strbuf_release(&buffer);
-	it->entry_count = i;
+	it->entry_count = to_invalidate ? -i : i;
 #if DEBUG
 	fprintf(stderr, "cache-tree update-one (%d ent, %d subtree) %s\n",
 		it->entry_count, it->subtree_nr,
@@ -381,6 +404,15 @@ int cache_tree_update(struct cache_tree *it,
 	i = update_one(it, cache, entries, "", 0, flags);
 	if (i < 0)
 		return i;
+	/*
+	 * update_one() uses negative entry_count as a way to mark an
+	 * entry invalid _and_ pass the number of entries back to
+	 * itself at the parent level. This is for internal use and
+	 * should not be leaked out after the top-level update_one
+	 * exits.
+	 */
+	if (it->entry_count < 0)
+		it->entry_count = -1;
 	return 0;
 }
 
diff --git a/t/t2203-add-intent.sh b/t/t2203-add-intent.sh
index ec35409..2a4a749 100755
--- a/t/t2203-add-intent.sh
+++ b/t/t2203-add-intent.sh
@@ -62,5 +62,25 @@ test_expect_success 'can "commit -a" with an i-t-a entry' '
 	git commit -a -m all
 '
 
+test_expect_success 'cache-tree invalidates i-t-a paths' '
+	git reset --hard &&
+	mkdir dir &&
+	: >dir/foo &&
+	git add dir/foo &&
+	git commit -m foo &&
+
+	: >dir/bar &&
+	git add -N dir/bar &&
+	git diff --cached --name-only >actual &&
+	echo dir/bar >expect &&
+	test_cmp expect actual &&
+
+	git write-tree >/dev/null &&
+
+	git diff --cached --name-only >actual &&
+	echo dir/bar >expect &&
+	test_cmp expect actual
+'
+
 test_done
 
-- 
1.8.0.rc2.23.g1fb49df