cache-tree: make sure to "touch" tree objects the cache-tree recordsjc/cache-tree-freshen

The cache_tree_fully_valid() function is called by callers that want
to know if they need to call cache_tree_update(), i.e. as an attempt
to optimize. They all want to have a fully valid cache-tree in the
end so that they can write a tree object out.

We used to check if the cached tree object is up-to-date (i.e. the
index entires covered by the cache-tree entry hasn't been changed
since the roll-up hash was computed for the cache-tree entry) and
made sure the tree object is already in the object store.  Since the
top-level tree we would soon be asked to write out (and would find
in the object store) may not be anchored to any refs or commits
immediately, freshen the tree object when it happens.

Similarly, when we actually compute the cache-tree entries in
cache_tree_update(), we refrained from writing a tree object out
when it already exists in the object store.  We would want to
freshen the tree object in that case to protect it from premature
pruning.

Strictly speaking, freshing these tree objects at each and every
level is probably unnecessary, given that anything reachable from a
young object inherits the youth from the referring object to be
protected from pruning.  It should be sufficient to freshen only the
very top-level tree instead.  Benchmarking and optimization is left
as an exercise for later days.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/cache-tree.c b/cache-tree.c
index 3ebf9c3aa4..c8c74a1e07 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -225,7 +225,7 @@ int cache_tree_fully_valid(struct cache_tree *it)
 	int i;
 	if (!it)
 		return 0;
-	if (it->entry_count < 0 || !has_sha1_file(it->sha1))
+	if (it->entry_count < 0 || !freshen_object(it->sha1))
 		return 0;
 	for (i = 0; i < it->subtree_nr; i++) {
 		if (!cache_tree_fully_valid(it->down[i]->cache_tree))
@@ -253,7 +253,7 @@ static int update_one(struct cache_tree *it,
 
 	*skip_count = 0;
 
-	if (0 <= it->entry_count && has_sha1_file(it->sha1))
+	if (0 <= it->entry_count && freshen_object(it->sha1))
 		return it->entry_count;
 
 	/*
@@ -393,7 +393,7 @@ static int update_one(struct cache_tree *it,
 	if (repair) {
 		unsigned char sha1[20];
 		hash_sha1_file(buffer.buf, buffer.len, tree_type, sha1);
-		if (has_sha1_file(sha1))
+		if (freshen_object(sha1))
 			hashcpy(it->sha1, sha1);
 		else
 			to_invalidate = 1;