Re: [RFC] notes: avoid recommitting identical trees

Jeff King venit, vidit, dixit 31.08.2010 18:01:

On Tue, Aug 31, 2010 at 05:16:17PM +0200, Michael J Gruber wrote:

quoted

Currently, "git notes" behaves like "git commit --allow-empty" when
committing notes trees. In particular, removing nonexisting notes leads
to empty commits "commits with no diff".

Change this to avoid unnecessary notes commits.

Is this a sufficient check in the case of notes? Is it possible that we
re-balanced the fanout of the notes tree and got a different tree sha1,
even though there is nothing interesting to commit?

Yes, but I don't think this hurts. The main thrust here is to catch the
case of repeated "git notes remove". Also, we might even want to record
the history when there is rebalancing since this is indeed a tree change.

Johan's (later ;) ) approach, while being more intrusive, catches this
at the point of removal - if there's nothing to remove, nothing gets
rewritten.

quoted

+	if (!parent || parse_commit(parent->item) || parse_tree(parent->item->tree) ||
+		hashcmp(parent->item->tree->object.sha1, tree_sha1)) {

I didn't check, but I can imagine you can drop the parse_tree here. We
should know the object sha1 once the commit is parsed.

parse_commit() does a lookup_tree() but I don't think that it parses the
tree, i.e. I don't hink it fills in tree->object.sha1. At least it
segfaulted without that ;)

Michael