Re: [PATCH v3 1/3] refs/files-backend: add longer-scoped copy of string to list

[Jeff King <peff@peff.net>]

On Tue, Sep 05, 2017 at 07:24:18PM +0200, Martin Ågren wrote:

> > And from that point of view, doesn't split_head_update() wants a
> > similar fix?  It attempts to insert "HEAD", makes sure it hasn't
> > been inserted and then hangs a new update transaction as its util.
> > It is not wrong per-se from purely leak-prevention point of view,
> > as that "HEAD" is a literal string we woudn't even want to free,
> > but from logical/"what each data means" point of view, it still
> > feels wrong.
> 
> There is a "Special hack" comment related to this, and I don't feel
> particularly confident that I could make any meaningful contribution in
> this area. To be honest, I don't immediately see in which direction your
> suggestion/idea/thought is going, which tells me I should not be making
> a mess out of it. :-)

I noticed the HEAD funniness, too, when looking at this earlier. I agree
with Junio that it's not quite consistent with the general rule of
"string list items point to their refnames", but I don't think it
matters in practice.

I think the fix, if we wanted to do one, would be similar to what you
did in split_symref_update(). Like:

diff --git a/refs/files-backend.c b/refs/files-backend.c
index f3455609d6..3f9deff902 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2095,8 +2095,7 @@ static int split_head_update(struct ref_update *update,
 	 * transaction. This insertion is O(N) in the transaction
 	 * size, but it happens at most once per transaction.
 	 */
-	item = string_list_insert(affected_refnames, "HEAD");
-	if (item->util) {
+	if (string_list_has_string(affected_refnames, "HEAD")) {
 		/* An entry already existed */
 		strbuf_addf(err,
 			    "multiple updates for 'HEAD' (including one "
@@ -2111,6 +2110,7 @@ static int split_head_update(struct ref_update *update,
 			update->new_oid.hash, update->old_oid.hash,
 			update->msg);
 
+	item = string_list_insert(affected_refnames, new_update->refname);
 	item->util = new_update;
 
 	return 0;

-Peff