Re: [PATCH v4] refs: implement reference transaction hook

[Taylor Blau <me@ttaylorr.com>]

On Fri, Oct 23, 2020 at 03:57:21PM -0400, Taylor Blau wrote:
> It should be possible to keep track of the old and new OIDs via a
> non-copied pointer, but I have to untangle this code a little bit more
> before I can be sure.

This may be both easier and harder than I was imagining ;-). In the
easier direction, the following patch is sufficient to get the tests
passing again:

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 04e85e7002..744c93b7ff 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2311,12 +2311,11 @@ static int split_symref_update(struct ref_update *update,
 	new_update->parent_update = update;

 	/*
-	 * Change the symbolic ref update to log only. Also, it
-	 * doesn't need to check its old OID value, as that will be
-	 * done when new_update is processed.
+	 * Change the symbolic ref update to log only. Though we don't
+	 * need to check its old OID value, leave REF_HAVE_OLD alone so
+	 * we can propagate it to the ref transaction hook.
 	 */
 	update->flags |= REF_LOG_ONLY | REF_NO_DEREF;
-	update->flags &= ~REF_HAVE_OLD;

 	/*
 	 * Add the referent. This insertion is O(N) in the transaction

But, it also means that we're now needlessly re-verifying the before
state of symrefs (or so I think, I haven't yet proved it one way or the
other).

So, I need to look into that before deciding if this is a good direction
to go.

Thanks,
Taylor