>From a thread on Hacker News. It seems that if a user does not have
access to the remote's reflog and accidentally forces a push to a ref,
how does he recover it? In order to force push again to revert it
back, he would need to know the remote's old SHA-1. Local reflog does
not help because remote refs are not updated during a push.

This patch prints the latest SHA-1 before the forced push in full. He
then can do

    git push <remote> +<old-sha1>:<ref>

He does not even need to have the objects that <old-sha1> refers
to. We could simply push an empty pack and the the remote will happily
accept the force, assuming garbage collection has not happened. But
that's another and a little more complex patch.

Is there any other way to undo a forced push?

-- 8< --
diff --git a/transport.c b/transport.c
index f080e93..6bd6a64 100644
--- a/transport.c
+++ b/transport.c
@@ -657,16 +657,17 @@ static void print_ok_ref_status(struct ref *ref, int 
porcelain)
                        "[new branch]"),
                        ref, ref->peer_ref, NULL, porcelain);
        else {
-               char quickref[84];
+               char quickref[104];
                char type;
                const char *msg;
 
-               strcpy(quickref, status_abbrev(ref->old_sha1));
                if (ref->forced_update) {
+                       strcpy(quickref, sha1_to_hex(ref->old_sha1));
                        strcat(quickref, "...");
                        type = '+';
                        msg = "forced update";
                } else {
+                       strcpy(quickref, status_abbrev(ref->old_sha1));
                        strcat(quickref, "..");
                        type = ' ';
                        msg = NULL;
-- 8< --
--
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