Patrick Steinhardt [off-list ref] writes:
+test_expect_success 'backfill failure causes command to fail' '
+ git init clone5 &&
+
+ write_script clone5/.git/hooks/reference-transaction <<-EOF &&
+ while read oldrev newrev reference
+ do
+ if test "\$reference" = refs/tags/tag1
+ then
+ # Create a nested tag below the actual tag we
+ # wanted to write, which causes a D/F conflict
+ # later when we want to commit refs/tags/tag1.
+ # We cannot just `exit 1` here given that this
+ # would cause us to die immediately.
+ git update-ref refs/tags/tag1/nested $B
+ exit \$!
+ fi
+ done
+ EOF
I think I've reviewed the previous round of these patches in
detail. I by mistake sent a comment for this step in v2, but I
think the same puzzlement exists in this round, too.