refs: do not execute reference-transaction hook on packing refs

The reference-transaction hook is supposed to track logical changes to
references, but it currently also gets executed when packing refs in a
repository. This is unexpected and ultimately not all that useful:
packing refs is not supposed to result in any user-visible change to the
refs' state, and it ultimately is an implementation detail of how refs
stores work.

Fix this excessive execution of the hook when packing refs.

Reported-by: Waleed Khan <[email protected]>
Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

refs/files-backend.c

@@ -1121,7 +1121,8 @@ static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 	if (check_refname_format(r->name, 0))
 		return;
 
-	transaction = ref_store_transaction_begin(&refs->base, 0, &err);
+	transaction = ref_store_transaction_begin(&refs->base,
+						  REF_TRANSACTION_SKIP_HOOK, &err);
 	if (!transaction)
 		goto cleanup;
 	ref_transaction_add_update(
@@ -1192,7 +1193,8 @@ static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
 	struct strbuf err = STRBUF_INIT;
 	struct ref_transaction *transaction;
 
-	transaction = ref_store_transaction_begin(refs->packed_ref_store, 0, &err);
+	transaction = ref_store_transaction_begin(refs->packed_ref_store,
+						  REF_TRANSACTION_SKIP_HOOK, &err);
 	if (!transaction)
 		return -1;
 

t/t1416-ref-transaction-hooks.sh

@@ -150,21 +150,12 @@ test_expect_success 'hook does not get called on packing refs' '
 	git pack-refs --all &&
 
 	# We only expect a single hook invocation, which is the call to
-	# git-update-ref(1). But currently, packing refs will also trigger the
-	# hook.
+	# git-update-ref(1).
 	cat >expect <<-EOF &&
 		prepared
 		$ZERO_OID $POST_OID refs/heads/unpacked-ref
 		committed
 		$ZERO_OID $POST_OID refs/heads/unpacked-ref
-		prepared
-		$ZERO_OID $POST_OID refs/heads/unpacked-ref
-		committed
-		$ZERO_OID $POST_OID refs/heads/unpacked-ref
-		prepared
-		$POST_OID $ZERO_OID refs/heads/unpacked-ref
-		committed
-		$POST_OID $ZERO_OID refs/heads/unpacked-ref
 	EOF
 
 	test_cmp expect actual