[PATCH v3 1/6] refs: create and use `ref_update_expects_existing_old_ref()`

[Karthik Nayak <karthik.188@gmail.com>]

From: Karthik Nayak <karthik.188@gmail.com>

The files and reftable backend, need to check if a ref must exist, so
that the required validation can be done. A ref must exist only when the
`old_oid` value of the update has been explicitly set and it is not the
`null_oid` value.

Since we also support symrefs now, we need to ensure that even when
`old_target` is set a ref must exist. While this was missed when we
added symref support in transactions, there are no active users of this
path. As we introduce the 'symref-verify' command in the upcoming
commits, it is important to fix this.

So let's export this to a function called
`ref_update_expects_existing_old_ref()` and expose it internally via
'refs-internal.h'.

Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs.c                  | 6 ++++++
 refs/files-backend.c    | 3 +--
 refs/refs-internal.h    | 6 ++++++
 refs/reftable-backend.c | 2 +-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/refs.c b/refs.c
index 8260c27cde..50d8d7d777 100644
--- a/refs.c
+++ b/refs.c
@@ -2679,3 +2679,9 @@ int ref_update_check_old_target(const char *referent, struct ref_update *update,
 			    referent, update->old_target);
 	return -1;
 }
+
+int ref_update_expects_existing_old_ref(struct ref_update *update)
+{
+	return (update->flags & REF_HAVE_OLD) &&
+		(!is_null_oid(&update->old_oid) || update->old_target);
+}
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 5f3089d947..194e74eb4d 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2412,8 +2412,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			       struct strbuf *err)
 {
 	struct strbuf referent = STRBUF_INIT;
-	int mustexist = (update->flags & REF_HAVE_OLD) &&
-		!is_null_oid(&update->old_oid);
+	int mustexist = ref_update_expects_existing_old_ref(update);
 	int ret = 0;
 	struct ref_lock *lock;
 
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 53a6c5d842..ee298ec0d5 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -765,4 +765,10 @@ int ref_update_has_null_new_value(struct ref_update *update);
 int ref_update_check_old_target(const char *referent, struct ref_update *update,
 				struct strbuf *err);
 
+/*
+ * Check if the ref must exist, this means that the old_oid or
+ * old_target is non NULL.
+ */
+int ref_update_expects_existing_old_ref(struct ref_update *update);
+
 #endif /* REFS_REFS_INTERNAL_H */
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 1af86bbdec..b838cf8f00 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -824,7 +824,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 					      &current_oid, &referent, &u->type);
 		if (ret < 0)
 			goto done;
-		if (ret > 0 && (!(u->flags & REF_HAVE_OLD) || is_null_oid(&u->old_oid))) {
+		if (ret > 0 && !ref_update_expects_existing_old_ref(u)) {
 			/*
 			 * The reference does not exist, and we either have no
 			 * old object ID or expect the reference to not exist.
-- 
2.43.GIT