Merge branch 'kn/ref-transaction-symref' into seenNotice: this object is not reachable from any branch.

* kn/ref-transaction-symref:
  refs: remove `create_symref` and associated dead code
  refs: rename `refs_create_symref()` to `refs_update_symref()`
  refs: use transaction in `refs_create_symref()`
  refs: add support for transactional symref updates
  refs: support symrefs in 'reference-transaction' hook
  files-backend: extract out `create_symref_lock()`
  refs: accept symref values in `ref_transaction_update()`
Notice: this object is not reachable from any branch.

21 files changed, 350 insertions, 264 deletions

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index ee9b92c90d..06e997131b 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -486,7 +486,7 @@ reference-transaction
 This hook is invoked by any Git command that performs reference
 updates. It executes whenever a reference transaction is prepared,
 committed or aborted and may thus get called multiple times. The hook
-does not cover symbolic references (but that may change in the future).
+also supports symbolic reference updates.
 
 The hook takes exactly one argument, which is the current state the
 given reference transaction is in:
@@ -503,16 +503,20 @@ given reference transaction is in:
 For each reference update that was added to the transaction, the hook
 receives on standard input a line of the format:
 
-  <old-oid> SP <new-oid> SP <ref-name> LF
+  <old-value> SP <new-value> SP <ref-name> LF
 
-where `<old-oid>` is the old object name passed into the reference
-transaction, `<new-oid>` is the new object name to be stored in the
+where `<old-value>` is the old object name passed into the reference
+transaction, `<new-value>` is the new object name to be stored in the
 ref and `<ref-name>` is the full name of the ref. When force updating
 the reference regardless of its current value or when the reference is
-to be created anew, `<old-oid>` is the all-zeroes object name. To
+to be created anew, `<old-value>` is the all-zeroes object name. To
 distinguish these cases, you can inspect the current value of
 `<ref-name>` via `git rev-parse`.
 
+For symbolic reference updates the `<old_value>` and `<new-value>`
+fields could denote references instead of objects. A reference will be
+denoted with a 'ref:' prefix, like `ref:<ref-target>`.
+
 The exit status of the hook is ignored for any state except for the
 "prepared" state. In the "prepared" state, a non-zero exit status will
 cause the transaction to be aborted. The hook will not be called with
diff --git a/branch.c b/branch.c
index e4a738fc7b..48af4c3ceb 100644
--- a/branch.c
+++ b/branch.c
@@ -627,7 +627,7 @@ void create_branch(struct repository *r,
 	if (!transaction ||
 		ref_transaction_update(transaction, ref.buf,
 					&oid, forcing ? NULL : null_oid(),
-					0, msg, &err) ||
+					NULL, NULL, 0, msg, &err) ||
 		ref_transaction_commit(transaction, &err))
 		die("%s", err.buf);
 	ref_transaction_free(transaction);
diff --git a/builtin/branch.c b/builtin/branch.c
index dd3e3a7dc0..4491f7a20c 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -555,7 +555,7 @@ static int replace_each_worktree_head_symref(struct worktree **worktrees,
 			continue;
 
 		refs = get_worktree_ref_store(worktrees[i]);
-		if (refs_create_symref(refs, "HEAD", newref, logmsg))
+		if (refs_update_symref(refs, "HEAD", newref, logmsg))
 			ret = error(_("HEAD of working tree %s is not updated"),
 				    worktrees[i]->path);
 	}
diff --git a/builtin/fast-import.c b/builtin/fast-import.c
index 279d97b731..f3c37f2c86 100644
--- a/builtin/fast-import.c
+++ b/builtin/fast-import.c
@@ -1634,7 +1634,7 @@ static int update_branch(struct branch *b)
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, b->name, &b->oid, &old_oid,
-				   0, msg, &err) ||
+				   NULL, NULL, 0, msg, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
 		error("%s", err.buf);
@@ -1675,7 +1675,8 @@ static void dump_tags(void)
 		strbuf_addf(&ref_name, "refs/tags/%s", t->name);
 
 		if (ref_transaction_update(transaction, ref_name.buf,
-					   &t->oid, NULL, 0, msg, &err)) {
+					   &t->oid, NULL, NULL, NULL,
+					   0, msg, &err)) {
 			failure |= error("%s", err.buf);
 			goto cleanup;
 		}
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 5857d860db..66840b7c5b 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -668,7 +668,7 @@ static int s_update_ref(const char *action,
 
 	ret = ref_transaction_update(transaction, ref->name, &ref->new_oid,
 				     check_old ? &ref->old_oid : NULL,
-				     0, msg, &err);
+				     NULL, NULL, 0, msg, &err);
 	if (ret) {
 		ret = STORE_REF_ERROR_OTHER;
 		goto out;
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index e8d7df14b6..b150ef39a8 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1595,6 +1595,7 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 		if (ref_transaction_update(transaction,
 					   namespaced_name,
 					   new_oid, old_oid,
+					   NULL, NULL,
 					   0, "push",
 					   &err)) {
 			rp_error("%s", err.buf);
diff --git a/builtin/replace.c b/builtin/replace.c
index da59600ad2..7690687b0e 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -201,7 +201,7 @@ static int replace_object_oid(const char *object_ref,
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, repl, &prev,
-				   0, NULL, &err) ||
+				   NULL, NULL, 0, NULL, &err) ||
 	    ref_transaction_commit(transaction, &err))
 		res = error("%s", err.buf);
 
diff --git a/builtin/tag.c b/builtin/tag.c
index 9a33cb50b4..40a65fdebc 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -660,6 +660,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 	transaction = ref_transaction_begin(&err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, &object, &prev,
+				   NULL, NULL,
 				   create_reflog ? REF_FORCE_CREATE_REFLOG : 0,
 				   reflog_msg.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index e46afbc46d..21fdbf6ac8 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -204,6 +204,7 @@ static void parse_cmd_update(struct ref_transaction *transaction,
 
 	if (ref_transaction_update(transaction, refname,
 				   &new_oid, have_old ? &old_oid : NULL,
+				   NULL, NULL,
 				   update_flags | create_reflog_flag,
 				   msg, &err))
 		die("%s", err.buf);
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 7c6c72536b..480202c517 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -517,7 +517,7 @@ static int add_worktree(const char *path, const char *refname,
 		ret = refs_update_ref(wt_refs, NULL, "HEAD", &commit->object.oid,
 				      NULL, 0, UPDATE_REFS_MSG_ON_ERR);
 	else
-		ret = refs_create_symref(wt_refs, "HEAD", symref.buf, NULL);
+		ret = refs_update_symref(wt_refs, "HEAD", symref.buf, NULL);
 	if (ret)
 		goto done;
 
diff --git a/refs.c b/refs.c
index 7c3c7465a4..89e6647c02 100644
--- a/refs.c
+++ b/refs.c
@@ -1257,6 +1257,8 @@ void ref_transaction_free(struct ref_transaction *transaction)
 
 	for (i = 0; i < transaction->nr; i++) {
 		free(transaction->updates[i]->msg);
+		free((char *)transaction->updates[i]->new_target);
+		free((char *)transaction->updates[i]->old_target);
 		free(transaction->updates[i]);
 	}
 	free(transaction->updates);
@@ -1268,6 +1270,7 @@ struct ref_update *ref_transaction_add_update(
 		const char *refname, unsigned int flags,
 		const struct object_id *new_oid,
 		const struct object_id *old_oid,
+		const char *new_target, const char *old_target,
 		const char *msg)
 {
 	struct ref_update *update;
@@ -1275,16 +1278,24 @@ struct ref_update *ref_transaction_add_update(
 	if (transaction->state != REF_TRANSACTION_OPEN)
 		BUG("update called for transaction that is not open");
 
+	if (old_oid && !is_null_oid(old_oid) && old_target)
+		BUG("only one of old_oid and old_target should be non NULL");
+	if (new_oid && !is_null_oid(new_oid) && new_target)
+		BUG("only one of new_oid and new_target should be non NULL");
+
 	FLEX_ALLOC_STR(update, refname, refname);
 	ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
 	transaction->updates[transaction->nr++] = update;
 
 	update->flags = flags;
 
-	if (flags & REF_HAVE_NEW)
+	update->new_target = xstrdup_or_null(new_target);
+	update->old_target = xstrdup_or_null(old_target);
+	if ((flags & REF_HAVE_NEW) && new_oid)
 		oidcpy(&update->new_oid, new_oid);
-	if (flags & REF_HAVE_OLD)
+	if ((flags & REF_HAVE_OLD) && old_oid)
 		oidcpy(&update->old_oid, old_oid);
+
 	update->msg = normalize_reflog_message(msg);
 	return update;
 }
@@ -1293,6 +1304,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
 			   const char *refname,
 			   const struct object_id *new_oid,
 			   const struct object_id *old_oid,
+			   const char *new_target,
+			   const char *old_target,
 			   unsigned int flags, const char *msg,
 			   struct strbuf *err)
 {
@@ -1325,9 +1338,11 @@ int ref_transaction_update(struct ref_transaction *transaction,
 	flags &= REF_TRANSACTION_UPDATE_ALLOWED_FLAGS;
 
 	flags |= (new_oid ? REF_HAVE_NEW : 0) | (old_oid ? REF_HAVE_OLD : 0);
+	flags |= (new_target ? REF_HAVE_NEW : 0) | (old_target ? REF_HAVE_OLD : 0);
 
 	ref_transaction_add_update(transaction, refname, flags,
-				   new_oid, old_oid, msg);
+				   new_oid, old_oid, new_target,
+				   old_target, msg);
 	return 0;
 }
 
@@ -1342,7 +1357,8 @@ int ref_transaction_create(struct ref_transaction *transaction,
 		return 1;
 	}
 	return ref_transaction_update(transaction, refname, new_oid,
-				      null_oid(), flags, msg, err);
+				      null_oid(), NULL, NULL, flags,
+				      msg, err);
 }
 
 int ref_transaction_delete(struct ref_transaction *transaction,
@@ -1355,7 +1371,8 @@ int ref_transaction_delete(struct ref_transaction *transaction,
 		BUG("delete called with old_oid set to zeros");
 	return ref_transaction_update(transaction, refname,
 				      null_oid(), old_oid,
-				      flags, msg, err);
+				      NULL, NULL, flags,
+				      msg, err);
 }
 
 int ref_transaction_verify(struct ref_transaction *transaction,
@@ -1368,6 +1385,7 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 		BUG("verify called with old_oid set to NULL");
 	return ref_transaction_update(transaction, refname,
 				      NULL, old_oid,
+				      NULL, NULL,
 				      flags, NULL, err);
 }
 
@@ -1382,8 +1400,8 @@ int refs_update_ref(struct ref_store *refs, const char *msg,
 
 	t = ref_store_transaction_begin(refs, &err);
 	if (!t ||
-	    ref_transaction_update(t, refname, new_oid, old_oid, flags, msg,
-				   &err) ||
+	    ref_transaction_update(t, refname, new_oid, old_oid, NULL, NULL,
+				   flags, msg, &err) ||
 	    ref_transaction_commit(t, &err)) {
 		ret = 1;
 		ref_transaction_free(t);
@@ -2282,25 +2300,33 @@ int peel_iterated_oid(const struct object_id *base, struct object_id *peeled)
 	return peel_object(base, peeled) ? -1 : 0;
 }
 
-int refs_create_symref(struct ref_store *refs,
-		       const char *ref_target,
-		       const char *refs_heads_master,
-		       const char *logmsg)
+int refs_update_symref(struct ref_store *refs, const char *ref,
+		       const char *target, const char *logmsg)
 {
-	char *msg;
-	int retval;
+	struct ref_transaction *transaction;
+	struct strbuf err = STRBUF_INIT;
+	int ret = 0;
 
-	msg = normalize_reflog_message(logmsg);
-	retval = refs->be->create_symref(refs, ref_target, refs_heads_master,
-					 msg);
-	free(msg);
-	return retval;
+	transaction = ref_store_transaction_begin(refs, &err);
+	if (!transaction ||
+	    ref_transaction_update(transaction, ref, NULL, NULL,
+				   target, NULL, REF_NO_DEREF,
+				   logmsg, &err) ||
+	    ref_transaction_commit(transaction, &err)) {
+		ret = error("%s", err.buf);
+	}
+
+	strbuf_release(&err);
+	if (transaction)
+		ref_transaction_free(transaction);
+
+	return ret;
 }
 
 int create_symref(const char *ref_target, const char *refs_heads_master,
 		  const char *logmsg)
 {
-	return refs_create_symref(get_main_ref_store(the_repository), ref_target,
+	return refs_update_symref(get_main_ref_store(the_repository), ref_target,
 				  refs_heads_master, logmsg);
 }
 
@@ -2354,10 +2380,22 @@ static int run_transaction_hook(struct ref_transaction *transaction,
 		struct ref_update *update = transaction->updates[i];
 
 		strbuf_reset(&buf);
-		strbuf_addf(&buf, "%s %s %s\n",
-			    oid_to_hex(&update->old_oid),
-			    oid_to_hex(&update->new_oid),
-			    update->refname);
+
+		if (!(update->flags & REF_HAVE_OLD))
+			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid()));
+		else if (update->old_target)
+			strbuf_addf(&buf, "ref:%s ", update->old_target);
+		else
+			strbuf_addf(&buf, "%s ", oid_to_hex(&update->old_oid));
+
+		if (!(update->flags & REF_HAVE_NEW))
+			strbuf_addf(&buf, "%s ", oid_to_hex(null_oid()));
+		else if (update->new_target)
+			strbuf_addf(&buf, "ref:%s ", update->new_target);
+		else
+			strbuf_addf(&buf, "%s ", oid_to_hex(&update->new_oid));
+
+		strbuf_addf(&buf, "%s\n", update->refname);
 
 		if (write_in_full(proc.in, buf.buf, buf.len) < 0) {
 			if (errno != EPIPE) {
@@ -2806,3 +2844,8 @@ int copy_existing_ref(const char *oldref, const char *newref, const char *logmsg
 {
 	return refs_copy_existing_ref(get_main_ref_store(the_repository), oldref, newref, logmsg);
 }
+
+int ref_update_has_null_new_value(struct ref_update *update)
+{
+	return !update->new_target && is_null_oid(&update->new_oid);
+}
diff --git a/refs.h b/refs.h
index 8255989e7e..7c69e8cc0d 100644
--- a/refs.h
+++ b/refs.h
@@ -606,7 +606,7 @@ int refs_copy_existing_ref(struct ref_store *refs, const char *oldref,
 int copy_existing_ref(const char *oldref, const char *newref,
 			const char *logmsg);
 
-int refs_create_symref(struct ref_store *refs, const char *refname,
+int refs_update_symref(struct ref_store *refs, const char *refname,
 		       const char *target, const char *logmsg);
 int create_symref(const char *refname, const char *target, const char *logmsg);
 
@@ -648,6 +648,16 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
  *         before the update. A copy of this value is made in the
  *         transaction.
  *
+ *     new_target -- the target reference that the reference will be
+ *         updated to point to. If the reference is a regular reference,
+ *         it will be converted to a symbolic reference. Cannot be set
+ *         together with `new_oid`. A copy of this value is made in the
+ *         transaction.
+ *
+ *     old_target -- the reference that the reference must be pointing to.
+ *         Canont be set together with `old_oid`. A copy of this value is
+ *         made in the transaction.
+ *
  *     flags -- flags affecting the update, passed to
  *         update_ref_lock(). Possible flags: REF_NO_DEREF,
  *         REF_FORCE_CREATE_REFLOG. See those constants for more
@@ -713,7 +723,11 @@ struct ref_transaction *ref_transaction_begin(struct strbuf *err);
  * beforehand. The old value is checked after the lock is taken to
  * prevent races. If the old value doesn't agree with old_oid, the
  * whole transaction fails. If old_oid is NULL, then the previous
- * value is not checked.
+ * value is not checked. If `old_target` is not NULL, treat the reference
+ * as a symbolic ref and validate that its target before the update is
+ * `old_target`. If the `new_target` is not NULL, then the reference
+ * will be updated to a symbolic ref which targets `new_target`.
+ * Together, these allow us to update between regular refs and symrefs.
  *
  * See the above comment "Reference transaction updates" for more
  * information.
@@ -722,6 +736,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
 			   const char *refname,
 			   const struct object_id *new_oid,
 			   const struct object_id *old_oid,
+			   const char *new_target,
+			   const char *old_target,
 			   unsigned int flags, const char *msg,
 			   struct strbuf *err);
 
diff --git a/refs/debug.c b/refs/debug.c
index c7531b17f0..8be316bb67 100644
--- a/refs/debug.c
+++ b/refs/debug.c
@@ -131,18 +131,6 @@ static int debug_pack_refs(struct ref_store *ref_store, struct pack_refs_opts *o
 	return res;
 }
 
-static int debug_create_symref(struct ref_store *ref_store,
-			       const char *ref_name, const char *target,
-			       const char *logmsg)
-{
-	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
-	int res = drefs->refs->be->create_symref(drefs->refs, ref_name, target,
-						 logmsg);
-	trace_printf_key(&trace_refs, "create_symref: %s -> %s \"%s\": %d\n", ref_name,
-		target, logmsg, res);
-	return res;
-}
-
 static int debug_rename_ref(struct ref_store *ref_store, const char *oldref,
 			    const char *newref, const char *logmsg)
 {
@@ -441,7 +429,6 @@ struct ref_storage_be refs_be_debug = {
 	.initial_transaction_commit = debug_initial_transaction_commit,
 
 	.pack_refs = debug_pack_refs,
-	.create_symref = debug_create_symref,
 	.rename_ref = debug_rename_ref,
 	.copy_ref = debug_copy_ref,
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ea927c516d..8cc223a205 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1197,7 +1197,7 @@ static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 	ref_transaction_add_update(
 			transaction, r->name,
 			REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
-			null_oid(), &r->oid, NULL);
+			null_oid(), &r->oid, NULL, NULL, NULL);
 	if (ref_transaction_commit(transaction, &err))
 		goto cleanup;
 
@@ -1291,7 +1291,7 @@ static int files_pack_refs(struct ref_store *ref_store,
 		 * packed-refs transaction:
 		 */
 		if (ref_transaction_update(transaction, iter->refname,
-					   iter->oid, NULL,
+					   iter->oid, NULL, NULL, NULL,
 					   REF_NO_DEREF, NULL, &err))
 			die("failure preparing to create packed reference %s: %s",
 			    iter->refname, err.buf);
@@ -1902,66 +1902,23 @@ static int create_ref_symlink(struct ref_lock *lock, const char *target)
 	return ret;
 }
 
-static void update_symref_reflog(struct files_ref_store *refs,
-				 struct ref_lock *lock, const char *refname,
-				 const char *target, const char *logmsg)
+static int create_symref_lock(struct files_ref_store *refs,
+			      struct ref_lock *lock, const char *refname,
+			      const char *target, struct strbuf *err)
 {
-	struct strbuf err = STRBUF_INIT;
-	struct object_id new_oid;
-
-	if (logmsg &&
-	    refs_resolve_ref_unsafe(&refs->base, target,
-				    RESOLVE_REF_READING, &new_oid, NULL) &&
-	    files_log_ref_write(refs, refname, &lock->old_oid,
-				&new_oid, logmsg, 0, &err)) {
-		error("%s", err.buf);
-		strbuf_release(&err);
-	}
-}
-
-static int create_symref_locked(struct files_ref_store *refs,
-				struct ref_lock *lock, const char *refname,
-				const char *target, const char *logmsg)
-{
-	if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
-		update_symref_reflog(refs, lock, refname, target, logmsg);
-		return 0;
+	if (!fdopen_lock_file(&lock->lk, "w")) {
+		strbuf_addf(err, "unable to fdopen %s: %s",
+			     get_lock_file_path(&lock->lk), strerror(errno));
+		return -1;
 	}
 
-	if (!fdopen_lock_file(&lock->lk, "w"))
-		return error("unable to fdopen %s: %s",
+	if (fprintf(get_lock_file_fp(&lock->lk), "ref: %s\n", target) < 0) {
+		strbuf_addf(err, "unable to write to %s: %s",
 			     get_lock_file_path(&lock->lk), strerror(errno));
-
-	update_symref_reflog(refs, lock, refname, target, logmsg);
-
-	/* no error check; commit_ref will check ferror */
-	fprintf(get_lock_file_fp(&lock->lk), "ref: %s\n", target);
-	if (commit_ref(lock) < 0)
-		return error("unable to write symref for %s: %s", refname,
-			     strerror(errno));
-	return 0;
-}
-
-static int files_create_symref(struct ref_store *ref_store,
-			       const char *refname, const char *target,
-			       const char *logmsg)
-{
-	struct files_ref_store *refs =
-		files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
-	struct strbuf err = STRBUF_INIT;
-	struct ref_lock *lock;
-	int ret;
-
-	lock = lock_ref_oid_basic(refs, refname, &err);
-	if (!lock) {
-		error("%s", err.buf);
-		strbuf_release(&err);
 		return -1;
 	}
 
-	ret = create_symref_locked(refs, lock, refname, target, logmsg);
-	unlock_ref(lock);
-	return ret;
+	return 0;
 }
 
 static int files_reflog_exists(struct ref_store *ref_store,
@@ -2308,7 +2265,7 @@ static int split_head_update(struct ref_update *update,
 			transaction, "HEAD",
 			update->flags | REF_LOG_ONLY | REF_NO_DEREF,
 			&update->new_oid, &update->old_oid,
-			update->msg);
+			NULL, NULL, update->msg);
 
 	/*
 	 * Add "HEAD". This insertion is O(N) in the transaction
@@ -2371,7 +2328,7 @@ static int split_symref_update(struct ref_update *update,
 	new_update = ref_transaction_add_update(
 			transaction, referent, new_flags,
 			&update->new_oid, &update->old_oid,
-			update->msg);
+			NULL, NULL, update->msg);
 
 	new_update->parent_update = update;
 
@@ -2411,6 +2368,36 @@ static const char *original_update_refname(struct ref_update *update)
 }
 
 /*
+ * Check whether the old_target values stored in update are consistent
+ * with current_target, which is the symbolic reference's current value.
+ * If everything is OK, return 0; otherwise, write an error message to
+ * err and return -1.
+ */
+static int check_old_target(struct ref_update *update,
+			    const char *current_target,
+			    struct strbuf *err)
+{
+	if (!update->old_target)
+		BUG("called without old_target set");
+
+	if (!strcmp(update->old_target, current_target))
+		return 0;
+
+	if (!strcmp(current_target, ""))
+		strbuf_addf(err, "cannot lock ref '%s': "
+			    "reference is missing but expected %s",
+			    original_update_refname(update),
+			    update->old_target);
+	else
+		strbuf_addf(err, "cannot lock ref '%s': "
+			    "is at %s but expected %s",
+			    original_update_refname(update),
+			    current_target, update->old_target);
+
+	return -1;
+}
+
+/*
  * Check whether the REF_HAVE_OLD and old_oid values stored in update
  * are consistent with oid, which is the reference's current value. If
  * everything is OK, return 0; otherwise, write an error message to
@@ -2470,7 +2457,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 
 	files_assert_main_repository(refs, "lock_ref_for_update");
 
-	if ((update->flags & REF_HAVE_NEW) && is_null_oid(&update->new_oid))
+	if ((update->flags & REF_HAVE_NEW) && ref_update_has_null_new_value(update))
 		update->flags |= REF_DELETING;
 
 	if (head_ref) {
@@ -2513,7 +2500,14 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 					ret = TRANSACTION_GENERIC_ERROR;
 					goto out;
 				}
-			} else if (check_old_oid(update, &lock->old_oid, err)) {
+			}
+
+			if (update->old_target) {
+				if (check_old_target(update, referent.buf, err)) {
+					ret = TRANSACTION_GENERIC_ERROR;
+					goto out;
+				}
+			} else if  (check_old_oid(update, &lock->old_oid, err)) {
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto out;
 			}
@@ -2534,7 +2528,17 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 	} else {
 		struct ref_update *parent_update;
 
-		if (check_old_oid(update, &lock->old_oid, err)) {
+		/*
+		 * Even if the ref is a regular ref, if `old_target` is set, we
+		 * check the referent value. Ideally `old_target` should only
+		 * be set for symrefs, but we're strict about its usage.
+		 */
+		if (update->old_target) {
+			if (check_old_target(update, referent.buf, err)) {
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto out;
+			}
+		} else if  (check_old_oid(update, &lock->old_oid, err)) {
 			ret = TRANSACTION_GENERIC_ERROR;
 			goto out;
 		}
@@ -2552,9 +2556,27 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 		}
 	}
 
-	if ((update->flags & REF_HAVE_NEW) &&
-	    !(update->flags & REF_DELETING) &&
-	    !(update->flags & REF_LOG_ONLY)) {
+	if (update->new_target && !(update->flags & REF_LOG_ONLY)) {
+		if (create_symref_lock(refs, lock, update->refname, update->new_target, err)) {
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto out;
+		}
+
+		if (close_ref_gently(lock)) {
+			strbuf_addf(err, "couldn't close '%s.lock'",
+				    update->refname);
+			ret = TRANSACTION_GENERIC_ERROR;
+			goto out;
+		}
+
+		/*
+		 * Once we have created the symref lock, the commit
+		 * phase of the transaction only needs to commit the lock.
+		 */
+		update->flags |= REF_NEEDS_COMMIT;
+	} else if ((update->flags & REF_HAVE_NEW) &&
+		   !(update->flags & REF_DELETING) &&
+		   !(update->flags & REF_LOG_ONLY)) {
 		if (!(update->type & REF_ISSYMREF) &&
 		    oideq(&lock->old_oid, &update->new_oid)) {
 			/*
@@ -2762,7 +2784,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 					packed_transaction, update->refname,
 					REF_HAVE_NEW | REF_NO_DEREF,
 					&update->new_oid, NULL,
-					NULL);
+					NULL, NULL, NULL);
 		}
 	}
 
@@ -2817,6 +2839,43 @@ cleanup:
 	return ret;
 }
 
+static int parse_and_write_reflog(struct files_ref_store *refs,
+				  struct ref_update *update,
+				  struct ref_lock *lock,
+				  struct strbuf *err)
+{
+	if (update->new_target) {
+		/*
+		 * We want to get the resolved OID for the target, to ensure
+		 * that the correct value is added to the reflog.
+		 */
+		if (!refs_resolve_ref_unsafe(&refs->base, update->new_target,
+					     RESOLVE_REF_READING,
+					     &update->new_oid, NULL)) {
+			/*
+			 * TODO: currently we skip creating reflogs for dangling
+			 * symref updates. It would be nice to capture this as
+			 * zero oid updates however.
+			 */
+			return 0;
+		}
+	}
+
+	if (files_log_ref_write(refs, lock->ref_name, &lock->old_oid,
+				&update->new_oid, update->msg, update->flags, err)) {
+		char *old_msg = strbuf_detach(err, NULL);
+
+		strbuf_addf(err, "cannot update the ref '%s': %s",
+			    lock->ref_name, old_msg);
+		free(old_msg);
+		unlock_ref(lock);
+		update->backend_data = NULL;
+		return -1;
+	}
+
+	return 0;
+}
+
 static int files_transaction_finish(struct ref_store *ref_store,
 				    struct ref_transaction *transaction,
 				    struct strbuf *err)
@@ -2847,23 +2906,20 @@ static int files_transaction_finish(struct ref_store *ref_store,
 
 		if (update->flags & REF_NEEDS_COMMIT ||
 		    update->flags & REF_LOG_ONLY) {
-			if (files_log_ref_write(refs,
-						lock->ref_name,
-						&lock->old_oid,
-						&update->new_oid,
-						update->msg, update->flags,
-						err)) {
-				char *old_msg = strbuf_detach(err, NULL);
-
-				strbuf_addf(err, "cannot update the ref '%s': %s",
-					    lock->ref_name, old_msg);
-				free(old_msg);
-				unlock_ref(lock);
-				update->backend_data = NULL;
+			if (parse_and_write_reflog(refs, update, lock, err)) {
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto cleanup;
 			}
 		}
+
+		/*
+		 * We try creating a symlink, if that succeeds we continue to the
+		 * next update. If not, we try and create a regular symref.
+		 */
+		if (update->new_target && prefer_symlink_refs)
+			if (!create_ref_symlink(lock, update->new_target))
+				continue;
+
 		if (update->flags & REF_NEEDS_COMMIT) {
 			clear_loose_ref_cache(refs);
 			if (commit_ref(lock)) {
@@ -3047,7 +3103,7 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
 		ref_transaction_add_update(packed_transaction, update->refname,
 					   update->flags & ~REF_HAVE_OLD,
 					   &update->new_oid, &update->old_oid,
-					   NULL);
+					   NULL, NULL, NULL);
 	}
 
 	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
@@ -3290,7 +3346,6 @@ struct ref_storage_be refs_be_files = {
 	.initial_transaction_commit = files_initial_transaction_commit,
 
 	.pack_refs = files_pack_refs,
-	.create_symref = files_create_symref,
 	.rename_ref = files_rename_ref,
 	.copy_ref = files_copy_ref,
 
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 4e826c05ff..a937e7dbfc 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1714,7 +1714,6 @@ struct ref_storage_be refs_be_packed = {
 	.initial_transaction_commit = packed_initial_transaction_commit,
 
 	.pack_refs = packed_pack_refs,
-	.create_symref = NULL,
 	.rename_ref = NULL,
 	.copy_ref = NULL,
 
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 56641aa57a..0c620d4bce 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -125,6 +125,19 @@ struct ref_update {
 	struct object_id old_oid;
 
 	/*
+	 * If set, point the reference to this value. This can also be
+	 * used to convert regular references to become symbolic refs.
+	 * Cannot be set together with `new_oid`.
+	 */
+	const char *new_target;
+
+	/*
+	 * If set, check that the reference previously pointed to this
+	 * value. Cannot be set together with `old_oid`.
+	 */
+	const char *old_target;
+
+	/*
 	 * One or more of REF_NO_DEREF, REF_FORCE_CREATE_REFLOG,
 	 * REF_HAVE_NEW, REF_HAVE_OLD, or backend-specific flags.
 	 */
@@ -173,6 +186,7 @@ struct ref_update *ref_transaction_add_update(
 		const char *refname, unsigned int flags,
 		const struct object_id *new_oid,
 		const struct object_id *old_oid,
+		const char *new_target, const char *old_target,
 		const char *msg);
 
 /*
@@ -552,10 +566,6 @@ typedef int ref_transaction_commit_fn(struct ref_store *refs,
 
 typedef int pack_refs_fn(struct ref_store *ref_store,
 			 struct pack_refs_opts *opts);
-typedef int create_symref_fn(struct ref_store *ref_store,
-			     const char *ref_target,
-			     const char *refs_heads_master,
-			     const char *logmsg);
 typedef int rename_ref_fn(struct ref_store *ref_store,
 			  const char *oldref, const char *newref,
 			  const char *logmsg);
@@ -676,7 +686,6 @@ struct ref_storage_be {
 	ref_transaction_commit_fn *initial_transaction_commit;
 
 	pack_refs_fn *pack_refs;
-	create_symref_fn *create_symref;
 	rename_ref_fn *rename_ref;
 	copy_ref_fn *copy_ref;
 
@@ -735,4 +744,11 @@ void base_ref_store_init(struct ref_store *refs, struct repository *repo,
  */
 struct ref_store *maybe_debug_wrap_ref_store(const char *gitdir, struct ref_store *store);
 
+/*
+ * Helper function to check if the new value is null, this
+ * takes into consideration that the update could be a regular
+ * ref or a symbolic ref.
+ */
+int ref_update_has_null_new_value(struct ref_update *update);
+
 #endif /* REFS_REFS_INTERNAL_H */
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 10ee92e1f7..405de86b41 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -870,7 +870,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 			new_update = ref_transaction_add_update(
 					transaction, "HEAD",
 					u->flags | REF_LOG_ONLY | REF_NO_DEREF,
-					&u->new_oid, &u->old_oid, u->msg);
+					&u->new_oid, &u->old_oid, NULL, NULL, u->msg);
 			string_list_insert(&affected_refnames, new_update->refname);
 		}
 
@@ -897,7 +897,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 			 * There is no need to write the reference deletion
 			 * when the reference in question doesn't exist.
 			 */
-			 if (u->flags & REF_HAVE_NEW && !is_null_oid(&u->new_oid)) {
+			 if ((u->flags & REF_HAVE_NEW) && !ref_update_has_null_new_value(u)) {
 				 ret = queue_transaction_update(refs, tx_data, u,
 								&current_oid, err);
 				 if (ret)
@@ -948,8 +948,10 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 				 * intertwined with the locking in files-backend.c.
 				 */
 				new_update = ref_transaction_add_update(
-						transaction, referent.buf, new_flags,
-						&u->new_oid, &u->old_oid, u->msg);
+					transaction, referent.buf, new_flags,
+					&u->new_oid, &u->old_oid, u->new_target,
+					u->old_target, u->msg);
+
 				new_update->parent_update = u;
 
 				/*
@@ -979,7 +981,22 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		 * individual refs. But the error messages match what the files
 		 * backend returns, which keeps our tests happy.
 		 */
-		if (u->flags & REF_HAVE_OLD && !oideq(&current_oid, &u->old_oid)) {
+		if (u->old_target) {
+			if (strcmp(referent.buf, u->old_target)) {
+				if (!strcmp(referent.buf, ""))
+					strbuf_addf(err, "verifying symref target: '%s': "
+						    "reference is missing but expected %s",
+						    original_update_refname(u),
+						    u->old_target);
+				else
+					strbuf_addf(err, "verifying symref target: '%s': "
+						    "is at %s but expected %s",
+						    original_update_refname(u),
+						    referent.buf, u->old_target);
+				ret = -1;
+				goto done;
+			}
+		} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
 			if (is_null_oid(&u->old_oid))
 				strbuf_addf(err, _("cannot lock ref '%s': "
 					    "reference already exists"),
@@ -1090,7 +1107,7 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 		 * - `core.logAllRefUpdates` tells us to create the reflog for
 		 *   the given ref.
 		 */
-		if (u->flags & REF_HAVE_NEW && !(u->type & REF_ISSYMREF) && is_null_oid(&u->new_oid)) {
+		if ((u->flags & REF_HAVE_NEW) && !(u->type & REF_ISSYMREF) && ref_update_has_null_new_value(u)) {
 			struct reftable_log_record log = {0};
 			struct reftable_iterator it = {0};
 
@@ -1131,24 +1148,50 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 			   (u->flags & REF_FORCE_CREATE_REFLOG ||
 			    should_write_log(&arg->refs->base, u->refname))) {
 			struct reftable_log_record *log;
+			int create_reflog = 1;
+
+			if (u->new_target) {
+				if (!refs_resolve_ref_unsafe(&arg->refs->base, u->new_target,
+							     RESOLVE_REF_READING, &u->new_oid, NULL)) {
+					/*
+					 * TODO: currently we skip creating reflogs for dangling
+					 * symref updates. It would be nice to capture this as
+					 * zero oid updates however.
+					 */
+					create_reflog = 0;
+				}
+			}
 
-			ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
-			log = &logs[logs_nr++];
-			memset(log, 0, sizeof(*log));
-
-			fill_reftable_log_record(log, &committer_ident);
-			log->update_index = ts;
-			log->refname = xstrdup(u->refname);
-			memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
-			memcpy(log->value.update.old_hash, tx_update->current_oid.hash, GIT_MAX_RAWSZ);
-			log->value.update.message =
-				xstrndup(u->msg, arg->refs->write_options.block_size / 2);
+			if (create_reflog) {
+				ALLOC_GROW(logs, logs_nr + 1, logs_alloc);
+				log = &logs[logs_nr++];
+				memset(log, 0, sizeof(*log));
+
+				fill_reftable_log_record(log, &committer_ident);
+				log->update_index = ts;
+				log->refname = xstrdup(u->refname);
+				memcpy(log->value.update.new_hash, u->new_oid.hash, GIT_MAX_RAWSZ);
+				memcpy(log->value.update.old_hash, tx_update->current_oid.hash, GIT_MAX_RAWSZ);
+				log->value.update.message =
+					xstrndup(u->msg, arg->refs->write_options.block_size / 2);
+			}
 		}
 
 		if (u->flags & REF_LOG_ONLY)
 			continue;
 
-		if (u->flags & REF_HAVE_NEW && is_null_oid(&u->new_oid)) {
+		if (u->new_target) {
+			struct reftable_ref_record ref = {
+				.refname = (char *)u->refname,
+				.value_type = REFTABLE_REF_SYMREF,
+				.value.symref = (char *)u->new_target,
+				.update_index = ts,
+			};
+
+			ret = reftable_writer_add_ref(writer, &ref);
+			if (ret < 0)
+				goto done;
+		} else if ((u->flags & REF_HAVE_NEW) && ref_update_has_null_new_value(u)) {
 			struct reftable_ref_record ref = {
 				.refname = (char *)u->refname,
 				.update_index = ts,
@@ -1280,110 +1323,6 @@ struct write_create_symref_arg {
 	const char *logmsg;
 };
 
-static int write_create_symref_table(struct reftable_writer *writer, void *cb_data)
-{
-	struct write_create_symref_arg *create = cb_data;
-	uint64_t ts = reftable_stack_next_update_index(create->stack);
-	struct reftable_ref_record ref = {
-		.refname = (char *)create->refname,
-		.value_type = REFTABLE_REF_SYMREF,
-		.value.symref = (char *)create->target,
-		.update_index = ts,
-	};
-	struct ident_split committer_ident = {0};
-	struct reftable_log_record log = {0};
-	struct object_id new_oid;
-	struct object_id old_oid;
-	const char *committer_info;
-	int ret;
-
-	reftable_writer_set_limits(writer, ts, ts);
-
-	ret = refs_verify_refname_available(&create->refs->base, create->refname,
-					    NULL, NULL, create->err);
-	if (ret < 0)
-		return ret;
-
-	ret = reftable_writer_add_ref(writer, &ref);
-	if (ret)
-		return ret;
-
-	/*
-	 * Note that it is important to try and resolve the reference before we
-	 * write the log entry. This is because `should_write_log()` will munge
-	 * `core.logAllRefUpdates`, which is undesirable when we create a new
-	 * repository because it would be written into the config. As HEAD will
-	 * not resolve for new repositories this ordering will ensure that this
-	 * never happens.
-	 */
-	if (!create->logmsg ||
-	    !refs_resolve_ref_unsafe(&create->refs->base, create->target,
-				     RESOLVE_REF_READING, &new_oid, NULL) ||
-	    !should_write_log(&create->refs->base, create->refname))
-		return 0;
-
-	committer_info = git_committer_info(0);
-	if (split_ident_line(&committer_ident, committer_info, strlen(committer_info)))
-		BUG("failed splitting committer info");
-
-	fill_reftable_log_record(&log, &committer_ident);
-	log.refname = xstrdup(create->refname);
-	log.update_index = ts;
-	log.value.update.message = xstrndup(create->logmsg,
-					    create->refs->write_options.block_size / 2);
-	memcpy(log.value.update.new_hash, new_oid.hash, GIT_MAX_RAWSZ);
-	if (refs_resolve_ref_unsafe(&create->refs->base, create->refname,
-				    RESOLVE_REF_READING, &old_oid, NULL))
-		memcpy(log.value.update.old_hash, old_oid.hash, GIT_MAX_RAWSZ);
-
-	ret = reftable_writer_add_log(writer, &log);
-	reftable_log_record_release(&log);
-	return ret;
-}
-
-static int reftable_be_create_symref(struct ref_store *ref_store,
-				     const char *refname,
-				     const char *target,
-				     const char *logmsg)
-{
-	struct reftable_ref_store *refs =
-		reftable_be_downcast(ref_store, REF_STORE_WRITE, "create_symref");
-	struct reftable_stack *stack = stack_for(refs, refname, &refname);
-	struct strbuf err = STRBUF_INIT;
-	struct write_create_symref_arg arg = {
-		.refs = refs,
-		.stack = stack,
-		.refname = refname,
-		.target = target,
-		.logmsg = logmsg,
-		.err = &err,
-	};
-	int ret;
-
-	ret = refs->err;
-	if (ret < 0)
-		goto done;
-
-	ret = reftable_stack_reload(stack);
-	if (ret)
-		goto done;
-
-	ret = reftable_stack_add(stack, &write_create_symref_table, &arg);
-
-done:
-	assert(ret != REFTABLE_API_ERROR);
-	if (ret) {
-		if (err.len)
-			error("%s", err.buf);
-		else
-			error("unable to write symref for %s: %s", refname,
-			      reftable_error_str(ret));
-	}
-
-	strbuf_release(&err);
-	return ret;
-}
-
 struct write_copy_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
@@ -2298,7 +2237,6 @@ struct ref_storage_be refs_be_reftable = {
 	.initial_transaction_commit = reftable_be_initial_transaction_commit,
 
 	.pack_refs = reftable_be_pack_refs,
-	.create_symref = reftable_be_create_symref,
 	.rename_ref = reftable_be_rename_ref,
 	.copy_ref = reftable_be_copy_ref,
 
diff --git a/sequencer.c b/sequencer.c
index 612622eb67..ab4cb5630d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -662,7 +662,7 @@ static int fast_forward_to(struct repository *r,
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD",
 				   to, unborn && !is_rebase_i(opts) ?
-				   null_oid() : from,
+				   null_oid() : from, NULL, NULL,
 				   0, sb.buf, &err) ||
 	    ref_transaction_commit(transaction, &err)) {
 		ref_transaction_free(transaction);
@@ -1295,7 +1295,7 @@ int update_head_with_reflog(const struct commit *old_head,
 	if (!transaction ||
 	    ref_transaction_update(transaction, "HEAD", new_head,
 				   old_head ? &old_head->object.oid : null_oid(),
-				   0, sb.buf, err) ||
+				   NULL, NULL, 0, sb.buf, err) ||
 	    ref_transaction_commit(transaction, err)) {
 		ret = -1;
 	}
@@ -3863,8 +3863,9 @@ static int do_label(struct repository *r, const char *name, int len)
 	} else if (repo_get_oid(r, "HEAD", &head_oid)) {
 		error(_("could not read HEAD"));
 		ret = -1;
-	} else if (ref_transaction_update(transaction, ref_name.buf, &head_oid,
-					  NULL, 0, msg.buf, &err) < 0 ||
+	} else if (ref_transaction_update(transaction, ref_name.buf,
+					  &head_oid, NULL, NULL, NULL,
+					  0, msg.buf, &err) < 0 ||
 		   ref_transaction_commit(transaction, &err)) {
 		error("%s", err.buf);
 		ret = -1;
diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c
index 82bbf6e2e6..4651e4ced7 100644
--- a/t/helper/test-ref-store.c
+++ b/t/helper/test-ref-store.c
@@ -118,7 +118,7 @@ static int cmd_create_symref(struct ref_store *refs, const char **argv)
 	const char *target = notnull(*argv++, "target");
 	const char *logmsg = *argv++;
 
-	return refs_create_symref(refs, refname, target, logmsg);
+	return refs_update_symref(refs, refname, target, logmsg);
 }
 
 static struct flag_definition transaction_flags[] = {
diff --git a/t/t1416-ref-transaction-hooks.sh b/t/t1416-ref-transaction-hooks.sh
index 2092488090..067fd57290 100755
--- a/t/t1416-ref-transaction-hooks.sh
+++ b/t/t1416-ref-transaction-hooks.sh
@@ -134,4 +134,27 @@ test_expect_success 'interleaving hook calls succeed' '
 	test_cmp expect target-repo.git/actual
 '
 
+test_expect_success 'hook captures git-symbolic-ref updates' '
+	test_when_finished "rm actual" &&
+
+	test_hook reference-transaction <<-\EOF &&
+		echo "$*" >>actual
+		while read -r line
+		do
+			printf "%s\n" "$line"
+		done >>actual
+	EOF
+
+	git symbolic-ref refs/heads/symref refs/heads/main &&
+
+	cat >expect <<-EOF &&
+	prepared
+	$ZERO_OID ref:refs/heads/main refs/heads/symref
+	committed
+	$ZERO_OID ref:refs/heads/main refs/heads/symref
+	EOF
+
+	test_cmp expect actual
+'
+
 test_done
diff --git a/walker.c b/walker.c
index c0fd632d92..1b3df43906 100644
--- a/walker.c
+++ b/walker.c
@@ -324,7 +324,7 @@ int walker_fetch(struct walker *walker, int targets, char **target,
 		strbuf_reset(&refname);
 		strbuf_addf(&refname, "refs/%s", write_ref[i]);
 		if (ref_transaction_update(transaction, refname.buf,
-					   oids + i, NULL, 0,
+					   oids + i, NULL, NULL, NULL, 0,
 					   msg ? msg : "fetch (unknown)",
 					   &err)) {
 			error("%s", err.buf);