refs: use transaction in refs_create_symref()

The `refs_create_symref()` function updates a symref to a given new
target. To do this, it uses a ref-backend specific function
`create_symref()`.

In the previous commits, we introduced symref support in transactions.
This means we can now use transactions to perform symref updates and
don't have to resort to `create_symref()`. Doing this allows us to
remove and cleanup `create_symref()`, which we will do in the following
commit.

Modify the expected error message for a test in
't/t0610-reftable-basics.sh', since the error is now thrown from
'refs.c'. This is because in transactional updates, F/D conflicts are
caught before we're in the reference backend.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -2289,14 +2289,24 @@ int refs_create_symref(struct ref_store *refs,
 		       const char *refs_heads_master,
 		       const char *logmsg)
 {
-	char *msg;
+	struct ref_transaction *transaction;
-	int retval;
+	struct strbuf err = STRBUF_INIT;
+	int ret = 0;
 
-	msg = normalize_reflog_message(logmsg);
+	transaction = ref_store_transaction_begin(refs, &err);
-	retval = refs->be->create_symref(refs, ref_target, refs_heads_master,
+	if (!transaction ||
-					 msg);
+	    ref_transaction_update(transaction, ref_target, NULL, NULL,
-	free(msg);
+				   refs_heads_master, NULL, REF_NO_DEREF,
-	return retval;
+				   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,

t/t0610-reftable-basics.sh

@@ -255,7 +255,7 @@ test_expect_success 'ref transaction: creating symbolic ref fails with F/D confl
 	git init repo &&
 	test_commit -C repo A &&
 	cat >expect <<-EOF &&
-	error: unable to write symref for refs/heads: file/directory conflict
+	error: ${SQ}refs/heads/main${SQ} exists; cannot create ${SQ}refs/heads${SQ}
 	EOF
 	test_must_fail git -C repo symbolic-ref refs/heads refs/heads/foo 2>err &&
 	test_cmp expect err

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