Skip generation of empty or invalid relationships in PlantUML output

src/util/error.h

@@ -0,0 +1,29 @@
+/**
+ * src/util/error.h
+ *
+ * Copyright (c) 2021 Bartek Kryza <bkryza@gmail.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <stdexcept>
+
+namespace clanguml::error {
+struct uml_alias_missing : public virtual std::runtime_error {
+    uml_alias_missing(const std::string &message)
+        : std::runtime_error(message)
+    {
+    }
+};
+}

src/util/util.h

@@ -34,6 +34,10 @@ std::string trim(const std::string &s);
 #define __FILENAME__                                                           \
     (strrchr(__FILE__, '/') ? strrchr(__FILE__, '/') + 1 : __FILE__)
 
+#define LOG_ERROR(fmt__, ...)                                                   \
+    spdlog::error(std::string("[{}:{}] ") + fmt__, __FILENAME__, __LINE__,      \
+        ##__VA_ARGS__)
+
 #define LOG_WARN(fmt__, ...)                                                   \
     spdlog::warn(std::string("[{}:{}] ") + fmt__, __FILENAME__, __LINE__,      \
         ##__VA_ARGS__)