Added default diagram generation error for empty diagrams (#246)

src/common/generators/generators.cc

@@ -95,11 +95,17 @@ void generate_diagram_select_generator(const std::string &od,
     using diagram_generator =
         typename diagram_generator_t<DiagramConfig, GeneratorTag>::type;
 
+    std::stringstream buffer;
+    buffer << diagram_generator(
+        dynamic_cast<DiagramConfig &>(*diagram), *model);
+
+    // Only open the file after the diagram has been generated successfully
+    // in order not to overwrite previous diagram in case of failure
     auto path = std::filesystem::path{od} /
         fmt::format("{}.{}", name, GeneratorTag::extension);
     std::ofstream ofs;
     ofs.open(path, std::ofstream::out | std::ofstream::trunc);
-    ofs << diagram_generator(dynamic_cast<DiagramConfig &>(*diagram), *model);
+    ofs << buffer.str();
 
     ofs.close();
 
@@ -258,11 +264,12 @@ void generate_diagrams(const std::vector<std::string> &diagram_names,
                 if (indicator)
                     indicator->complete(name);
             }
-            catch (std::exception &e) {
+            catch (const std::exception &e) {
                 if (indicator)
                     indicator->fail(name);
 
-                LOG_ERROR(e.what());
+                LOG_ERROR(
+                    "ERROR: Failed to generate diagram {}: {}", name, e.what());
             }
         };
 

src/common/generators/json/generator.h

@@ -107,11 +107,19 @@ std::ostream &operator<<(
 template <typename C, typename D>
 void generator<C, D>::generate(std::ostream &ostr) const
 {
+    const auto &config = generators::generator<C, D>::config();
+    const auto &model = generators::generator<C, D>::model();
+
+    if (!config.allow_empty_diagrams() && model.is_empty()) {
+        throw clanguml::error::empty_diagram_error{
+            "Diagram configuration resulted in empty diagram."};
+    }
+
     nlohmann::json j;
-    j["name"] = generators::generator<C, D>::model().name();
-    j["diagram_type"] = to_string(generators::generator<C, D>::model().type());
-    if (generators::generator<C, D>::config().title) {
-        j["title"] = generators::generator<C, D>::config().title();
+    j["name"] = model.name();
+    j["diagram_type"] = to_string(model.type());
+    if (config.title) {
+        j["title"] = config.title();
     }
 
     generate_diagram(j);

src/common/generators/mermaid/generator.h

@@ -250,6 +250,13 @@ template <typename C, typename D>
 void generator<C, D>::generate(std::ostream &ostr) const
 {
     const auto &config = generators::generator<C, D>::config();
+    const auto &model = generators::generator<C, D>::model();
+
+    if (!config.allow_empty_diagrams() && model.is_empty() &&
+        config.mermaid().before.empty() && config.mermaid().after.empty()) {
+        throw clanguml::error::empty_diagram_error{
+            "Diagram configuration resulted in empty diagram."};
+    }
 
     update_context();
 

src/common/generators/plantuml/generator.h

@@ -21,6 +21,7 @@
 #include "common/model/diagram_filter.h"
 #include "common/model/relationship.h"
 #include "config/config.h"
+#include "error.h"
 #include "util/error.h"
 #include "util/util.h"
 #include "version.h"
@@ -265,9 +266,16 @@ template <typename C, typename D>
 void generator<C, D>::generate(std::ostream &ostr) const
 {
     const auto &config = generators::generator<C, D>::config();
+    const auto &model = generators::generator<C, D>::model();
 
     update_context();
 
+    if (!config.allow_empty_diagrams() && model.is_empty() &&
+        config.puml().before.empty() && config.puml().after.empty()) {
+        throw clanguml::error::empty_diagram_error{
+            "Diagram configuration resulted in empty diagram."};
+    }
+
     ostr << "@startuml" << '\n';
 
     generate_title(ostr);

src/common/model/diagram.h

@@ -164,6 +164,13 @@ public:
      */
     virtual inja::json context() const = 0;
 
+    /**
+     * @brief Check whether the diagram is empty
+     *
+     * @return True, if diagram is empty
+     */
+    virtual bool is_empty() const = 0;
+
 private:
     std::string name_;
     std::unique_ptr<diagram_filter> filter_;

src/common/model/element_view.h

@@ -69,6 +69,13 @@ public:
         return {};
     }
 
+    /**
+     * @brief Check whether the element view is empty
+     *
+     * @return True, if the view does not contain any elements
+     */
+    bool is_empty() const { return elements_.empty(); }
+
 private:
     reference_vector<T> elements_;
 };