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

src/cli/cli_handler.cc

@@ -107,6 +107,8 @@ cli_flow_t cli_handler::parse(int argc, const char **argv)
         "Query the specific compiler driver to extract system paths and add to "
         "compile commands (e.g. arm-none-eabi-g++)");
 #endif
+    app.add_flag("--allow-empty-diagrams", allow_empty_diagrams,
+        "Do not raise an error when generated diagram model is empty");
     app.add_option(
         "--add-class-diagram", add_class_diagram, "Add class diagram config");
     app.add_option("--add-sequence-diagram", add_sequence_diagram,
@@ -302,6 +304,10 @@ cli_flow_t cli_handler::handle_post_config_options()
 
     LOG_INFO("Loaded clang-uml config from {}", config_path);
 
+    if (allow_empty_diagrams) {
+        config.allow_empty_diagrams.set(true);
+    }
+
     //
     // Override selected config options from command line
     //

src/cli/cli_handler.h

@@ -165,6 +165,7 @@ public:
     bool list_diagrams{false};
     bool quiet{false};
     bool initialize{false};
+    bool allow_empty_diagrams{false};
     std::optional<std::vector<std::string>> add_compile_flag;
     std::optional<std::vector<std::string>> remove_compile_flag;
 #if !defined(_WIN32)