Use subcommands.

gz-sim-model.patch

diff --git a/src/cmd/model_main.cc b/src/cmd/model_main.cc
index 4d1cabda5..ccc994c5d 100644
--- a/src/cmd/model_main.cc
+++ b/src/cmd/model_main.cc
@@ -27,21 +27,9 @@
 #include "ModelCommandAPI.hh"

 //////////////////////////////////////////////////
-/// \brief Enumeration of available model commands
-enum class ModelCommand
+/// \brief Structure to hold model info options
+struct ModelInfoOptions
 {
-  kNone,
-  kModelList,
-  kModelInfo
-};
-
-//////////////////////////////////////////////////
-/// \brief Structure to hold all available model options
-struct ModelOptions
-{
-  /// \brief Command to execute
-  ModelCommand command{ModelCommand::kNone};
-
   /// \brief Name of the model to show
   std::string modelName{""};

@@ -62,94 +50,82 @@ struct ModelOptions
 };

 //////////////////////////////////////////////////
-/// \brief Callback fired when options are successfully parsed
-void runModelCommand(const ModelOptions &_opt)
+/// \brief Callback fired when executing list subcommand
+void runListCommand()
 {
-  switch(_opt.command)
-  {
-    case ModelCommand::kModelList:
-      cmdModelList();
-      break;
-    case ModelCommand::kModelInfo:
-      {
-        const char *linkName{nullptr};
-        if(_opt.linkName.has_value())
-          linkName = _opt.linkName.value().c_str();
-
-        const char *jointName{nullptr};
-        if(_opt.jointName.has_value())
-          jointName = _opt.jointName.value().c_str();
-
-        const char *sensorName{nullptr};
-        if(_opt.sensorName.has_value())
-          sensorName = _opt.sensorName.value().c_str();
-
-        cmdModelInfo(_opt.modelName.c_str(), _opt.pose, linkName,
-                     jointName, sensorName);
-      }
-      break;
-    case ModelCommand::kNone:
-    default:
-      throw CLI::CallForHelp();
-  }
+  cmdModelList();
 }

 //////////////////////////////////////////////////
-void addModelFlags(CLI::App &_app)
+/// \brief Callback fired when executing model info subcommand
+void runModelCommand(const ModelInfoOptions &_opt)
 {
-  auto opt = std::make_shared<ModelOptions>();
+  const char *linkName{nullptr};
+  if(_opt.linkName.has_value())
+    linkName = _opt.linkName.value().c_str();

-  auto command = _app.add_option_group("command", "Command to be executed.");
+  const char *jointName{nullptr};
+  if(_opt.jointName.has_value())
+    jointName = _opt.jointName.value().c_str();

-  command->add_flag_callback("--list",
-    [opt](){
-      opt->command = ModelCommand::kModelList;
-    },
-    "Get a list of available models.");
+  const char *sensorName{nullptr};
+  if(_opt.sensorName.has_value())
+    sensorName = _opt.sensorName.value().c_str();

-  auto modelCmd = command->add_option_function<std::string>("-m,--model",
-    [opt](const std::string &_modelName){
-      opt->command = ModelCommand::kModelInfo;
-      opt->modelName = _modelName;
-    },
-    "Select the model to be shown.");
+  cmdModelInfo(_opt.modelName.c_str(), _opt.pose, linkName,
+               jointName, sensorName);
+}

-  auto linkCmd = command->add_option_function<std::string>("-l,--link",
-    [opt](const std::string &_linkName){
-      opt->linkName = _linkName;
-    },
+//////////////////////////////////////////////////
+void addModelCommands(CLI::App &_app)
+{
+  // Create subcommand for listing models
+  auto listCmd = _app.add_subcommand("list", "Get a list of available models.");
+  listCmd->callback([]() {
+    runListCommand();
+  });
+
+  // Create subcommand for model info
+  auto modelCmd = _app.add_subcommand("model", "Select a model to be shown.");
+
+  auto modelOpt = std::make_shared<ModelInfoOptions>();
+
+  modelCmd->add_option("name",
+    modelOpt->modelName,
+    "Model name")->required();
+
+  // Add options to the model subcommand
+  modelCmd->add_option("-l,--link",
+    modelOpt->linkName,
     "Select a link to show its properties.\n"
     "If no arg is passed all links are printed.")
-    ->needs(modelCmd)
     ->expected(0, 1)
     ->default_val("");

-  command->add_option_function<std::string>("-s,--sensor",
-    [opt](const std::string &_sensorName){
-      opt->sensorName = _sensorName;
-    },
+  modelCmd->add_option("-s,--sensor",
+      modelOpt->sensorName,
     "Select a sensor to show its properties.\n"
     "If no arg is passed all sensors are printed.")
-    ->needs(modelCmd)
-    ->needs(linkCmd)
     ->expected(0, 1)
     ->default_val("");

-  command->add_option_function<std::string>("-j,--joint",
-    [opt](const std::string &_jointName){
-      opt->jointName = _jointName;
-    },
+  modelCmd->add_option("-j,--joint",
+      modelOpt->jointName,
     "Select a joint to show its properties.\n"
     "If no arg is passed all joints are printed.")
-    ->needs(modelCmd)
     ->expected(0, 1)
     ->default_val("");

-  command->add_flag("-p,--pose", opt->pose,
-                "Print the pose of the model.")
-                ->needs(modelCmd);
+  modelCmd->add_option("-p,--pose",
+    modelOpt->pose,
+    "Print the pose of the model.");
+
+  modelCmd->callback([modelOpt](){
+    runModelCommand(*modelOpt);
+  });

-  _app.callback([opt](){ runModelCommand(*opt); });
+  // Require one subcommand
+  _app.require_subcommand(1, 1);
 }

 //////////////////////////////////////////////////
@@ -167,7 +143,7 @@ int main(int argc, char** argv)
   app.add_flag("--force-version", "Use a specific library version.");
   app.add_flag("--versions", "Show the available versions.");

-  addModelFlags(app);
+  addModelCommands(app);
   app.formatter(std::make_shared<GzFormatter>(&app));
   CLI11_PARSE(app, argc, argv);
 }