[MISC] Allow recursive subcommands

Author: eseiler

include/sharg/parser.hpp

@@ -186,21 +186,13 @@ class parser
            char const * const * const argv,
            update_notifications version_updates = update_notifications::on,
            std::vector<std::string> subcommands = {}) :
-        version_check_dev_decision{version_updates},
-        subcommands{std::move(subcommands)}
+        argc{argc},
+        argv{argv},
+        version_check_dev_decision{version_updates}
     {
-        for (auto & sub : this->subcommands)
-        {
-            if (!std::regex_match(sub, app_name_regex))
-            {
-                throw design_error{"The subcommand name must only contain alpha-numeric characters or '_' and '-' "
-                                   "(regex: \"^[a-zA-Z0-9_-]+$\")."};
-            }
-        }
-
         info.app_name = app_name;
 
-        init(argc, argv);
+        add_subcommands(std::move(subcommands));
     }
 
     //!\brief The destructor.
@@ -666,13 +658,88 @@ class parser
      */
     parser_meta_data info;
 
+    void add_subcommands(std::vector<std::string> const & subcommands)
+    {
+        for (auto const & sub : subcommands)
+        {
+            if (!std::regex_match(sub, app_name_regex))
+            {
+                std::string const error_message =
+                    detail::to_string(std::quoted(info.app_name),
+                                      " contains an invalid subcommand name: ",
+                                      std::quoted(sub),
+                                      ". The subcommand name must only contain alpha-numeric characters ",
+                                      "or '_' and '-' (regex: \"^[a-zA-Z0-9_-]+$\").");
+                throw design_error{error_message};
+            };
+        }
+
+        auto & parser_subcommands = this->subcommands;
+
+#if 0
+        auto sorted = subcommands;
+        std::ranges::sort(sorted);
+        std::vector<std::string> difference{};
+        std::ranges::set_intersection(sorted, std::ranges::unique(sorted), std::back_inserter(difference));
+        if (!difference.empty())
+        {
+            auto view = std::views::transform(difference,
+                                              [](auto const & val)
+                                              {
+                                                  return std::quoted(val);
+                                              });
+            std::string const error_message =
+                detail::to_string("add_subcommands()'s arguments list contains duplicate elements for ",
+                                  std::quoted(info.app_name),
+                                  " : ",
+                                  view,
+                                  ".");
+            throw design_error{error_message};
+        }
+
+        auto duplicate_subcommands = std::ranges::search(parser_subcommands, subcommands);
+        if (duplicate_subcommands)
+        {
+            auto view = std::views::transform(duplicate_subcommands,
+                                              [](auto const & val)
+                                              {
+                                                  return std::quoted(val);
+                                              });
+            std::string const error_message =
+                detail::to_string(std::quoted(info.app_name), " already contains subcommands: ", view, ".");
+            throw design_error{error_message};
+        }
+#endif
+
+#ifdef __cpp_lib_containers_ranges
+        parser_subcommands.append_range(subcommands);
+#else
+        parser_subcommands.insert(parser_subcommands.end(), subcommands.cbegin(), subcommands.cend());
+#endif
+
+        std::ranges::sort(parser_subcommands);
+        auto const [first, last] = std::ranges::unique(parser_subcommands);
+        parser_subcommands.erase(first, last);
+
+        init();
+    }
+
 private:
     //!\brief Keeps track of whether the parse function has been called already.
     bool parse_was_called{false};
 
+    //!\brief Keeps track of whether the init function has been called already.
+    bool init_was_called{false};
+
     //!\brief Keeps track of whether the user has added a positional list option to check if this was the very last.
     bool has_positional_list_option{false};
 
+    //!\brief The number of command line arguments.
+    int argc{};
+
+    //!\brief The command line arguments.
+    char const * const * argv{nullptr};
+
     //!\brief Set on construction and indicates whether the developer deactivates the version check calls completely.
     update_notifications version_check_dev_decision{};
 
@@ -755,10 +822,19 @@ class parser
      *
      * If `--export-help` is specified with a value other than html, man, cwl or ctd, an sharg::parser_error is thrown.
      */
-    void init(int argc, char const * const * const argv)
+    void init()
     {
         assert(argc > 0);
-        executable_name.emplace_back(argv[0]);
+
+        if (init_was_called)
+        {
+            cmd_arguments.clear();
+        }
+        else
+        {
+            executable_name.emplace_back(argv[0]);
+            init_was_called = true;
+        }
 
         bool special_format_was_set{false};