Add a Argument::hidden() method to prevent an argument from appearing in usage or help

README.md

@@ -39,7 +39,7 @@
      *    [Parent Parsers](#parent-parsers)
      *    [Subcommands](#subcommands)
      *    [Parse Known Args](#parse-known-args)
-     *    [Hidden alias](#hidden-alias)
+     *    [Hidden argument and alias](#hidden-argument-alias)
      *    [ArgumentParser in bool Context](#argumentparser-in-bool-context)
      *    [Custom Prefix Characters](#custom-prefix-characters)
      *    [Custom Assignment Characters](#custom-assignment-characters)
@@ -1003,7 +1003,7 @@ int main(int argc, char *argv[]) {
 }
 ```
 
-### Hidden alias
+### Hidden argument and alias
 
 It is sometimes desirable to offer an alias for an argument, but without it
 appearing it in the usage. For example, to phase out a deprecated wording of
@@ -1017,6 +1017,18 @@ auto &arg = program.add_argument("--suppress").flag();
 program.add_hidden_alias_for(arg, "--supress"); // old misspelled alias
 ```
 
+The ``Argument::hidden()`` method can also be used to prevent a (generally
+optional) argument from appearing in the usage or help.
+
+```cpp
+argparse::ArgumentParser program("test");
+
+program.add_argument("--non-documented").flag().hidden();
+```
+
+This can also be used on positional arguments, but in that later case it only
+makes sense in practice for the last ones.
+
 ### ArgumentParser in bool Context
 
 An `ArgumentParser` is `false` until it (or one of its subparsers) have extracted

include/argparse/argparse.hpp

@@ -606,7 +606,7 @@ class Argument {
       : m_accepts_optional_like_value(false),
         m_is_optional((is_optional(a[I], prefix_chars) || ...)),
         m_is_required(false), m_is_repeatable(false), m_is_used(false),
-        m_prefix_chars(prefix_chars) {
+        m_is_hidden(false), m_prefix_chars(prefix_chars) {
     ((void)m_names.emplace_back(a[I]), ...);
     std::sort(
         m_names.begin(), m_names.end(), [](const auto &lhs, const auto &rhs) {
@@ -745,6 +745,12 @@ public:
     return *this;
   }
 
+  // Cause the argument to be invisible in usage and help
+  auto &hidden() {
+    m_is_hidden = true;
+    return *this;
+  }
+
   template <char Shape, typename T>
   auto scan() -> std::enable_if_t<std::is_arithmetic_v<T>, Argument &> {
     static_assert(!(std::is_const_v<T> || std::is_volatile_v<T>),
@@ -1531,6 +1537,7 @@ private:
   bool m_is_required : 1;
   bool m_is_repeatable : 1;
   bool m_is_used : 1;
+  bool m_is_hidden : 1;            // if set, does not appear in usage or help
   std::string_view m_prefix_chars; // ArgumentParser has the prefix_chars
   int m_usage_newline_counter = 0;
   std::size_t m_group_idx = 0;
@@ -1910,22 +1917,30 @@ public:
       stream << parser.m_description << "\n\n";
     }
 
-    if (!parser.m_positional_arguments.empty()) {
+    const bool has_visible_positional_args = std::find_if(
+      parser.m_positional_arguments.begin(),
+      parser.m_positional_arguments.end(),
+      [](const auto &argument) {
+      return !argument.m_is_hidden; }) !=
+      parser.m_positional_arguments.end();
+    if (has_visible_positional_args) {
       stream << "Positional arguments:\n";
     }
 
     for (const auto &argument : parser.m_positional_arguments) {
-      stream.width(static_cast<std::streamsize>(longest_arg_length));
+      if (!argument.m_is_hidden) {
-      stream << argument;
+        stream.width(static_cast<std::streamsize>(longest_arg_length));
+        stream << argument;
+      }
     }
 
     if (!parser.m_optional_arguments.empty()) {
-      stream << (parser.m_positional_arguments.empty() ? "" : "\n")
+      stream << (!has_visible_positional_args ? "" : "\n")
              << "Optional arguments:\n";
     }
 
     for (const auto &argument : parser.m_optional_arguments) {
-      if (argument.m_group_idx == 0) {
+      if (argument.m_group_idx == 0 && !argument.m_is_hidden) {
         stream.width(static_cast<std::streamsize>(longest_arg_length));
         stream << argument;
       }
@@ -1934,7 +1949,7 @@ public:
     for (size_t i_group = 0; i_group < parser.m_group_names.size(); ++i_group) {
       stream << "\n" << parser.m_group_names[i_group] << " (detailed usage):\n";
       for (const auto &argument : parser.m_optional_arguments) {
-        if (argument.m_group_idx == i_group + 1) {
+        if (argument.m_group_idx == i_group + 1 && !argument.m_is_hidden) {
           stream.width(static_cast<std::streamsize>(longest_arg_length));
           stream << argument;
         }
@@ -2006,6 +2021,9 @@ public:
       const MutuallyExclusiveGroup *cur_mutex = nullptr;
       int usage_newline_counter = -1;
       for (const auto &argument : this->m_optional_arguments) {
+        if (argument.m_is_hidden) {
+          continue;
+        }
         if (multiline_usage) {
           if (argument.m_group_idx != group_idx) {
             continue;
@@ -2078,6 +2096,9 @@ public:
     }
     // Put positional arguments after the optionals
     for (const auto &argument : this->m_positional_arguments) {
+      if (argument.m_is_hidden) {
+        continue;
+      }
       const std::string pos_arg = !argument.m_metavar.empty()
                                       ? argument.m_metavar
                                       : argument.m_names.front();

test/CMakeLists.txt

@@ -37,6 +37,8 @@ file(GLOB ARGPARSE_TEST_SOURCES
     test_error_reporting.cpp
     test_get.cpp
     test_help.cpp
+    test_hidden_alias.cpp
+    test_hidden_argument.cpp
     test_invalid_arguments.cpp
     test_is_used.cpp
     test_issue_37.cpp
@@ -56,7 +58,6 @@ file(GLOB ARGPARSE_TEST_SOURCES
     test_parse_known_args.cpp
     test_equals_form.cpp
     test_prefix_chars.cpp
-    test_hidden_alias.cpp
 )
 set_source_files_properties(main.cpp
     PROPERTIES

test/test_hidden_argument.cpp

@@ -0,0 +1,36 @@
+#ifdef WITH_MODULE
+import argparse;
+#else
+#include <argparse/argparse.hpp>
+#endif
+#include <doctest.hpp>
+
+using doctest::test_suite;
+
+TEST_CASE("Test setting a hidden argument" * test_suite("hidden_argument")) {
+  argparse::ArgumentParser program("program");
+  program.add_argument("--hidden").flag().hidden();
+  program.add_argument("--regular").flag();
+  program.add_argument("regular_positional");
+  // only makes sense if last and optional...
+  program.add_argument("hidden_positional").nargs(0, 1).hidden();
+
+  program.parse_args({"./test.exe", "--hidden", "--regular",
+                      "regular_positional_val", "hidden_positional_val"});
+  REQUIRE(program.get<bool>("--hidden") == true);
+  REQUIRE(program.get<bool>("--regular") == true);
+  REQUIRE(program.get<std::string>("regular_positional") ==
+          "regular_positional_val");
+  REQUIRE(program.get<std::string>("hidden_positional") ==
+          "hidden_positional_val");
+
+  REQUIRE(program.usage() ==
+          "Usage: program [--help] [--version] [--regular] regular_positional");
+
+  std::ostringstream s;
+  s << program;
+  // std::cout << "DEBUG:" << s.str() << std::endl;
+  REQUIRE(s.str().find("hidden") == std::string::npos);
+  REQUIRE(s.str().find("--regular") != std::string::npos);
+  REQUIRE(s.str().find("regular_positional") != std::string::npos);
+}