Allow removal of default arguments (i.e. --help and --version)

The help and version arguments are still included by default, but which
default arguments to include can be overridden at ArgumentParser creation.

argparse generally copies Python argparse behavior.  This includes a
default `--help`/`-h` argument to print a help message and exit.  Some
developers using argparse find the automatic exit to be undesirable.

The Python argparse has an opt-out parameter when constructing an
ArgumentParser.  Using `add_help=False` avoids adding a default `--help`
argument and allows the developer to implement a custom help.

This commit adds a similar opt-out to our C++ argparse, but keeps the
current behavior as the default.  The `--help`/`-h` and `--version`/`-v`
Arguments handle their own output and exit rather than specially treating
them in ArgumentParser::parse_args_internal.

Closes #119
Closes #138
Closes #139

Signed-off-by: Sean Robinson <sean.robinson@scottsdalecc.edu>

README.md

@@ -455,6 +455,27 @@ The grammar follows `std::from_chars`, but does not exactly duplicate it. For ex
 | 'u'        | decimal (unsigned)                        |
 | 'x' or 'X' | hexadecimal (unsigned)                    |
 
+### Default Arguments
+
+`argparse` provides predefined arguments and actions for `-h`/`--help` and `-v`/`--version`. These default actions exit the program after displaying a help or version message, respectively. These defaults arguments can be disabled during `ArgumentParser` creation so that you can handle these arguments in your own way. (Note that a program name and version must be included when choosing default arguments.)
+
+```cpp
+argparse::ArgumentParser program("test", "1.0", default_arguments::none);
+
+program.add_argument("-h", "--help")
+  .action([=](const std::string& s) {
+    std::cout << help().str();
+  })
+  .default_value(false)
+  .help("shows help message")
+  .implicit_value(true)
+  .nargs(0);
+```
+
+The above code snippet outputs a help message and continues to run. It does not support a `--version` argument.
+
+The default is `default_arguments::all` for included arguments. No default arguments will be added with `default_arguments::none`. `default_arguments::help` and `default_arguments::version` will individually add `--help` and `--version`.
+
 ### Gathering Remaining Arguments
 
 `argparse` supports gathering "remaining" arguments at the end of the command, e.g., for use in a compiler:

include/argparse/argparse.hpp

@@ -312,6 +312,17 @@ template <class T> struct parse_number<T, chars_format::fixed> {
 
 } // namespace details
 
+enum class default_arguments : unsigned int {
+  none = 0,
+  help = 1,
+  version = 2,
+  all = help | version,
+};
+
+inline bool operator& (const default_arguments &a, const default_arguments &b) {
+  return static_cast<unsigned int>(a) & static_cast<unsigned int>(b);
+}
+
 class ArgumentParser;
 
 class Argument {
@@ -814,17 +825,32 @@ private:
 class ArgumentParser {
 public:
   explicit ArgumentParser(std::string aProgramName = {},
-                          std::string aVersion = "1.0")
+                          std::string aVersion = "1.0",
+                          default_arguments aArgs = default_arguments::all)
       : mProgramName(std::move(aProgramName)), mVersion(std::move(aVersion)) {
-    add_argument("-h", "--help").help("shows help message and exits").nargs(0);
-#ifndef ARGPARSE_LONG_VERSION_ARG_ONLY
-    add_argument("-v", "--version")
-#else
-	add_argument("--version")
-#endif
-        .help("prints version information and exits")
+    if (aArgs & default_arguments::help) {
+      add_argument("-h", "--help")
+        .action([&](const auto &) {
+          std::cout << help().str();
+          std::exit(0);
+        })
+        .default_value(false)
+        .help("shows help message and exits")
+        .implicit_value(true)
         .nargs(0);
     }
+    if (aArgs & default_arguments::version) {
+      add_argument("-v", "--version")
+        .action([&](const auto &) {
+          std::cout << mVersion;
+          std::exit(0);
+        })
+        .default_value(false)
+        .help("prints version information and exits")
+        .implicit_value(true)
+        .nargs(0);
+    }
+  }
 
   ArgumentParser(ArgumentParser &&) noexcept = default;
   ArgumentParser &operator=(ArgumentParser &&) = default;
@@ -1051,18 +1077,6 @@ private:
       auto tIterator = mArgumentMap.find(tCurrentArgument);
       if (tIterator != mArgumentMap.end()) {
         auto tArgument = tIterator->second;
-
-        // the first optional argument is --help
-        if (tArgument == mOptionalArguments.begin()) {
-          std::cout << *this;
-          std::exit(0);
-        }
-        // the second optional argument is --version
-        else if (tArgument == std::next(mOptionalArguments.begin(), 1)) {
-          std::cout << mVersion << "\n";
-          std::exit(0);
-        }
-
         it = tArgument->consume(std::next(it), end, tIterator->first);
       } else if (const auto &tCompoundArgument = tCurrentArgument;
                  tCompoundArgument.size() > 1 && tCompoundArgument[0] == '-' &&

test/CMakeLists.txt

@@ -30,6 +30,7 @@ file(GLOB ARGPARSE_TEST_SOURCES
     test_compound_arguments.cpp
     test_container_arguments.cpp
     test_const_correct.cpp
+    test_default_args.cpp
     test_get.cpp
     test_help.cpp
     test_invalid_arguments.cpp

test/test_default_args.cpp

@@ -0,0 +1,19 @@
+#include <argparse/argparse.hpp>
+#include <doctest.hpp>
+
+using doctest::test_suite;
+
+TEST_CASE("Include all default arguments" * test_suite("default_args")) {
+  argparse::ArgumentParser parser("test");
+  auto help_msg { parser.help().str() };
+  REQUIRE(help_msg.find("shows help message") != std::string::npos);
+  REQUIRE(help_msg.find("prints version information") != std::string::npos);
+}
+
+TEST_CASE("Do not include default arguments" * test_suite("default_args")) {
+  argparse::ArgumentParser parser("test", "1.0",
+                                  argparse::default_arguments::none);
+  parser.parse_args({"test"});
+  REQUIRE_THROWS_AS(parser.get("--help"), std::logic_error);
+  REQUIRE_THROWS_AS(parser.get("--version"), std::logic_error);
+}

test/test_help.cpp

@@ -1,5 +1,6 @@
 #include <argparse/argparse.hpp>
 #include <doctest.hpp>
+#include <sstream>
 
 using doctest::test_suite;
 
@@ -51,3 +52,26 @@ TEST_CASE("Users can override the help options" * test_suite("help")) {
     }
   }
 }
+
+TEST_CASE("Users can disable default -h/--help" * test_suite("help")) {
+  argparse::ArgumentParser program("test", "1.0",
+                                   argparse::default_arguments::version);
+  REQUIRE_THROWS_AS(program.parse_args({"test", "-h"}), std::runtime_error);
+}
+
+TEST_CASE("Users can replace default -h/--help" * test_suite("help")) {
+  argparse::ArgumentParser program("test", "1.0",
+                                   argparse::default_arguments::version);
+  std::stringstream buffer;
+  program.add_argument("-h", "--help")
+    .action([&](const auto &) {
+      buffer << program;
+    })
+    .default_value(false)
+    .implicit_value(true)
+    .nargs(0);
+
+  REQUIRE(buffer.str().empty());
+  program.parse_args({"test", "--help"});
+  REQUIRE_FALSE(buffer.str().empty());
+}

test/test_version.cpp

@@ -1,5 +1,6 @@
 #include <doctest.hpp>
 #include <argparse/argparse.hpp>
+#include <sstream>
 
 using doctest::test_suite;
 
@@ -11,3 +12,28 @@ TEST_CASE("Users can print version and exit" * test_suite("version")
   program.parse_args( { "test", "--version" });
   REQUIRE(program.get("--version") == "1.9.0");
 }
+
+TEST_CASE("Users can disable default -v/--version" * test_suite("version")) {
+  argparse::ArgumentParser program("test", "1.0",
+                                   argparse::default_arguments::help);
+  REQUIRE_THROWS_AS(program.parse_args({"test", "--version"}),
+                    std::runtime_error);
+}
+
+TEST_CASE("Users can replace default -v/--version" * test_suite("version")) {
+  std::string version { "3.1415" };
+  argparse::ArgumentParser program("test", version,
+                                   argparse::default_arguments::help);
+  std::stringstream buffer;
+  program.add_argument("-v", "--version")
+    .action([&](const auto &) {
+      buffer << version;
+    })
+    .default_value(true)
+    .implicit_value(false)
+    .nargs(0);
+
+  REQUIRE(buffer.str().empty());
+  program.parse_args({"test", "--version"});
+  REQUIRE_FALSE(buffer.str().empty());
+}