Allow to customize help flag.

README.md

@@ -161,7 +161,7 @@ The add commands return a pointer to an internally stored `Option`. If you set t
 * `->check(CLI::NonexistentPath)`: Requires that the path does not exist.
 * `->check(CLI::Range(min,max))`: Requires that the option be between min and max (make sure to use floating point if needed). Min defaults to 0.
 
-These options return the `Option` pointer, so you can chain them together, and even skip storing the pointer entirely. Check takes any function that has the signature `bool(std::string)`. If you want to change the default help option, it is available through `get_help_ptr`. If you just want to see the unconverted values, use `.results()` to get the `std::vector<std::string>` of results.
+These options return the `Option` pointer, so you can chain them together, and even skip storing the pointer entirely. Check takes any function that has the signature `bool(std::string)`. If you just want to see the unconverted values, use `.results()` to get the `std::vector<std::string>` of results.
 
 
 On the command line, options can be given as:
@@ -244,7 +244,7 @@ arguments, use `.config_to_str(default_also=false)`, where `default_also` will a
 
 ## Subclassing
 
-The App class was designed allow toolkits to subclass it, to provide default options and setup/teardown code. Subcommands remain an unsubclassed `App`, since those are not expected to need setup and teardown. The default `App` only adds a help flag, `-h,--help`, but provides an option to disable it in the constructor (and in `add_subcommand`). You can remove options if you have pointers to them using `.remove_option(opt)`. You can add a `pre_callback` override to customize the after parse
+The App class was designed allow toolkits to subclass it, to provide default options and setup/teardown code. Subcommands remain an unsubclassed `App`, since those are not expected to need setup and teardown. The default `App` only adds a help flag, `-h,--help`, but provides an option to disable it in the constructor (and in `add_subcommand`), and can removed/replaced using `.set_help_flag(name, help_string)`. You can remove options if you have pointers to them using `.remove_option(opt)`. You can add a `pre_callback` override to customize the after parse
 but before run behavior, while
 still giving the user freedom to `set_callback` on the main app.  
 

include/CLI/App.hpp

@@ -137,7 +137,7 @@ class App {
     App(std::string description_, bool help, detail::enabler) : description_(std::move(description_)) {
 
         if(help)
-            help_ptr_ = add_flag("-h,--help", "Print this help message and exit");
+            set_help_flag("-h,--help", "Print this help message and exit");
     }
 
   public:
@@ -322,6 +322,20 @@ class App {
         return opt;
     }
 
+    /// Set a help flag, replaced the existing one if present
+    Option *set_help_flag(std::string name = "", std::string description = "") {
+        if(help_ptr_ != nullptr) {
+            remove_option(help_ptr_);
+            help_ptr_ = nullptr;
+        }
+
+        // Empty name will simply remove the help flag
+        if(!name.empty())
+            help_ptr_ = add_flag(name, description);
+
+        return help_ptr_;
+    }
+
     /// Add option for flag
     Option *add_flag(std::string name, std::string description = "") {
         CLI::callback_t fun = [](CLI::results_t) { return true; };

tests/HelpTest.cpp

@@ -270,6 +270,76 @@ TEST(THelp, SetLower) {
     EXPECT_THAT(help, HasSubstr("THREE"));
 }
 
+TEST(THelp, OnlyOneHelp) {
+    CLI::App app{"My prog"};
+
+    // It is not supported to have more than one help flag, last one wins
+    app.set_help_flag("--help", "No short name allowed");
+    app.set_help_flag("--yelp", "Alias for help");
+
+    std::vector<std::string> input{"--help"};
+    EXPECT_THROW(app.parse(input), CLI::ExtrasError);
+}
+
+TEST(THelp, RemoveHelp) {
+    CLI::App app{"My prog"};
+    app.set_help_flag();
+
+    std::string help = app.help();
+
+    EXPECT_THAT(help, HasSubstr("My prog"));
+    EXPECT_THAT(help, Not(HasSubstr("-h,--help")));
+    EXPECT_THAT(help, Not(HasSubstr("Options:")));
+    EXPECT_THAT(help, HasSubstr("Usage:"));
+
+    std::vector<std::string> input{"--help"};
+    try {
+        app.parse(input);
+    } catch(const CLI::ParseError &e) {
+        EXPECT_EQ(static_cast<int>(CLI::ExitCodes::Extras), e.get_exit_code());
+    }
+}
+
+TEST(THelp, NoHelp) {
+    CLI::App app{"My prog", false};
+
+    std::string help = app.help();
+
+    EXPECT_THAT(help, HasSubstr("My prog"));
+    EXPECT_THAT(help, Not(HasSubstr("-h,--help")));
+    EXPECT_THAT(help, Not(HasSubstr("Options:")));
+    EXPECT_THAT(help, HasSubstr("Usage:"));
+
+    std::vector<std::string> input{"--help"};
+    try {
+        app.parse(input);
+    } catch(const CLI::ParseError &e) {
+        EXPECT_EQ(static_cast<int>(CLI::ExitCodes::Extras), e.get_exit_code());
+    }
+}
+
+TEST(THelp, CustomHelp) {
+    CLI::App app{"My prog", false};
+
+    CLI::Option *help_option = app.set_help_flag("--yelp", "display help and exit");
+    EXPECT_EQ(app.get_help_ptr(), help_option);
+
+    std::string help = app.help();
+
+    EXPECT_THAT(help, HasSubstr("My prog"));
+    EXPECT_THAT(help, Not(HasSubstr("-h,--help")));
+    EXPECT_THAT(help, HasSubstr("--yelp"));
+    EXPECT_THAT(help, HasSubstr("Options:"));
+    EXPECT_THAT(help, HasSubstr("Usage:"));
+
+    std::vector<std::string> input{"--yelp"};
+    try {
+        app.parse(input);
+    } catch(const CLI::CallForHelp &e) {
+        EXPECT_EQ(static_cast<int>(CLI::ExitCodes::Success), e.get_exit_code());
+    }
+}
+
 TEST(Exit, ErrorWithHelp) {
     CLI::App app{"My prog"};