Custom help option always requires an argument

[wfxr]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

rustc 1.66.0-nightly (a6b7274a4 2022-10-10)

Clap Version

4.0.12

Minimal reproducible code

use clap::{ArgAction, Parser};

#[derive(Parser)]
#[command(about, version)]
#[command(disable_help_flag = true)]
pub struct App {
    #[arg(short = 'h', long, default_value = "localhost")]
    pub host: String,

    #[arg(long, action = ArgAction::Help)]
    pub help: bool,
}

fn main() {
    App::parse();
}

Steps to reproduce the bug with the above code

cargo run

Actual Behaviour

The following message was printed:

error: The following required argument was not provided: help

Usage: clap-demo [OPTIONS]

Expected Behaviour

No error printed.

Additional Context

No response

Debug Output

[      clap::builder::command]  Command::_do_parse
[      clap::builder::command]  Command::_build: name="clap-demo"
[      clap::builder::command]  Command::_propagate:clap-demo
[      clap::builder::command]  Command::_check_help_and_version:clap-demo expand_help_tree=false
[      clap::builder::command]  Command::long_help_exists
[      clap::builder::command]  Command::_check_help_and_version: Building default --version
[      clap::builder::command]  Command::_propagate_global_args:clap-demo
[clap::builder::debug_asserts]  Command::_debug_asserts
[clap::builder::debug_asserts]  Arg::_debug_asserts:host
[clap::builder::debug_asserts]  Arg::_debug_asserts:help
[clap::builder::debug_asserts]  Arg::_debug_asserts:version
[clap::builder::debug_asserts]  Command::_verify_positionals
[        clap::parser::parser]  Parser::get_matches_with
[        clap::parser::parser]  Parser::add_defaults
[        clap::parser::parser]  Parser::add_defaults:iter:host:
[        clap::parser::parser]  Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser]  Parser::add_default_value:iter:host: has default vals
[        clap::parser::parser]  Parser::add_default_value:iter:host: wasn't used
[        clap::parser::parser]  Parser::react action=Set, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher]  ArgMatcher::start_custom_arg: id="host", source=DefaultValue
[      clap::builder::command]  Command::groups_for_arg: id="host"
[   clap::parser::arg_matcher]  ArgMatcher::start_custom_arg: id="App", source=DefaultValue
[        clap::parser::parser]  Parser::push_arg_values: ["localhost"]
[        clap::parser::parser]  Parser::add_single_val_to_arg: cur_idx:=1
[      clap::builder::command]  Command::groups_for_arg: id="host"
[   clap::parser::arg_matcher]  ArgMatcher::needs_more_vals: o=host, pending=0
[   clap::parser::arg_matcher]  ArgMatcher::needs_more_vals: expected=1, actual=0
[        clap::parser::parser]  Parser::react not enough values passed in, leaving it to the validator to complain
[        clap::parser::parser]  Parser::add_defaults:iter:help:
[        clap::parser::parser]  Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser]  Parser::add_default_value:iter:help: doesn't have default vals
[        clap::parser::parser]  Parser::add_defaults:iter:version:
[        clap::parser::parser]  Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser]  Parser::add_default_value:iter:version: doesn't have default vals
[     clap::parser::validator]  Validator::validate
[     clap::parser::validator]  Validator::validate_conflicts
[     clap::parser::validator]  Validator::validate_exclusive
[     clap::parser::validator]  Validator::validate_required: required=ChildGraph([])
[     clap::parser::validator]  Validator::gather_requires
[     clap::parser::validator]  Validator::validate_required: is_exclusive_present=false
[   clap::parser::arg_matcher]  ArgMatcher::get_global_values: global_arg_vec=[]
[      clap::builder::command]  Command::_build: name="clap-demo"
[      clap::builder::command]  Command::_propagate:clap-demo
[      clap::builder::command]  Command::_check_help_and_version:clap-demo expand_help_tree=false
[      clap::builder::command]  Command::long_help_exists
[      clap::builder::command]  Command::_check_help_and_version: Building default --version
[      clap::builder::command]  Command::_propagate_global_args:clap-demo
[clap::builder::debug_asserts]  Command::_debug_asserts
[clap::builder::debug_asserts]  Arg::_debug_asserts:host
[clap::builder::debug_asserts]  Arg::_debug_asserts:help
[clap::builder::debug_asserts]  Arg::_debug_asserts:version
[clap::builder::debug_asserts]  Command::_verify_positionals
[      clap::builder::command]  Command::_build: name="clap-demo"
[      clap::builder::command]  Command::_build: already built
[         clap::output::usage]  Usage::create_usage_with_title
[         clap::output::usage]  Usage::create_usage_no_title
[         clap::output::usage]  Usage::create_help_usage; incl_reqs=true
[         clap::output::usage]  Usage::needs_options_tag
[         clap::output::usage]  Usage::needs_options_tag:iter: f=host
[      clap::builder::command]  Command::groups_for_arg: id="host"
[         clap::output::usage]  Usage::needs_options_tag:iter:iter: grp_s="App"
[         clap::output::usage]  Usage::needs_options_tag:iter: [OPTIONS] required
[         clap::output::usage]  Usage::get_args: incls=[]
[         clap::output::usage]  Usage::get_args: unrolled_reqs=[]
[         clap::output::usage]  Usage::get_args: ret_val=[]
[         clap::output::usage]  Usage::create_help_usage: usage=clap-demo [OPTIONS]
[      clap::builder::command]  Command::color: Color setting...
[      clap::builder::command]  Auto
[      clap::builder::command]  Command::color: Color setting...
[      clap::builder::command]  Auto
error: The following required argument was not provided: help

Usage: clap-demo [OPTIONS]

[epage]

A workaround:

#!/usr/bin/env -S rust-script

//! ```cargo
//! [dependencies]
//! clap = { version = "=4.0.12", features = ["derive"] }
//! ```

use clap::{ArgAction, Parser};

#[derive(Parser)]
#[command(about, version)]
#[command(disable_help_flag = true)]
pub struct App {
    #[arg(short = 'h', long, default_value = "localhost")]
    pub host: String,

    #[arg(long, action = ArgAction::Help, default_value = "false")]
    pub help: bool,
}

fn main() {
    App::parse();
}

[epage]

We probably should set the default value_parser, value, and missing value for this like other flags but I suspect that would be a breaking change.

I have also been considering adding support for () as a type to mean" don't bother reading it" which would be more appropriate.

[epage]

Except that workaround doesn't work because we take any value to mean to show help./

Bleh. The joy of not realizing a test doesn't cover all cases

[epage]

#4371 will allow

#[test]
fn custom_help_flag() {
    #[derive(Debug, Clone, Parser)]
    #[command(disable_help_flag = true)]
    struct CliOptions {
        #[arg(short = 'h', long = "verbose-help", action = ArgAction::Help, value_parser = clap::value_parser!(bool))]
        help: (),
    }

    let result = CliOptions::try_parse_from(["cmd", "--verbose-help"]);
    let err = result.unwrap_err();
    assert_eq!(err.kind(), clap::error::ErrorKind::DisplayHelp);

    CliOptions::try_parse_from(["cmd"]).unwrap();
}

[wfxr]

@epage Great! #4371 solves the problem perfectly. Thanks you!

[epage]

Going to re-open as I feel like we should add a default value parser and value for Help and Version actions so they can be used with less ceremony