making custom help optional with default_value_t panicks

[erazor-de]

Please complete the following tasks

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

Rust Version

rustc 1.64.0 (a55dd71d5 2022-09-19)

Clap Version

4.0.7

Minimal reproducible code

[package]
name = "claptest"
version = "0.1.0"
edition = "2021"

[dependencies]
clap = { version = "4", features = ["derive", "debug"] }

use clap::{ArgAction, Parser};

#[derive(Parser)]
#[command(disable_help_flag = true)]
struct Args {
    #[arg(long, action = ArgAction::Help, default_value_t = false)]
    help: bool,
}

fn main() {
    let _args = Args::parse();
}

Steps to reproduce the bug with the above code

cargo run

Actual Behaviour

thread 'main' panicked at 'assertion failed: (left == right)
left: ["false"],
right: []', /home/stefan/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.7/src/parser/parser.rs:1277:17

Expected Behaviour

No panick, no output.

Additional Context

I try to get rid of the short help '-h' by removing default behaviour and creating own help argument with only long version using default functionality.
With using only #[arg(long, action = ArgAction::Help)] help is required.
Making the argument optional with default_value_t = false leads to panick.
Using help: Option<bool>, works and can be used as workaround.

Debug Output

[ clap::builder::command] Command::_do_parse
[ clap::builder::command] Command::_build: name="claptest"
[ clap::builder::command] Command::_propagate:claptest
[ clap::builder::command] Command::_check_help_and_version:claptest expand_help_tree=false
[ clap::builder::command] Command::long_help_exists
[ clap::builder::command] Command::_propagate_global_args:claptest
[clap::builder::debug_asserts] Command::_debug_asserts
[clap::builder::debug_asserts] Arg::_debug_asserts:help
[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:help:
[ clap::parser::parser] Parser::add_default_value: doesn't have conditional defaults
[ clap::parser::parser] Parser::add_default_value:iter:help: has default vals
[ clap::parser::parser] Parser::add_default_value:iter:help: wasn't used
[ clap::parser::parser] Parser::react action=Help, identifier=None, source=DefaultValue
thread 'main' panicked at 'assertion failed: (left == right)
left: ["false"],
right: []', /home/stefan/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.7/src/parser/parser.rs:1277:17
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

[epage]

The assert is removed in 4.0.8. I've also considered adding support for () as a type to say "don't bother reading a value". If you are interested in that for this case, feel free to create an issue