Using help_heading in one place requires using it on all Flags to get a Unified experience

[epage]

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• I have searched the discussions
• I have searched the existing issues

Rust Version

rustc 1.55.0 (c8dfcfe04 2021-09-06)

Clap Version

v3.0.0-beta.4

Minimal reproducible code

fn main() {
    use clap::*;
    let app = App::new("myTest")
        .name("test")
        .author("Kevin K.")
        .about("tests stuff")
        .version("1.3")
        .arg(Arg::from("-f, --flag 'some flag'"))
        .arg(Arg::from("[arg] 'some pos arg'"))
        .arg(Arg::from("--option [opt] 'some option'"))
        .arg(Arg::from("-v, --verbose 'Extra info'").help_heading(Some("Debug")))
        .arg(Arg::from("-q, --quiet 'Less info'").help_heading(Some("Debug")));
    app.get_matches();
}

or

fn main() {
    use clap::*;
    let app = App::new("myTest")
        .name("test")
        .author("Kevin K.")
        .about("tests stuff")
        .version("1.3")
        .setting(AppSettings::UnifiedHelpMessage)
        .arg(Arg::from("-f, --flag 'some flag'"))
        .arg(Arg::from("[arg] 'some pos arg'"))
        .arg(Arg::from("--option [opt] 'some option'"))
        .arg(Arg::from("-v, --verbose 'Extra info'").help_heading(Some("Debug")))
        .arg(Arg::from("-q, --quiet 'Less info'").help_heading(Some("Debug")));
    app.get_matches();
}

Steps to reproduce the bug with the above code

cargo run -- --help

Actual Behaviour

❯ cargo run -- --help
   Compiling test-clap v0.1.0 (/home/epage/src/personal/test-clap)
    Finished dev [unoptimized + debuginfo] target(s) in 0.60s
     Running `target/debug/test-clap --help`
test 1.3

Kevin K.

tests stuff

USAGE:
    test-clap [FLAGS] [OPTIONS] [arg]

ARGS:
    <arg>    some pos arg

FLAGS:
    -f, --flag       some flag
    -h, --help       Print help information
    -V, --version    Print version information

OPTIONS:
        --option <opt>    some option

Debug:
    -q, --quiet      Less info
    -v, --verbose    Extra info

or

❯ cargo run -- --help
   Compiling test-clap v0.1.0 (/home/epage/src/personal/test-clap)
    Finished dev [unoptimized + debuginfo] target(s) in 0.63s
     Running `target/debug/test-clap --help`
test 1.3

Kevin K.

tests stuff

USAGE:
    test-clap [OPTIONS] [arg]

ARGS:
    <arg>    some pos arg

OPTIONS:
    -f, --flag            some flag
    -h, --help            Print help information
        --option <opt>    some option
    -q, --quiet           Less info
    -v, --verbose         Extra info
    -V, --version         Print version information

Expected Behaviour

Without having to override help_heading on every flag:

❯ cargo run -- --help
   Compiling test-clap v0.1.0 (/home/epage/src/personal/test-clap)
    Finished dev [unoptimized + debuginfo] target(s) in 0.60s
     Running `target/debug/test-clap --help`
test 1.3

Kevin K.

tests stuff

USAGE:
    test-clap [FLAGS] [OPTIONS] [arg]

ARGS:
    <arg>    some pos arg

OPTIONS:
    -f, --flag       some flag
    -h, --help       Print help information
    -V, --version    Print version information
        --option <opt>    some option

Debug:
    -q, --quiet      Less info
    -v, --verbose    Extra info

Additional Context

This is split off of #2807

We could fix this by respecting help_heading with UnifiedHelpMessage but it then seems like a misnomer because it is no longer unified.

Debug Output

No response