Optional, nested flatten gets ignored (nested ArgGroups are unsupported)

[jeertmans]

Please complete the following tasks

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

Rust Version

rustc 1.67.0-nightly (e631891f7 2022-11-13)

Clap Version

4.1.4

Minimal reproducible code

Link to the Rust Playground

/// Command that defaults to `Main` if no
/// subcommand is provided.
#[derive(Debug, Parser)]
#[clap(args_conflicts_with_subcommands = true)]
#[clap(subcommand_negates_reqs = true)]
struct MainCommand {
    /// Arguments for main command
    #[clap(flatten)]
    args: Option<Main>,
    /* comment above and uncomment next: */
    //#[clap(flatten)]
    //args: Option<LoginArgs>,

    /// Subcommand
    #[command(subcommand)]
    command: Option<Command>,
}

#[derive(Args, Clone, Debug)]
struct Main {
    #[clap(flatten)]
    login_args: LoginArgs,
    
    #[clap(long)]
    flag_main: bool,
}

#[derive(Clone, Debug, Subcommand)]
enum Command {
    Subcmd(SecondaryCommand),
}

#[derive(Args, Clone, Debug)]
struct SecondaryCommand {
    #[clap(flatten)]
    login_args: LoginArgs,
    
    #[clap(long)]
    flag_sub: bool,
}

#[derive(Args, Clone, Debug)]
struct LoginArgs {
    #[clap(short, required = true)]
    username: Option<String>,
}

fn main() {
    assert!(MainCommand::try_parse_from(["playground"]).is_err());
    
    let m = MainCommand::parse_from(["playground", "-u", "jeertmans"]);

    // When we use args: Option<Main>,
    // args is None, and should be Some
    // 
    // If we use args: Option<LoginArgs>,
    // args is Some as expected
    println!("Calling main:\n{:#?}\n", m);

    assert!(MainCommand::try_parse_from(["playground", "subcmd"]).is_err());
    
    let m = MainCommand::parse_from(["playground", "subcmd", "-u", "jeertmans"]);

    // Here, args is None as expected
    println!("Calling sub:\n{:#?}\n", m);
}

See #5435 for another variant of this problem

Steps to reproduce the bug with the above code

Simply run the code twice: first, with args: Option<Main>, and, second, with args: Option<LoginArgs>. Using the playground should be fine for testing.

Comments in the main() function explain what is expected.

The fact that args contains nested flatten seems to be the problem (?).

Actual Behaviour

Even if the arguments defined in Main are all valid, i.e., all required arguments are specified, the args field is None.

Expected Behaviour

I'd like the args field to be Some in the first case, when args: Option<Main>.

Additional Context

I am aware of #3123 and #4350, but I am not sure whether what I observe it normal or not.

Debug Output

    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/claptest`
[      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::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_check_help_and_version: Building help subcommand
[      clap::builder::command] 	Command::_propagate_global_args:claptest
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_main
[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:username:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:username: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:flag_main:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: has default vals
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: wasn't used
[        clap::parser::parser] 	Parser::react action=SetTrue, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="flag_main", source=DefaultValue
[        clap::parser::parser] 	Parser::push_arg_values: ["false"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=1
[        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::validator] 	Validator::validate
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "username", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[     clap::parser::validator] 	Validator::validate_required:iter:aog="username"
[     clap::parser::validator] 	Validator::validate_required:iter: This is an arg
[     clap::parser::validator] 	Validator::is_missing_required_ok: username
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="username"
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="username", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="LoginArgs"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="LoginArgs", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required:iter: Missing "username"
[     clap::parser::validator] 	Validator::missing_required_error; incl=["username"]
[     clap::parser::validator] 	Validator::missing_required_error: reqs=ChildGraph([Child { id: "username", children: [] }])
[         clap::output::usage] 	Usage::get_required_usage_from: incls=["username"], matcher=true, incl_last=true
[         clap::output::usage] 	Usage::get_required_usage_from: unrolled_reqs=["username"]
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"username" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"username" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from: ret_val=[StyledStr { pieces: [(Some(Literal), "-"), (Some(Literal), "u"), (Some(Placeholder), " "), (Some(Placeholder), "<USERNAME>")] }]
[     clap::parser::validator] 	Validator::missing_required_error: req_args=[
    "-u <USERNAME>",
]
[         clap::output::usage] 	Usage::create_usage_with_title
[         clap::output::usage] 	Usage::create_usage_no_title
[         clap::output::usage] 	Usage::create_smart_usage
[         clap::output::usage] 	Usage::get_args: incls=["username"]
[         clap::output::usage] 	Usage::get_args: unrolled_reqs=["username"]
[         clap::output::usage] 	Usage::get_args: ret_val=[StyledStr { pieces: [(Some(Literal), "-"), (Some(Literal), "u"), (Some(Placeholder), " "), (Some(Placeholder), "<USERNAME>")] }]
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
[      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::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_check_help_and_version: Building help subcommand
[      clap::builder::command] 	Command::_propagate_global_args:claptest
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_main
[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::get_matches_with: Begin parsing 'RawOsStr("-u")' ([45, 117])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("-u")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::parse_short_arg: short_arg=ShortFlags { inner: RawOsStr("u"), utf8_prefix: CharIndices { front_offset: 0, iter: Chars(['u']) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u: Found valid opt or flag
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u: val=RawOsStr("") (bytes), val=[] (ascii), short_arg=ShortFlags { inner: RawOsStr("u"), utf8_prefix: CharIndices { front_offset: 1, iter: Chars([]) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_opt_value; arg=username, val=None, has_eq=false
[        clap::parser::parser] 	Parser::parse_opt_value; arg.settings=ArgFlags(REQUIRED)
[        clap::parser::parser] 	Parser::parse_opt_value; Checking for val...
[        clap::parser::parser] 	Parser::parse_opt_value: More arg vals required...
[        clap::parser::parser] 	Parser::get_matches_with: After parse_short_arg Opt("username")
[        clap::parser::parser] 	Parser::get_matches_with: Begin parsing 'RawOsStr("jeertmans")' ([106, 101, 101, 114, 116, 109, 97, 110, 115])
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=username, pending=1
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: expected=1, actual=1
[        clap::parser::parser] 	Parser::resolve_pending: id="username"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Short), source=CommandLine
[        clap::parser::parser] 	Parser::react: cur_idx:=1
[        clap::parser::parser] 	Parser::remove_overrides: id="username"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="username", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="LoginArgs", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["jeertmans"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=2
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=username, 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
[        clap::parser::parser] 	Parser::add_defaults:iter:username:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:username: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:flag_main:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: has default vals
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: wasn't used
[        clap::parser::parser] 	Parser::react action=SetTrue, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="flag_main", source=DefaultValue
[        clap::parser::parser] 	Parser::push_arg_values: ["false"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=3
[        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::validator] 	Validator::validate
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="username", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="LoginArgs", conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "username", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::gather_requires:iter:"username"
[     clap::parser::validator] 	Validator::gather_requires:iter:"LoginArgs"
[     clap::parser::validator] 	Validator::gather_requires:iter:"LoginArgs":group
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[   clap::parser::arg_matcher] 	ArgMatcher::get_global_values: global_arg_vec=[]
Calling main:
MainCommand {
    args: None,
    command: None,
}

[      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::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_check_help_and_version: Building help subcommand
[      clap::builder::command] 	Command::_propagate_global_args:claptest
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_main
[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::get_matches_with: Begin parsing 'RawOsStr("subcmd")' ([115, 117, 98, 99, 109, 100])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("subcmd")
[        clap::parser::parser] 	Parser::get_matches_with: sc=Some("subcmd")
[        clap::parser::parser] 	Parser::parse_subcommand
[      clap::builder::command] 	Command::_build_subcommand Setting bin_name of subcmd to "playground subcmd"
[      clap::builder::command] 	Command::_build_subcommand Setting display_name of subcmd to "claptest-subcmd"
[      clap::builder::command] 	Command::_build: name="subcmd"
[      clap::builder::command] 	Command::_propagate:subcmd
[      clap::builder::command] 	Command::_check_help_and_version:subcmd expand_help_tree=false
[      clap::builder::command] 	Command::long_help_exists
[      clap::builder::command] 	Command::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_propagate_global_args:subcmd
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_sub
[clap::builder::debug_asserts] 	Arg::_debug_asserts:help
[clap::builder::debug_asserts] 	Command::_verify_positionals
[        clap::parser::parser] 	Parser::parse_subcommand: About to parse sc=subcmd
[        clap::parser::parser] 	Parser::get_matches_with
[        clap::parser::parser] 	Parser::add_defaults
[        clap::parser::parser] 	Parser::add_defaults:iter:username:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:username: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:flag_sub:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_sub: has default vals
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_sub: wasn't used
[        clap::parser::parser] 	Parser::react action=SetTrue, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="flag_sub", source=DefaultValue
[        clap::parser::parser] 	Parser::push_arg_values: ["false"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=1
[        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::validator] 	Validator::validate
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "username", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[     clap::parser::validator] 	Validator::validate_required:iter:aog="username"
[     clap::parser::validator] 	Validator::validate_required:iter: This is an arg
[     clap::parser::validator] 	Validator::is_missing_required_ok: username
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="username"
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="username", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="LoginArgs"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="LoginArgs", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required:iter: Missing "username"
[     clap::parser::validator] 	Validator::missing_required_error; incl=["username"]
[     clap::parser::validator] 	Validator::missing_required_error: reqs=ChildGraph([Child { id: "username", children: [] }])
[         clap::output::usage] 	Usage::get_required_usage_from: incls=["username"], matcher=true, incl_last=true
[         clap::output::usage] 	Usage::get_required_usage_from: unrolled_reqs=["username"]
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"username" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"username" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from: ret_val=[StyledStr { pieces: [(Some(Literal), "-"), (Some(Literal), "u"), (Some(Placeholder), " "), (Some(Placeholder), "<USERNAME>")] }]
[     clap::parser::validator] 	Validator::missing_required_error: req_args=[
    "-u <USERNAME>",
]
[         clap::output::usage] 	Usage::create_usage_with_title
[         clap::output::usage] 	Usage::create_usage_no_title
[         clap::output::usage] 	Usage::create_smart_usage
[         clap::output::usage] 	Usage::get_args: incls=["username"]
[         clap::output::usage] 	Usage::get_args: unrolled_reqs=["username"]
[         clap::output::usage] 	Usage::get_args: ret_val=[StyledStr { pieces: [(Some(Literal), "-"), (Some(Literal), "u"), (Some(Placeholder), " "), (Some(Placeholder), "<USERNAME>")] }]
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
[      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::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_check_help_and_version: Building help subcommand
[      clap::builder::command] 	Command::_propagate_global_args:claptest
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_main
[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::get_matches_with: Begin parsing 'RawOsStr("subcmd")' ([115, 117, 98, 99, 109, 100])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("subcmd")
[        clap::parser::parser] 	Parser::get_matches_with: sc=Some("subcmd")
[        clap::parser::parser] 	Parser::parse_subcommand
[      clap::builder::command] 	Command::_build_subcommand Setting bin_name of subcmd to "playground subcmd"
[      clap::builder::command] 	Command::_build_subcommand Setting display_name of subcmd to "claptest-subcmd"
[      clap::builder::command] 	Command::_build: name="subcmd"
[      clap::builder::command] 	Command::_propagate:subcmd
[      clap::builder::command] 	Command::_check_help_and_version:subcmd expand_help_tree=false
[      clap::builder::command] 	Command::long_help_exists
[      clap::builder::command] 	Command::_check_help_and_version: Building default --help
[      clap::builder::command] 	Command::_propagate_global_args:subcmd
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:username
[clap::builder::debug_asserts] 	Arg::_debug_asserts:flag_sub
[clap::builder::debug_asserts] 	Arg::_debug_asserts:help
[clap::builder::debug_asserts] 	Command::_verify_positionals
[        clap::parser::parser] 	Parser::parse_subcommand: About to parse sc=subcmd
[        clap::parser::parser] 	Parser::get_matches_with
[        clap::parser::parser] 	Parser::get_matches_with: Begin parsing 'RawOsStr("-u")' ([45, 117])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("-u")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::parse_short_arg: short_arg=ShortFlags { inner: RawOsStr("u"), utf8_prefix: CharIndices { front_offset: 0, iter: Chars(['u']) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u: Found valid opt or flag
[        clap::parser::parser] 	Parser::parse_short_arg:iter:u: val=RawOsStr("") (bytes), val=[] (ascii), short_arg=ShortFlags { inner: RawOsStr("u"), utf8_prefix: CharIndices { front_offset: 1, iter: Chars([]) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_opt_value; arg=username, val=None, has_eq=false
[        clap::parser::parser] 	Parser::parse_opt_value; arg.settings=ArgFlags(REQUIRED)
[        clap::parser::parser] 	Parser::parse_opt_value; Checking for val...
[        clap::parser::parser] 	Parser::parse_opt_value: More arg vals required...
[        clap::parser::parser] 	Parser::get_matches_with: After parse_short_arg Opt("username")
[        clap::parser::parser] 	Parser::get_matches_with: Begin parsing 'RawOsStr("jeertmans")' ([106, 101, 101, 114, 116, 109, 97, 110, 115])
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=username, pending=1
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: expected=1, actual=1
[        clap::parser::parser] 	Parser::resolve_pending: id="username"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Short), source=CommandLine
[        clap::parser::parser] 	Parser::react: cur_idx:=1
[        clap::parser::parser] 	Parser::remove_overrides: id="username"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="username", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="LoginArgs", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["jeertmans"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=2
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=username, 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
[        clap::parser::parser] 	Parser::add_defaults:iter:username:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:username: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:flag_sub:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_sub: has default vals
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_sub: wasn't used
[        clap::parser::parser] 	Parser::react action=SetTrue, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="flag_sub", source=DefaultValue
[        clap::parser::parser] 	Parser::push_arg_values: ["false"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=3
[        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::validator] 	Validator::validate
[      clap::builder::command] 	Command::groups_for_arg: id="username"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="username", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="LoginArgs", conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="username"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "username", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::gather_requires:iter:"username"
[     clap::parser::validator] 	Validator::gather_requires:iter:"LoginArgs"
[     clap::parser::validator] 	Validator::gather_requires:iter:"LoginArgs":group
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[        clap::parser::parser] 	Parser::add_defaults
[        clap::parser::parser] 	Parser::add_defaults:iter:username:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:username: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:flag_main:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: has default vals
[        clap::parser::parser] 	Parser::add_default_value:iter:flag_main: wasn't used
[        clap::parser::parser] 	Parser::react action=SetTrue, identifier=None, source=DefaultValue
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="flag_main", source=DefaultValue
[        clap::parser::parser] 	Parser::push_arg_values: ["false"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=1
[        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::validator] 	Validator::validate
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[   clap::parser::arg_matcher] 	ArgMatcher::get_global_values: global_arg_vec=[]
Calling sub:
MainCommand {
    args: None,
    command: Some(
        Subcmd(
            SecondaryCommand {
                login_args: LoginArgs {
                    username: Some(
                        "jeertmans",
                    ),
                },
                flag_sub: false,
            },
        ),
    ),
}

[epage]

This was previously a task list item in #3165, so I've updated it to point to this issue

[jeertmans]

Thanks for the update! I don't think I know Clap well enough to help with #3165, but I hope someone will :D