allow_missing_positional with allow_hyphen_values not working

[ismell]

Please complete the following tasks

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

Rust Version

rustc 1.66.0 (69f9c33d7 2022-12-12)

Clap Version

4.0.29

Minimal reproducible code

#[derive(Parser, Debug, PartialEq, Eq)]
#[command(allow_missing_positional = true)]
pub struct Args {
    /// Version number.
    /// If not specified the PVR variable is used.
    #[arg(allow_hyphen_values = true)]
    v1: Option<String>,

    /// -gt, -ge, -lt, -le, -eq, -ne
    #[arg(allow_hyphen_values = true)]
    op: String,

    /// Version number.
    v2: String,
}

#[test]
fn test_three_args() -> Result<()> {  // <-- This works
    let args = Args::try_parse_from(vec!["prog", "0.3", "-gt", "0.2"])?;
    assert_eq!(
        args,
        Args {
            v1: Some("0.3".to_owned()),
            op: "-gt".to_owned(),
            v2: "0.2".to_owned(),
        }
    );

    Ok(())
}

#[test]
fn test_two_args() -> Result<()> { // <-- This fails
    let args = Args::try_parse_from(vec!["prog", "-gt", "0.2"])?;
    assert_eq!(
        args,
        Args {
            v1: None,
            op: "-gt".to_owned(),
            v2: "0.2".to_owned(),
        }
    );

    Ok(())
}

Steps to reproduce the bug with the above code

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1b582ab81b2884b8696d70789b6e9ed4

Actual Behaviour

---- test_two_args stdout ----
Error: error: The following required arguments were not provided:
  <OP>

Usage: prog <V1> <OP> <V2>

Expected Behaviour

There should be no parsing error and the v1 Option should be None.

Additional Context

The command I'm replicating is documented here: https://mgorny.pl/articles/the-ultimate-guide-to-eapi-7.html#version-comparison-ver-test

Debug Output

running 2 tests
test ver_test::tests::test_three_args ... [      clap::builder::command] 	Command::_do_parse
[      clap::builder::command] 	Command::_build: name="ver_test"
[      clap::builder::command] 	Command::_propagate:ver_test
[      clap::builder::command] 	Command::_check_help_and_version:ver_test 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:ver_test
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:v1
[clap::builder::debug_asserts] 	Arg::_debug_asserts:op
[clap::builder::debug_asserts] 	Arg::_debug_asserts:v2
[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("0.3")' ([48, 46, 51])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("0.3")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::get_matches_with: Positional counter...1
[        clap::parser::parser] 	Parser::get_matches_with: Low index multiples...false
[        clap::parser::parser] 	Parser::get_matches_with: Begin parsing 'RawOsStr("-gt")' ([45, 103, 116])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("-gt")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::parse_short_arg: short_arg=ShortFlags { inner: RawOsStr("gt"), utf8_prefix: CharIndices { front_offset: 0, iter: Chars(['g', 't']) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_short_args: positional at 2 allows hyphens
[        clap::parser::parser] 	Parser::get_matches_with: After parse_short_arg MaybeHyphenValue
[        clap::parser::parser] 	Parser::get_matches_with: Positional counter...2
[        clap::parser::parser] 	Parser::get_matches_with: Low index multiples...false
[        clap::parser::parser] 	Parser::is_new_arg: RawOsStr("0.2"):op
[        clap::parser::parser] 	Parser::is_new_arg: Allow hyphen
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("0.2")
[        clap::parser::parser] 	Parser::resolve_pending: id="v1"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Index), source=CommandLine
[        clap::parser::parser] 	Parser::remove_overrides: id="v1"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="v1", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="v1"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="Args", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["0.3"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=1
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=v1, 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::get_matches_with: Begin parsing 'RawOsStr("0.2")' ([48, 46, 50])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("0.2")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::get_matches_with: Positional counter...3
[        clap::parser::parser] 	Parser::get_matches_with: Low index multiples...false
[        clap::parser::parser] 	Parser::resolve_pending: id="op"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Index), source=CommandLine
[        clap::parser::parser] 	Parser::remove_overrides: id="op"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="op", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="op"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="Args", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["-gt"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=2
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=op, 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::resolve_pending: id="v2"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Index), source=CommandLine
[        clap::parser::parser] 	Parser::remove_overrides: id="v2"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="v2", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="v2"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="Args", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["0.2"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=3
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=v2, 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:v1:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:v1: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:op:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:op: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:v2:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:v2: doesn't have default vals
[        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="v1"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="v1", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="Args", conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="op"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="op", conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="v2"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="v2", conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"v1"
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"Args"
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"op"
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"v2"
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="v1"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="v1"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="op"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="op"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="v2"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="v2"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "op", children: [] }, Child { id: "v2", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::gather_requires:iter:"v1"
[     clap::parser::validator] 	Validator::gather_requires:iter:"Args"
[     clap::parser::validator] 	Validator::gather_requires:iter:"Args":group
[     clap::parser::validator] 	Validator::gather_requires:iter:"op"
[     clap::parser::validator] 	Validator::gather_requires:iter:"v2"
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[   clap::parser::arg_matcher] 	ArgMatcher::get_global_values: global_arg_vec=[]
ok
test ver_test::tests::test_two_args ... [      clap::builder::command] 	Command::_do_parse
[      clap::builder::command] 	Command::_build: name="ver_test"
[      clap::builder::command] 	Command::_propagate:ver_test
[      clap::builder::command] 	Command::_check_help_and_version:ver_test 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:ver_test
[clap::builder::debug_asserts] 	Command::_debug_asserts
[clap::builder::debug_asserts] 	Arg::_debug_asserts:v1
[clap::builder::debug_asserts] 	Arg::_debug_asserts:op
[clap::builder::debug_asserts] 	Arg::_debug_asserts:v2
[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("-gt")' ([45, 103, 116])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("-gt")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::parse_short_arg: short_arg=ShortFlags { inner: RawOsStr("gt"), utf8_prefix: CharIndices { front_offset: 0, iter: Chars(['g', 't']) }, invalid_suffix: None }
[        clap::parser::parser] 	Parser::parse_short_args: positional at 1 allows hyphens
[        clap::parser::parser] 	Parser::get_matches_with: After parse_short_arg MaybeHyphenValue
[        clap::parser::parser] 	Parser::get_matches_with: Positional counter...1
[        clap::parser::parser] 	Parser::get_matches_with: Low index multiples...false
[        clap::parser::parser] 	Parser::get_matches_with: Begin parsing 'RawOsStr("0.2")' ([48, 46, 50])
[        clap::parser::parser] 	Parser::possible_subcommand: arg=Ok("0.2")
[        clap::parser::parser] 	Parser::get_matches_with: sc=None
[        clap::parser::parser] 	Parser::get_matches_with: Positional counter...2
[        clap::parser::parser] 	Parser::get_matches_with: Low index multiples...false
[        clap::parser::parser] 	Parser::get_matches_with: Bumping the positional counter...
[        clap::parser::parser] 	Parser::resolve_pending: id="v1"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Index), source=CommandLine
[        clap::parser::parser] 	Parser::remove_overrides: id="v1"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="v1", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="v1"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="Args", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["-gt"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=1
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=v1, 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::resolve_pending: id="v2"
[        clap::parser::parser] 	Parser::react action=Set, identifier=Some(Index), source=CommandLine
[        clap::parser::parser] 	Parser::remove_overrides: id="v2"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="v2", source=CommandLine
[      clap::builder::command] 	Command::groups_for_arg: id="v2"
[   clap::parser::arg_matcher] 	ArgMatcher::start_custom_arg: id="Args", source=CommandLine
[        clap::parser::parser] 	Parser::push_arg_values: ["0.2"]
[        clap::parser::parser] 	Parser::add_single_val_to_arg: cur_idx:=2
[   clap::parser::arg_matcher] 	ArgMatcher::needs_more_vals: o=v2, 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:v1:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:v1: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:op:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:op: doesn't have default vals
[        clap::parser::parser] 	Parser::add_defaults:iter:v2:
[        clap::parser::parser] 	Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser] 	Parser::add_default_value:iter:v2: doesn't have default vals
[        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="v1"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="v1", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="Args", conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="v2"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="v2", conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts
[     clap::parser::validator] 	Validator::validate_exclusive
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"v1"
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"Args"
[     clap::parser::validator] 	Validator::validate_exclusive:iter:"v2"
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="v1"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="v1"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_conflicts::iter: id="v2"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="v2"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required: required=ChildGraph([Child { id: "op", children: [] }, Child { id: "v2", children: [] }])
[     clap::parser::validator] 	Validator::gather_requires
[     clap::parser::validator] 	Validator::gather_requires:iter:"v1"
[     clap::parser::validator] 	Validator::gather_requires:iter:"Args"
[     clap::parser::validator] 	Validator::gather_requires:iter:"Args":group
[     clap::parser::validator] 	Validator::gather_requires:iter:"v2"
[     clap::parser::validator] 	Validator::validate_required: is_exclusive_present=false
[     clap::parser::validator] 	Validator::validate_required:iter:aog="op"
[     clap::parser::validator] 	Validator::validate_required:iter: This is an arg
[     clap::parser::validator] 	Validator::is_missing_required_ok: op
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="op"
[      clap::builder::command] 	Command::groups_for_arg: id="op"
[     clap::parser::validator] 	Conflicts::gather_direct_conflicts id="op", conflicts=[]
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[      clap::builder::command] 	Command::groups_for_arg: id="op"
[     clap::parser::validator] 	Conflicts::gather_conflicts: arg="Args"
[     clap::parser::validator] 	Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator] 	Validator::validate_required:iter: Missing "op"
[     clap::parser::validator] 	Validator::missing_required_error; incl=["op"]
[     clap::parser::validator] 	Validator::missing_required_error: reqs=ChildGraph([Child { id: "op", children: [] }, Child { id: "v2", children: [] }])
[         clap::output::usage] 	Usage::get_required_usage_from: incls=["op"], matcher=true, incl_last=true
[         clap::output::usage] 	Usage::get_required_usage_from: unrolled_reqs=["op", "v2"]
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"op" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"v2" arg is_present=true
[         clap::output::usage] 	Usage::get_required_usage_from:iter:"op" arg is_present=false
[         clap::output::usage] 	Usage::get_required_usage_from: ret_val=[StyledStr { pieces: [(Some(Placeholder), "<OP>")] }]
[     clap::parser::validator] 	Validator::missing_required_error: req_args=[
    "<OP>",
]
[         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=["v1", "v2", "op"]
[         clap::output::usage] 	Usage::get_args: unrolled_reqs=["op", "v2"]
[         clap::output::usage] 	Usage::get_args: ret_val=[StyledStr { pieces: [(Some(Placeholder), "<V1>")] }, StyledStr { pieces: [(Some(Placeholder), "<OP>")] }, StyledStr { pieces: [(Some(Placeholder), "<V2>")] }]
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
[      clap::builder::command] 	Command::color: Color setting...
[      clap::builder::command] 	Auto
FAILED

failures:

---- ver_test::tests::test_two_args stdout ----
Error: error: The following required arguments were not provided:
  <OP>

Usage: prog <V1> <OP> <V2>

For more information try '--help'

Backtrace:
   0: clap::error::Backtrace::new
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/error/mod.rs:839:19
   1: clap::error::Error<F>::new
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/error/mod.rs:135:28
   2: clap::error::Error<F>::missing_required_argument
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/error/mod.rs:488:23
   3: clap::parser::validator::Validator::missing_required_error
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/parser/validator.rs:454:13
   4: clap::parser::validator::Validator::validate_required
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/parser/validator.rs:366:17
   5: clap::parser::validator::Validator::validate
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/parser/validator.rs:85:17
   6: clap::parser::parser::Parser::get_matches_with
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/parser/parser.rs:481:9
   7: clap::builder::command::Command::_do_parse
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/builder/command.rs:3796:29
   8: clap::builder::command::Command::try_get_matches_from_mut
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/builder/command.rs:708:9
   9: clap::builder::command::Command::try_get_matches_from
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/builder/command.rs:624:9
  10: clap::derive::Parser::try_parse_from
             at /home/rrangel/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-4.0.32/src/derive.rs:126:31
  11: alchemist::ver_test::tests::test_two_args
             at src/bin/alchemist/ver_test.rs:79:20

[epage]

As a heads up, the reproduction case for ths is a lot simpler; allow_hyphen_values is not needed:

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

//! ```cargo
//! [dependencies]
//! clap = { path = "../clap", features = ["derive"] }
//! ```

use clap::Parser;

#[derive(Parser, Debug, PartialEq, Eq)]
#[command(allow_missing_positional = true)]
pub struct Args {
    /// Version number.
    /// If not specified the PVR variable is used.
    v1: Option<String>,

    /// -gt, -ge, -lt, -le, -eq, -ne
    op: String,

    /// Version number.
    v2: String,
}

fn main() {
    let args = Args::parse();
    println!("{:?}", args);
}

[epage]

allow_missing_positional is fairly limited without using --: it only allows the second-to-last positional to be skipped, causing op to be skipped. Since op is required, we then error when we get to the required checks.

I would likely implement this as

pub struct Args {
    #[arg(allow_hyphen_values = true, required = true, num_args=2..=3)]
    args: Vec<String>,
}

and then extract the arguments as needed

[ismell]

That's what I ended up using after trying to get clap to parse the args correctly. It's not a blocker for me, but a nice to have :)

[epage]

The challenge is getting all of the semantics right as you can't interpret an argument context-free but instead need to process all previous arguments to know what the next one will look like.

This can be faked with the second to last argument because we can peek at the next and make a guess as to whether it is a positional or not. If its not, we assume we need to skip the second to last. To get an idea of how complex this is, see our code for skipping. This does include one other case (low_index_mults) but that isn't a major part of the code.

Even still, I can think of cases that break this, like if you had a positional followed by flag and then a positional.

Similarly, we could make this also consider required = true but that would exclude support for global requireds that require holistic knowledge to support or that a conflict can disable a required = true.666