clap: Regression from 3.1 -> 3.2 in `values_of` (i think)

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• I have searched the open and rejected issues

Rust Version

rustc 1.60.0 (7737e0b5c 2022-04-04)

Clap Version

3.2.1

Minimal reproducible code

use clap::{Arg, Command};

const INCLUDE: &str = "include";

fn arg_include() -> Arg<'static> {
    Arg::new(INCLUDE)
        .long(INCLUDE)
        .short('i')
        .takes_value(true)
        .multiple_occurrences(true)
        .allow_invalid_utf8(true)
}

fn app() -> Command<'static> {
    Command::new("test").arg(arg_include())
}

#[derive(Copy, Clone, PartialEq, Debug)]
pub enum IncludeKind {
    Quoted,
    Bracketed,
}

#[derive(Clone, PartialEq, Debug)]
pub struct Include {
    pub path: String,
    pub kind: IncludeKind,
}

#[derive(Debug)]
struct Opt {
    include: Vec<Include>,
}

fn parse() -> Opt {
    let matches = app().get_matches_from(&["test", "--include", "/path/to/foo"]);
    
    let include = matches
        .values_of(INCLUDE)
        .unwrap_or_default()
        .map(|include| {
            if include.starts_with('<') && include.ends_with('>') {
                Include {
                    path: include[1..include.len() - 1].to_owned(),
                    kind: IncludeKind::Bracketed,
                }
            } else {
                Include {
                    path: include.to_owned(),
                    kind: IncludeKind::Quoted,
                }
            }
        })
        .collect();
    Opt {
        include
    }
}

fn main() {
    dbg!(parse());
    
}

Steps to reproduce the bug with the above code

Using clap = "3.2" with cargo run --release, I get:

$ cargo run --release
thread 'main' panicked at 'Must use `_os` lookups with `Arg::allow_invalid_utf8`', /var/home/walters/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-3.2.1/src/parser/matches/arg_matches.rs:1651:13
stack backtrace:
   0: rust_begin_unwind
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/core/src/panicking.rs:143:14
   2: clap::parser::matches::arg_matches::unwrap_string
   3: <clap::parser::matches::arg_matches::OsValues as core::iter::traits::iterator::Iterator>::next
   4: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
   5: clap_regression::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Yet specifying clap = ">= 3.1, < 3.2" (resolving to v3.1.18), the program succeeds.

Actual Behaviour

Panic

Expected Behaviour

Don’t panic

Additional Context

This was seen in https://github.com/dtolnay/cxx/pull/1057

Debug Output

    Finished release [optimized] target(s) in 12.03s
     Running `target/release/clap-regression`
[      clap::builder::command]  Command::_do_parse
[      clap::builder::command]  Command::_build: name="test"
[      clap::builder::command]  Command::_propagate:test
[      clap::builder::command]  Command::_check_help_and_version: test
[      clap::builder::command]  Command::_check_help_and_version: Removing generated version
[      clap::builder::command]  Command::_propagate_global_args:test
[      clap::builder::command]  Command::_derive_display_order:test
[        clap::parser::parser]  Parser::get_matches_with
[        clap::parser::parser]  Parser::get_matches_with: Begin parsing 'RawOsStr("--include")' ([45, 45, 105, 110, 99, 108, 117, 100, 101])
[        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::possible_subcommand: arg=Ok("--include")
[        clap::parser::parser]  Parser::get_matches_with: sc=None
[        clap::parser::parser]  Parser::parse_long_arg
[        clap::parser::parser]  Parser::parse_long_arg: Does it contain '='...
[        clap::parser::parser]  Parser::parse_long_arg: Found valid arg or flag '--include <include>'
[        clap::parser::parser]  Parser::parse_long_arg("include"): Found an arg with value 'None'
[        clap::parser::parser]  Parser::parse_opt_value; arg=include, val=None, has_eq=false
[        clap::parser::parser]  Parser::parse_opt_value; arg.settings=ArgFlags(MULTIPLE_OCC | TAKES_VAL | UTF8_NONE)
[        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_long_arg Opt([hash: E81C2B1E12CC3D28])
[        clap::parser::parser]  Parser::get_matches_with: Begin parsing 'RawOsStr("/path/to/foo")' ([47, 112, 97, 116, 104, 47, 116, 111, 47, 102, 111, 111])
[        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::split_arg_values; arg=include, val=RawOsStr("/path/to/foo")
[        clap::parser::parser]  Parser::split_arg_values; trailing_values=false, DontDelimTrailingVals=false
[   clap::parser::arg_matcher]  ArgMatcher::needs_more_vals: o=include, resolved=0, pending=1
[        clap::parser::parser]  Parser::resolve_pending: id=[hash: E81C2B1E12CC3D28]
[        clap::parser::parser]  Parser::react action=StoreValue, identifier=Some(Long), source=CommandLine
[        clap::parser::parser]  Parser::react: cur_idx:=1
[        clap::parser::parser]  Parser::remove_overrides: id=[hash: E81C2B1E12CC3D28]
[   clap::parser::arg_matcher]  ArgMatcher::start_occurrence_of_arg: id=[hash: E81C2B1E12CC3D28]
[      clap::builder::command]  Command::groups_for_arg: id=[hash: E81C2B1E12CC3D28]
[        clap::parser::parser]  Parser::push_arg_values: ["/path/to/foo"]
[        clap::parser::parser]  Parser::add_single_val_to_arg: cur_idx:=2
[      clap::builder::command]  Command::groups_for_arg: id=[hash: E81C2B1E12CC3D28]
[        clap::parser::parser]  Parser::add_defaults
[        clap::parser::parser]  Parser::add_defaults:iter:help:
[        clap::parser::parser]  Parser::add_default_value:iter:help: doesn't have default missing vals
[        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:include:
[        clap::parser::parser]  Parser::add_default_value:iter:include: doesn't have default missing vals
[        clap::parser::parser]  Parser::add_default_value: doesn't have conditional defaults
[        clap::parser::parser]  Parser::add_default_value:iter:include: 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_conflicts::iter: id=[hash: E81C2B1E12CC3D28]
[     clap::parser::validator]  Conflicts::gather_conflicts: arg=[hash: E81C2B1E12CC3D28]
[     clap::parser::validator]  Conflicts::gather_conflicts: conflicts=[]
[     clap::parser::validator]  Validator::validate_required: required=ChildGraph([])
[     clap::parser::validator]  Validator::gather_requires
[     clap::parser::validator]  Validator::gather_requires:iter:[hash: E81C2B1E12CC3D28]
[     clap::parser::validator]  Validator::validate_required: is_exclusive_present=false
[     clap::parser::validator]  Validator::validate_required_unless
[     clap::parser::validator]  Validator::validate_matched_args
[     clap::parser::validator]  Validator::validate_matched_args:iter:[hash: E81C2B1E12CC3D28]: vals=Flatten {
    inner: FlattenCompat {
        iter: Fuse {
            iter: Some(
                Iter(
                    [
                        [
                            AnyValue {
                                inner: TypeId {
                                    t: 4040081991788025797,
                                },
                            },
                        ],
                    ],
                ),
            ),
        },
        frontiter: None,
        backiter: None,
    },
}
[     clap::parser::validator]  Validator::validate_arg_num_vals
[     clap::parser::validator]  Validator::validate_arg_values: arg="include"
[     clap::parser::validator]  Validator::validate_arg_num_occurs: "include"=1
[   clap::parser::arg_matcher]  ArgMatcher::get_global_values: global_arg_vec=[[hash: 59636393CFFBFE5F]]
thread 'main' panicked at 'Must use `_os` lookups with `Arg::allow_invalid_utf8`', /var/home/walters/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-3.2.1/src/parser/matches/arg_matches.rs:1651:13
stack backtrace:
   0: rust_begin_unwind
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c/library/core/src/panicking.rs:143:14
   2: clap::parser::matches::arg_matches::unwrap_string
   3: <clap::parser::matches::arg_matches::Values as core::iter::traits::iterator::Iterator>::next
   4: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
   5: clap_regression::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.