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Optional option-argument parsing is incorrect
Please complete the following tasks
- [X] I have searched the discussions
- [X] I have searched the existing issues
Rust Version
rustc 1.56.0 (09c42c458 2021-10-18)
Clap Version
master
Minimal reproducible code
use clap::Parser;
#[derive(Parser, Debug)]
struct Opt {
#[clap(short,long)]
foo: Option<Option<String>>,
input: String,
}
fn main() {
let opt = Opt::parse();
println!("{:?}", opt);
}
Steps to reproduce the bug with the above code
cargo run -- -f input
or
cargo run -- --foo input
Actual Behaviour
error: The following required arguments were not provided:
<INPUT>
USAGE:
clap-test --foo <FOO> <INPUT>
For more information try --help
Expected Behaviour
Opt { foo: Some(None), input: "input" }
Additional Context
There needs to be some special handling of options with optional arguments.
Optional option-arguments are bad
First of all, users really need to be discouraged (if we ever add some lint-like feature, e.g. #[clap(enable-warnings)
).
POSIX says:
Option-arguments should not be optional.
Solaris says:
Option-arguments cannot be optional.
Parsing
I know some people have a preference for -f OptArg
over -fOptArg
, but if the option-argument is optional, then only the latter is correct. If there is a space, it means the optional argument is not there.
From POSIX.1-2017 - Ch. 12: Utility Conventions:
a conforming application shall place any option-argument for that option directly adjacent to the option in the same argument string, without intervening
<blank>
characters
If the utility receives an argument containing only the option, it shall behave as specified in its description for an omitted option-argument; it shall not treat the next argument (if any) as the option-argument for that option.
Same thing with the long option, which is a GNU extension.
From GNU C Library Reference Manual - Ch. 25.1.1: Program Argument Syntax Conventions:
To specify an argument for a long option, write
--name=value
. This syntax enables a long option to accept an argument that is itself optional.
See this SO question about how getopt
handles this: getopt
does not parse optional arguments to parameters.
In clap terms, these are saying we should only allow
-
--long
-
--long=value
-
-s
-
-svalue
In contrast, clap supports
- Default:
-
--long
-
--long=value
-
--long value
-
-s
-
-s value
-
-s=value
-
-svalue
-
-
requires_equals(true)
-
--long
-
--long=value
-
-s
-
-s=value
-
Debug Output
[ clap::build::app] App::_do_parse
[ clap::build::app] App::_build
[ clap::build::app] App::_propagate:clap-test
[ clap::build::app] App::_check_help_and_version
[ clap::build::app] App::_check_help_and_version: Removing generated version
[ clap::build::app] App::_propagate_global_args:clap-test
[ clap::build::app] App::_derive_display_order:clap-test
[clap::build::app::debug_asserts] App::_debug_asserts
[clap::build::arg::debug_asserts] Arg::_debug_asserts:help
[clap::build::arg::debug_asserts] Arg::_debug_asserts:foo
[clap::build::arg::debug_asserts] Arg::_debug_asserts:input
[ clap::parse::parser] Parser::get_matches_with
[ clap::parse::parser] Parser::_build
[ clap::parse::parser] Parser::_verify_positionals
[ clap::parse::parser] Parser::get_matches_with: Begin parsing 'RawOsStr("-f")' ([45, 102])
[ clap::parse::parser] Parser::get_matches_with: Positional counter...1
[ clap::parse::parser] Parser::get_matches_with: Low index multiples...false
[ clap::parse::parser] Parser::possible_subcommand: arg=RawOsStr("-f")
[ clap::parse::parser] Parser::get_matches_with: sc=None
[ clap::parse::parser] Parser::parse_short_arg: short_arg=RawOsStr("f")
[ clap::parse::parser] Parser::parse_short_arg:iter:f
[ clap::parse::parser] Parser::parse_short_arg:iter:f: cur_idx:=1
[ clap::parse::parser] Parser::parse_short_arg:iter:f: Found valid opt or flag
[ clap::parse::parser] Parser::parse_short_arg:iter:f: val=RawOsStr("") (bytes), val=[] (ascii), short_arg=RawOsStr("f")
[ clap::parse::parser] Parser::parse_opt; opt=foo, val=None
[ clap::parse::parser] Parser::parse_opt; opt.settings=ArgFlags(TAKES_VAL)
[ clap::parse::parser] Parser::parse_opt; Checking for val...
[ clap::parse::parser] Parser::parse_opt: More arg vals required...
[ clap::parse::arg_matcher] ArgMatcher::inc_occurrence_of: arg=foo
[ clap::build::app] App::groups_for_arg: id=foo
[ clap::build::app] App::groups_for_arg: id=foo
[ clap::parse::parser] Parser::get_matches_with: After parse_short_arg Opt(foo)
[ clap::parse::parser] Parser::get_matches_with: Begin parsing 'RawOsStr("input")' ([105, 110, 112, 117, 116])
[ clap::parse::parser] Parser::get_matches_with: Positional counter...1
[ clap::parse::parser] Parser::get_matches_with: Low index multiples...false
[ clap::parse::parser] Parser::add_val_to_arg; arg=foo, val=RawOsStr("input")
[ clap::parse::parser] Parser::add_val_to_arg; trailing_values=false, DontDelimTrailingVals=false
[ clap::parse::parser] Parser::add_single_val_to_arg: adding val..."input"
[ clap::parse::parser] Parser::add_single_val_to_arg: cur_idx:=2
[ clap::build::app] App::groups_for_arg: id=foo
[ clap::parse::arg_matcher] ArgMatcher::needs_more_vals: o=foo
[ clap::parse::arg_matcher] ArgMatcher::needs_more_vals: max_vals...1
[ clap::parse::parser] Parser::remove_overrides
[ clap::parse::parser] Parser::remove_overrides:iter:foo
[ clap::parse::validator] Validator::validate
[ clap::parse::parser] Parser::add_env: Checking arg `--help`
[ clap::parse::parser] Parser::add_env: Skipping existing arg `--foo <FOO>`
[ clap::parse::parser] Parser::add_env: Checking arg `<INPUT>`
[ clap::parse::parser] Parser::add_defaults
[ clap::parse::parser] Parser::add_defaults:iter:foo:
[ clap::parse::parser] Parser::add_value: doesn't have conditional defaults
[ clap::parse::parser] Parser::add_value:iter:foo: doesn't have default vals
[ clap::parse::parser] Parser::add_value:iter:foo: doesn't have default missing vals
[ clap::parse::parser] Parser::add_defaults:iter:input:
[ clap::parse::parser] Parser::add_value: doesn't have conditional defaults
[ clap::parse::parser] Parser::add_value:iter:input: doesn't have default vals
[ clap::parse::parser] Parser::add_value:iter:input: doesn't have default missing vals
[ clap::parse::validator] Validator::validate_conflicts
[ clap::parse::validator] Validator::validate_exclusive
[ clap::parse::validator] Validator::validate_exclusive:iter:foo
[ clap::parse::validator] Validator::gather_conflicts
[ clap::parse::validator] Validator::gather_conflicts:iter: id=foo
[ clap::build::app] App::groups_for_arg: id=foo
[ clap::parse::validator] Validator::validate_required: required=ChildGraph([Child { id: input, children: [] }])
[ clap::parse::validator] Validator::gather_requirements
[ clap::parse::validator] Validator::gather_requirements:iter:foo
[ clap::parse::validator] Validator::validate_required:iter:aog=input
[ clap::parse::validator] Validator::validate_required:iter: This is an arg
[ clap::parse::validator] Validator::is_missing_required_ok: input
[ clap::parse::validator] Validator::validate_arg_conflicts: a="input"
[ clap::parse::validator] Validator::missing_required_error; incl=[]
[ clap::parse::validator] Validator::missing_required_error: reqs=ChildGraph([Child { id: input, children: [] }])
[ clap::output::usage] Usage::get_required_usage_from: incls=[], matcher=true, incl_last=true
[ clap::output::usage] Usage::get_required_usage_from: unrolled_reqs={input}
[ clap::output::usage] Usage::get_required_usage_from:iter:input
[ clap::output::usage] Usage::get_required_usage_from: ret_val=["<INPUT>"]
[ clap::parse::validator] Validator::missing_required_error: req_args=[
"<INPUT>",
]
[ 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_required_usage_from: incls=[foo], matcher=false, incl_last=true
[ clap::output::usage] Usage::get_required_usage_from: unrolled_reqs={input}
[ clap::output::usage] Usage::get_required_usage_from:iter:foo
[ clap::output::usage] Usage::get_required_usage_from:iter:input
[ clap::output::usage] Usage::get_required_usage_from: ret_val=["--foo <FOO>", "<INPUT>"]
[ clap::build::app] App::color: Color setting...
[ clap::build::app] Auto
[ clap::output::fmt] is_a_tty: stderr=true