Conflicting Flags Error message contains the same flag twice

[lucidBrot]

Rust Version

$ rustc -V
rustc 1.39.0 (4560ea788 2019-11-04)

Affected Version of clap

$ grep clap debugcli/Cargo.toml
clap = { git = "https://github.com/clap-rs/clap.git", rev = "1c3958c", features = ["color", "suggestions", "derive"] }

$ grep clap debugcli/Cargo.lock
name = "clap"
source = "git+https://github.com/clap-rs/clap.git?rev=1c3958c#1c3958c56eca35235ed6837c666adb8ede979961"
 "clap_derive 0.3.0 (git+https://github.com/clap-rs/clap_derive)",
name = "clap_derive"
source = "git+https://github.com/clap-rs/clap_derive#2622165be3f061f65fe6b345f4235e7365918244"
 "clap 3.0.0-beta.1 (git+https://github.com/clap-rs/clap.git?rev=1c3958c)",
"checksum clap 3.0.0-beta.1 (git+https://github.com/clap-rs/clap.git?rev=1c3958c)" = "<none>"
"checksum clap_derive 0.3.0 (git+https://github.com/clap-rs/clap_derive)" = "<none>"

Expected Behavior Summary

I have two conflicting flags -d and -D. When the user passes -dD I expect the output to contain

error: The argument '-d' cannot be used with '-D'

Actual Behavior Summary

The output instead contains

error: The argument '-d' cannot be used with '-d'

Same happens if the flags have a long name as well.

Steps to Reproduce the issue

cargo new --bin debugcli

Set up Cargo.toml as follows:

[package]
name = "debugcli"
version = "0.1.0"
authors = ["Eric Mink <eric@mink.li>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
clap = { git = "https://github.com/clap-rs/clap.git", rev = "1c3958c", features = ["color", "suggestions", "derive"] }

[workspace]

Set up src/main.rs as follows:

extern crate clap;
use clap::*;

#[derive(Clap)]
struct Opts {
    /// Print debug info
    #[clap(short = "d", conflicts_with = "not_debug")]
    debug: bool,
    /// Explicitly disable debug printing
    #[clap(short = "D")]
    not_debug: bool,

}

fn main() {
    let t: Opts = Opts::parse();

    // You can handle information about subcommands by requesting their matches by name
    // (as below), requesting just the name used, or both at the same time
            if t.debug { println!("testing with debug output on."); }
            if t.not_debug { println!("testing with debug output off."); }
            if t.debug && t.not_debug { println!("WTF!"); }
            if !t.debug && !t.not_debug { println!("Defaulting to testing with debug output off"); }
    }

Run it with various combinations:

$ cargo run -- -h
    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target\debug\debugcli.exe -h`
debugcli 0.1.0
Eric Mink <eric@mink.li>

USAGE:
    debugcli.exe [FLAGS]

FLAGS:
    -d               Print debug info
    -h, --help       Prints help information
    -D               Explicitly disable debug printing
    -V, --version    Prints version information

$ cargo run --
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `target\debug\debugcli.exe`
Defaulting to testing with debug output off
$ cargo run -- -D
    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target\debug\debugcli.exe -D`
testing with debug output off.
$ cargo run -- -d
    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target\debug\debugcli.exe -d`
testing with debug output on.
$ cargo run -- -dD
    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target\debug\debugcli.exe -dD`
error: The argument '-d' cannot be used with '-d'

USAGE:
    debugcli.exe [FLAGS]

For more information try --help
error: process didn't exit successfully: `target\debug\debugcli.exe -dD` (exit code: 1)
$ cargo run -- -Dd
    Finished dev [unoptimized + debuginfo] target(s) in 0.06s
     Running `target\debug\debugcli.exe -Dd`
error: The argument '-D' cannot be used with '-D'

USAGE:
    debugcli.exe [FLAGS]

For more information try --help
error: process didn't exit successfully: `target\debug\debugcli.exe -Dd` (exit code: 1)

It is worth noting that in above pasted output, it is once The argument '-D' cannot be used with '-D' and once The argument '-d' cannot be used with '-d'. But when you use the program exactly as I above, it will always be The argument '-d' cannot be used with '-d'.
The program that produced the above output had one difference to the program I pasted here: It had a conflicts_with = "debug" annotation for the D flag.

Debug output

Debug Output

$ cargo run -- -dD

Compiling clap v3.0.0-beta.1 (https://github.com/clap-rs/clap.git?rev=1c3958c#1c3958c5)

Compiling debugcli v0.1.0 (C:\Users\eric\Documents\projects\cevi-versand\debugcli)

Finished dev [unoptimized + debuginfo] target(s) in 14.49s

Running target\debug\debugcli.exe -dD

DEBUG:clap:App::_do_parse;

DEBUG:clap:App::_build;

DEBUG:clap:App::_derive_display_order:debugcli

DEBUG:clap:App::_create_help_and_version;

DEBUG:clap:App::_create_help_and_version: Building --help

DEBUG:clap:App::_create_help_and_version: Building --version

DEBUG:clap:App::_arg_debug_asserts:debug

DEBUG:clap:App::_arg_debug_asserts:not_debug

DEBUG:clap:App::_arg_debug_asserts:help

DEBUG:clap:App::_arg_debug_asserts:version

DEBUG:clap:App::_app_debug_asserts;

DEBUG:clap:Parser::get_matches_with;

DEBUG:clap:Parser::_build;

DEBUG:clap:Parser::_verify_positionals;

DEBUG:clap:Parser::get_matches_with: Begin parsing '"-dD"' ([45, 100, 68])

DEBUG:clap:Parser::is_new_arg:"-dD":NotFound

DEBUG:clap:Parser::is_new_arg: arg_allows_tac=false

DEBUG:clap:Parser::is_new_arg: - found

DEBUG:clap:Parser::is_new_arg: starts_new_arg=true

DEBUG:clap:Parser::possible_subcommand: arg="-dD"

DEBUG:clap:Parser::get_matches_with: possible_sc=false, sc=None

DEBUG:clap:Parser::parse_short_arg: full_arg="-dD"

DEBUG:clap:Parser::parse_short_arg:iter:d

DEBUG:clap:Parser::parse_short_arg:iter:d: Found valid opt or flag

DEBUG:clap:Parser::check_for_help_and_version_char;

DEBUG:clap:Parser::check_for_help_and_version_char: Checking if -d is help or version...Neither

DEBUG:clap:Parser::parse_flag;

DEBUG:clap:ArgMatcher::inc_occurrence_of: arg=353070537278882053

DEBUG:clap:ArgMatcher::inc_occurrence_of: first instance

DEBUG:clap:Parser::groups_for_arg: name=353070537278882053

DEBUG:clap:Parser::parse_short_arg:iter:D

DEBUG:clap:Parser::parse_short_arg:iter:D: Found valid opt or flag

DEBUG:clap:Parser::check_for_help_and_version_char;

DEBUG:clap:Parser::check_for_help_and_version_char: Checking if -D is help or version...Neither

DEBUG:clap:Parser::parse_flag;

DEBUG:clap:ArgMatcher::inc_occurrence_of: arg=15241144975642668291

DEBUG:clap:ArgMatcher::inc_occurrence_of: first instance

DEBUG:clap:Parser::groups_for_arg: name=15241144975642668291

DEBUG:clap:Parser:get_matches_with: After parse_short_arg Flag

DEBUG:clap:Parser::remove_overrides;

DEBUG:clap:Parser::remove_overrides:iter:353070537278882053;

DEBUG:clap:Parser::remove_overrides:iter:15241144975642668291;

DEBUG:clap:Validator::validate;

DEBUG:clap:Parser::add_defaults;

DEBUG:clap:Validator::validate_conflicts;

DEBUG:clap:Validator::gather_conflicts;

DEBUG:clap:Validator::gather_conflicts:iter:353070537278882053;

DEBUG:clap:Parser::groups_for_arg: name=353070537278882053

DEBUG:clap:Validator::gather_conflicts:iter:15241144975642668291;

DEBUG:clap:Parser::groups_for_arg: name=15241144975642668291

DEBUG:clap:Validator::validate_conflicts:iter:15241144975642668291;

DEBUG:clap:Validator::validate_conflicts:iter:15241144975642668291: matcher contains it...

DEBUG:clap:build_err!: name=15241144975642668291

DEBUG:clap:usage::create_usage_with_title;

DEBUG:clap:usage::create_usage_no_title;

DEBUG:clap:Usage::create_help_usage; incl_reqs=true

DEBUG:clap:Usage::get_required_usage_from: incls=[], matcher=false, incl_last=false

DEBUG:clap:Usage::get_required_usage_from: ret_val=[]

DEBUG:clap:usage::needs_flags_tag;

DEBUG:clap:usage::needs_flags_tag:iter: f=debug;

DEBUG:clap:Parser::groups_for_arg: name=353070537278882053

DEBUG:clap:usage::needs_flags_tag:iter: [FLAGS] required

DEBUG:clap:usage::create_help_usage: usage=debugcli.exe [FLAGS]

DEBUG:clap:App::color;

DEBUG:clap:App::color: Color setting...Auto

DEBUG:clap:is_a_tty: stderr=true

DEBUG:clap:Colorizer::warning;

DEBUG:clap:Colorizer::warning;

DEBUG:clap:Colorizer::error;

DEBUG:clap:Colorizer::good;

error: The argument '-d' cannot be used with '-d'
USAGE:

debugcli.exe [FLAGS]
For more information try --help

error: process didn't exit successfully: target\debug\debugcli.exe -dD (exit code: 1)

Please excuse if this has been already mentioned, I did not find any open issue for it.

[sphinxc0re]

I believe these are the affected lines (180 is the culprit):

clap/src/parse/validator.rs

Lines 177 to 184 in e4a7f50

	if v.contains(&name) {
	return Err(Error::argument_conflict(
	a,
	Some(a.to_string()),
	&*usg,
	self.p.app.color(),
	));
	}

[pksunkara]

Will you be sending a PR? I can fix this tonight if not.