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    /// Command line argument parser kind of error
    #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
    #[non_exhaustive]
    pub enum ErrorKind {
        /// Occurs when an [`Arg`][crate::Arg] has a set of possible values,
        /// and the user provides a value which isn't in that set.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("speed")
        ///         .value_parser(["fast", "slow"]))
        ///     .try_get_matches_from(vec!["prog", "other"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::InvalidValue);
        /// ```
        InvalidValue,

        /// Occurs when a user provides a flag, option, argument or subcommand which isn't defined.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .arg(arg!(--flag "some flag"))
        ///     .try_get_matches_from(vec!["prog", "--other"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::UnknownArgument);
        /// ```
        UnknownArgument,

        /// Occurs when the user provides an unrecognized [`Subcommand`] which meets the threshold for
        /// being similar enough to an existing subcommand.
        /// If it doesn't meet the threshold, or the 'suggestions' feature is disabled,
        /// the more general [`UnknownArgument`] error is returned.
        ///
        /// # Examples
        ///
        #[cfg_attr(not(feature = "suggestions"), doc = " ```no_run")]
        #[cfg_attr(feature = "suggestions", doc = " ```")]
        /// # use clap::{Command, Arg, error::ErrorKind, };
        /// let result = Command::new("prog")
        ///     .subcommand(Command::new("config")
        ///         .about("Used for configuration")
        ///         .arg(Arg::new("config_file")
        ///             .help("The configuration file to use")))
        ///     .try_get_matches_from(vec!["prog", "confi"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::InvalidSubcommand);
        /// ```
        ///
        /// [`Subcommand`]: crate::Subcommand
        /// [`UnknownArgument`]: ErrorKind::UnknownArgument
        InvalidSubcommand,

        /// Occurs when the user doesn't use equals for an option that requires equal
        /// sign to provide values.
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind, ArgAction};
        /// let res = Command::new("prog")
        ///     .arg(Arg::new("color")
        ///          .action(ArgAction::Set)
        ///          .require_equals(true)
        ///          .long("color"))
        ///     .try_get_matches_from(vec!["prog", "--color", "red"]);
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind(), ErrorKind::NoEquals);
        /// ```
        NoEquals,

        /// Occurs when the user provides a value for an argument with a custom validation and the
        /// value fails that validation.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind, value_parser};
        /// fn is_numeric(val: &str) -> Result<(), String> {
        ///     match val.parse::<i64>() {
        ///         Ok(..) => Ok(()),
        ///         Err(..) => Err(String::from("Value wasn't a number!")),
        ///     }
        /// }
        ///
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("num")
        ///          .value_parser(value_parser!(u8)))
        ///     .try_get_matches_from(vec!["prog", "NotANumber"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::ValueValidation);
        /// ```
        ValueValidation,

        /// Occurs when a user provides more values for an argument than were defined by setting
        /// [`Arg::num_args`].
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("arg")
        ///         .num_args(1..=2))
        ///     .try_get_matches_from(vec!["prog", "too", "many", "values"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::TooManyValues);
        /// ```
        /// [`Arg::num_args`]: crate::Arg::num_args()
        TooManyValues,

        /// Occurs when the user provides fewer values for an argument than were defined by setting
        /// [`Arg::num_args`].
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("some_opt")
        ///         .long("opt")
        ///         .num_args(3..))
        ///     .try_get_matches_from(vec!["prog", "--opt", "too", "few"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::TooFewValues);
        /// ```
        /// [`Arg::num_args`]: crate::Arg::num_args()
        TooFewValues,

        /// Occurs when the user provides a different number of values for an argument than what's
        /// been defined by setting [`Arg::num_args`] or than was implicitly set by
        /// [`Arg::value_names`].
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind, ArgAction};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("some_opt")
        ///         .long("opt")
        ///         .action(ArgAction::Set)
        ///         .num_args(2))
        ///     .try_get_matches_from(vec!["prog", "--opt", "wrong"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::WrongNumberOfValues);
        /// ```
        ///
        /// [`Arg::num_args`]: crate::Arg::num_args()
        /// [`Arg::value_names`]: crate::Arg::value_names()
        WrongNumberOfValues,

        /// Occurs when the user provides two values which conflict with each other and can't be used
        /// together.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind, ArgAction};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("debug")
        ///         .long("debug")
        ///         .action(ArgAction::SetTrue)
        ///         .conflicts_with("color"))
        ///     .arg(Arg::new("color")
        ///         .long("color")
        ///         .action(ArgAction::SetTrue))
        ///     .try_get_matches_from(vec!["prog", "--debug", "--color"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::ArgumentConflict);
        /// ```
        ArgumentConflict,

        /// Occurs when the user does not provide one or more required arguments.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("debug")
        ///         .required(true))
        ///     .try_get_matches_from(vec!["prog"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);
        /// ```
        MissingRequiredArgument,

        /// Occurs when a subcommand is required (as defined by [`Command::subcommand_required`]),
        /// but the user does not provide one.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, error::ErrorKind};
        /// let err = Command::new("prog")
        ///     .subcommand_required(true)
        ///     .subcommand(Command::new("test"))
        ///     .try_get_matches_from(vec![
        ///         "myprog",
        ///     ]);
        /// assert!(err.is_err());
        /// assert_eq!(err.unwrap_err().kind(), ErrorKind::MissingSubcommand);
        /// # ;
        /// ```
        ///
        /// [`Command::subcommand_required`]: crate::Command::subcommand_required
        MissingSubcommand,

        /// Occurs when the user provides a value containing invalid UTF-8.
        ///
        /// To allow arbitrary data
        /// - Set [`Arg::value_parser(value_parser!(OsString))`] for argument values
        /// - Set [`Command::external_subcommand_value_parser`] for external-subcommand
        ///   values
        ///
        /// # Platform Specific
        ///
        /// Non-Windows platforms only (such as Linux, Unix, OSX, etc.)
        ///
        /// # Examples
        ///
        #[cfg_attr(not(unix), doc = " ```ignore")]
        #[cfg_attr(unix, doc = " ```")]
        /// # use clap::{Command, Arg, error::ErrorKind, ArgAction};
        /// # use std::os::unix::ffi::OsStringExt;
        /// # use std::ffi::OsString;
        /// let result = Command::new("prog")
        ///     .arg(Arg::new("utf8")
        ///         .short('u')
        ///         .action(ArgAction::Set))
        ///     .try_get_matches_from(vec![OsString::from("myprog"),
        ///                                 OsString::from("-u"),
        ///                                 OsString::from_vec(vec![0xE9])]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::InvalidUtf8);
        /// ```
        ///
        /// [`Arg::allow_invalid_utf8`]: crate::Arg::allow_invalid_utf8
        /// [`Command::external_subcommand_value_parser`]: crate::Command::external_subcommand_value_parser
        InvalidUtf8,

        /// Not a true "error" as it means `--help` or similar was used.
        /// The help message will be sent to `stdout`.
        ///
        /// **Note**: If the help is displayed due to an error (such as missing subcommands) it will
        /// be sent to `stderr` instead of `stdout`.
        ///
        /// # Examples
        ///
        #[cfg_attr(not(feature = "help"), doc = " ```ignore")]
        #[cfg_attr(feature = "help", doc = " ```")]
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .try_get_matches_from(vec!["prog", "--help"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::DisplayHelp);
        /// ```
        DisplayHelp,

        /// Occurs when either an argument or a [`Subcommand`] is required, as defined by
        /// [`Command::arg_required_else_help`] , but the user did not provide
        /// one.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind, };
        /// let result = Command::new("prog")
        ///     .arg_required_else_help(true)
        ///     .subcommand(Command::new("config")
        ///         .about("Used for configuration")
        ///         .arg(Arg::new("config_file")
        ///             .help("The configuration file to use")))
        ///     .try_get_matches_from(vec!["prog"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::DisplayHelpOnMissingArgumentOrSubcommand);
        /// ```
        ///
        /// [`Subcommand`]: crate::Subcommand
        /// [`Command::arg_required_else_help`]: crate::Command::arg_required_else_help
        DisplayHelpOnMissingArgumentOrSubcommand,

        /// Not a true "error" as it means `--version` or similar was used.
        /// The message will be sent to `stdout`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{Command, Arg, error::ErrorKind};
        /// let result = Command::new("prog")
        ///     .version("3.0")
        ///     .try_get_matches_from(vec!["prog", "--version"]);
        /// assert!(result.is_err());
        /// assert_eq!(result.unwrap_err().kind(), ErrorKind::DisplayVersion);
        /// ```
        DisplayVersion,

        /// Represents an [I/O error].
        /// Can occur when writing to `stderr` or `stdout` or reading a configuration file.
        ///
        /// [I/O error]: std::io::Error
        Io,

        /// Represents a [Format error] (which is a part of [`Display`]).
        /// Typically caused by writing to `stderr` or `stdout`.
        ///
        /// [`Display`]: std::fmt::Display
        /// [Format error]: std::fmt::Error
        Format,
    }

    impl ErrorKind {
        /// End-user description of the error case, where relevant
        pub fn as_str(self) -> Option<&'static str> {
            match self {
                Self::InvalidValue => Some("One of the values isn't valid for an argument"),
                Self::UnknownArgument => {
                    Some("Found an argument which wasn't expected or isn't valid in this context")
                }
                Self::InvalidSubcommand => Some("A subcommand wasn't recognized"),
                Self::NoEquals => Some("Equal is needed when assigning values to one of the arguments"),
                Self::ValueValidation => Some("Invalid value for one of the arguments"),
                Self::TooManyValues => Some("An argument received an unexpected value"),
                Self::TooFewValues => Some("An argument requires more values"),
                Self::WrongNumberOfValues => Some("An argument received too many or too few values"),
                Self::ArgumentConflict => {
                    Some("An argument cannot be used with one or more of the other specified arguments")
                }
                Self::MissingRequiredArgument => {
                    Some("One or more required arguments were not provided")
                }
                Self::MissingSubcommand => Some("A subcommand is required but one was not provided"),
                Self::InvalidUtf8 => Some("Invalid UTF-8 was detected in one or more arguments"),
                Self::DisplayHelp => None,
                Self::DisplayHelpOnMissingArgumentOrSubcommand => None,
                Self::DisplayVersion => None,
                Self::Io => None,
                Self::Format => None,
            }
        }
    }

    impl std::fmt::Display for ErrorKind {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            self.as_str().unwrap_or_default().fmt(f)
        }
    }