clap 4.0.0-rc.1

A simple to use, efficient, and full-featured Command Line Argument Parser
Documentation 
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/// Semantics for a piece of error information
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
#[non_exhaustive]
#[cfg(feature = "error-context")]
pub enum ContextKind {
    /// The cause of the error
    InvalidSubcommand,
    /// The cause of the error
    InvalidArg,
    /// Existing arguments
    PriorArg,
    /// Accepted values
    ValidValue,
    /// Rejected values
    InvalidValue,
    /// Number of values present
    ActualNumValues,
    /// Number of allowed values
    ExpectedNumValues,
    /// Minimum number of allowed values
    MinValues,
    /// Potential fix for the user
    SuggestedCommand,
    /// Potential fix for the user
    SuggestedSubcommand,
    /// Potential fix for the user
    SuggestedArg,
    /// Potential fix for the user
    SuggestedValue,
    /// Trailing argument
    TrailingArg,
    /// A usage string
    Usage,
    /// An opaque message to the user
    Custom,
}

impl ContextKind {
    /// End-user description of the error case, where relevant
    pub fn as_str(self) -> Option<&'static str> {
        match self {
            Self::InvalidSubcommand => Some("Invalid Subcommand"),
            Self::InvalidArg => Some("Invalid Argument"),
            Self::PriorArg => Some("Prior Argument"),
            Self::ValidValue => Some("Value Value"),
            Self::InvalidValue => Some("Invalid Value"),
            Self::ActualNumValues => Some("Actual Number of Values"),
            Self::ExpectedNumValues => Some("Expected Number of Values"),
            Self::MinValues => Some("Minimum Number of Values"),
            Self::SuggestedCommand => Some("Suggested Command"),
            Self::SuggestedSubcommand => Some("Suggested Subcommand"),
            Self::SuggestedArg => Some("Suggested Argument"),
            Self::SuggestedValue => Some("Suggested Value"),
            Self::TrailingArg => Some("Trailing Argument"),
            Self::Usage => None,
            Self::Custom => None,
        }
    }
}

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

/// A piece of error information
#[derive(Clone, Debug, PartialEq, Eq)]
#[non_exhaustive]
#[cfg(feature = "error-context")]
pub enum ContextValue {
    /// [`ContextKind`] is self-sufficient, no additional information needed
    None,
    /// A single value
    Bool(bool),
    /// A single value
    String(String),
    /// Many values
    Strings(Vec<String>),
    /// A single value
    StyledStr(crate::builder::StyledStr),
    /// A single value
    Number(isize),
}

impl std::fmt::Display for ContextValue {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::None => "".fmt(f),
            Self::Bool(v) => v.fmt(f),
            Self::String(v) => v.fmt(f),
            Self::Strings(v) => v.join(", ").fmt(f),
            Self::StyledStr(v) => v.fmt(f),
            Self::Number(v) => v.fmt(f),
        }
    }
}