Struct clap::error::Error

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pub struct Error<F: ErrorFormatter = DefaultFormatter> { /* private fields */ }

Expand description

Command Line Argument Parser Error

See Command::error to create an error.

Implementations§

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impl<F: ErrorFormatter> Error<F>

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pub fn raw(kind: ErrorKind, message: impl Display) -> Self

Create an unformatted error

This is for you need to pass the error up to a place that has access to the Command at which point you can call Error::format.

Prefer Command::error for generating errors.

Examples found in repository ?

examples/derive_ref/hand_subcommand.rs (lines 26-29)

    fn from_arg_matches(matches: &ArgMatches) -> Result<Self, Error> {
        match matches.subcommand() {
            Some(("add", args)) => Ok(Self::Add(AddArgs::from_arg_matches(args)?)),
            Some(("remove", args)) => Ok(Self::Remove(RemoveArgs::from_arg_matches(args)?)),
            Some((_, _)) => Err(Error::raw(
                ErrorKind::InvalidSubcommand,
                "Valid subcommands are `add` and `remove`",
            )),
            None => Err(Error::raw(
                ErrorKind::MissingSubcommand,
                "Valid subcommands are `add` and `remove`",
            )),
        }
    }
    fn update_from_arg_matches(&mut self, matches: &ArgMatches) -> Result<(), Error> {
        match matches.subcommand() {
            Some(("add", args)) => *self = Self::Add(AddArgs::from_arg_matches(args)?),
            Some(("remove", args)) => *self = Self::Remove(RemoveArgs::from_arg_matches(args)?),
            Some((_, _)) => {
                return Err(Error::raw(
                    ErrorKind::InvalidSubcommand,
                    "Valid subcommands are `add` and `remove`",
                ))
            }
            None => (),
        };
        Ok(())
    }

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pub fn format(self, cmd: &mut Command) -> Self

Format the existing message with the Command’s context

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pub fn new(kind: ErrorKind) -> Self

Create an error with a pre-defined message

Example


let cmd = clap::Command::new("prog");

let mut err = clap::Error::new(ErrorKind::ValueValidation)
   .with_cmd(&cmd);
err.insert(ContextKind::InvalidArg, ContextValue::String("--foo".to_owned()));
err.insert(ContextKind::InvalidValue, ContextValue::String("bar".to_owned()));

err.print();

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pub fn with_cmd(self, cmd: &Command) -> Self

Apply Command’s formatting to the error

Generally, this is used with Error::new

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pub fn apply<EF: ErrorFormatter>(self) -> Error<EF>

Apply an alternative formatter to the error

Example

let cmd = Command::new("foo")
    .arg(Arg::new("input").required(true));
let matches = cmd
    .try_get_matches_from(["foo", "input.txt"])
    .map_err(|e| e.apply::<KindFormatter>())
    .unwrap_or_else(|e| e.exit());

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pub fn kind(&self) -> ErrorKind

Type of error for programmatic processing

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pub fn context(&self) -> impl Iterator<Item = (ContextKind, &ContextValue)>

Additional information to further qualify the error

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pub fn get(&self, kind: ContextKind) -> Option<&ContextValue>

Lookup a piece of context

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pub fn insert(
 &mut self,
 kind: ContextKind,
 value: ContextValue
) -> Option<ContextValue>

Insert a piece of context

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pub fn use_stderr(&self) -> bool

Should the message be written to stdout or not?

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pub fn exit(&self) -> !

Prints the error and exits.

Depending on the error kind, this either prints to stderr and exits with a status of 2 or prints to stdout and exits with a status of 0.

Examples found in repository ?

examples/derive_ref/augment_subcommands.rs (line 18)

fn main() {
    let cli = Command::new("Built CLI");
    // Augment with derived subcommands
    let cli = Subcommands::augment_subcommands(cli);

    let matches = cli.get_matches();
    let derived_subcommands = Subcommands::from_arg_matches(&matches)
        .map_err(|err| err.exit())
        .unwrap();
    println!("Derived subcommands: {:#?}", derived_subcommands);
}

More examples

Hide additional examples

examples/derive_ref/augment_args.rs (line 24)

fn main() {
    let cli = Command::new("CLI").arg(arg!(-b - -built).action(clap::ArgAction::SetTrue));
    // Augment built args with derived args
    let cli = DerivedArgs::augment_args(cli);

    let matches = cli.get_matches();
    println!("Value of built: {:?}", matches.get_flag("built"));
    println!(
        "Value of derived via ArgMatches: {:?}",
        matches.get_flag("derived")
    );

    // Since DerivedArgs implements FromArgMatches, we can extract it from the unstructured ArgMatches.
    // This is the main benefit of using derived arguments.
    let derived_matches = DerivedArgs::from_arg_matches(&matches)
        .map_err(|err| err.exit())
        .unwrap();
    println!("Value of derived: {:#?}", derived_matches);
}

examples/tutorial_derive/04_04_custom.rs (line 50)

fn main() {
    let cli = Cli::parse();

    // Let's assume the old version 1.2.3
    let mut major = 1;
    let mut minor = 2;
    let mut patch = 3;

    // See if --set-ver was used to set the version manually
    let version = if let Some(ver) = cli.set_ver.as_deref() {
        if cli.major || cli.minor || cli.patch {
            let mut cmd = Cli::command();
            cmd.error(
                ErrorKind::ArgumentConflict,
                "Can't do relative and absolute version change",
            )
            .exit();
        }
        ver.to_string()
    } else {
        // Increment the one requested (in a real program, we'd reset the lower numbers)
        let (maj, min, pat) = (cli.major, cli.minor, cli.patch);
        match (maj, min, pat) {
            (true, false, false) => major += 1,
            (false, true, false) => minor += 1,
            (false, false, true) => patch += 1,
            _ => {
                let mut cmd = Cli::command();
                cmd.error(
                    ErrorKind::ArgumentConflict,
                    "Can only modify one version field",
                )
                .exit();
            }
        };
        format!("{}.{}.{}", major, minor, patch)
    };

    println!("Version: {}", version);

    // Check for usage of -c
    if let Some(config) = cli.config.as_deref() {
        let input = cli
            .input_file
            .as_deref()
            // 'or' is preferred to 'or_else' here since `Option::as_deref` is 'const'
            .or(cli.spec_in.as_deref())
            .unwrap_or_else(|| {
                let mut cmd = Cli::command();
                cmd.error(
                    ErrorKind::MissingRequiredArgument,
                    "INPUT_FILE or --spec-in is required when using --config",
                )
                .exit()
            });
        println!("Doing work using input {} and config {}", input, config);
    }
}

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pub fn print(&self) -> Result<()>

Prints formatted and colored error to stdout or stderr according to its error kind

Example

use clap::Command;

match Command::new("Command").try_get_matches() {
    Ok(matches) => {
        // do_something
    },
    Err(err) => {
        err.print().expect("Error writing Error");
        // do_something
    },
};

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pub fn render(&self) -> StyledStr

Render the error message to a StyledStr.

Example

use clap::Command;

match Command::new("Command").try_get_matches() {
    Ok(matches) => {
        // do_something
    },
    Err(err) => {
        let err = err.render();
        println!("{}", err);
        // do_something
    },
};