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## Error

# Struct Error

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    pub struct Error<F = RichFormatter>where
        F: ErrorFormatter,{ /* private fields */ }

Expand description

Command Line Argument Parser Error

See `Command::error` to create an error.

## Implementations§

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### impl<F> Error<F>
where F: ErrorFormatter,

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#### pub fn raw(kind: ErrorKind, message: impl Display) -> Error<F>

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 27-30)

    23    fn from_arg_matches(matches: &ArgMatches) -> Result<Self, Error> {
    24        match matches.subcommand() {
    25            Some(("add", args)) => Ok(Self::Add(AddArgs::from_arg_matches(args)?)),
    26            Some(("remove", args)) => Ok(Self::Remove(RemoveArgs::from_arg_matches(args)?)),
    27            Some((_, _)) => Err(Error::raw(
    28                ErrorKind::InvalidSubcommand,
    29                "Valid subcommands are `add` and `remove`",
    30            )),
    31            None => Err(Error::raw(
    32                ErrorKind::MissingSubcommand,
    33                "Valid subcommands are `add` and `remove`",
    34            )),
    35        }
    36    }
    37    fn update_from_arg_matches(&mut self, matches: &ArgMatches) -> Result<(), Error> {
    38        match matches.subcommand() {
    39            Some(("add", args)) => *self = Self::Add(AddArgs::from_arg_matches(args)?),
    40            Some(("remove", args)) => *self = Self::Remove(RemoveArgs::from_arg_matches(args)?),
    41            Some((_, _)) => {
    42                return Err(Error::raw(
    43                    ErrorKind::InvalidSubcommand,
    44                    "Valid subcommands are `add` and `remove`",
    45                ));
    46            }
    47            None => (),
    48        };
    49        Ok(())
    50    }

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#### pub fn format(self, cmd: &mut Command) -> Error<F>

Format the existing message with the Command’s context

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#### pub fn new(kind: ErrorKind) -> Error<F>

Create an error with a pre-defined message

See also

- `Error::insert`
- `Error::with_cmd`

##### §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) -> Error<F>

Apply `Command`’s formatting to the error

Generally, this is used with `Error::new`

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

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)>

Available on crate feature `error-context` only.

Additional information to further qualify the error

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

Available on crate feature `error-context` only.

Lookup a piece of context

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

Available on crate feature `error-context` only.

Insert a piece of context

If this `ContextKind` is already present, its value is replaced and the old value is returned.

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

Available on crate feature `error-context` only.

Remove a piece of context, return the old value if any

The context is currently implemented in a vector, so `remove` takes linear time.

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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_code(&self) -> i32

Returns the exit code that `.exit` will exit the process with.

When the error’s kind would print to `stderr` this returns `2`, else it returns `0`.

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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)

    11fn main() {
    12    let cli = Command::new("Built CLI");
    13    // Augment with derived subcommands
    14    let cli = Subcommands::augment_subcommands(cli);
    15
    16    let matches = cli.get_matches();
    17    let derived_subcommands = Subcommands::from_arg_matches(&matches)
    18        .map_err(|err| err.exit())
    19        .unwrap();
    20    println!("Derived subcommands: {derived_subcommands:#?}");
    21}

More examples
Hide additional examples
examples/derive_ref/augment_args.rs (line 24)

    9fn main() {
    10    let cli = Command::new("CLI").arg(arg!(-b - -built).action(clap::ArgAction::SetTrue));
    11    // Augment built args with derived args
    12    let cli = DerivedArgs::augment_args(cli);
    13
    14    let matches = cli.get_matches();
    15    println!("Value of built: {:?}", matches.get_flag("built"));
    16    println!(
    17        "Value of derived via ArgMatches: {:?}",
    18        matches.get_flag("derived")
    19    );
    20
    21    // Since DerivedArgs implements FromArgMatches, we can extract it from the unstructured ArgMatches.
    22    // This is the main benefit of using derived arguments.
    23    let derived_matches = DerivedArgs::from_arg_matches(&matches)
    24        .map_err(|err| err.exit())
    25        .unwrap();
    26    println!("Value of derived: {derived_matches:#?}");
    27}

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

    34fn main() {
    35    let cli = Cli::parse();
    36
    37    // Let's assume the old version 1.2.3
    38    let mut major = 1;
    39    let mut minor = 2;
    40    let mut patch = 3;
    41
    42    // See if --set-ver was used to set the version manually
    43    let version = if let Some(ver) = cli.set_ver.as_deref() {
    44        if cli.major || cli.minor || cli.patch {
    45            let mut cmd = Cli::command();
    46            cmd.error(
    47                ErrorKind::ArgumentConflict,
    48                "Can't do relative and absolute version change",
    49            )
    50            .exit();
    51        }
    52        ver.to_owned()
    53    } else {
    54        // Increment the one requested (in a real program, we'd reset the lower numbers)
    55        let (maj, min, pat) = (cli.major, cli.minor, cli.patch);
    56        match (maj, min, pat) {
    57            (true, false, false) => major += 1,
    58            (false, true, false) => minor += 1,
    59            (false, false, true) => patch += 1,
    60            _ => {
    61                let mut cmd = Cli::command();
    62                cmd.error(
    63                    ErrorKind::ArgumentConflict,
    64                    "Can only modify one version field",
    65                )
    66                .exit();
    67            }
    68        };
    69        format!("{major}.{minor}.{patch}")
    70    };
    71
    72    println!("Version: {version}");
    73
    74    // Check for usage of -c
    75    if let Some(config) = cli.config.as_deref() {
    76        let input = cli
    77            .input_file
    78            .as_deref()
    79            // 'or' is preferred to 'or_else' here since `Option::as_deref` is 'const'
    80            .or(cli.spec_in.as_deref())
    81            .unwrap_or_else(|| {
    82                let mut cmd = Cli::command();
    83                cmd.error(
    84                    ErrorKind::MissingRequiredArgument,
    85                    "INPUT_FILE or --spec-in is required when using --config",
    86                )
    87                .exit()
    88            });
    89        println!("Doing work using input {input} and config {config}");
    90    }
    91}

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#### pub fn print(&self) -> Result<(), Error>

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
        },
    };

## Trait Implementations§

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### impl<F> Debug for Error<F>
where F: ErrorFormatter,

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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### impl<F> Display for Error<F>
where F: ErrorFormatter,

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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### impl<F> Error for Error<F>
where F: ErrorFormatter,

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#### fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any. Read more
1.0.0 · Source§

#### fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

Read more
1.0.0 · Source§

#### fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

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#### fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (`error_generic_member_access`)
Provides type-based access to context intended for error reports. Read more
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### impl<F> From<Error> for Error<F>
where F: ErrorFormatter,

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#### fn from(e: Error) -> Error<F>

Converts to this type from the input type.
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### impl<F> From<Error> for Error<F>
where F: ErrorFormatter,

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#### fn from(e: Error) -> Error<F>

Converts to this type from the input type.

## Auto Trait Implementations§

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### impl<F = RichFormatter> !RefUnwindSafe for Error<F>

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### impl<F = RichFormatter> !UnwindSafe for Error<F>

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### impl<F> Freeze for Error<F>

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### impl<F> Send for Error<F>
where F: Send,

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### impl<F> Sync for Error<F>
where F: Sync,

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### impl<F> Unpin for Error<F>
where F: Unpin,

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### impl<F> UnsafeUnpin for Error<F>

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToString for T
where T: Display + ?Sized,

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#### fn to_string(&self) -> String

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.