Enum docopt::Error

pub enum Error {
    Usage(String),
    Argv(String),
    NoMatch,
    Deserialize(String),
    WithProgramUsage(Box<Error>, String),
    Help,
    Version(String),
}

Represents the different types of Docopt errors.

This error type has a lot of variants. In the common case, you probably don’t care why Docopt has failed, and would rather just quit the program and show an error message instead. The exit method defined on the Error type will do just that. It will also set the exit code appropriately (no error for --help or --version, but an error code for bad usage, bad argv, no match or bad decode).

Example

Generally, you want to parse the usage string, try to match the argv and then quit the program if there was an error reported at any point in that process. This can be achieved like so:

use docopt::Docopt;

const USAGE: &'static str = "
Usage: ...
";

let args = Docopt::new(USAGE)
                  .and_then(|d| d.parse())
                  .unwrap_or_else(|e| e.exit());

Variants

Usage(String)

Parsing the usage string failed.

This error can only be triggered by the programmer, i.e., the writer of the Docopt usage string. This error is usually indicative of a bug in your program.

Argv(String)

Parsing the argv specified failed.

The payload is a string describing why the arguments provided could not be parsed.

This is distinct from NoMatch because it will catch errors like using flags that aren’t defined in the usage string.

NoMatch

The given argv parsed successfully, but it did not match any example usage of the program.

Regrettably, there is no descriptive message describing why the given argv didn’t match any of the usage strings.

Deserialize(String)

This indicates a problem deserializing a successful argv match into a deserializable value.

WithProgramUsage(Box<Error>, String)

Parsing failed, and the program usage should be printed next to the failure message. Typically this wraps Argv and NoMatch errors.

Help

Decoding or parsing failed because the command line specified that the help message should be printed.

Version(String)

Decoding or parsing failed because the command line specified that the version should be printed

The version is included as a payload to this variant.

Implementations

impl Error

pub fn fatal(&self) -> bool

Return whether this was a fatal error or not.

Non-fatal errors include requests to print the help or version information of a program, while fatal errors include those such as failing to decode or parse.

pub fn exit(&self) -> !

Print this error and immediately exit the program.

If the error is non-fatal (e.g., Help or Version), then the error is printed to stdout and the exit status will be 0. Otherwise, when the error is fatal, the error is printed to stderr and the exit status will be 1.

Trait Implementations

impl Debug for Error

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

Formats the value using the given formatter.

impl Display for Error

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

Formats the value using the given formatter.

impl Error for Error

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

The lower-level source of this error, if any.

fn backtrace(&self) -> Option<&Backtrace>

🔬 This is a nightly-only experimental API. (backtrace)

Returns a stack backtrace, if available, of where this error occurred.

fn description(&self) -> &str

👎 Deprecated since 1.42.0:

use the Display impl or to_string()

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

👎 Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

impl Error for Error

fn custom<T: Display>(msg: T) -> Self

Raised when there is general error when deserializing a type.

fn invalid_type(unexp: Unexpected<'_>, exp: &dyn Expected) -> Self

Raised when a Deserialize receives a type different from what it was expecting.

fn invalid_value(unexp: Unexpected<'_>, exp: &dyn Expected) -> Self

Raised when a Deserialize receives a value of the right type but that is wrong for some other reason.

fn invalid_length(len: usize, exp: &dyn Expected) -> Self

Raised when deserializing a sequence or map and the input data contains too many or too few elements.

fn unknown_variant(variant: &str, expected: &'static [&'static str]) -> Self

Raised when a Deserialize enum type received a variant with an unrecognized name.

fn unknown_field(field: &str, expected: &'static [&'static str]) -> Self

Raised when a Deserialize struct type received a field with an unrecognized name.

fn missing_field(field: &'static str) -> Self

Raised when a Deserialize struct type expected to receive a required field with a particular name but that field was not present in the input.

fn duplicate_field(field: &'static str) -> Self

Raised when a Deserialize struct type received more than one of the same field.