Enum Error 

pub enum Error {
    CommandNotFound {
        command: String,
        suggestions: Vec<String>,
    },
    SubcommandRequired(String),
    NoRunFunction(String),
    FlagParsing {
        message: String,
        flag: Option<String>,
        suggestions: Vec<String>,
    },
    ArgumentParsing(String),
    ArgumentValidation {
        message: String,
        expected: String,
        received: usize,
    },
    Validation(String),
    Completion(String),
    Io(Error),
    Custom(Box<dyn Error + Send + Sync>),
}

The main error type for the flag framework

This enum represents all possible errors that can occur during command parsing, validation, and execution.

Variants

CommandNotFound

The specified command was not found

This error occurs when a user tries to run a subcommand that doesn’t exist.

Fields

command: String

The name of the unknown command

suggestions: Vec<String>

Suggested similar commands

SubcommandRequired(String)

A command requires a subcommand but none was provided

This error occurs when a parent command has no run function and the user doesn’t specify which subcommand to run. Contains the parent command name.

NoRunFunction(String)

A command has no run function defined

This error occurs when trying to execute a command that has no run handler. Contains the command name.

FlagParsing

An error occurred while parsing flag values

This error occurs when a flag value cannot be parsed as the expected type (e.g., “abc” for an integer flag).

Fields

message: String

Description of the error

flag: Option<String>

The flag that caused the error

suggestions: Vec<String>

Suggested valid values or format

ArgumentParsing(String)

An error occurred while parsing command arguments

This error occurs when command arguments don’t meet requirements. Contains a description of the error.

ArgumentValidation

Argument validation failed

This error occurs when arguments don’t meet validation constraints.

Fields

message: String

Description of the validation failure

expected: String

Expected argument pattern

received: usize

Number of arguments received

Validation(String)

A validation error occurred

This error occurs when custom validation logic fails. Contains a description of the validation failure.

Completion(String)

An error occurred during shell completion

This error occurs when completion functions fail. Contains a description of the error.

Io(Error)

An I/O error occurred

Wraps standard I/O errors that may occur during command execution.

Custom(Box<dyn Error + Send + Sync>)

A custom error from user code

Allows command handlers to return their own error types.

Implementations

impl Error

pub fn flag_parsing(message: impl Into<String>) -> Self

Create a simple flag parsing error

pub fn flag_parsing_with_suggestions( message: impl Into<String>, flag: impl Into<String>, suggestions: Vec<String>, ) -> Self

Create a flag parsing error with suggestions

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 Error + 'static)>

Returns the lower-level source of this error, if any.

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

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.

impl From<Error> for Error

fn from(err: Error) -> Self

Converts to this type from the input type.