error-rules

Archived

Project archived. I recommend to use anyhow + thiserror.

Intro

error-rules is a derive macro to implement error handler with a errors chaining. Macro automatically implements conversion of any error type into the inner enum field.

Error conversion

#[error_from] attribute implements an automatically conversion from any error type. Converted type should implements std::error::Error interface.

use error_rules::*;

#[derive(Debug, Error)]
enum AppError {
    #[error_from("App IO: {}", 0)]
    Io(std::io::Error),
}

type Result<T> = std::result::Result<T, AppError>;

fn example() -> Result<()> {
    let _file = std::fs::File::open("not-found.txt")?;
    unreachable!()
}

let error = example().unwrap_err();
assert_eq!(error.to_string().as_str(),
    "App IO: No such file or directory (os error 2)");

Custom error kind

#[error_kind] attribute describes custom error kind. Could be defined without fields or with fields tuple.

use error_rules::*;

#[derive(Debug, Error)]
enum AppError {
    #[error_kind("App: error without arguments")]
    E1,
    #[error_kind("App: code:{} message:{}", 0, 1)]
    E2(usize, String),
}

type Result<T> = std::result::Result<T, AppError>;

fn example_1() -> Result<()> {
    Err(AppError::E1)
}

fn example_2() -> Result<()> {
    Err(AppError::E2(404, "Not Found".to_owned()))
}

let error = example_1().unwrap_err();
assert_eq!(error.to_string().as_str(),
    "App: error without arguments");

let error = example_2().unwrap_err();
assert_eq!(error.to_string().as_str(),
    "App: code:404 message:Not Found");

Display attributes

#[error_from] and #[error_kind] contain list of attributes to display error. First attribute should be literal string. Other attributes is a number of the unnamed field in the tuple. Started from 0.

#[error_from] could defined without attributes it's equal to #[error_from("{}", 0)]

Error prefix

#[error_prefix] attribute should be defined before enum declaration and appends prefix into error text.

use error_rules::*;

#[derive(Debug, Error)]
#[error_prefx = "App"]
enum AppError {
    #[error_from]
    Io(std::io::Error),
}

type Result<T> = std::result::Result<T, AppError>;

fn example() -> Result<()> {
    let _file = std::fs::File::open("not-found.txt")?;
    unreachable!()
}

let error = example().unwrap_err();
assert_eq!(error.to_string().as_str(),
    "App: No such file or directory (os error 2)");

Error chain

By implementing error for nested modules the primary error handler returns full chain of the error.

use error_rules::*;

#[derive(Debug, Error)]
#[error_prefix = "Mod"]
enum ModError {
    #[error_from]
    Io(std::io::Error),
}

fn mod_example() -> Result<(), ModError> {
    let _file = std::fs::File::open("not-found.txt")?;
    unreachable!()
}

#[derive(Debug, Error)]
#[error_prefix = "App"]
enum AppError {
    #[error_from]
    Mod(ModError),
}

fn app_example() -> Result<(), AppError> {
    mod_example()?;
    unreachable!()
}

let error = app_example().unwrap_err();
assert_eq!(error.to_string().as_str(),
    "App: Mod: No such file or directory (os error 2)");