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//! # Easy-error //! //! This crate is a lightweight error handling library meant to play well with //! the standard `Error` trait. It is designed for quick prototyping or for //! Command-line applications where any error will simply bubble up to the user. //! There are four major components of this crate: //! //! 1. A basic, string-based error type that is meant for either quick //! prototyping or human-facing errors. //! 2. A nice way to iterate over the causes of an error. //! 3. Some macros that make returning errors slightly more ergonomic. //! 4. A "termination" type that produces nicely formatted error messages when //! returned from the `main` function. //! //! ## Rust Version Requirements //! //! The current version requires **Rustc 1.32 or newer**. //! In general, this crate will be compilable with the Rustc version available //! on the oldest Ubuntu LTS release. Any change that requires a new Rustc //! version will be considered a breaking change and will be handled //! accordingly. //! //! ## Example //! //! ```no_run //! use std::{fs::File, io::Read}; //! use easy_error::{bail, ensure, Result, ResultExt, termination}; //! //! fn from_file() -> Result<i32> { //! let file_name = "example.txt"; //! let mut file = File::open(file_name).context("Could not open file")?; //! //! let mut contents = String::new(); //! file.read_to_string(&mut contents).context("Unable to read file")?; //! //! contents.trim().parse().context("Could not parse file") //! } //! //! fn validate(value: i32) -> Result<()> { //! ensure!(value > 0, "Value must be greater than zero (found {})", value); //! //! if value % 2 == 1 { //! bail!("Only even numbers can be used"); //! } //! //! Ok(()) //! } //! //! fn main() -> termination::Result { //! let value = from_file().context("Unable to get value from file")?; //! validate(value).context("Value is not acceptable")?; //! //! println!("Value = {}", value); //! Ok(()) //! } //! ``` // Just bunches of Clippy lints. #![deny(clippy::all)] #![warn(clippy::nursery)] #![warn(clippy::pedantic)] #![allow(clippy::use_self)] use std::{error::Error as StdError, fmt, result::Result as StdResult}; mod macros; pub mod termination; pub type Result<T> = StdResult<T, Error>; /// An error that is a human-targetted string plus an optional cause. #[derive(Debug)] pub struct Error { /// The human-targetting error string. pub ctx: String, /// The optional cause of the error. pub cause: Option<Box<dyn StdError + 'static>>, } impl Error { /// Create a new error with the given cause. pub fn new<S, E>(ctx: S, cause: E) -> Error where S: Into<String>, E: StdError + 'static, { let ctx = ctx.into(); let cause: Option<Box<dyn StdError + 'static>> = Some(Box::new(cause)); Error { ctx, cause } } /// Iterates over the causes of the error. pub fn iter_causes(&self) -> Causes { Causes { cause: self.cause.as_ref().map(Box::as_ref) } } } impl fmt::Display for Error { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{}", self.ctx) } } impl StdError for Error { fn description(&self) -> &str { &self.ctx } fn source(&self) -> Option<&(dyn StdError + 'static)> { self.cause.as_ref().map(Box::as_ref) } } /// An iterator over the causes of an error. pub struct Causes<'a> { /// The next cause to display. cause: Option<&'a (dyn StdError + 'static)>, } impl<'a> Iterator for Causes<'a> { type Item = &'a (dyn StdError + 'static); fn next(&mut self) -> Option<Self::Item> { let cause = self.cause.take(); self.cause = cause.and_then(StdError::source); cause } } /// Extention methods to the `Result` type. pub trait ResultExt<T> { /// Adds some context to the error. fn context<S: Into<String>>(self, ctx: S) -> Result<T>; } impl<T, E: StdError + 'static> ResultExt<T> for StdResult<T, E> { fn context<S: Into<String>>(self, ctx: S) -> Result<T> { self.map_err(|e| Error { ctx: ctx.into(), cause: Some(Box::new(e)) }) } } /// Creates an error message from the provided string. #[inline] pub fn err_msg<S: Into<String>>(ctx: S) -> Error { Error { ctx: ctx.into(), cause: None } } /// Returns an iterator over the causes of an error. #[inline] pub fn iter_causes<E: StdError + ?Sized>(e: &E) -> Causes { Causes { cause: e.source() } }