| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/thiserror-1.0.40/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../thiserror/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../thiserror/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="doccomment">//! [![github]](https://github.com/dtolnay/thiserror)&ensp;[![crates-io]](https://crates.io/crates/thiserror)&ensp;[![docs-rs]](https://docs.rs/thiserror) |
| //! |
| //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github |
| //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust |
| //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs |
| //! |
| //! <br> |
| //! |
| //! This library provides a convenient derive macro for the standard library's |
| //! [`std::error::Error`] trait. |
| //! |
| //! [`std::error::Error`]: https://doc.rust-lang.org/std/error/trait.Error.html |
| //! |
| //! <br> |
| //! |
| //! # Example |
| //! |
| //! ```rust |
| //! # use std::io; |
| //! use thiserror::Error; |
| //! |
| //! #[derive(Error, Debug)] |
| //! pub enum DataStoreError { |
| //! #[error("data store disconnected")] |
| //! Disconnect(#[from] io::Error), |
| //! #[error("the data for key `{0}` is not available")] |
| //! Redaction(String), |
| //! #[error("invalid header (expected {expected:?}, found {found:?})")] |
| //! InvalidHeader { |
| //! expected: String, |
| //! found: String, |
| //! }, |
| //! #[error("unknown data store error")] |
| //! Unknown, |
| //! } |
| //! ``` |
| //! |
| //! <br> |
| //! |
| //! # Details |
| //! |
| //! - Thiserror deliberately does not appear in your public API. You get the |
| //! same thing as if you had written an implementation of `std::error::Error` |
| //! by hand, and switching from handwritten impls to thiserror or vice versa |
| //! is not a breaking change. |
| //! |
| //! - Errors may be enums, structs with named fields, tuple structs, or unit |
| //! structs. |
| //! |
| //! - A `Display` impl is generated for your error if you provide |
| //! `#[error("...")]` messages on the struct or each variant of your enum, as |
| //! shown above in the example. |
| //! |
| //! The messages support a shorthand for interpolating fields from the error. |
| //! |
| //! - `#[error("{var}")]`&ensp;⟶&ensp;`write!("{}", self.var)` |
| //! - `#[error("{0}")]`&ensp;⟶&ensp;`write!("{}", self.0)` |
| //! - `#[error("{var:?}")]`&ensp;⟶&ensp;`write!("{:?}", self.var)` |
| //! - `#[error("{0:?}")]`&ensp;⟶&ensp;`write!("{:?}", self.0)` |
| //! |
| //! These shorthands can be used together with any additional format args, |
| //! which may be arbitrary expressions. For example: |
| //! |
| //! ```rust |
| //! # use std::i32; |
| //! # use thiserror::Error; |
| //! # |
| //! #[derive(Error, Debug)] |
| //! pub enum Error { |
| //! #[error("invalid rdo_lookahead_frames {0} (expected < {})", i32::MAX)] |
| //! InvalidLookahead(u32), |
| //! } |
| //! ``` |
| //! |
| //! If one of the additional expression arguments needs to refer to a field of |
| //! the struct or enum, then refer to named fields as `.var` and tuple fields |
| //! as `.0`. |
| //! |
| //! ```rust |
| //! # use thiserror::Error; |
| //! # |
| //! # fn first_char(s: &String) -> char { |
| //! # s.chars().next().unwrap() |
| //! # } |
| //! # |
| //! # #[derive(Debug)] |
| //! # struct Limits { |
| //! # lo: usize, |
| //! # hi: usize, |
| //! # } |
| //! # |
| //! #[derive(Error, Debug)] |
| //! pub enum Error { |
| //! #[error("first letter must be lowercase but was {:?}", first_char(.0))] |
| //! WrongCase(String), |
| //! #[error("invalid index {idx}, expected at least {} and at most {}", .limits.lo, .limits.hi)] |
| //! OutOfBounds { idx: usize, limits: Limits }, |
| //! } |
| //! ``` |
| //! |
| //! - A `From` impl is generated for each variant containing a `#[from]` |
| //! attribute. |
| //! |
| //! Note that the variant must not contain any other fields beyond the source |
| //! error and possibly a backtrace. A backtrace is captured from within the |
| //! `From` impl if there is a field for it. |
| //! |
| //! ```rust |
| //! # const IGNORE: &str = stringify! { |
| //! #[derive(Error, Debug)] |
| //! pub enum MyError { |
| //! Io { |
| //! #[from] |
| //! source: io::Error, |
| //! backtrace: Backtrace, |
| //! }, |
| //! } |
| //! # }; |
| //! ``` |
| //! |
| //! - The Error trait's `source()` method is implemented to return whichever |
| //! field has a `#[source]` attribute or is named `source`, if any. This is |
| //! for identifying the underlying lower level error that caused your error. |
| //! |
| //! The `#[from]` attribute always implies that the same field is `#[source]`, |
| //! so you don't ever need to specify both attributes. |
| //! |
| //! Any error type that implements `std::error::Error` or dereferences to `dyn |
| //! std::error::Error` will work as a source. |
| //! |
| //! ```rust |
| //! # use std::fmt::{self, Display}; |
| //! # use thiserror::Error; |
| //! # |
| //! #[derive(Error, Debug)] |
| //! pub struct MyError { |
| //! msg: String, |
| //! #[source] // optional if field name is `source` |
| //! source: anyhow::Error, |
| //! } |
| //! # |
| //! # impl Display for MyError { |
| //! # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { |
| //! # unimplemented!() |
| //! # } |
| //! # } |
| //! ``` |
| //! |
| //! - The Error trait's `provide()` method is implemented to provide whichever |
| //! field has a type named `Backtrace`, if any, as a |
| //! `std::backtrace::Backtrace`. |
| //! |
| //! ```rust |
| //! # const IGNORE: &str = stringify! { |
| //! use std::backtrace::Backtrace; |
| //! |
| //! #[derive(Error, Debug)] |
| //! pub struct MyError { |
| //! msg: String, |
| //! backtrace: Backtrace, // automatically detected |
| //! } |
| //! # }; |
| //! ``` |
| //! |
| //! - If a field is both a source (named `source`, or has `#[source]` or |
| //! `#[from]` attribute) *and* is marked `#[backtrace]`, then the Error |
| //! trait's `provide()` method is forwarded to the source's `provide` so that |
| //! both layers of the error share the same backtrace. |
| //! |
| //! ```rust |
| //! # const IGNORE: &str = stringify! { |
| //! #[derive(Error, Debug)] |
| //! pub enum MyError { |
| //! Io { |
| //! #[backtrace] |
| //! source: io::Error, |
| //! }, |
| //! } |
| //! # }; |
| //! ``` |
| //! |
| //! - Errors may use `error(transparent)` to forward the source and Display |
| //! methods straight through to an underlying error without adding an |
| //! additional message. This would be appropriate for enums that need an |
| //! "anything else" variant. |
| //! |
| //! ``` |
| //! # use thiserror::Error; |
| //! # |
| //! #[derive(Error, Debug)] |
| //! pub enum MyError { |
| //! # /* |
| //! ... |
| //! # */ |
| //! |
| //! #[error(transparent)] |
| //! Other(#[from] anyhow::Error), // source and Display delegate to anyhow::Error |
| //! } |
| //! ``` |
| //! |
| //! Another use case is hiding implementation details of an error |
| //! representation behind an opaque error type, so that the representation is |
| //! able to evolve without breaking the crate's public API. |
| //! |
| //! ``` |
| //! # use thiserror::Error; |
| //! # |
| //! // PublicError is public, but opaque and easy to keep compatible. |
| //! #[derive(Error, Debug)] |
| //! #[error(transparent)] |
| //! pub struct PublicError(#[from] ErrorRepr); |
| //! |
| //! impl PublicError { |
| //! // Accessors for anything we do want to expose publicly. |
| //! } |
| //! |
| //! // Private and free to change across minor version of the crate. |
| //! #[derive(Error, Debug)] |
| //! enum ErrorRepr { |
| //! # /* |
| //! ... |
| //! # */ |
| //! } |
| //! ``` |
| //! |
| //! - See also the [`anyhow`] library for a convenient single error type to use |
| //! in application code. |
| //! |
| //! [`anyhow`]: https://github.com/dtolnay/anyhow |
| |
| </span><span class="attribute">#![doc(html_root_url = <span class="string">"https://docs.rs/thiserror/1.0.40"</span>)] |
| #![allow( |
| <span class="comment">// Clippy bug: https://github.com/rust-lang/rust-clippy/issues/7421 |
| </span>clippy::doc_markdown, |
| clippy::module_name_repetitions, |
| clippy::return_self_not_must_use, |
| clippy::wildcard_imports, |
| )] |
| #![cfg_attr(provide_any, feature(provide_any))] |
| |
| </span><span class="kw">mod </span>aserror; |
| <span class="kw">mod </span>display; |
| <span class="attribute">#[cfg(provide_any)] |
| </span><span class="kw">mod </span>provide; |
| |
| <span class="kw">pub use </span>thiserror_impl::<span class="kw-2">*</span>; |
| |
| <span class="comment">// Not public API. |
| </span><span class="attribute">#[doc(hidden)] |
| </span><span class="kw">pub mod </span>__private { |
| <span class="kw">pub use </span><span class="kw">crate</span>::aserror::AsDynError; |
| <span class="kw">pub use </span><span class="kw">crate</span>::display::{DisplayAsDisplay, PathAsDisplay}; |
| <span class="attribute">#[cfg(provide_any)] |
| </span><span class="kw">pub use </span><span class="kw">crate</span>::provide::ThiserrorProvide; |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="thiserror" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
