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Merge commit '6eba9cd92c295c5389944f6adda1f1e83b2cb008' as 'subprojects/thiserror'

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John Turner
2025-11-15 20:18:36 +00:00
parent 0436fbc770 6eba9cd92c
commit c0bd0c9efd
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//! [![github]](https://github.com/dtolnay/thiserror) [![crates-io]](https://crates.io/crates/thiserror) [![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.
//!
//! <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 core::i32;
//! # use thiserror::Error;
//! #
//! #[derive(Error, Debug)]
//! pub enum Error {
//! #[error("invalid rdo_lookahead_frames {0} (expected < {max})", max = 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 that contains a `#[from]`
//! attribute.
//!
//! The variant using `#[from]` must not contain any other fields beyond the
//! source error (and possibly a backtrace &mdash; see below). Usually
//! `#[from]` fields are unnamed, but `#[from]` is allowed on a named field
//! too.
//!
//! ```rust
//! # use core::fmt::{self, Display};
//! # use std::io;
//! # use thiserror::Error;
//! #
//! # mod globset {
//! # #[derive(thiserror::Error, Debug)]
//! # #[error("...")]
//! # pub struct Error;
//! # }
//! #
//! #[derive(Error, Debug)]
//! pub enum MyError {
//! Io(#[from] io::Error),
//! Glob(#[from] globset::Error),
//! }
//! #
//! # impl Display for MyError {
//! # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
//! # unimplemented!()
//! # }
//! # }
//! ```
//!
//! - 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 core::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`]. Using `Backtrace` in errors requires a
//! nightly compiler with Rust version 1.73 or newer.
//!
//! ```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. The `#[backtrace]`
//! attribute requires a nightly compiler with Rust version 1.73 or newer.
//!
//! ```rust
//! # const IGNORE: &str = stringify! {
//! #[derive(Error, Debug)]
//! pub enum MyError {
//! Io {
//! #[backtrace]
//! source: io::Error,
//! },
//! }
//! # };
//! ```
//!
//! - For variants that use `#[from]` and also contain a `Backtrace` field, a
//! backtrace is captured from within the `From` impl.
//!
//! ```rust
//! # const IGNORE: &str = stringify! {
//! #[derive(Error, Debug)]
//! pub enum MyError {
//! Io {
//! #[from]
//! source: io::Error,
//! backtrace: Backtrace,
//! },
//! }
//! # };
//! ```
//!
//! - 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
//! [`source()`]: std::error::Error::source
//! [`provide()`]: std::error::Error::provide
//! [`Display`]: std::fmt::Display
#![no_std]
#![doc(html_root_url = "https://docs.rs/thiserror/2.0.17")]
#![allow(
clippy::elidable_lifetime_names,
clippy::module_name_repetitions,
clippy::needless_lifetimes,
clippy::return_self_not_must_use,
clippy::wildcard_imports
)]
#![cfg_attr(error_generic_member_access, feature(error_generic_member_access))]
#[cfg(all(thiserror_nightly_testing, not(error_generic_member_access)))]
compile_error!("Build script probe failed to compile.");
#[cfg(feature = "std")]
extern crate std;
#[cfg(feature = "std")]
extern crate std as core;
mod aserror;
mod display;
#[cfg(error_generic_member_access)]
mod provide;
mod var;
pub use thiserror_impl::*;
mod private;
include!(concat!(env!("OUT_DIR"), "/private.rs"));