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diff --git a/vendor/thiserror/README.md b/vendor/thiserror/README.md new file mode 100644 index 0000000..9de063c --- /dev/null +++ b/vendor/thiserror/README.md @@ -0,0 +1,222 @@ +derive(Error) +============= + +[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/thiserror-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/thiserror) +[<img alt="crates.io" src="https://img.shields.io/crates/v/thiserror.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/thiserror) +[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-thiserror-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/thiserror) +[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/thiserror/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/thiserror/actions?query=branch%3Amaster) + +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 + +```toml +[dependencies] +thiserror = "1.0" +``` + +*Compiler support: requires rustc 1.56+* + +<br> + +## Example + +```rust +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}")]` ⟶ `write!("{}", self.var)` + - `#[error("{0}")]` ⟶ `write!("{}", self.0)` + - `#[error("{var:?}")]` ⟶ `write!("{:?}", self.var)` + - `#[error("{0:?}")]` ⟶ `write!("{:?}", self.0)` + + These shorthands can be used together with any additional format args, which + may be arbitrary expressions. For example: + + ```rust + #[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 + #[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 + #[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 + #[derive(Error, Debug)] + pub struct MyError { + msg: String, + #[source] // optional if field name is `source` + source: anyhow::Error, + } + ``` + +- 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 + 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 + #[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. + + ```rust + #[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. + + ```rust + // 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 + +<br> + +## Comparison to anyhow + +Use thiserror if you care about designing your own dedicated error type(s) so +that the caller receives exactly the information that you choose in the event of +failure. This most often applies to library-like code. Use [Anyhow] if you don't +care what error type your functions return, you just want it to be easy. This is +common in application-like code. + +[Anyhow]: https://github.com/dtolnay/anyhow + +<br> + +#### License + +<sup> +Licensed under either of <a href="LICENSE-APACHE">Apache License, Version +2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option. +</sup> + +<br> + +<sub> +Unless you explicitly state otherwise, any contribution intentionally submitted +for inclusion in this crate by you, as defined in the Apache-2.0 license, shall +be dual licensed as above, without any additional terms or conditions. +</sub> |