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+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&logoColor=white&logo=data:image/svg+xml;base64,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" height="20">](https://docs.rs/thiserror)
+[<img alt="build status" src="https://img.shields.io/github/workflow/status/dtolnay/thiserror/CI/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 1.31+*
+
+<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}")]`&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
+  #[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 `backtrace()` method is implemented to return whichever
+  field has a type named `Backtrace`, if any.
+
+  ```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
+  `backtrace()` method is forwarded to the source's 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
+  }
+  ```
+
+- 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>