Anyhow&ensp;¯\\\_(°ペ)\_/¯==========================[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/anyhow-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/anyhow)[<img alt="crates.io" src="https://img.shields.io/crates/v/anyhow.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/anyhow)[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-anyhow-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/anyhow)[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/anyhow/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/anyhow/actions?query=branch%3Amaster)This library provides [`anyhow::Error`][Error], a trait object based error typefor easy idiomatic error handling in Rust applications.[Error]: https://docs.rs/anyhow/1.0/anyhow/struct.Error.html```toml[dependencies]anyhow = "1.0"```<br>## Details- Use `Result<T, anyhow::Error>`, or equivalently `anyhow::Result<T>`, as the  return type of any fallible function.  Within the function, use `?` to easily propagate any error that implements the  [`std::error::Error`] trait.  ```rust  use anyhow::Result;  fn get_cluster_info() -> Result<ClusterMap> {      let config = std::fs::read_to_string("cluster.json")?;      let map: ClusterMap = serde_json::from_str(&config)?;      Ok(map)  }  ```  [`std::error::Error`]: https://doc.rust-lang.org/std/error/trait.Error.html- Attach context to help the person troubleshooting the error understand where  things went wrong. A low-level error like "No such file or directory" can be  annoying to debug without more context about what higher level step the  application was in the middle of.  ```rust  use anyhow::{Context, Result};  fn main() -> Result<()> {      ...      it.detach().context("Failed to detach the important thing")?;      let content = std::fs::read(path)          .with_context(|| format!("Failed to read instrs from {}", path))?;      ...  }  ```  ```console  Error: Failed to read instrs from ./path/to/instrs.json  Caused by:      No such file or directory (os error 2)  ```- Downcasting is supported and can be by value, by shared reference, or by  mutable reference as needed.  ```rust  // If the error was caused by redaction, then return a  // tombstone instead of the content.  match root_cause.downcast_ref::<DataStoreError>() {      Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),      None => Err(error),  }  ```- If using Rust &ge; 1.65, a backtrace is captured and printed with the error if  the underlying error type does not already provide its own. In order to see  backtraces, they must be enabled through the environment variables described  in [`std::backtrace`]:  - If you want panics and errors to both have backtraces, set    `RUST_BACKTRACE=1`;  - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;  - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and    `RUST_LIB_BACKTRACE=0`.  [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables- Anyhow works with any error type that has an impl of `std::error::Error`,  including ones defined in your crate. We do not bundle a `derive(Error)` macro  but you can write the impls yourself or use a standalone macro like  [thiserror].  ```rust  use thiserror::Error;  #[derive(Error, Debug)]  pub enum FormatError {      #[error("Invalid header (expected {expected:?}, got {found:?})")]      InvalidHeader {          expected: String,          found: String,      },      #[error("Missing attribute: {0}")]      MissingAttribute(String),  }  ```- One-off error messages can be constructed using the `anyhow!` macro, which  supports string interpolation and produces an `anyhow::Error`.  ```rust  return Err(anyhow!("Missing attribute: {}", missing));  ```  A `bail!` macro is provided as a shorthand for the same early return.  ```rust  bail!("Missing attribute: {}", missing);  ```<br>## No-std supportIn no_std mode, almost all of the same API is available and works the same way.To depend on Anyhow in no_std mode, disable our default enabled "std" feature inCargo.toml. A global allocator is required.```toml[dependencies]anyhow = { version = "1.0", default-features = false }```With versions of Rust older than 1.81, no_std mode may require an additional`.map_err(Error::msg)` when working with a non-Anyhow error type inside afunction that returns Anyhow's error type, as the trait that `?`-based errorconversions are defined by is only available in std in those old versions.<br>## Comparison to failureThe `anyhow::Error` type works something like `failure::Error`, but unlikefailure ours is built around the standard library's `std::error::Error` traitrather than a separate trait `failure::Fail`. The standard library has adoptedthe necessary improvements for this to be possible as part of [RFC 2504].[RFC 2504]: https://github.com/rust-lang/rfcs/blob/master/text/2504-fix-error.md<br>## Comparison to thiserrorUse Anyhow if you don't care what error type your functions return, you justwant it to be easy. This is common in application code. Use [thiserror] if youare a library that wants to design your own dedicated error type(s) so that onfailures the caller gets exactly the information that you choose.[thiserror]: https://github.com/dtolnay/thiserror<br>#### License<sup>Licensed under either of <a href="LICENSE-APACHE">Apache License, Version2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.</sup><br><sub>Unless you explicitly state otherwise, any contribution intentionally submittedfor inclusion in this crate by you, as defined in the Apache-2.0 license, shallbe dual licensed as above, without any additional terms or conditions.</sub>