---
source: tests/output.rs
expression: "get_stdout(path, &[\"anyhow\"])"
---
anyhow                                      Module anyhow                                  rusty-man

DESCRIPTION
      [[github]][1] [[crates-io]][2] [[docs-rs]][3]
      
      This library provides `anyhow::Error`, a trait object based error type for easy idiomatic
      error handling in Rust applications.
      
      
      # 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.
        
        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)
        }
      * 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.
        
        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))?;
            ...
        }
        `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.
        
        // 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 the nightly channel, 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`][1]:
        
        * 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`.
        
        The tracking issue for this feature is [rust-lang/rust#53487][2].
        
        [1] https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
        [2] https://github.com/rust-lang/rust/issues/53487
      * 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][1].
        
        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),
        }
        
        [1] https://github.com/dtolnay/thiserror
      * One-off error messages can be constructed using the `anyhow!` macro, which supports string
        interpolation and produces an `anyhow::Error`.
        
        return Err(anyhow!("Missing attribute: {}", missing));
      
      
      
      # No-std support
      
      In no_std mode, the same API is almost all available and works the same way. To depend on
      Anyhow in no_std mode, disable our default enabled “std” feature in Cargo.toml. A global
      allocator is required.
      
      `[dependencies]
      anyhow = { version = "1.0", default-features = false }
      `
      
      Since the `?`-based error conversions would normally rely on the `std::error::Error` trait
      which is only available through std, no_std mode will require an explicit
      `.map_err(Error::msg)` when working with a non-Anyhow error type inside a function that
      returns Anyhow’s error type.
      
      [1] https://github.com/dtolnay/anyhow
      [2] https://crates.io/crates/anyhow
      [3] https://docs.rs/anyhow

MACROS
      anyhow
            Construct an ad-hoc error from a string.

      bail
            Return early with an error.

      ensure
            Return early with an error if a condition is not satisfied.

STRUCTS
      Chain
            Iterator of a chain of source errors.

      Error
            The `Error` type, a wrapper around a dynamic error type.

TRAITS
      Context
            Provides the `context` method for `Result`.

TYPEDEFS
      Result
            `Result<T, Error>`