//! This library provides [`anyhow::Error`][Error], a trait object based error
//! type for easy idiomatic error handling in Rust applications.
//!
//! <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.
//!
//! ```
//! # pub trait Deserialize {}
//! #
//! # mod serde_json {
//! # use super::Deserialize;
//! # use std::io;
//! #
//! # pub fn from_str<T: Deserialize>(json: &str) -> io::Result<T> {
//! # unimplemented!()
//! # }
//! # }
//! #
//! # struct ClusterMap;
//! #
//! # impl Deserialize for ClusterMap {}
//! #
//! 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)
//! }
//! #
//! # fn main() {}
//! ```
//!
//! - 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.
//!
//! ```
//! # struct It;
//! #
//! # impl It {
//! # fn detach(&self) -> Result<()> {
//! # unimplemented!()
//! # }
//! # }
//! #
//! use anyhow::{Context, Result};
//!
//! fn main() -> Result<()> {
//! # return Ok(());
//! #
//! # const _: &str = stringify! {
//! ...
//! # };
//! #
//! # let it = It;
//! # let path = "./path/to/instrs.jsox";
//! #
//! it.detach().context("failed to detach the important thing")?;
//!
//! let content = std::fs::read(path)
//! .with_context(|| format!("failed to read instrs from {}", path))?;
//! #
//! # const _: &str = stringify! {
//! ...
//! # };
//! #
//! # Ok(())
//! }
//! ```
//!
//! ```console
//! Error: failed to read instrs from ./path/to/instrs.jsox
//!
//! 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.
//!
//! ```
//! # use anyhow::anyhow;
//! # use std::fmt::{self, Display};
//! # use std::task::Poll;
//! #
//! # #[derive(Debug)]
//! # enum DataStoreError {
//! # Censored(()),
//! # }
//! #
//! # impl Display for DataStoreError {
//! # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
//! # unimplemented!()
//! # }
//! # }
//! #
//! # impl std::error::Error for DataStoreError {}
//! #
//! # const REDACTED_CONTENT: () = ();
//! #
//! # let error = anyhow!("...");
//! # let root_cause = &error;
//! #
//! # let ret =
//! // 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),
//! }
//! # ;
//! ```
//!
//! - 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, the
//! `RUST_LIB_BACKTRACE=1` environment variable must be defined.
//!
//! - 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].
//!
//! [thiserror]: https://github.com/dtolnay/thiserror
//!
//! ```
//! 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`.
//!
//! ```
//! # use anyhow::{anyhow, Result};
//! #
//! # fn demo() -> Result<()> {
//! # let missing = "...";
//! return Err(anyhow!("missing attribute: {}", missing));
//! # Ok(())
//! # }
//! ```
//!
//! <br>
//!
//! # Acknowledgements
//!
//! The implementation of the `anyhow::Error` type is originally forked from
//! `fehler::Exception` ([https://github.com/withoutboats/fehler][fehler]). This
//! library exposes it under the more standard `Error` / `Result` terminology
//! rather than the `throw!` / `#[throws]` / `Exception` language of exceptions.
//!
//! [fehler]: https://github.com/withoutboats/fehler
compile_error!;
pub use crate Context;
pub use crate;
/// `Result<T, Error>`
///
/// This is a reasonable return type to use throughout your application but also
/// for `fn main`; if you do, failures will be printed along with any
/// [context][Context] and a backtrace if one was captured.
///
/// # Example
///
/// ```
/// # pub trait Deserialize {}
/// #
/// # mod serde_json {
/// # use super::Deserialize;
/// # use std::io;
/// #
/// # pub fn from_str<T: Deserialize>(json: &str) -> io::Result<T> {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # #[derive(Debug)]
/// # struct ClusterMap;
/// #
/// # impl Deserialize for ClusterMap {}
/// #
/// use anyhow::Result;
///
/// fn main() -> Result<()> {
/// # return Ok(());
/// let config = std::fs::read_to_string("cluster.json")?;
/// let map: ClusterMap = serde_json::from_str(&config)?;
/// println!("cluster info: {:#?}", map);
/// Ok(())
/// }
/// ```
pub type Result<T, E = Error> = Result;
/// Return early with an error.
///
/// This macro is equivalent to `return Err(From::from($err))`.
///
/// # Example
///
/// ```
/// # use anyhow::{bail, Result};
/// #
/// # fn has_permission(user: usize, resource: usize) -> bool {
/// # true
/// # }
/// #
/// # fn main() -> Result<()> {
/// # let user = 0;
/// # let resource = 0;
/// #
/// if !has_permission(user, resource) {
/// bail!("permission denied for accessing {}", resource);
/// }
/// # Ok(())
/// # }
/// ```
///
/// ```
/// # use anyhow::{bail, Result};
/// # use std::fmt::{self, Display};
/// #
/// # #[derive(Debug)]
/// # enum ScienceError {
/// # RecursionLimitExceeded,
/// # }
/// #
/// # impl std::error::Error for ScienceError {}
/// #
/// # impl Display for ScienceError {
/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # const MAX_DEPTH: usize = 1;
/// #
/// # const IGNORE: &str = stringify! {
/// #[derive(Error, Debug)]
/// enum ScienceError {
/// #[error(display = "recursion limit exceeded")]
/// RecursionLimitExceeded,
/// ...
/// }
/// # };
///
/// # fn main() -> Result<()> {
/// # let depth = 0;
/// #
/// if depth > MAX_DEPTH {
/// bail!(ScienceError::RecursionLimitExceeded);
/// }
/// # Ok(())
/// # }
/// ```
/// Return early with an error if a condition is not satisfied.
///
/// This macro is equivalent to `if !$cond { return Err(From::from($err)); }`.
///
/// Analogously to `assert!`, `ensure!` takes a condition and exits the function
/// if the condition fails. Unlike `assert!`, `ensure!` returns an `Error`
/// rather than panicking.
///
/// # Example
///
/// ```
/// # use anyhow::{ensure, Result};
/// #
/// # fn main() -> Result<()> {
/// # let user = 0;
/// #
/// ensure!(user == 0, "only user 0 is allowed");
/// # Ok(())
/// # }
/// ```
///
/// ```
/// # use anyhow::{ensure, Result};
/// # use std::fmt::{self, Display};
/// #
/// # #[derive(Debug)]
/// # enum ScienceError {
/// # RecursionLimitExceeded,
/// # }
/// #
/// # impl std::error::Error for ScienceError {}
/// #
/// # impl Display for ScienceError {
/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # const MAX_DEPTH: usize = 1;
/// #
/// # const IGNORE: &str = stringify! {
/// #[derive(Error, Debug)]
/// enum ScienceError {
/// #[error(display = "recursion limit exceeded")]
/// RecursionLimitExceeded,
/// ...
/// }
/// # };
///
/// # fn main() -> Result<()> {
/// # let depth = 0;
/// #
/// ensure!(depth <= MAX_DEPTH, ScienceError::RecursionLimitExceeded);
/// # Ok(())
/// # }
/// ```
/// Construct an ad-hoc error from a string.
///
/// This evaluates to an `Error`. It can take either just a string, or a format
/// string with arguments. It also can take any custom type which implements
/// `Debug` and `Display`.
///
/// # Example
///
/// ```
/// # type V = ();
/// #
/// use anyhow::{anyhow, Result};
///
/// fn lookup(key: &str) -> Result<V> {
/// if key.len() != 16 {
/// return Err(anyhow!("key length must be 16 characters, got {:?}", key));
/// }
///
/// // ...
/// # Ok(())
/// }
/// ```
// Not public API.