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</pre><pre class="rust ">
<span class="attribute">#<span class="op">!</span>[<span class="ident">deny</span>(<span class="ident">missing_docs</span>)]</span>
<span class="doccomment">//! A library for consistent and reliable error handling</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! error-chain makes it easy to take full advantage of Rust's</span>
<span class="doccomment">//! powerful error handling features without the overhead of</span>
<span class="doccomment">//! maintaining boilerplate error types and conversions. It implements</span>
<span class="doccomment">//! an opinionated strategy for defining your own error types, as well</span>
<span class="doccomment">//! as conversions from others' error types.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Quick start</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! If you just want to set up your new project with error-chain,</span>
<span class="doccomment">//! follow the [quickstart.rs] template, and read this [intro]</span>
<span class="doccomment">//! to error-chain.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [quickstart.rs]: https://github.com/brson/error-chain/blob/master/examples/quickstart.rs</span>
<span class="doccomment">//! [intro]: http://brson.github.io/2016/11/30/starting-with-error-chain</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Why error chain?</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * error-chain is easy to configure. Handle errors robustly with minimal</span>
<span class="doccomment">//! effort.</span>
<span class="doccomment">//! * Basic error handling requires no maintenance of custom error types</span>
<span class="doccomment">//! nor the `From` conversions that make `?` work.</span>
<span class="doccomment">//! * error-chain scales from simple error handling strategies to more</span>
<span class="doccomment">//! rigorous. Return formatted strings for simple errors, only</span>
<span class="doccomment">//! introducing error variants and their strong typing as needed for</span>
<span class="doccomment">//! advanced error recovery.</span>
<span class="doccomment">//! * error-chain makes it trivial to correctly manage the [cause] of</span>
<span class="doccomment">//! the errors generated by your own code. This is the "chaining"</span>
<span class="doccomment">//! in "error-chain".</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [cause]: https://doc.rust-lang.org/std/error/trait.Error.html#method.cause</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Principles of error-chain</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! error-chain is based on the following principles:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * No error should ever be discarded. This library primarily</span>
<span class="doccomment">//! makes it easy to "chain" errors with the `chain_err` method.</span>
<span class="doccomment">//! * Introducing new errors is trivial. Simple errors can be introduced</span>
<span class="doccomment">//! at the error site with just a string.</span>
<span class="doccomment">//! * Handling errors is possible with pattern matching.</span>
<span class="doccomment">//! * Conversions between error types are done in an automatic and</span>
<span class="doccomment">//! consistent way - `From` conversion behavior is never specified</span>
<span class="doccomment">//! explicitly.</span>
<span class="doccomment">//! * Errors implement Send.</span>
<span class="doccomment">//! * Errors can carry backtraces.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Similar to other libraries like [error-type] and [quick-error],</span>
<span class="doccomment">//! this library introduces the error chaining mechanism originally</span>
<span class="doccomment">//! employed by Cargo. The `error_chain!` macro declares the types</span>
<span class="doccomment">//! and implementation boilerplate necessary for fulfilling a</span>
<span class="doccomment">//! particular error-handling strategy. Most importantly it defines a</span>
<span class="doccomment">//! custom error type (called `Error` by convention) and the `From`</span>
<span class="doccomment">//! conversions that let the `try!` macro and `?` operator work.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This library differs in a few ways from previous error libs:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * Instead of defining the custom `Error` type as an enum, it is a</span>
<span class="doccomment">//! struct containing an `ErrorKind` (which defines the</span>
<span class="doccomment">//! `description` and `display` methods for the error), an opaque,</span>
<span class="doccomment">//! optional, boxed `std::error::Error + Send + 'static` object</span>
<span class="doccomment">//! (which defines the `cause`, and establishes the links in the</span>
<span class="doccomment">//! error chain), and a `Backtrace`.</span>
<span class="doccomment">//! * The macro also defines a `ResultExt` trait that defines a</span>
<span class="doccomment">//! `chain_err` method. This method on all `std::error::Error + Send + 'static`</span>
<span class="doccomment">//! types extends the error chain by boxing the current</span>
<span class="doccomment">//! error into an opaque object and putting it inside a new concrete</span>
<span class="doccomment">//! error.</span>
<span class="doccomment">//! * It provides automatic `From` conversions between other error types</span>
<span class="doccomment">//! defined by the `error_chain!` that preserve type information,</span>
<span class="doccomment">//! and facilitate seamless error composition and matching of composed</span>
<span class="doccomment">//! errors.</span>
<span class="doccomment">//! * It provides automatic `From` conversions between any other error</span>
<span class="doccomment">//! type that hides the type of the other error in the `cause` box.</span>
<span class="doccomment">//! * If `RUST_BACKTRACE` is enabled, it collects a single backtrace at</span>
<span class="doccomment">//! the earliest opportunity and propagates it down the stack through</span>
<span class="doccomment">//! `From` and `ResultExt` conversions.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! To accomplish its goals it makes some tradeoffs:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * The split between the `Error` and `ErrorKind` types can make it</span>
<span class="doccomment">//! slightly more cumbersome to instantiate new (unchained) errors,</span>
<span class="doccomment">//! requiring an `Into` or `From` conversion; as well as slightly</span>
<span class="doccomment">//! more cumbersome to match on errors with another layer of types</span>
<span class="doccomment">//! to match.</span>
<span class="doccomment">//! * Because the error type contains `std::error::Error + Send + 'static` objects,</span>
<span class="doccomment">//! it can't implement `PartialEq` for easy comparisons.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Declaring error types</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Generally, you define one family of error types per crate, though</span>
<span class="doccomment">//! it's also perfectly fine to define error types on a finer-grained</span>
<span class="doccomment">//! basis, such as per module.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Assuming you are using crate-level error types, typically you will</span>
<span class="doccomment">//! define an `errors` module and inside it call `error_chain!`:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! mod other_error {</span>
<span class="doccomment">//! error_chain! {}</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! // The type defined for this error. These are the conventional</span>
<span class="doccomment">//! // and recommended names, but they can be arbitrarily chosen.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // It is also possible to leave this section out entirely, or</span>
<span class="doccomment">//! // leave it empty, and these names will be used automatically.</span>
<span class="doccomment">//! types {</span>
<span class="doccomment">//! Error, ErrorKind, ResultExt, Result;</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Without the `Result` wrapper:</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // types {</span>
<span class="doccomment">//! // Error, ErrorKind, ResultExt;</span>
<span class="doccomment">//! // }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Automatic conversions between this error chain and other</span>
<span class="doccomment">//! // error chains. In this case, it will e.g. generate an</span>
<span class="doccomment">//! // `ErrorKind` variant called `Another` which in turn contains</span>
<span class="doccomment">//! // the `other_error::ErrorKind`, with conversions from</span>
<span class="doccomment">//! // `other_error::Error`.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // Optionally, some attributes can be added to a variant.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // This section can be empty.</span>
<span class="doccomment">//! links {</span>
<span class="doccomment">//! Another(other_error::Error, other_error::ErrorKind) #[cfg(unix)];</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Automatic conversions between this error chain and other</span>
<span class="doccomment">//! // error types not defined by the `error_chain!`. These will be</span>
<span class="doccomment">//! // wrapped in a new error with, in the first case, the</span>
<span class="doccomment">//! // `ErrorKind::Fmt` variant. The description and cause will</span>
<span class="doccomment">//! // forward to the description and cause of the original error.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // Optionally, some attributes can be added to a variant.</span>
<span class="doccomment">//! //</span>
<span class="doccomment">//! // This section can be empty.</span>
<span class="doccomment">//! foreign_links {</span>
<span class="doccomment">//! Fmt(::std::fmt::Error);</span>
<span class="doccomment">//! Io(::std::io::Error) #[cfg(unix)];</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Define additional `ErrorKind` variants. The syntax here is</span>
<span class="doccomment">//! // the same as `quick_error!`, but the `from()` and `cause()`</span>
<span class="doccomment">//! // syntax is not supported.</span>
<span class="doccomment">//! errors {</span>
<span class="doccomment">//! InvalidToolchainName(t: String) {</span>
<span class="doccomment">//! description("invalid toolchain name")</span>
<span class="doccomment">//! display("invalid toolchain name: '{}'", t)</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // You can also add commas after description/display.</span>
<span class="doccomment">//! // This may work better with some editor auto-indentation modes:</span>
<span class="doccomment">//! UnknownToolchainVersion(v: String) {</span>
<span class="doccomment">//! description("unknown toolchain version"), // note the ,</span>
<span class="doccomment">//! display("unknown toolchain version: '{}'", v), // trailing comma is allowed</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Each section, `types`, `links`, `foreign_links`, and `errors` may</span>
<span class="doccomment">//! be omitted if it is empty.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This populates the module with a number of definitions,</span>
<span class="doccomment">//! the most important of which are the `Error` type</span>
<span class="doccomment">//! and the `ErrorKind` type. An example of generated code can be found in the</span>
<span class="doccomment">//! [example_generated](example_generated) module.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Returning new errors</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Introducing new error chains, with a string message:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # error_chain! {}</span>
<span class="doccomment">//! fn foo() -> Result<()> {</span>
<span class="doccomment">//! Err("foo error!".into())</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Introducing new error chains, with an `ErrorKind`:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! errors { FooError }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn foo() -> Result<()> {</span>
<span class="doccomment">//! Err(ErrorKind::FooError.into())</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Note that the return type is the typedef `Result`, which is</span>
<span class="doccomment">//! defined by the macro as `pub type Result<T> =</span>
<span class="doccomment">//! ::std::result::Result<T, Error>`. Note that in both cases</span>
<span class="doccomment">//! `.into()` is called to convert a type into the `Error` type; both</span>
<span class="doccomment">//! strings and `ErrorKind` have `From` conversions to turn them into</span>
<span class="doccomment">//! `Error`.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! When the error is emitted inside a `try!` macro or behind the</span>
<span class="doccomment">//! `?` operator, the explicit conversion isn't needed; `try!` will</span>
<span class="doccomment">//! automatically convert `Err(ErrorKind)` to `Err(Error)`. So the</span>
<span class="doccomment">//! below is equivalent to the previous:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # error_chain! { errors { FooError } }</span>
<span class="doccomment">//! fn foo() -> Result<()> {</span>
<span class="doccomment">//! Ok(try!(Err(ErrorKind::FooError)))</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn bar() -> Result<()> {</span>
<span class="doccomment">//! Ok(try!(Err("bogus!")))</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## The `bail!` macro</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The above method of introducing new errors works but is a little</span>
<span class="doccomment">//! verbose. Instead, we can use the `bail!` macro, which performs an early return</span>
<span class="doccomment">//! with conversions done automatically.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! With `bail!` the previous examples look like:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # error_chain! { errors { FooError } }</span>
<span class="doccomment">//! fn foo() -> Result<()> {</span>
<span class="doccomment">//! if true {</span>
<span class="doccomment">//! bail!(ErrorKind::FooError);</span>
<span class="doccomment">//! } else {</span>
<span class="doccomment">//! Ok(())</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn bar() -> Result<()> {</span>
<span class="doccomment">//! if true {</span>
<span class="doccomment">//! bail!("bogus!");</span>
<span class="doccomment">//! } else {</span>
<span class="doccomment">//! Ok(())</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Chaining errors</span>
<span class="doccomment">//! error-chain supports extending an error chain by appending new errors.</span>
<span class="doccomment">//! This can be done on a Result or on an existing Error.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! To extend the error chain:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # error_chain! {}</span>
<span class="doccomment">//! # fn do_something() -> Result<()> { unimplemented!() }</span>
<span class="doccomment">//! # fn test() -> Result<()> {</span>
<span class="doccomment">//! let res: Result<()> = do_something().chain_err(|| "something went wrong");</span>
<span class="doccomment">//! # Ok(())</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! `chain_err` can be called on any `Result` type where the contained</span>
<span class="doccomment">//! error type implements `std::error::Error + Send + 'static`, as long as</span>
<span class="doccomment">//! the `Result` type's corresponding `ResultExt` trait is in scope. If</span>
<span class="doccomment">//! the `Result` is an `Err` then `chain_err` evaluates the closure,</span>
<span class="doccomment">//! which returns *some type that can be converted to `ErrorKind`*,</span>
<span class="doccomment">//! boxes the original error to store as the cause, then returns a new</span>
<span class="doccomment">//! error containing the original error.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Calling `chain_err` on an existing `Error` instance has the same</span>
<span class="doccomment">//! signature and produces the same outcome as being called on a `Result`</span>
<span class="doccomment">//! matching the properties described above. This is most useful when</span>
<span class="doccomment">//! partially handling errors using the `map_err` function.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! To chain an error directly, use `with_chain`:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # error_chain! {}</span>
<span class="doccomment">//! # fn do_something() -> Result<()> { unimplemented!() }</span>
<span class="doccomment">//! # fn test() -> Result<()> {</span>
<span class="doccomment">//! let res: Result<()> =</span>
<span class="doccomment">//! do_something().map_err(|e| Error::with_chain(e, "something went wrong"));</span>
<span class="doccomment">//! # Ok(())</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Linking errors</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! To convert an error from another error chain to this error chain:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! # mod other { error_chain! {} }</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! links {</span>
<span class="doccomment">//! OtherError(other::Error, other::ErrorKind);</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn do_other_thing() -> other::Result<()> { unimplemented!() }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # fn test() -> Result<()> {</span>
<span class="doccomment">//! let res: Result<()> = do_other_thing().map_err(|e| e.into());</span>
<span class="doccomment">//! # Ok(())</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The `Error` and `ErrorKind` types implements `From` for the corresponding</span>
<span class="doccomment">//! types of all linked error chains. Linked errors do not introduce a new</span>
<span class="doccomment">//! cause to the error chain.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Matching errors</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! error-chain error variants are matched with simple patterns.</span>
<span class="doccomment">//! `Error` is a tuple struct and its first field is the `ErrorKind`,</span>
<span class="doccomment">//! making dispatching on error kinds relatively compact:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! # fn main() {</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! errors {</span>
<span class="doccomment">//! InvalidToolchainName(t: String) {</span>
<span class="doccomment">//! description("invalid toolchain name")</span>
<span class="doccomment">//! display("invalid toolchain name: '{}'", t)</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! match Error::from("error!") {</span>
<span class="doccomment">//! Error(ErrorKind::InvalidToolchainName(_), _) => { }</span>
<span class="doccomment">//! Error(ErrorKind::Msg(_), _) => { }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Chained errors are also matched with (relatively) compact syntax</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">//! mod utils {</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! errors {</span>
<span class="doccomment">//! BadStuff {</span>
<span class="doccomment">//! description("bad stuff")</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! mod app {</span>
<span class="doccomment">//! error_chain! {</span>
<span class="doccomment">//! links {</span>
<span class="doccomment">//! Utils(::utils::Error, ::utils::ErrorKind);</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # fn main() {</span>
<span class="doccomment">//! match app::Error::from("error!") {</span>
<span class="doccomment">//! app::Error(app::ErrorKind::Utils(utils::ErrorKind::BadStuff), _) => { }</span>
<span class="doccomment">//! _ => { }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! # }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Foreign links</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Errors that do not conform to the same conventions as this library</span>
<span class="doccomment">//! can still be included in the error chain. They are considered "foreign</span>
<span class="doccomment">//! errors", and are declared using the `foreign_links` block of the</span>
<span class="doccomment">//! `error_chain!` macro. `Error`s are automatically created from</span>
<span class="doccomment">//! foreign errors by the `try!` macro.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Foreign links and regular links have one crucial difference:</span>
<span class="doccomment">//! `From` conversions for regular links *do not introduce a new error</span>
<span class="doccomment">//! into the error chain*, while conversions for foreign links *always</span>
<span class="doccomment">//! introduce a new error into the error chain*. So for the example</span>
<span class="doccomment">//! above all errors deriving from the `std::fmt::Error` type will be</span>
<span class="doccomment">//! presented to the user as a new `ErrorKind::Fmt` variant, and the</span>
<span class="doccomment">//! cause will be the original `std::fmt::Error` error. In contrast, when</span>
<span class="doccomment">//! `other_error::Error` is converted to `Error` the two `ErrorKind`s</span>
<span class="doccomment">//! are converted between each other to create a new `Error` but the</span>
<span class="doccomment">//! old error is discarded; there is no "cause" created from the</span>
<span class="doccomment">//! original error.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Backtraces</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! If the `RUST_BACKTRACE` environment variable is set to anything</span>
<span class="doccomment">//! but ``0``, the earliest non-foreign error to be generated creates</span>
<span class="doccomment">//! a single backtrace, which is passed through all `From` conversions</span>
<span class="doccomment">//! and `chain_err` invocations of compatible types. To read the</span>
<span class="doccomment">//! backtrace just call the `backtrace()` method.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Backtrace generation can be disabled by turning off the `backtrace` feature.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ## Iteration</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The `iter` method returns an iterator over the chain of error boxes.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [error-type]: https://github.com/DanielKeep/rust-error-type</span>
<span class="doccomment">//! [quick-error]: https://github.com/tailhook/quick-error</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">backtrace</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">error</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>::<span class="ident">Iterator</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">Arc</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">backtrace</span>::<span class="ident">Backtrace</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>))]</span>
<span class="doccomment">/// Dummy type used when the `backtrace` feature is disabled.</span>
<span class="kw">pub</span> <span class="kw">type</span> <span class="ident">Backtrace</span> <span class="op">=</span> ();
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">mod</span> <span class="ident">quick_error</span>;
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">mod</span> <span class="ident">error_chain</span>;
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">mod</span> <span class="ident">quick_main</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">quick_main</span>::<span class="ident">ExitCode</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"example_generated"</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">example_generated</span>;
<span class="doccomment">/// Iterator over the error chain using the `Error::cause()` method.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ErrorChainIter</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="kw">pub</span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span>);
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">ErrorChainIter</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">error</span>::<span class="ident">Error</span>;
<span class="kw">fn</span> <span class="ident">next</span><span class="op"><</span><span class="lifetime">'b</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'b</span> <span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="number">0</span>.<span class="ident">take</span>() {
<span class="prelude-val">Some</span>(<span class="ident">e</span>) <span class="op">=></span> {
<span class="self">self</span>.<span class="number">0</span> <span class="op">=</span> <span class="ident">e</span>.<span class="ident">cause</span>();
<span class="prelude-val">Some</span>(<span class="ident">e</span>)
}
<span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">None</span>,
}
}
}
<span class="doccomment">/// Returns a backtrace of the current call stack if `RUST_BACKTRACE`</span>
<span class="doccomment">/// is set to anything but ``0``, and `None` otherwise. This is used</span>
<span class="doccomment">/// in the generated error implementations.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">make_backtrace</span>() <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Backtrace</span><span class="op">>></span> {
<span class="kw">match</span> <span class="ident">std</span>::<span class="ident">env</span>::<span class="ident">var_os</span>(<span class="string">"RUST_BACKTRACE"</span>) {
<span class="prelude-val">Some</span>(<span class="kw-2">ref</span> <span class="ident">val</span>) <span class="kw">if</span> <span class="ident">val</span> <span class="op">!=</span> <span class="string">"0"</span> <span class="op">=></span> <span class="prelude-val">Some</span>(<span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Backtrace</span>::<span class="ident">new</span>())),
_ <span class="op">=></span> <span class="prelude-val">None</span>,
}
}
<span class="doccomment">/// This trait is implemented on all the errors generated by the `error_chain`</span>
<span class="doccomment">/// macro.</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">ChainedError</span>: <span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span> {
<span class="doccomment">/// Associated kind type.</span>
<span class="kw">type</span> <span class="ident">ErrorKind</span>;
<span class="doccomment">/// Constructs an error from a kind, and generates a backtrace.</span>
<span class="kw">fn</span> <span class="ident">from_kind</span>(<span class="ident">kind</span>: <span class="self">Self</span>::<span class="ident">ErrorKind</span>) <span class="op">-></span> <span class="self">Self</span> <span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>;
<span class="doccomment">/// Constructs a chained error from another error and a kind, and generates a backtrace.</span>
<span class="kw">fn</span> <span class="ident">with_chain</span><span class="op"><</span><span class="ident">E</span>, <span class="ident">K</span><span class="op">></span>(<span class="ident">error</span>: <span class="ident">E</span>, <span class="ident">kind</span>: <span class="ident">K</span>) <span class="op">-></span> <span class="self">Self</span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>,
<span class="ident">E</span>: ::<span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span>,
<span class="ident">K</span>: <span class="ident">Into</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">ErrorKind</span><span class="op">></span>;
<span class="doccomment">/// Returns the kind of the error.</span>
<span class="kw">fn</span> <span class="ident">kind</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">ErrorKind</span>;
<span class="doccomment">/// Iterates over the error chain.</span>
<span class="kw">fn</span> <span class="ident">iter</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">ErrorChainIter</span>;
<span class="doccomment">/// Returns the backtrace associated with this error.</span>
<span class="kw">fn</span> <span class="ident">backtrace</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Backtrace</span><span class="op">></span>;
<span class="doccomment">/// Returns an object which implements `Display` for printing the full</span>
<span class="doccomment">/// context of this error.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The full cause chain and backtrace, if present, will be printed.</span>
<span class="kw">fn</span> <span class="ident">display</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'a</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Display</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="self">Self</span><span class="op">></span> {
<span class="ident">Display</span>(<span class="self">self</span>)
}
<span class="doccomment">/// Extends the error chain with a new entry.</span>
<span class="kw">fn</span> <span class="ident">chain_err</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">EK</span><span class="op">></span>(<span class="self">self</span>, <span class="ident">error</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="self">Self</span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-></span> <span class="ident">EK</span>,
<span class="ident">EK</span>: <span class="ident">Into</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">ErrorKind</span><span class="op">></span>;
<span class="doccomment">/// Creates an error from its parts.</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">kind</span>: <span class="self">Self</span>::<span class="ident">ErrorKind</span>, <span class="ident">state</span>: <span class="ident">State</span>) <span class="op">-></span> <span class="self">Self</span> <span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>;
<span class="doccomment">/// Returns the first known backtrace, either from its State or from one</span>
<span class="doccomment">/// of the errors from `foreign_links`.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">fn</span> <span class="ident">extract_backtrace</span>(<span class="ident">e</span>: <span class="kw-2">&</span>(<span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'static</span>)) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Backtrace</span><span class="op">>></span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>;
}
<span class="doccomment">/// A struct which formats an error for output.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Display</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="lifetime">'a</span> <span class="op">+</span> <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">T</span>);
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Display</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">ChainedError</span>
{
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">fmt</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">try</span><span class="macro">!</span>(<span class="macro">writeln</span><span class="macro">!</span>(<span class="ident">fmt</span>, <span class="string">"Error: {}"</span>, <span class="self">self</span>.<span class="number">0</span>));
<span class="kw">for</span> <span class="ident">e</span> <span class="kw">in</span> <span class="self">self</span>.<span class="number">0</span>.<span class="ident">iter</span>().<span class="ident">skip</span>(<span class="number">1</span>) {
<span class="macro">try</span><span class="macro">!</span>(<span class="macro">writeln</span><span class="macro">!</span>(<span class="ident">fmt</span>, <span class="string">"Caused by: {}"</span>, <span class="ident">e</span>));
}
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">backtrace</span>) <span class="op">=</span> <span class="self">self</span>.<span class="number">0</span>.<span class="ident">backtrace</span>() {
<span class="macro">try</span><span class="macro">!</span>(<span class="macro">writeln</span><span class="macro">!</span>(<span class="ident">fmt</span>, <span class="string">"{:?}"</span>, <span class="ident">backtrace</span>));
}
<span class="prelude-val">Ok</span>(())
}
}
<span class="doccomment">/// Common state between errors.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">State</span> {
<span class="doccomment">/// Next error in the error chain.</span>
<span class="kw">pub</span> <span class="ident">next_error</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">>></span>,
<span class="doccomment">/// Backtrace for the current error.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">pub</span> <span class="ident">backtrace</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Backtrace</span><span class="op">>></span>,
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">State</span> {
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">State</span> {
<span class="ident">State</span> {
<span class="ident">next_error</span>: <span class="prelude-val">None</span>,
<span class="ident">backtrace</span>: <span class="ident">make_backtrace</span>(),
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>))]</span>
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-></span> <span class="ident">State</span> {
<span class="ident">State</span> { <span class="ident">next_error</span>: <span class="prelude-val">None</span> }
}
}
<span class="kw">impl</span> <span class="ident">State</span> {
<span class="doccomment">/// Creates a new State type</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span><span class="op"><</span><span class="ident">CE</span>: <span class="ident">ChainedError</span><span class="op">></span>(<span class="ident">e</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">></span>) <span class="op">-></span> <span class="ident">State</span> {
<span class="kw">let</span> <span class="ident">backtrace</span> <span class="op">=</span> <span class="ident">CE</span>::<span class="ident">extract_backtrace</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">e</span>).<span class="ident">or_else</span>(<span class="ident">make_backtrace</span>);
<span class="ident">State</span> {
<span class="ident">next_error</span>: <span class="prelude-val">Some</span>(<span class="ident">e</span>),
<span class="ident">backtrace</span>: <span class="ident">backtrace</span>,
}
}
<span class="doccomment">/// Creates a new State type</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span><span class="op"><</span><span class="ident">CE</span>: <span class="ident">ChainedError</span><span class="op">></span>(<span class="ident">e</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">error</span>::<span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">></span>) <span class="op">-></span> <span class="ident">State</span> {
<span class="ident">State</span> { <span class="ident">next_error</span>: <span class="prelude-val">Some</span>(<span class="ident">e</span>) }
}
<span class="doccomment">/// Returns the inner backtrace if present.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">backtrace</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Backtrace</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">backtrace</span>.<span class="ident">as_ref</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">v</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">v</span>)
}
<span class="doccomment">/// Returns the inner backtrace if present.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"backtrace"</span>))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">backtrace</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Backtrace</span><span class="op">></span> {
<span class="prelude-val">None</span>
}
}
<span class="doccomment">/// Exits a function early with an error</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `bail!` macro provides an easy way to exit a function.</span>
<span class="doccomment">/// `bail!(expr)` is equivalent to writing.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">/// # error_chain! { }</span>
<span class="doccomment">/// # fn main() { }</span>
<span class="doccomment">/// # fn foo() -> Result<()> {</span>
<span class="doccomment">/// # let expr = "";</span>
<span class="doccomment">/// return Err(expr.into());</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// And as shorthand it takes a formatting string a la `println!`:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">/// # error_chain! { }</span>
<span class="doccomment">/// # fn main() { }</span>
<span class="doccomment">/// # fn foo() -> Result<()> {</span>
<span class="doccomment">/// # let n = 0;</span>
<span class="doccomment">/// bail!("bad number: {}", n);</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Bailing on a custom error:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">/// # fn main() {}</span>
<span class="doccomment">/// error_chain! {</span>
<span class="doccomment">/// errors { FooError }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn foo() -> Result<()> {</span>
<span class="doccomment">/// if bad_condition() {</span>
<span class="doccomment">/// bail!(ErrorKind::FooError);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Ok(())</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # fn bad_condition() -> bool { true }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Bailing on a formatted string:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">/// # fn main() {}</span>
<span class="doccomment">/// error_chain! { }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn foo() -> Result<()> {</span>
<span class="doccomment">/// if let Some(bad_num) = bad_condition() {</span>
<span class="doccomment">/// bail!("so bad: {}", bad_num);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Ok(())</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # fn bad_condition() -> Option<i8> { None }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">bail</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>) <span class="op">=></span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>.<span class="ident">into</span>());
};
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>:<span class="ident">tt</span>)<span class="op">+</span>) <span class="op">=></span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>)<span class="op">+</span>).<span class="ident">into</span>());
};
}
<span class="doccomment">/// Exits a function early with an error if the condition is not satisfied</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `ensure!` macro is a convenience helper that provides a way to exit</span>
<span class="doccomment">/// a function with an error if the given condition fails.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// As an example, `ensure!(condition, "error code: {}", errcode)` is equivalent to</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// # #[macro_use] extern crate error_chain;</span>
<span class="doccomment">/// # error_chain! { }</span>
<span class="doccomment">/// # fn main() { }</span>
<span class="doccomment">/// # fn foo() -> Result<()> {</span>
<span class="doccomment">/// # let errcode = 0u8;</span>
<span class="doccomment">/// # let condition = true;</span>
<span class="doccomment">/// if !condition {</span>
<span class="doccomment">/// bail!("error code: {}", errcode);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// # Ok(())</span>
<span class="doccomment">/// # }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// See documentation for `bail!` macro for further details.</span>
<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">ensure</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>) <span class="op">=></span> {
<span class="kw">if</span> <span class="op">!</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>) {
<span class="macro">bail</span><span class="macro">!</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>);
}
};
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>:<span class="ident">expr</span>, <span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>:<span class="ident">tt</span>)<span class="op">+</span>) <span class="op">=></span> {
<span class="kw">if</span> <span class="op">!</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">cond</span>) {
<span class="macro">bail</span><span class="macro">!</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">fmt</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>)<span class="op">+</span>);
}
};
}
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">mock</span> {
<span class="macro">error_chain</span><span class="macro">!</span>{}
}
</pre>
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