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#![allow(unknown_lints, bare_trait_objects)] #![deny(missing_docs)] //! # SNAFU //! //! SNAFU is a library to easily assign underlying errors into //! domain-specific errors while adding context. For detailed //! information, please see the [user's guide](guide). //! //! ## Quick example //! //! This example mimics a (very poor) authentication process that //! opens a file, writes to a file, and checks the user's ID. While //! two of our operations involve an [`io::Error`](std::io::Error), //! these are different conceptual errors to us. //! //! SNAFU creates *context selectors* mirroring each error //! variant. These are used with the [`context`](ResultExt::context) //! method to provide ergonomic error handling. //! //! ```rust //! use snafu::{ensure, Backtrace, ErrorCompat, ResultExt, Snafu}; //! use std::{ //! fs, //! path::{Path, PathBuf}, //! }; //! //! #[derive(Debug, Snafu)] //! enum Error { //! #[snafu(display("Could not open config from {}: {}", filename.display(), source))] //! OpenConfig { //! filename: PathBuf, //! source: std::io::Error, //! }, //! #[snafu(display("Could not save config to {}: {}", filename.display(), source))] //! SaveConfig { //! filename: PathBuf, //! source: std::io::Error, //! }, //! #[snafu(display("The user id {} is invalid", user_id))] //! UserIdInvalid { user_id: i32, backtrace: Backtrace }, //! } //! //! type Result<T, E = Error> = std::result::Result<T, E>; //! //! fn log_in_user<P>(config_root: P, user_id: i32) -> Result<bool> //! where //! P: AsRef<Path>, //! { //! let config_root = config_root.as_ref(); //! let filename = &config_root.join("config.toml"); //! //! let config = fs::read(filename).context(OpenConfig { filename })?; //! // Perform updates to config //! fs::write(filename, config).context(SaveConfig { filename })?; //! //! ensure!(user_id == 42, UserIdInvalid { user_id }); //! //! Ok(true) //! } //! //! # const CONFIG_DIRECTORY: &str = "/does/not/exist"; //! # const USER_ID: i32 = 0; //! fn log_in() { //! match log_in_user(CONFIG_DIRECTORY, USER_ID) { //! Ok(true) => println!("Logged in!"), //! Ok(false) => println!("Not logged in!"), //! Err(e) => { //! eprintln!("An error occurred: {}", e); //! if let Some(backtrace) = ErrorCompat::backtrace(&e) { //! println!("{}", backtrace); //! } //! } //! } //! } //! ``` #[cfg(feature = "backtraces")] extern crate backtrace; #[cfg(feature = "backtraces")] mod backtrace_shim; #[cfg(feature = "backtraces")] pub use backtrace_shim::*; #[cfg(feature = "futures-01")] extern crate futures01 as futures01_crate; #[cfg(feature = "futures-01")] pub mod futures01; #[cfg(feature = "unstable-futures")] extern crate futures_core; #[cfg(feature = "unstable-futures")] extern crate pin_project; #[cfg(feature = "unstable-futures")] pub mod futures; #[cfg(feature = "rust_1_30")] extern crate snafu_derive; #[cfg(feature = "rust_1_30")] pub use snafu_derive::Snafu; #[cfg(feature = "rust_1_30")] extern crate doc_comment; #[cfg(feature = "rust_1_30")] macro_rules! generate_guide { (pub mod $name:ident; $($rest:tt)*) => { generate_guide!(@gen ".", pub mod $name { } $($rest)*); }; (pub mod $name:ident { $($children:tt)* } $($rest:tt)*) => { generate_guide!(@gen ".", pub mod $name { $($children)* } $($rest)*); }; (@gen $prefix:expr, ) => {}; (@gen $prefix:expr, pub mod $name:ident; $($rest:tt)*) => { generate_guide!(@gen $prefix, pub mod $name { } $($rest)*); }; (@gen $prefix:expr, pub mod $name:ident { $($children:tt)* } $($rest:tt)*) => { doc_comment::doc_comment! { include_str!(concat!($prefix, "/", stringify!($name), ".md")), pub mod $name { generate_guide!(@gen concat!($prefix, "/", stringify!($name)), $($children)*); } } generate_guide!(@gen $prefix, $($rest)*); }; } #[cfg(feature = "rust_1_30")] generate_guide! { pub mod guide { pub mod attributes; pub mod comparison { pub mod failure; } pub mod compatibility; pub mod feature_flags; pub mod generics; pub mod opaque; pub mod philosophy; pub mod the_macro; pub mod upgrading; } } #[cfg(feature = "rust_1_30")] doc_comment::doctest!("../README.md", readme_tests); use std::error; /// Ensure a condition is true. If it is not, return from the function /// with an error. /// /// ```rust /// use snafu::{ensure, Snafu}; /// /// #[derive(Debug, Snafu)] /// enum Error { /// InvalidUser { user_id: i32 }, /// } /// /// fn example(user_id: i32) -> Result<(), Error> { /// ensure!(user_id > 0, InvalidUser { user_id }); /// // After this point, we know that `user_id` is positive. /// let user_id = user_id as u32; /// Ok(()) /// } /// ``` #[macro_export] macro_rules! ensure { ($predicate:expr, $context_selector:expr) => { if !$predicate { return $context_selector.fail(); } }; } /// Additions to [`Result`](std::result::Result). pub trait ResultExt<T, E>: Sized { /// Extend a [`Result`]'s error with additional context-sensitive information. /// /// [`Result`]: std::result::Result /// /// ```rust /// use snafu::{ResultExt, Snafu}; /// /// #[derive(Debug, Snafu)] /// enum Error { /// Authenticating { /// user_name: String, /// user_id: i32, /// source: ApiError, /// }, /// } /// /// fn example() -> Result<(), Error> { /// another_function().context(Authenticating { /// user_name: "admin", /// user_id: 42, /// })?; /// Ok(()) /// } /// /// # type ApiError = Box<dyn std::error::Error>; /// fn another_function() -> Result<i32, ApiError> { /// /* ... */ /// # Ok(42) /// } /// ``` /// /// Note that the context selector will call /// [`Into::into`](std::convert::Into::into) on each field, so the types /// are not required to exactly match. fn context<C, E2>(self, context: C) -> Result<T, E2> where C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat; /// Extend a [`Result`][]'s error with lazily-generated context-sensitive information. /// /// [`Result`]: std::result::Result /// /// ```rust /// use snafu::{ResultExt, Snafu}; /// /// #[derive(Debug, Snafu)] /// enum Error { /// Authenticating { /// user_name: String, /// user_id: i32, /// source: ApiError, /// }, /// } /// /// fn example() -> Result<(), Error> { /// another_function().with_context(|| Authenticating { /// user_name: "admin".to_string(), /// user_id: 42, /// })?; /// Ok(()) /// } /// /// # type ApiError = std::io::Error; /// fn another_function() -> Result<i32, ApiError> { /// /* ... */ /// # Ok(42) /// } /// ``` /// /// Note that this *may not* be needed in many cases because the context /// selector will call [`Into::into`](std::convert::Into::into) on each /// field. fn with_context<F, C, E2>(self, context: F) -> Result<T, E2> where F: FnOnce() -> C, C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat; #[doc(hidden)] #[deprecated(since = "0.4.0", note = "use ResultExt::context instead")] fn eager_context<C, E2>(self, context: C) -> Result<T, E2> where C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat, { self.context(context) } #[doc(hidden)] #[deprecated(since = "0.4.0", note = "use ResultExt::with_context instead")] fn with_eager_context<F, C, E2>(self, context: F) -> Result<T, E2> where F: FnOnce() -> C, C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat, { self.with_context(context) } } impl<T, E> ResultExt<T, E> for std::result::Result<T, E> { fn context<C, E2>(self, context: C) -> Result<T, E2> where C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat, { self.map_err(|error| context.into_error(error)) } fn with_context<F, C, E2>(self, context: F) -> Result<T, E2> where F: FnOnce() -> C, C: IntoError<E2, Source = E>, E2: std::error::Error + ErrorCompat, { self.map_err(|error| { let context = context(); context.into_error(error) }) } } /// A temporary error type used when converting an [`Option`][] into a /// [`Result`][] /// /// [`Option`]: std::option::Option /// [`Result`]: std::result::Result pub struct NoneError; /// Additions to [`Option`](std::option::Option). pub trait OptionExt<T>: Sized { /// Convert an [`Option`][] into a [`Result`][] with additional /// context-sensitive information. /// /// [Option]: std::option::Option /// [Result]: std::option::Result /// /// ```rust /// use snafu::{OptionExt, Snafu}; /// /// #[derive(Debug, Snafu)] /// enum Error { /// UserLookup { user_id: i32 }, /// } /// /// fn example(user_id: i32) -> Result<(), Error> { /// let name = username(user_id).context(UserLookup { user_id })?; /// println!("Username was {}", name); /// Ok(()) /// } /// /// fn username(user_id: i32) -> Option<String> { /// /* ... */ /// # None /// } /// ``` /// /// Note that the context selector will call /// [`Into::into`](std::convert::Into::into) on each field, so the types /// are not required to exactly match. fn context<C, E>(self, context: C) -> Result<T, E> where C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat; /// Convert an [`Option`][] into a [`Result`][] with /// lazily-generated context-sensitive information. /// /// [`Option`]: std::option::Option /// [`Result`]: std::result::Result /// /// ``` /// use snafu::{OptionExt, Snafu}; /// /// #[derive(Debug, Snafu)] /// enum Error { /// UserLookup { /// user_id: i32, /// previous_ids: Vec<i32>, /// }, /// } /// /// fn example(user_id: i32) -> Result<(), Error> { /// let name = username(user_id).with_context(|| UserLookup { /// user_id, /// previous_ids: Vec::new(), /// })?; /// println!("Username was {}", name); /// Ok(()) /// } /// /// fn username(user_id: i32) -> Option<String> { /// /* ... */ /// # None /// } /// ``` /// /// Note that this *may not* be needed in many cases because the context /// selector will call [`Into::into`](std::convert::Into::into) on each /// field. fn with_context<F, C, E>(self, context: F) -> Result<T, E> where F: FnOnce() -> C, C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat; #[doc(hidden)] #[deprecated(since = "0.4.0", note = "use OptionExt::context instead")] fn eager_context<C, E>(self, context: C) -> Result<T, E> where C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat, { self.context(context).map_err(Into::into) } #[doc(hidden)] #[deprecated(since = "0.4.0", note = "use OptionExt::with_context instead")] fn with_eager_context<F, C, E>(self, context: F) -> Result<T, E> where F: FnOnce() -> C, C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat, { self.with_context(context).map_err(Into::into) } } impl<T> OptionExt<T> for Option<T> { fn context<C, E>(self, context: C) -> Result<T, E> where C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat, { self.ok_or_else(|| context.into_error(NoneError)) } fn with_context<F, C, E>(self, context: F) -> Result<T, E> where F: FnOnce() -> C, C: IntoError<E, Source = NoneError>, E: std::error::Error + ErrorCompat, { self.ok_or_else(|| context().into_error(NoneError)) } } /// Backports changes to the [`Error`](std::error::Error) trait to /// versions of Rust lacking them. /// /// It is recommended to always call these methods explicitly so that /// it is easy to replace usages of this trait when you start /// supporting a newer version of Rust. /// /// ``` /// # use snafu::{Snafu, ErrorCompat}; /// # #[derive(Debug, Snafu)] enum Example {}; /// # fn example(error: Example) { /// ErrorCompat::backtrace(&error); // Recommended /// error.backtrace(); // Discouraged /// # } /// ``` pub trait ErrorCompat { /// Returns a [`Backtrace`](Backtrace) that may be printed. #[cfg(feature = "backtraces")] fn backtrace(&self) -> Option<&Backtrace> { None } } impl<'a, E> ErrorCompat for &'a E where E: ErrorCompat, { #[cfg(feature = "backtraces")] fn backtrace(&self) -> Option<&Backtrace> { (**self).backtrace() } } impl<E> ErrorCompat for Box<E> where E: ErrorCompat, { #[cfg(feature = "backtraces")] fn backtrace(&self) -> Option<&Backtrace> { (**self).backtrace() } } /// Converts the receiver into an [`Error`][] trait object, suitable /// for use in [`Error::source`][]. /// /// It is expected that most users of SNAFU will not directly interact /// with this trait. /// /// [`Error`]: std::error::Error /// [`Error::source`]: std::error::Error::source // // Given an error enum with multiple types of underlying causes: // // ```rust // enum Error { // BoxTraitObjectSendSync(Box<dyn error::Error + Send + Sync + 'static>), // BoxTraitObject(Box<dyn error::Error + 'static>), // Boxed(Box<io::Error>), // Unboxed(io::Error), // } // ``` // // This trait provides the answer to what consistent expression can go // in each match arm: // // ```rust // impl error::Error for Error { // fn source(&self) -> Option<&(dyn error::Error + 'static)> { // use Error::*; // // let v = match *self { // BoxTraitObjectSendSync(ref e) => ..., // BoxTraitObject(ref e) => ..., // Boxed(ref e) => ..., // Unboxed(ref e) => ..., // }; // // Some(v) // } // } // // Existing methods like returning `e`, `&**e`, `Borrow::borrow(e)`, // `Deref::deref(e)`, and `AsRef::as_ref(e)` do not work for various // reasons. pub trait AsErrorSource { /// For maximum effectiveness, this needs to be called as a method /// to benefit from Rust's automatic dereferencing of method /// receivers. fn as_error_source(&self) -> &(error::Error + 'static); } impl AsErrorSource for error::Error + 'static { fn as_error_source(&self) -> &(error::Error + 'static) { self } } impl AsErrorSource for error::Error + Send + 'static { fn as_error_source(&self) -> &(error::Error + 'static) { self } } impl AsErrorSource for error::Error + Sync + 'static { fn as_error_source(&self) -> &(error::Error + 'static) { self } } impl AsErrorSource for error::Error + Send + Sync + 'static { fn as_error_source(&self) -> &(error::Error + 'static) { self } } impl<T: error::Error + 'static> AsErrorSource for T { fn as_error_source(&self) -> &(error::Error + 'static) { self } } /// Combines an underlying error with additional information /// about the error. /// /// It is expected that most users of SNAFU will not directly interact /// with this trait. pub trait IntoError<Error> where Error: std::error::Error + ErrorCompat, { /// The underlying error type Source; /// Combine the information to produce the error fn into_error(self, source: Self::Source) -> Error; }