509 lines
16 KiB
Rust
509 lines
16 KiB
Rust
#![doc = include_str!("error.md")]
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#![unstable(feature = "error_in_core", issue = "none")]
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#[cfg(test)]
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mod tests;
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use crate::any::{Demand, Provider, TypeId};
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use crate::fmt::{Debug, Display};
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/// `Error` is a trait representing the basic expectations for error values,
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/// i.e., values of type `E` in [`Result<T, E>`].
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///
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/// Errors must describe themselves through the [`Display`] and [`Debug`]
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/// traits. Error messages are typically concise lowercase sentences without
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/// trailing punctuation:
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///
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/// ```
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/// let err = "NaN".parse::<u32>().unwrap_err();
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/// assert_eq!(err.to_string(), "invalid digit found in string");
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/// ```
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///
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/// Errors may provide cause information. [`Error::source()`] is generally
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/// used when errors cross "abstraction boundaries". If one module must report
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/// an error that is caused by an error from a lower-level module, it can allow
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/// accessing that error via [`Error::source()`]. This makes it possible for the
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/// high-level module to provide its own errors while also revealing some of the
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/// implementation for debugging.
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#[stable(feature = "rust1", since = "1.0.0")]
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#[cfg_attr(not(test), rustc_diagnostic_item = "Error")]
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#[rustc_has_incoherent_inherent_impls]
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pub trait Error: Debug + Display {
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/// The lower-level source of this error, if any.
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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///
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/// #[derive(Debug)]
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/// struct SuperError {
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/// source: SuperErrorSideKick,
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/// }
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///
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/// impl fmt::Display for SuperError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperError is here!")
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/// }
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/// }
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///
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/// impl Error for SuperError {
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/// fn source(&self) -> Option<&(dyn Error + 'static)> {
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/// Some(&self.source)
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/// }
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/// }
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///
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/// #[derive(Debug)]
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/// struct SuperErrorSideKick;
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///
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/// impl fmt::Display for SuperErrorSideKick {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "SuperErrorSideKick is here!")
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/// }
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/// }
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///
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/// impl Error for SuperErrorSideKick {}
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///
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/// fn get_super_error() -> Result<(), SuperError> {
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/// Err(SuperError { source: SuperErrorSideKick })
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/// }
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///
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/// fn main() {
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/// match get_super_error() {
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/// Err(e) => {
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/// println!("Error: {e}");
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/// println!("Caused by: {}", e.source().unwrap());
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/// }
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/// _ => println!("No error"),
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/// }
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/// }
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/// ```
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#[stable(feature = "error_source", since = "1.30.0")]
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fn source(&self) -> Option<&(dyn Error + 'static)> {
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None
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}
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/// Gets the `TypeId` of `self`.
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#[doc(hidden)]
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#[unstable(
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feature = "error_type_id",
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reason = "this is memory-unsafe to override in user code",
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issue = "60784"
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)]
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fn type_id(&self, _: private::Internal) -> TypeId
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where
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Self: 'static,
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{
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TypeId::of::<Self>()
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}
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/// ```
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/// if let Err(e) = "xc".parse::<u32>() {
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/// // Print `e` itself, no need for description().
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/// eprintln!("Error: {e}");
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[deprecated(since = "1.42.0", note = "use the Display impl or to_string()")]
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fn description(&self) -> &str {
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"description() is deprecated; use Display"
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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#[deprecated(
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since = "1.33.0",
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note = "replaced by Error::source, which can support downcasting"
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)]
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#[allow(missing_docs)]
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fn cause(&self) -> Option<&dyn Error> {
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self.source()
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}
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/// Provides type based access to context intended for error reports.
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///
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/// Used in conjunction with [`Demand::provide_value`] and [`Demand::provide_ref`] to extract
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/// references to member variables from `dyn Error` trait objects.
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///
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/// # Example
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///
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/// ```rust
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/// #![feature(provide_any)]
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/// #![feature(error_generic_member_access)]
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/// use core::fmt;
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/// use core::any::Demand;
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///
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/// #[derive(Debug)]
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/// struct MyBacktrace {
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/// // ...
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/// }
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///
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/// impl MyBacktrace {
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/// fn new() -> MyBacktrace {
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/// // ...
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/// # MyBacktrace {}
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/// }
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/// }
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///
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/// #[derive(Debug)]
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/// struct SourceError {
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/// // ...
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/// }
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///
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/// impl fmt::Display for SourceError {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "Example Source Error")
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/// }
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/// }
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///
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/// impl std::error::Error for SourceError {}
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///
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/// #[derive(Debug)]
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/// struct Error {
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/// source: SourceError,
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/// backtrace: MyBacktrace,
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/// }
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///
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/// impl fmt::Display for Error {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "Example Error")
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/// }
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/// }
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///
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/// impl std::error::Error for Error {
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/// fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
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/// demand
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/// .provide_ref::<MyBacktrace>(&self.backtrace)
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/// .provide_ref::<dyn std::error::Error + 'static>(&self.source);
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/// }
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/// }
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///
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/// fn main() {
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/// let backtrace = MyBacktrace::new();
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/// let source = SourceError {};
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/// let error = Error { source, backtrace };
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/// let dyn_error = &error as &dyn std::error::Error;
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/// let backtrace_ref = dyn_error.request_ref::<MyBacktrace>().unwrap();
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///
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/// assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
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/// }
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/// ```
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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#[allow(unused_variables)]
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fn provide<'a>(&'a self, demand: &mut Demand<'a>) {}
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}
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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impl<E> Provider for E
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where
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E: Error + ?Sized,
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{
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fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
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self.provide(demand)
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}
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}
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mod private {
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// This is a hack to prevent `type_id` from being overridden by `Error`
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// implementations, since that can enable unsound downcasting.
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#[unstable(feature = "error_type_id", issue = "60784")]
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#[derive(Debug)]
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pub struct Internal;
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}
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#[unstable(feature = "never_type", issue = "35121")]
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impl Error for ! {}
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impl<'a> dyn Error + 'a {
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/// Request a reference of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_ref<T: ?Sized + 'static>(&'a self) -> Option<&'a T> {
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core::any::request_ref(self)
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}
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/// Request a value of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_value<T: 'static>(&'a self) -> Option<T> {
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core::any::request_value(self)
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}
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}
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// Copied from `any.rs`.
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impl dyn Error + 'static {
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/// Returns `true` if the inner type is the same as `T`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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// Get `TypeId` of the type this function is instantiated with.
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let t = TypeId::of::<T>();
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// Get `TypeId` of the type in the trait object (`self`).
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let concrete = self.type_id(private::Internal);
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// Compare both `TypeId`s on equality.
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t == concrete
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}
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/// Returns some reference to the inner value if it is of type `T`, or
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/// `None` if it isn't.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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if self.is::<T>() {
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// SAFETY: `is` ensures this type cast is correct
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unsafe { Some(&*(self as *const dyn Error as *const T)) }
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} else {
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None
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}
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}
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/// Returns some mutable reference to the inner value if it is of type `T`, or
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/// `None` if it isn't.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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if self.is::<T>() {
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// SAFETY: `is` ensures this type cast is correct
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unsafe { Some(&mut *(self as *mut dyn Error as *mut T)) }
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} else {
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None
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}
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}
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}
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impl dyn Error + 'static + Send {
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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<dyn Error + 'static>::is::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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<dyn Error + 'static>::downcast_ref::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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<dyn Error + 'static>::downcast_mut::<T>(self)
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}
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/// Request a reference of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
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<dyn Error>::request_ref(self)
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}
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/// Request a value of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_value<T: 'static>(&self) -> Option<T> {
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<dyn Error>::request_value(self)
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}
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}
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impl dyn Error + 'static + Send + Sync {
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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<dyn Error + 'static>::is::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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<dyn Error + 'static>::downcast_ref::<T>(self)
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}
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/// Forwards to the method defined on the type `dyn Error`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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<dyn Error + 'static>::downcast_mut::<T>(self)
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}
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/// Request a reference of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
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<dyn Error>::request_ref(self)
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}
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/// Request a value of type `T` as context about this error.
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#[unstable(feature = "error_generic_member_access", issue = "99301")]
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pub fn request_value<T: 'static>(&self) -> Option<T> {
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<dyn Error>::request_value(self)
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}
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}
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impl dyn Error {
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/// Returns an iterator starting with the current error and continuing with
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/// recursively calling [`Error::source`].
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///
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/// If you want to omit the current error and only use its sources,
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/// use `skip(1)`.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(error_iter)]
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/// use std::error::Error;
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/// use std::fmt;
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///
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/// #[derive(Debug)]
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/// struct A;
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///
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/// #[derive(Debug)]
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/// struct B(Option<Box<dyn Error + 'static>>);
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///
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/// impl fmt::Display for A {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "A")
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/// }
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/// }
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///
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/// impl fmt::Display for B {
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/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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/// write!(f, "B")
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/// }
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/// }
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///
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/// impl Error for A {}
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///
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/// impl Error for B {
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/// fn source(&self) -> Option<&(dyn Error + 'static)> {
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/// self.0.as_ref().map(|e| e.as_ref())
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/// }
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/// }
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///
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/// let b = B(Some(Box::new(A)));
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///
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/// // let err : Box<Error> = b.into(); // or
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/// let err = &b as &(dyn Error);
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///
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/// let mut iter = err.sources();
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///
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/// assert_eq!("B".to_string(), iter.next().unwrap().to_string());
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/// assert_eq!("A".to_string(), iter.next().unwrap().to_string());
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/// assert!(iter.next().is_none());
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/// assert!(iter.next().is_none());
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/// ```
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#[unstable(feature = "error_iter", issue = "58520")]
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#[inline]
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pub fn sources(&self) -> Source<'_> {
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// You may think this method would be better in the Error trait, and you'd be right.
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// Unfortunately that doesn't work, not because of the object safety rules but because we
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// save a reference to self in Sources below as a trait object. If this method was
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// declared in Error, then self would have the type &T where T is some concrete type which
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// implements Error. We would need to coerce self to have type &dyn Error, but that requires
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// that Self has a known size (i.e., Self: Sized). We can't put that bound on Error
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// since that would forbid Error trait objects, and we can't put that bound on the method
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// because that means the method can't be called on trait objects (we'd also need the
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// 'static bound, but that isn't allowed because methods with bounds on Self other than
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// Sized are not object-safe). Requiring an Unsize bound is not backwards compatible.
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Source { current: Some(self) }
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}
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}
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/// An iterator over an [`Error`] and its sources.
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///
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/// If you want to omit the initial error and only process
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/// its sources, use `skip(1)`.
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#[unstable(feature = "error_iter", issue = "58520")]
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#[derive(Clone, Debug)]
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pub struct Source<'a> {
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current: Option<&'a (dyn Error + 'static)>,
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}
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#[unstable(feature = "error_iter", issue = "58520")]
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impl<'a> Iterator for Source<'a> {
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type Item = &'a (dyn Error + 'static);
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fn next(&mut self) -> Option<Self::Item> {
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let current = self.current;
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self.current = self.current.and_then(Error::source);
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current
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}
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}
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#[stable(feature = "error_by_ref", since = "1.51.0")]
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impl<'a, T: Error + ?Sized> Error for &'a T {
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#[allow(deprecated, deprecated_in_future)]
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fn description(&self) -> &str {
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Error::description(&**self)
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}
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#[allow(deprecated)]
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fn cause(&self) -> Option<&dyn Error> {
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Error::cause(&**self)
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}
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fn source(&self) -> Option<&(dyn Error + 'static)> {
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Error::source(&**self)
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}
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fn provide<'b>(&'b self, demand: &mut Demand<'b>) {
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Error::provide(&**self, demand);
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}
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}
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#[stable(feature = "fmt_error", since = "1.11.0")]
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impl Error for crate::fmt::Error {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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"an error occurred when formatting an argument"
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}
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}
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#[stable(feature = "try_borrow", since = "1.13.0")]
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impl Error for crate::cell::BorrowError {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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"already mutably borrowed"
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}
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}
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#[stable(feature = "try_borrow", since = "1.13.0")]
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impl Error for crate::cell::BorrowMutError {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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"already borrowed"
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}
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}
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#[stable(feature = "try_from", since = "1.34.0")]
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impl Error for crate::char::CharTryFromError {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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"converted integer out of range for `char`"
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}
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}
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#[stable(feature = "char_from_str", since = "1.20.0")]
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impl Error for crate::char::ParseCharError {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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self.__description()
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}
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}
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#[unstable(feature = "duration_checked_float", issue = "83400")]
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impl Error for crate::time::FromFloatSecsError {}
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#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
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impl Error for crate::ffi::FromBytesWithNulError {
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#[allow(deprecated)]
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fn description(&self) -> &str {
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self.__description()
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}
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}
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#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
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impl Error for crate::ffi::FromBytesUntilNulError {}
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