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#![doc = include_str!("../../core/src/error.md")]
#![stable(feature = "rust1", since = "1.0.0")]
#[cfg(test)]
mod tests;
use crate::backtrace::Backtrace;
use crate::fmt::{self, Write};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::error::Error;
#[unstable(feature = "error_generic_member_access", issue = "99301")]
pub use core::error::{request_ref, request_value, Request};
/// An error reporter that prints an error and its sources.
///
/// Report also exposes configuration options for formatting the error sources, either entirely on a
/// single line, or in multi-line format with each source on a new line.
///
/// `Report` only requires that the wrapped error implement `Error`. It doesn't require that the
/// wrapped error be `Send`, `Sync`, or `'static`.
///
/// # Examples
///
/// ```rust
/// #![feature(error_reporter)]
/// use std::error::{Error, Report};
/// use std::fmt;
///
/// #[derive(Debug)]
/// struct SuperError {
/// source: SuperErrorSideKick,
/// }
///
/// impl fmt::Display for SuperError {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "SuperError is here!")
/// }
/// }
///
/// impl Error for SuperError {
/// fn source(&self) -> Option<&(dyn Error + 'static)> {
/// Some(&self.source)
/// }
/// }
///
/// #[derive(Debug)]
/// struct SuperErrorSideKick;
///
/// impl fmt::Display for SuperErrorSideKick {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "SuperErrorSideKick is here!")
/// }
/// }
///
/// impl Error for SuperErrorSideKick {}
///
/// fn get_super_error() -> Result<(), SuperError> {
/// Err(SuperError { source: SuperErrorSideKick })
/// }
///
/// fn main() {
/// match get_super_error() {
/// Err(e) => println!("Error: {}", Report::new(e)),
/// _ => println!("No error"),
/// }
/// }
/// ```
///
/// This example produces the following output:
///
/// ```console
/// Error: SuperError is here!: SuperErrorSideKick is here!
/// ```
///
/// ## Output consistency
///
/// Report prints the same output via `Display` and `Debug`, so it works well with
/// [`Result::unwrap`]/[`Result::expect`] which print their `Err` variant via `Debug`:
///
/// ```should_panic
/// #![feature(error_reporter)]
/// use std::error::Report;
/// # use std::error::Error;
/// # use std::fmt;
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKick;
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKick {}
/// # fn get_super_error() -> Result<(), SuperError> {
/// # Err(SuperError { source: SuperErrorSideKick })
/// # }
///
/// get_super_error().map_err(Report::new).unwrap();
/// ```
///
/// This example produces the following output:
///
/// ```console
/// thread 'main' panicked at src/error.rs:34:40:
/// called `Result::unwrap()` on an `Err` value: SuperError is here!: SuperErrorSideKick is here!
/// note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
/// ```
///
/// ## Return from `main`
///
/// `Report` also implements `From` for all types that implement [`Error`]; this when combined with
/// the `Debug` output means `Report` is an ideal starting place for formatting errors returned
/// from `main`.
///
/// ```should_panic
/// #![feature(error_reporter)]
/// use std::error::Report;
/// # use std::error::Error;
/// # use std::fmt;
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKick;
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKick {}
/// # fn get_super_error() -> Result<(), SuperError> {
/// # Err(SuperError { source: SuperErrorSideKick })
/// # }
///
/// fn main() -> Result<(), Report<SuperError>> {
/// get_super_error()?;
/// Ok(())
/// }
/// ```
///
/// This example produces the following output:
///
/// ```console
/// Error: SuperError is here!: SuperErrorSideKick is here!
/// ```
///
/// **Note**: `Report`s constructed via `?` and `From` will be configured to use the single line
/// output format. If you want to make sure your `Report`s are pretty printed and include backtrace
/// you will need to manually convert and enable those flags.
///
/// ```should_panic
/// #![feature(error_reporter)]
/// use std::error::Report;
/// # use std::error::Error;
/// # use std::fmt;
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKick;
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKick {}
/// # fn get_super_error() -> Result<(), SuperError> {
/// # Err(SuperError { source: SuperErrorSideKick })
/// # }
///
/// fn main() -> Result<(), Report<SuperError>> {
/// get_super_error()
/// .map_err(Report::from)
/// .map_err(|r| r.pretty(true).show_backtrace(true))?;
/// Ok(())
/// }
/// ```
///
/// This example produces the following output:
///
/// ```console
/// Error: SuperError is here!
///
/// Caused by:
/// SuperErrorSideKick is here!
/// ```
#[unstable(feature = "error_reporter", issue = "90172")]
pub struct Report<E = Box<dyn Error>> {
/// The error being reported.
error: E,
/// Whether a backtrace should be included as part of the report.
show_backtrace: bool,
/// Whether the report should be pretty-printed.
pretty: bool,
}
impl<E> Report<E>
where
Report<E>: From<E>,
{
/// Create a new `Report` from an input error.
#[unstable(feature = "error_reporter", issue = "90172")]
pub fn new(error: E) -> Report<E> {
Self::from(error)
}
}
impl<E> Report<E> {
/// Enable pretty-printing the report across multiple lines.
///
/// # Examples
///
/// ```rust
/// #![feature(error_reporter)]
/// use std::error::Report;
/// # use std::error::Error;
/// # use std::fmt;
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKick;
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKick {}
///
/// let error = SuperError { source: SuperErrorSideKick };
/// let report = Report::new(error).pretty(true);
/// eprintln!("Error: {report:?}");
/// ```
///
/// This example produces the following output:
///
/// ```console
/// Error: SuperError is here!
///
/// Caused by:
/// SuperErrorSideKick is here!
/// ```
///
/// When there are multiple source errors the causes will be numbered in order of iteration
/// starting from the outermost error.
///
/// ```rust
/// #![feature(error_reporter)]
/// use std::error::Report;
/// # use std::error::Error;
/// # use std::fmt;
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKick {
/// # source: SuperErrorSideKickSideKick,
/// # }
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKick {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// # #[derive(Debug)]
/// # struct SuperErrorSideKickSideKick;
/// # impl fmt::Display for SuperErrorSideKickSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKickSideKick is here!")
/// # }
/// # }
/// # impl Error for SuperErrorSideKickSideKick { }
///
/// let source = SuperErrorSideKickSideKick;
/// let source = SuperErrorSideKick { source };
/// let error = SuperError { source };
/// let report = Report::new(error).pretty(true);
/// eprintln!("Error: {report:?}");
/// ```
///
/// This example produces the following output:
///
/// ```console
/// Error: SuperError is here!
///
/// Caused by:
/// 0: SuperErrorSideKick is here!
/// 1: SuperErrorSideKickSideKick is here!
/// ```
#[unstable(feature = "error_reporter", issue = "90172")]
pub fn pretty(mut self, pretty: bool) -> Self {
self.pretty = pretty;
self
}
/// Display backtrace if available when using pretty output format.
///
/// # Examples
///
/// **Note**: Report will search for the first `Backtrace` it can find starting from the
/// outermost error. In this example it will display the backtrace from the second error in the
/// sources, `SuperErrorSideKick`.
///
/// ```rust
/// #![feature(error_reporter)]
/// #![feature(error_generic_member_access)]
/// # use std::error::Error;
/// # use std::fmt;
/// use std::error::Request;
/// use std::error::Report;
/// use std::backtrace::Backtrace;
///
/// # #[derive(Debug)]
/// # struct SuperError {
/// # source: SuperErrorSideKick,
/// # }
/// # impl fmt::Display for SuperError {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperError is here!")
/// # }
/// # }
/// # impl Error for SuperError {
/// # fn source(&self) -> Option<&(dyn Error + 'static)> {
/// # Some(&self.source)
/// # }
/// # }
/// #[derive(Debug)]
/// struct SuperErrorSideKick {
/// backtrace: Backtrace,
/// }
///
/// impl SuperErrorSideKick {
/// fn new() -> SuperErrorSideKick {
/// SuperErrorSideKick { backtrace: Backtrace::force_capture() }
/// }
/// }
///
/// impl Error for SuperErrorSideKick {
/// fn provide<'a>(&'a self, request: &mut Request<'a>) {
/// request.provide_ref::<Backtrace>(&self.backtrace);
/// }
/// }
///
/// // The rest of the example is unchanged ...
/// # impl fmt::Display for SuperErrorSideKick {
/// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// # write!(f, "SuperErrorSideKick is here!")
/// # }
/// # }
///
/// let source = SuperErrorSideKick::new();
/// let error = SuperError { source };
/// let report = Report::new(error).pretty(true).show_backtrace(true);
/// eprintln!("Error: {report:?}");
/// ```
///
/// This example produces something similar to the following output:
///
/// ```console
/// Error: SuperError is here!
///
/// Caused by:
/// SuperErrorSideKick is here!
///
/// Stack backtrace:
/// 0: rust_out::main::_doctest_main_src_error_rs_1158_0::SuperErrorSideKick::new
/// 1: rust_out::main::_doctest_main_src_error_rs_1158_0
/// 2: rust_out::main
/// 3: core::ops::function::FnOnce::call_once
/// 4: std::sys_common::backtrace::__rust_begin_short_backtrace
/// 5: std::rt::lang_start::{{closure}}
/// 6: std::panicking::try
/// 7: std::rt::lang_start_internal
/// 8: std::rt::lang_start
/// 9: main
/// 10: __libc_start_main
/// 11: _start
/// ```
#[unstable(feature = "error_reporter", issue = "90172")]
pub fn show_backtrace(mut self, show_backtrace: bool) -> Self {
self.show_backtrace = show_backtrace;
self
}
}
impl<E> Report<E>
where
E: Error,
{
fn backtrace(&self) -> Option<&Backtrace> {
// have to grab the backtrace on the first error directly since that error may not be
// 'static
let backtrace = request_ref(&self.error);
let backtrace = backtrace.or_else(|| {
self.error
.source()
.map(|source| source.sources().find_map(|source| request_ref(source)))
.flatten()
});
backtrace
}
/// Format the report as a single line.
#[unstable(feature = "error_reporter", issue = "90172")]
fn fmt_singleline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.error)?;
let sources = self.error.source().into_iter().flat_map(<dyn Error>::sources);
for cause in sources {
write!(f, ": {cause}")?;
}
Ok(())
}
/// Format the report as multiple lines, with each error cause on its own line.
#[unstable(feature = "error_reporter", issue = "90172")]
fn fmt_multiline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let error = &self.error;
write!(f, "{error}")?;
if let Some(cause) = error.source() {
write!(f, "\n\nCaused by:")?;
let multiple = cause.source().is_some();
for (ind, error) in cause.sources().enumerate() {
writeln!(f)?;
let mut indented = Indented { inner: f };
if multiple {
write!(indented, "{ind: >4}: {error}")?;
} else {
write!(indented, " {error}")?;
}
}
}
if self.show_backtrace {
let backtrace = self.backtrace();
if let Some(backtrace) = backtrace {
let backtrace = backtrace.to_string();
f.write_str("\n\nStack backtrace:\n")?;
f.write_str(backtrace.trim_end())?;
}
}
Ok(())
}
}
#[unstable(feature = "error_reporter", issue = "90172")]
impl<E> From<E> for Report<E>
where
E: Error,
{
fn from(error: E) -> Self {
Report { error, show_backtrace: false, pretty: false }
}
}
#[unstable(feature = "error_reporter", issue = "90172")]
impl<E> fmt::Display for Report<E>
where
E: Error,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if self.pretty { self.fmt_multiline(f) } else { self.fmt_singleline(f) }
}
}
// This type intentionally outputs the same format for `Display` and `Debug`for
// situations where you unwrap a `Report` or return it from main.
#[unstable(feature = "error_reporter", issue = "90172")]
impl<E> fmt::Debug for Report<E>
where
Report<E>: fmt::Display,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(self, f)
}
}
/// Wrapper type for indenting the inner source.
struct Indented<'a, D> {
inner: &'a mut D,
}
impl<T> Write for Indented<'_, T>
where
T: Write,
{
fn write_str(&mut self, s: &str) -> fmt::Result {
for (i, line) in s.split('\n').enumerate() {
if i > 0 {
self.inner.write_char('\n')?;
self.inner.write_str(" ")?;
}
self.inner.write_str(line)?;
}
Ok(())
}
}