1 //! Traits for working with Errors.
3 #![stable(feature = "rust1", since = "1.0.0")]
5 // A note about crates and the facade:
7 // Originally, the `Error` trait was defined in libcore, and the impls
8 // were scattered about. However, coherence objected to this
9 // arrangement, because to create the blanket impls for `Box` required
10 // knowing that `&str: !Error`, and we have no means to deal with that
11 // sort of conflict just now. Therefore, for the time being, we have
12 // moved the `Error` trait into libstd. As we evolve a sol'n to the
13 // coherence challenge (e.g., specialization, neg impls, etc) we can
14 // reconsider what crate these items belong in.
20 use core::convert::Infallible;
22 use crate::alloc::{AllocError, LayoutError};
23 use crate::any::TypeId;
24 use crate::backtrace::Backtrace;
25 use crate::borrow::Cow;
28 use crate::fmt::{self, Debug, Display, Write};
29 use crate::mem::transmute;
36 /// `Error` is a trait representing the basic expectations for error values,
37 /// i.e., values of type `E` in [`Result<T, E>`].
39 /// Errors must describe themselves through the [`Display`] and [`Debug`]
40 /// traits. Error messages are typically concise lowercase sentences without
41 /// trailing punctuation:
44 /// let err = "NaN".parse::<u32>().unwrap_err();
45 /// assert_eq!(err.to_string(), "invalid digit found in string");
48 /// Errors may provide cause chain information. [`Error::source()`] is generally
49 /// used when errors cross "abstraction boundaries". If one module must report
50 /// an error that is caused by an error from a lower-level module, it can allow
51 /// accessing that error via [`Error::source()`]. This makes it possible for the
52 /// high-level module to provide its own errors while also revealing some of the
53 /// implementation for debugging via `source` chains.
54 #[stable(feature = "rust1", since = "1.0.0")]
55 pub trait Error: Debug + Display {
56 /// The lower-level source of this error, if any.
61 /// use std::error::Error;
65 /// struct SuperError {
66 /// source: SuperErrorSideKick,
69 /// impl fmt::Display for SuperError {
70 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
71 /// write!(f, "SuperError is here!")
75 /// impl Error for SuperError {
76 /// fn source(&self) -> Option<&(dyn Error + 'static)> {
77 /// Some(&self.source)
82 /// struct SuperErrorSideKick;
84 /// impl fmt::Display for SuperErrorSideKick {
85 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
86 /// write!(f, "SuperErrorSideKick is here!")
90 /// impl Error for SuperErrorSideKick {}
92 /// fn get_super_error() -> Result<(), SuperError> {
93 /// Err(SuperError { source: SuperErrorSideKick })
97 /// match get_super_error() {
99 /// println!("Error: {e}");
100 /// println!("Caused by: {}", e.source().unwrap());
102 /// _ => println!("No error"),
106 #[stable(feature = "error_source", since = "1.30.0")]
107 fn source(&self) -> Option<&(dyn Error + 'static)> {
111 /// Gets the `TypeId` of `self`.
114 feature = "error_type_id",
115 reason = "this is memory-unsafe to override in user code",
118 fn type_id(&self, _: private::Internal) -> TypeId
125 /// Returns a stack backtrace, if available, of where this error occurred.
127 /// This function allows inspecting the location, in code, of where an error
128 /// happened. The returned `Backtrace` contains information about the stack
129 /// trace of the OS thread of execution of where the error originated from.
131 /// Note that not all errors contain a `Backtrace`. Also note that a
132 /// `Backtrace` may actually be empty. For more information consult the
133 /// `Backtrace` type itself.
134 #[unstable(feature = "backtrace", issue = "53487")]
135 fn backtrace(&self) -> Option<&Backtrace> {
140 /// if let Err(e) = "xc".parse::<u32>() {
141 /// // Print `e` itself, no need for description().
142 /// eprintln!("Error: {e}");
145 #[stable(feature = "rust1", since = "1.0.0")]
146 #[rustc_deprecated(since = "1.42.0", reason = "use the Display impl or to_string()")]
147 fn description(&self) -> &str {
148 "description() is deprecated; use Display"
151 #[stable(feature = "rust1", since = "1.0.0")]
154 reason = "replaced by Error::source, which can support downcasting"
156 #[allow(missing_docs)]
157 fn cause(&self) -> Option<&dyn Error> {
163 // This is a hack to prevent `type_id` from being overridden by `Error`
164 // implementations, since that can enable unsound downcasting.
165 #[unstable(feature = "error_type_id", issue = "60784")]
170 #[stable(feature = "rust1", since = "1.0.0")]
171 impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
172 /// Converts a type of [`Error`] into a box of dyn [`Error`].
177 /// use std::error::Error;
184 /// impl fmt::Display for AnError {
185 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
186 /// write!(f, "An error")
190 /// impl Error for AnError {}
192 /// let an_error = AnError;
193 /// assert!(0 == mem::size_of_val(&an_error));
194 /// let a_boxed_error = Box::<dyn Error>::from(an_error);
195 /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
197 fn from(err: E) -> Box<dyn Error + 'a> {
202 #[stable(feature = "rust1", since = "1.0.0")]
203 impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
204 /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
205 /// dyn [`Error`] + [`Send`] + [`Sync`].
210 /// use std::error::Error;
217 /// impl fmt::Display for AnError {
218 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
219 /// write!(f, "An error")
223 /// impl Error for AnError {}
225 /// unsafe impl Send for AnError {}
227 /// unsafe impl Sync for AnError {}
229 /// let an_error = AnError;
230 /// assert!(0 == mem::size_of_val(&an_error));
231 /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
233 /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
235 fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
240 #[stable(feature = "rust1", since = "1.0.0")]
241 impl From<String> for Box<dyn Error + Send + Sync> {
242 /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
247 /// use std::error::Error;
250 /// let a_string_error = "a string error".to_string();
251 /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
253 /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
256 fn from(err: String) -> Box<dyn Error + Send + Sync> {
257 struct StringError(String);
259 impl Error for StringError {
261 fn description(&self) -> &str {
266 impl Display for StringError {
267 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
268 Display::fmt(&self.0, f)
272 // Purposefully skip printing "StringError(..)"
273 impl Debug for StringError {
274 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
275 Debug::fmt(&self.0, f)
279 Box::new(StringError(err))
283 #[stable(feature = "string_box_error", since = "1.6.0")]
284 impl From<String> for Box<dyn Error> {
285 /// Converts a [`String`] into a box of dyn [`Error`].
290 /// use std::error::Error;
293 /// let a_string_error = "a string error".to_string();
294 /// let a_boxed_error = Box::<dyn Error>::from(a_string_error);
295 /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
297 fn from(str_err: String) -> Box<dyn Error> {
298 let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
299 let err2: Box<dyn Error> = err1;
304 #[stable(feature = "rust1", since = "1.0.0")]
305 impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
306 /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
308 /// [`str`]: prim@str
313 /// use std::error::Error;
316 /// let a_str_error = "a str error";
317 /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
319 /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
322 fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> {
323 From::from(String::from(err))
327 #[stable(feature = "string_box_error", since = "1.6.0")]
328 impl From<&str> for Box<dyn Error> {
329 /// Converts a [`str`] into a box of dyn [`Error`].
331 /// [`str`]: prim@str
336 /// use std::error::Error;
339 /// let a_str_error = "a str error";
340 /// let a_boxed_error = Box::<dyn Error>::from(a_str_error);
341 /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
343 fn from(err: &str) -> Box<dyn Error> {
344 From::from(String::from(err))
348 #[stable(feature = "cow_box_error", since = "1.22.0")]
349 impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
350 /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
355 /// use std::error::Error;
357 /// use std::borrow::Cow;
359 /// let a_cow_str_error = Cow::from("a str error");
360 /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
362 /// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
364 fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
365 From::from(String::from(err))
369 #[stable(feature = "cow_box_error", since = "1.22.0")]
370 impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
371 /// Converts a [`Cow`] into a box of dyn [`Error`].
376 /// use std::error::Error;
378 /// use std::borrow::Cow;
380 /// let a_cow_str_error = Cow::from("a str error");
381 /// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
382 /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
384 fn from(err: Cow<'a, str>) -> Box<dyn Error> {
385 From::from(String::from(err))
389 #[unstable(feature = "never_type", issue = "35121")]
393 feature = "allocator_api",
394 reason = "the precise API and guarantees it provides may be tweaked.",
397 impl Error for AllocError {}
399 #[stable(feature = "alloc_layout", since = "1.28.0")]
400 impl Error for LayoutError {}
402 #[stable(feature = "rust1", since = "1.0.0")]
403 impl Error for str::ParseBoolError {
405 fn description(&self) -> &str {
406 "failed to parse bool"
410 #[stable(feature = "rust1", since = "1.0.0")]
411 impl Error for str::Utf8Error {
413 fn description(&self) -> &str {
414 "invalid utf-8: corrupt contents"
418 #[stable(feature = "rust1", since = "1.0.0")]
419 impl Error for num::ParseIntError {
421 fn description(&self) -> &str {
426 #[stable(feature = "try_from", since = "1.34.0")]
427 impl Error for num::TryFromIntError {
429 fn description(&self) -> &str {
434 #[stable(feature = "try_from", since = "1.34.0")]
435 impl Error for array::TryFromSliceError {
437 fn description(&self) -> &str {
442 #[stable(feature = "rust1", since = "1.0.0")]
443 impl Error for num::ParseFloatError {
445 fn description(&self) -> &str {
450 #[stable(feature = "rust1", since = "1.0.0")]
451 impl Error for string::FromUtf8Error {
453 fn description(&self) -> &str {
458 #[stable(feature = "rust1", since = "1.0.0")]
459 impl Error for string::FromUtf16Error {
461 fn description(&self) -> &str {
466 #[stable(feature = "str_parse_error2", since = "1.8.0")]
467 impl Error for Infallible {
468 fn description(&self) -> &str {
473 #[stable(feature = "decode_utf16", since = "1.9.0")]
474 impl Error for char::DecodeUtf16Error {
476 fn description(&self) -> &str {
477 "unpaired surrogate found"
481 #[stable(feature = "u8_from_char", since = "1.59.0")]
482 impl Error for char::TryFromCharError {}
484 #[unstable(feature = "map_try_insert", issue = "82766")]
485 impl<'a, K: Debug + Ord, V: Debug> Error
486 for crate::collections::btree_map::OccupiedError<'a, K, V>
489 fn description(&self) -> &str {
494 #[unstable(feature = "map_try_insert", issue = "82766")]
495 impl<'a, K: Debug, V: Debug> Error for crate::collections::hash_map::OccupiedError<'a, K, V> {
497 fn description(&self) -> &str {
502 #[stable(feature = "box_error", since = "1.8.0")]
503 impl<T: Error> Error for Box<T> {
504 #[allow(deprecated, deprecated_in_future)]
505 fn description(&self) -> &str {
506 Error::description(&**self)
510 fn cause(&self) -> Option<&dyn Error> {
511 Error::cause(&**self)
514 fn source(&self) -> Option<&(dyn Error + 'static)> {
515 Error::source(&**self)
519 #[unstable(feature = "thin_box", issue = "92791")]
520 impl<T: ?Sized + crate::error::Error> crate::error::Error for crate::boxed::ThinBox<T> {
521 fn source(&self) -> Option<&(dyn crate::error::Error + 'static)> {
522 use core::ops::Deref;
523 self.deref().source()
527 #[stable(feature = "error_by_ref", since = "1.51.0")]
528 impl<'a, T: Error + ?Sized> Error for &'a T {
529 #[allow(deprecated, deprecated_in_future)]
530 fn description(&self) -> &str {
531 Error::description(&**self)
535 fn cause(&self) -> Option<&dyn Error> {
536 Error::cause(&**self)
539 fn source(&self) -> Option<&(dyn Error + 'static)> {
540 Error::source(&**self)
543 fn backtrace(&self) -> Option<&Backtrace> {
544 Error::backtrace(&**self)
548 #[stable(feature = "arc_error", since = "1.52.0")]
549 impl<T: Error + ?Sized> Error for Arc<T> {
550 #[allow(deprecated, deprecated_in_future)]
551 fn description(&self) -> &str {
552 Error::description(&**self)
556 fn cause(&self) -> Option<&dyn Error> {
557 Error::cause(&**self)
560 fn source(&self) -> Option<&(dyn Error + 'static)> {
561 Error::source(&**self)
564 fn backtrace(&self) -> Option<&Backtrace> {
565 Error::backtrace(&**self)
569 #[stable(feature = "fmt_error", since = "1.11.0")]
570 impl Error for fmt::Error {
572 fn description(&self) -> &str {
573 "an error occurred when formatting an argument"
577 #[stable(feature = "try_borrow", since = "1.13.0")]
578 impl Error for cell::BorrowError {
580 fn description(&self) -> &str {
581 "already mutably borrowed"
585 #[stable(feature = "try_borrow", since = "1.13.0")]
586 impl Error for cell::BorrowMutError {
588 fn description(&self) -> &str {
593 #[stable(feature = "try_from", since = "1.34.0")]
594 impl Error for char::CharTryFromError {
596 fn description(&self) -> &str {
597 "converted integer out of range for `char`"
601 #[stable(feature = "char_from_str", since = "1.20.0")]
602 impl Error for char::ParseCharError {
604 fn description(&self) -> &str {
609 #[stable(feature = "try_reserve", since = "1.57.0")]
610 impl Error for alloc::collections::TryReserveError {}
612 #[unstable(feature = "duration_checked_float", issue = "83400")]
613 impl Error for time::FromFloatSecsError {}
615 // Copied from `any.rs`.
616 impl dyn Error + 'static {
617 /// Returns `true` if the inner type is the same as `T`.
618 #[stable(feature = "error_downcast", since = "1.3.0")]
620 pub fn is<T: Error + 'static>(&self) -> bool {
621 // Get `TypeId` of the type this function is instantiated with.
622 let t = TypeId::of::<T>();
624 // Get `TypeId` of the type in the trait object (`self`).
625 let concrete = self.type_id(private::Internal);
627 // Compare both `TypeId`s on equality.
631 /// Returns some reference to the inner value if it is of type `T`, or
632 /// `None` if it isn't.
633 #[stable(feature = "error_downcast", since = "1.3.0")]
635 pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
637 unsafe { Some(&*(self as *const dyn Error as *const T)) }
643 /// Returns some mutable reference to the inner value if it is of type `T`, or
644 /// `None` if it isn't.
645 #[stable(feature = "error_downcast", since = "1.3.0")]
647 pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
649 unsafe { Some(&mut *(self as *mut dyn Error as *mut T)) }
656 impl dyn Error + 'static + Send {
657 /// Forwards to the method defined on the type `dyn Error`.
658 #[stable(feature = "error_downcast", since = "1.3.0")]
660 pub fn is<T: Error + 'static>(&self) -> bool {
661 <dyn Error + 'static>::is::<T>(self)
664 /// Forwards to the method defined on the type `dyn Error`.
665 #[stable(feature = "error_downcast", since = "1.3.0")]
667 pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
668 <dyn Error + 'static>::downcast_ref::<T>(self)
671 /// Forwards to the method defined on the type `dyn Error`.
672 #[stable(feature = "error_downcast", since = "1.3.0")]
674 pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
675 <dyn Error + 'static>::downcast_mut::<T>(self)
679 impl dyn Error + 'static + Send + Sync {
680 /// Forwards to the method defined on the type `dyn Error`.
681 #[stable(feature = "error_downcast", since = "1.3.0")]
683 pub fn is<T: Error + 'static>(&self) -> bool {
684 <dyn Error + 'static>::is::<T>(self)
687 /// Forwards to the method defined on the type `dyn Error`.
688 #[stable(feature = "error_downcast", since = "1.3.0")]
690 pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
691 <dyn Error + 'static>::downcast_ref::<T>(self)
694 /// Forwards to the method defined on the type `dyn Error`.
695 #[stable(feature = "error_downcast", since = "1.3.0")]
697 pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
698 <dyn Error + 'static>::downcast_mut::<T>(self)
704 #[stable(feature = "error_downcast", since = "1.3.0")]
705 /// Attempts to downcast the box to a concrete type.
706 pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> {
709 let raw: *mut dyn Error = Box::into_raw(self);
710 Ok(Box::from_raw(raw as *mut T))
717 /// Returns an iterator starting with the current error and continuing with
718 /// recursively calling [`Error::source`].
720 /// If you want to omit the current error and only use its sources,
726 /// #![feature(error_iter)]
727 /// use std::error::Error;
734 /// struct B(Option<Box<dyn Error + 'static>>);
736 /// impl fmt::Display for A {
737 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
742 /// impl fmt::Display for B {
743 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
748 /// impl Error for A {}
750 /// impl Error for B {
751 /// fn source(&self) -> Option<&(dyn Error + 'static)> {
752 /// self.0.as_ref().map(|e| e.as_ref())
756 /// let b = B(Some(Box::new(A)));
758 /// // let err : Box<Error> = b.into(); // or
759 /// let err = &b as &(dyn Error);
761 /// let mut iter = err.chain();
763 /// assert_eq!("B".to_string(), iter.next().unwrap().to_string());
764 /// assert_eq!("A".to_string(), iter.next().unwrap().to_string());
765 /// assert!(iter.next().is_none());
766 /// assert!(iter.next().is_none());
768 #[unstable(feature = "error_iter", issue = "58520")]
770 pub fn chain(&self) -> Chain<'_> {
771 Chain { current: Some(self) }
775 /// An iterator over an [`Error`] and its sources.
777 /// If you want to omit the initial error and only process
778 /// its sources, use `skip(1)`.
779 #[unstable(feature = "error_iter", issue = "58520")]
780 #[derive(Clone, Debug)]
781 pub struct Chain<'a> {
782 current: Option<&'a (dyn Error + 'static)>,
785 #[unstable(feature = "error_iter", issue = "58520")]
786 impl<'a> Iterator for Chain<'a> {
787 type Item = &'a (dyn Error + 'static);
789 fn next(&mut self) -> Option<Self::Item> {
790 let current = self.current;
791 self.current = self.current.and_then(Error::source);
796 impl dyn Error + Send {
798 #[stable(feature = "error_downcast", since = "1.3.0")]
799 /// Attempts to downcast the box to a concrete type.
800 pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error + Send>> {
801 let err: Box<dyn Error> = self;
802 <dyn Error>::downcast(err).map_err(|s| unsafe {
803 // Reapply the `Send` marker.
804 transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
809 impl dyn Error + Send + Sync {
811 #[stable(feature = "error_downcast", since = "1.3.0")]
812 /// Attempts to downcast the box to a concrete type.
813 pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
814 let err: Box<dyn Error> = self;
815 <dyn Error>::downcast(err).map_err(|s| unsafe {
816 // Reapply the `Send + Sync` marker.
817 transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
822 /// An error reporter that print's an error and its sources.
824 /// Report also exposes configuration options for formatting the error chain, either entirely on a
825 /// single line, or in multi-line format with each cause in the error chain on a new line.
827 /// `Report` only requires that the wrapped error implements `Error`. It doesn't require that the
828 /// wrapped error be `Send`, `Sync`, or `'static`.
833 /// #![feature(error_reporter)]
834 /// use std::error::{Error, Report};
838 /// struct SuperError {
839 /// source: SuperErrorSideKick,
842 /// impl fmt::Display for SuperError {
843 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
844 /// write!(f, "SuperError is here!")
848 /// impl Error for SuperError {
849 /// fn source(&self) -> Option<&(dyn Error + 'static)> {
850 /// Some(&self.source)
855 /// struct SuperErrorSideKick;
857 /// impl fmt::Display for SuperErrorSideKick {
858 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
859 /// write!(f, "SuperErrorSideKick is here!")
863 /// impl Error for SuperErrorSideKick {}
865 /// fn get_super_error() -> Result<(), SuperError> {
866 /// Err(SuperError { source: SuperErrorSideKick })
870 /// match get_super_error() {
871 /// Err(e) => println!("Error: {}", Report::new(e)),
872 /// _ => println!("No error"),
877 /// This example produces the following output:
880 /// Error: SuperError is here!: SuperErrorSideKick is here!
883 /// ## Output consistency
885 /// Report prints the same output via `Display` and `Debug`, so it works well with
886 /// [`Result::unwrap`]/[`Result::expect`] which print their `Err` variant via `Debug`:
889 /// #![feature(error_reporter)]
890 /// use std::error::Report;
891 /// # use std::error::Error;
893 /// # #[derive(Debug)]
894 /// # struct SuperError {
895 /// # source: SuperErrorSideKick,
897 /// # impl fmt::Display for SuperError {
898 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
899 /// # write!(f, "SuperError is here!")
902 /// # impl Error for SuperError {
903 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
904 /// # Some(&self.source)
907 /// # #[derive(Debug)]
908 /// # struct SuperErrorSideKick;
909 /// # impl fmt::Display for SuperErrorSideKick {
910 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
911 /// # write!(f, "SuperErrorSideKick is here!")
914 /// # impl Error for SuperErrorSideKick {}
915 /// # fn get_super_error() -> Result<(), SuperError> {
916 /// # Err(SuperError { source: SuperErrorSideKick })
919 /// get_super_error().map_err(Report::new).unwrap();
922 /// This example produces the following output:
925 /// thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: SuperError is here!: SuperErrorSideKick is here!', src/error.rs:34:40
926 /// note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
929 /// ## Return from `main`
931 /// `Report` also implements `From` for all types that implement [`Error`], this when combined with
932 /// the `Debug` output means `Report` is an ideal starting place for formatting errors returned
936 /// #![feature(error_reporter)]
937 /// use std::error::Report;
938 /// # use std::error::Error;
940 /// # #[derive(Debug)]
941 /// # struct SuperError {
942 /// # source: SuperErrorSideKick,
944 /// # impl fmt::Display for SuperError {
945 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
946 /// # write!(f, "SuperError is here!")
949 /// # impl Error for SuperError {
950 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
951 /// # Some(&self.source)
954 /// # #[derive(Debug)]
955 /// # struct SuperErrorSideKick;
956 /// # impl fmt::Display for SuperErrorSideKick {
957 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
958 /// # write!(f, "SuperErrorSideKick is here!")
961 /// # impl Error for SuperErrorSideKick {}
962 /// # fn get_super_error() -> Result<(), SuperError> {
963 /// # Err(SuperError { source: SuperErrorSideKick })
966 /// fn main() -> Result<(), Report> {
967 /// get_super_error()?;
972 /// This example produces the following output:
975 /// Error: SuperError is here!: SuperErrorSideKick is here!
978 /// **Note**: `Report`s constructed via `?` and `From` will be configured to use the single line
979 /// output format, if you want to make sure your `Report`s are pretty printed and include backtrace
980 /// you will need to manually convert and enable those flags.
983 /// #![feature(error_reporter)]
984 /// use std::error::Report;
985 /// # use std::error::Error;
987 /// # #[derive(Debug)]
988 /// # struct SuperError {
989 /// # source: SuperErrorSideKick,
991 /// # impl fmt::Display for SuperError {
992 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
993 /// # write!(f, "SuperError is here!")
996 /// # impl Error for SuperError {
997 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
998 /// # Some(&self.source)
1001 /// # #[derive(Debug)]
1002 /// # struct SuperErrorSideKick;
1003 /// # impl fmt::Display for SuperErrorSideKick {
1004 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1005 /// # write!(f, "SuperErrorSideKick is here!")
1008 /// # impl Error for SuperErrorSideKick {}
1009 /// # fn get_super_error() -> Result<(), SuperError> {
1010 /// # Err(SuperError { source: SuperErrorSideKick })
1013 /// fn main() -> Result<(), Report> {
1014 /// get_super_error()
1015 /// .map_err(Report::from)
1016 /// .map_err(|r| r.pretty(true).show_backtrace(true))?;
1021 /// This example produces the following output:
1024 /// Error: SuperError is here!
1027 /// SuperErrorSideKick is here!
1029 #[unstable(feature = "error_reporter", issue = "90172")]
1030 pub struct Report<E = Box<dyn Error>> {
1031 /// The error being reported.
1033 /// Whether a backtrace should be included as part of the report.
1034 show_backtrace: bool,
1035 /// Whether the report should be pretty-printed.
1043 /// Create a new `Report` from an input error.
1044 #[unstable(feature = "error_reporter", issue = "90172")]
1045 pub fn new(error: E) -> Report<E> {
1051 /// Enable pretty-printing the report across multiple lines.
1056 /// #![feature(error_reporter)]
1057 /// use std::error::Report;
1058 /// # use std::error::Error;
1060 /// # #[derive(Debug)]
1061 /// # struct SuperError {
1062 /// # source: SuperErrorSideKick,
1064 /// # impl fmt::Display for SuperError {
1065 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1066 /// # write!(f, "SuperError is here!")
1069 /// # impl Error for SuperError {
1070 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
1071 /// # Some(&self.source)
1074 /// # #[derive(Debug)]
1075 /// # struct SuperErrorSideKick;
1076 /// # impl fmt::Display for SuperErrorSideKick {
1077 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1078 /// # write!(f, "SuperErrorSideKick is here!")
1081 /// # impl Error for SuperErrorSideKick {}
1083 /// let error = SuperError { source: SuperErrorSideKick };
1084 /// let report = Report::new(error).pretty(true);
1085 /// eprintln!("Error: {report:?}");
1088 /// This example produces the following output:
1091 /// Error: SuperError is here!
1094 /// SuperErrorSideKick is here!
1097 /// When there are multiple source errors the causes will be numbered in order of iteration
1098 /// starting from the outermost error.
1101 /// #![feature(error_reporter)]
1102 /// use std::error::Report;
1103 /// # use std::error::Error;
1105 /// # #[derive(Debug)]
1106 /// # struct SuperError {
1107 /// # source: SuperErrorSideKick,
1109 /// # impl fmt::Display for SuperError {
1110 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1111 /// # write!(f, "SuperError is here!")
1114 /// # impl Error for SuperError {
1115 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
1116 /// # Some(&self.source)
1119 /// # #[derive(Debug)]
1120 /// # struct SuperErrorSideKick {
1121 /// # source: SuperErrorSideKickSideKick,
1123 /// # impl fmt::Display for SuperErrorSideKick {
1124 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1125 /// # write!(f, "SuperErrorSideKick is here!")
1128 /// # impl Error for SuperErrorSideKick {
1129 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
1130 /// # Some(&self.source)
1133 /// # #[derive(Debug)]
1134 /// # struct SuperErrorSideKickSideKick;
1135 /// # impl fmt::Display for SuperErrorSideKickSideKick {
1136 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1137 /// # write!(f, "SuperErrorSideKickSideKick is here!")
1140 /// # impl Error for SuperErrorSideKickSideKick { }
1142 /// let source = SuperErrorSideKickSideKick;
1143 /// let source = SuperErrorSideKick { source };
1144 /// let error = SuperError { source };
1145 /// let report = Report::new(error).pretty(true);
1146 /// eprintln!("Error: {report:?}");
1149 /// This example produces the following output:
1152 /// Error: SuperError is here!
1155 /// 0: SuperErrorSideKick is here!
1156 /// 1: SuperErrorSideKickSideKick is here!
1158 #[unstable(feature = "error_reporter", issue = "90172")]
1159 pub fn pretty(mut self, pretty: bool) -> Self {
1160 self.pretty = pretty;
1164 /// Display backtrace if available when using pretty output format.
1168 /// **Note**: Report will search for the first `Backtrace` it can find starting from the
1169 /// outermost error. In this example it will display the backtrace from the second error in the
1170 /// chain, `SuperErrorSideKick`.
1173 /// #![feature(error_reporter)]
1174 /// #![feature(backtrace)]
1175 /// # use std::error::Error;
1177 /// use std::error::Report;
1178 /// use std::backtrace::Backtrace;
1180 /// # #[derive(Debug)]
1181 /// # struct SuperError {
1182 /// # source: SuperErrorSideKick,
1184 /// # impl fmt::Display for SuperError {
1185 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1186 /// # write!(f, "SuperError is here!")
1189 /// # impl Error for SuperError {
1190 /// # fn source(&self) -> Option<&(dyn Error + 'static)> {
1191 /// # Some(&self.source)
1194 /// #[derive(Debug)]
1195 /// struct SuperErrorSideKick {
1196 /// backtrace: Backtrace,
1199 /// impl SuperErrorSideKick {
1200 /// fn new() -> SuperErrorSideKick {
1201 /// SuperErrorSideKick { backtrace: Backtrace::force_capture() }
1205 /// impl Error for SuperErrorSideKick {
1206 /// fn backtrace(&self) -> Option<&Backtrace> {
1207 /// Some(&self.backtrace)
1211 /// // The rest of the example is unchanged ...
1212 /// # impl fmt::Display for SuperErrorSideKick {
1213 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1214 /// # write!(f, "SuperErrorSideKick is here!")
1218 /// let source = SuperErrorSideKick::new();
1219 /// let error = SuperError { source };
1220 /// let report = Report::new(error).pretty(true).show_backtrace(true);
1221 /// eprintln!("Error: {report:?}");
1224 /// This example produces something similar to the following output:
1227 /// Error: SuperError is here!
1230 /// SuperErrorSideKick is here!
1232 /// Stack backtrace:
1233 /// 0: rust_out::main::_doctest_main_src_error_rs_1158_0::SuperErrorSideKick::new
1234 /// 1: rust_out::main::_doctest_main_src_error_rs_1158_0
1235 /// 2: rust_out::main
1236 /// 3: core::ops::function::FnOnce::call_once
1237 /// 4: std::sys_common::backtrace::__rust_begin_short_backtrace
1238 /// 5: std::rt::lang_start::{{closure}}
1239 /// 6: std::panicking::try
1240 /// 7: std::rt::lang_start_internal
1241 /// 8: std::rt::lang_start
1243 /// 10: __libc_start_main
1246 #[unstable(feature = "error_reporter", issue = "90172")]
1247 pub fn show_backtrace(mut self, show_backtrace: bool) -> Self {
1248 self.show_backtrace = show_backtrace;
1257 fn backtrace(&self) -> Option<&Backtrace> {
1258 // have to grab the backtrace on the first error directly since that error may not be
1260 let backtrace = self.error.backtrace();
1261 let backtrace = backtrace.or_else(|| {
1264 .map(|source| source.chain().find_map(|source| source.backtrace()))
1270 /// Format the report as a single line.
1271 #[unstable(feature = "error_reporter", issue = "90172")]
1272 fn fmt_singleline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1273 write!(f, "{}", self.error)?;
1275 let sources = self.error.source().into_iter().flat_map(<dyn Error>::chain);
1277 for cause in sources {
1278 write!(f, ": {cause}")?;
1284 /// Format the report as multiple lines, with each error cause on its own line.
1285 #[unstable(feature = "error_reporter", issue = "90172")]
1286 fn fmt_multiline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1287 let error = &self.error;
1289 write!(f, "{error}")?;
1291 if let Some(cause) = error.source() {
1292 write!(f, "\n\nCaused by:")?;
1294 let multiple = cause.source().is_some();
1296 for (ind, error) in cause.chain().enumerate() {
1298 let mut indented = Indented { inner: f };
1300 write!(indented, "{ind: >4}: {error}")?;
1302 write!(indented, " {error}")?;
1307 if self.show_backtrace {
1308 let backtrace = self.backtrace();
1310 if let Some(backtrace) = backtrace {
1311 let backtrace = backtrace.to_string();
1313 f.write_str("\n\nStack backtrace:\n")?;
1314 f.write_str(backtrace.trim_end())?;
1322 impl Report<Box<dyn Error>> {
1323 fn backtrace(&self) -> Option<&Backtrace> {
1324 // have to grab the backtrace on the first error directly since that error may not be
1326 let backtrace = self.error.backtrace();
1327 let backtrace = backtrace.or_else(|| {
1330 .map(|source| source.chain().find_map(|source| source.backtrace()))
1336 /// Format the report as a single line.
1337 #[unstable(feature = "error_reporter", issue = "90172")]
1338 fn fmt_singleline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1339 write!(f, "{}", self.error)?;
1341 let sources = self.error.source().into_iter().flat_map(<dyn Error>::chain);
1343 for cause in sources {
1344 write!(f, ": {cause}")?;
1350 /// Format the report as multiple lines, with each error cause on its own line.
1351 #[unstable(feature = "error_reporter", issue = "90172")]
1352 fn fmt_multiline(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1353 let error = &self.error;
1355 write!(f, "{error}")?;
1357 if let Some(cause) = error.source() {
1358 write!(f, "\n\nCaused by:")?;
1360 let multiple = cause.source().is_some();
1362 for (ind, error) in cause.chain().enumerate() {
1364 let mut indented = Indented { inner: f };
1366 write!(indented, "{ind: >4}: {error}")?;
1368 write!(indented, " {error}")?;
1373 if self.show_backtrace {
1374 let backtrace = self.backtrace();
1376 if let Some(backtrace) = backtrace {
1377 let backtrace = backtrace.to_string();
1379 f.write_str("\n\nStack backtrace:\n")?;
1380 f.write_str(backtrace.trim_end())?;
1388 #[unstable(feature = "error_reporter", issue = "90172")]
1389 impl<E> From<E> for Report<E>
1393 fn from(error: E) -> Self {
1394 Report { error, show_backtrace: false, pretty: false }
1398 #[unstable(feature = "error_reporter", issue = "90172")]
1399 impl<'a, E> From<E> for Report<Box<dyn Error + 'a>>
1403 fn from(error: E) -> Self {
1404 let error = box error;
1405 Report { error, show_backtrace: false, pretty: false }
1409 #[unstable(feature = "error_reporter", issue = "90172")]
1410 impl<E> fmt::Display for Report<E>
1414 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1415 if self.pretty { self.fmt_multiline(f) } else { self.fmt_singleline(f) }
1419 #[unstable(feature = "error_reporter", issue = "90172")]
1420 impl fmt::Display for Report<Box<dyn Error>> {
1421 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1422 if self.pretty { self.fmt_multiline(f) } else { self.fmt_singleline(f) }
1426 // This type intentionally outputs the same format for `Display` and `Debug`for
1427 // situations where you unwrap a `Report` or return it from main.
1428 #[unstable(feature = "error_reporter", issue = "90172")]
1429 impl<E> fmt::Debug for Report<E>
1431 Report<E>: fmt::Display,
1433 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1434 fmt::Display::fmt(self, f)
1438 /// Wrapper type for indenting the inner source.
1439 struct Indented<'a, D> {
1443 impl<T> Write for Indented<'_, T>
1447 fn write_str(&mut self, s: &str) -> fmt::Result {
1448 for (i, line) in s.split('\n').enumerate() {
1450 self.inner.write_char('\n')?;
1451 self.inner.write_str(" ")?;
1454 self.inner.write_str(line)?;