use crate::chain::Chain;
use crate::ptr::{MutPtr, OwnedPtr, RefPtr};
use crate::EyreHandler;
use crate::{Report, StdError};
use core::any::TypeId;
use core::fmt::{self, Debug, Display};
use core::mem::{self, ManuallyDrop};
use core::ptr::{self, NonNull};
use core::ops::{Deref, DerefMut};
impl Report {
/// Create a new error object from any error type.
///
/// The error type must be threadsafe and `'static`, so that the `Report`
/// will be as well.
///
/// If the error type does not provide a backtrace, a backtrace will be
/// created here to ensure that a backtrace exists.
#[cfg_attr(track_caller, track_caller)]
pub fn new<E>(error: E) -> Self
where
E: StdError + Send + Sync + 'static,
{
Report::from_std(error)
}
/// Create a new error object from a printable error message.
///
/// If the argument implements std::error::Error, prefer `Report::new`
/// instead which preserves the underlying error's cause chain and
/// backtrace. If the argument may or may not implement std::error::Error
/// now or in the future, use `eyre!(err)` which handles either way
/// correctly.
///
/// `Report::msg("...")` is equivalent to `eyre!("...")` but occasionally
/// convenient in places where a function is preferable over a macro, such
/// as iterator or stream combinators:
///
/// ```
/// # mod ffi {
/// # pub struct Input;
/// # pub struct Output;
/// # pub async fn do_some_work(_: Input) -> Result<Output, &'static str> {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # use ffi::{Input, Output};
/// #
/// use eyre::{Report, Result};
/// use futures::stream::{Stream, StreamExt, TryStreamExt};
///
/// async fn demo<S>(stream: S) -> Result<Vec<Output>>
/// where
/// S: Stream<Item = Input>,
/// {
/// stream
/// .then(ffi::do_some_work) // returns Result<Output, &str>
/// .map_err(Report::msg)
/// .try_collect()
/// .await
/// }
/// ```
#[cfg_attr(track_caller, track_caller)]
pub fn msg<M>(message: M) -> Self
where
M: Display + Debug + Send + Sync + 'static,
{
Report::from_adhoc(message)
}
#[cfg_attr(track_caller, track_caller)]
/// Creates a new error from an implementor of [`std::error::Error`]
pub(crate) fn from_std<E>(error: E) -> Self
where
E: StdError + Send + Sync + 'static,
{
let vtable = &ErrorVTable {
object_drop: object_drop::<E>,
object_ref: object_ref::<E>,
object_mut: object_mut::<E>,
object_boxed: object_boxed::<E>,
object_downcast: object_downcast::<E>,
object_downcast_mut: object_downcast_mut::<E>,
object_drop_rest: object_drop_front::<E>,
};
// Safety: passing vtable that operates on the right type E.
let handler = Some(crate::capture_handler(&error));
unsafe { Report::construct(error, vtable, handler) }
}
#[cfg_attr(track_caller, track_caller)]
pub(crate) fn from_adhoc<M>(message: M) -> Self
where
M: Display + Debug + Send + Sync + 'static,
{
use crate::wrapper::MessageError;
let error: MessageError<M> = MessageError(message);
let vtable = &ErrorVTable {
object_drop: object_drop::<MessageError<M>>,
object_ref: object_ref::<MessageError<M>>,
object_mut: object_mut::<MessageError<M>>,
object_boxed: object_boxed::<MessageError<M>>,
object_downcast: object_downcast::<M>,
object_downcast_mut: object_downcast_mut::<M>,
object_drop_rest: object_drop_front::<M>,
};
// Safety: MessageError is repr(transparent) so it is okay for the
// vtable to allow casting the MessageError<M> to M.
let handler = Some(crate::capture_handler(&error));
unsafe { Report::construct(error, vtable, handler) }
}
#[cfg_attr(track_caller, track_caller)]
pub(crate) fn from_display<M>(message: M) -> Self
where
M: Display + Send + Sync + 'static,
{
use crate::wrapper::{DisplayError, NoneError};
let error: DisplayError<M> = DisplayError(message);
let vtable = &ErrorVTable {
object_drop: object_drop::<DisplayError<M>>,
object_ref: object_ref::<DisplayError<M>>,
object_mut: object_mut::<DisplayError<M>>,
object_boxed: object_boxed::<DisplayError<M>>,
object_downcast: object_downcast::<M>,
object_downcast_mut: object_downcast_mut::<M>,
object_drop_rest: object_drop_front::<M>,
};
// Safety: DisplayError is repr(transparent) so it is okay for the
// vtable to allow casting the DisplayError<M> to M.
let handler = Some(crate::capture_handler(&NoneError));
unsafe { Report::construct(error, vtable, handler) }
}
#[cfg_attr(track_caller, track_caller)]
pub(crate) fn from_msg<D, E>(msg: D, error: E) -> Self
where
D: Display + Send + Sync + 'static,
E: StdError + Send + Sync + 'static,
{
let error: ContextError<D, E> = ContextError { msg, error };
let vtable = &ErrorVTable {
object_drop: object_drop::<ContextError<D, E>>,
object_ref: object_ref::<ContextError<D, E>>,
object_mut: object_mut::<ContextError<D, E>>,
object_boxed: object_boxed::<ContextError<D, E>>,
object_downcast: context_downcast::<D, E>,
object_downcast_mut: context_downcast_mut::<D, E>,
object_drop_rest: context_drop_rest::<D, E>,
};
// Safety: passing vtable that operates on the right type.
let handler = Some(crate::capture_handler(&error));
unsafe { Report::construct(error, vtable, handler) }
}
#[cfg_attr(track_caller, track_caller)]
pub(crate) fn from_boxed(error: Box<dyn StdError + Send + Sync>) -> Self {
use crate::wrapper::BoxedError;
let error = BoxedError(error);
let handler = Some(crate::capture_handler(&error));
let vtable = &ErrorVTable {
object_drop: object_drop::<BoxedError>,
object_ref: object_ref::<BoxedError>,
object_mut: object_mut::<BoxedError>,
object_boxed: object_boxed::<BoxedError>,
object_downcast: object_downcast::<Box<dyn StdError + Send + Sync>>,
object_downcast_mut: object_downcast_mut::<Box<dyn StdError + Send + Sync>>,
object_drop_rest: object_drop_front::<Box<dyn StdError + Send + Sync>>,
};
// Safety: BoxedError is repr(transparent) so it is okay for the vtable
// to allow casting to Box<dyn StdError + Send + Sync>.
unsafe { Report::construct(error, vtable, handler) }
}
// Takes backtrace as argument rather than capturing it here so that the
// user sees one fewer layer of wrapping noise in the backtrace.
//
// Unsafe because the given vtable must have sensible behavior on the error
// value of type E.
unsafe fn construct<E>(
error: E,
vtable: &'static ErrorVTable,
handler: Option<Box<dyn EyreHandler>>,
) -> Self
where
E: StdError + Send + Sync + 'static,
{
let inner = ErrorImpl {
header: ErrorHeader { vtable, handler },
_object: error,
};
// Construct a new owned allocation through a raw pointer
//
// This does not keep the allocation around as a `Box` which would invalidate an
// references when moved
let ptr = OwnedPtr::<ErrorImpl<E>>::new(inner);
// Safety: the type
let ptr = ptr.cast::<ErrorImpl<()>>();
Report { inner: ptr }
}
/// Create a new error from an error message to wrap the existing error.
///
/// For attaching a higher level error message to a `Result` as it is propagated, the
/// [`WrapErr`][crate::WrapErr] extension trait may be more convenient than this function.
///
/// The primary reason to use `error.wrap_err(...)` instead of `result.wrap_err(...)` via the
/// `WrapErr` trait would be if the message needs to depend on some data held by the underlying
/// error:
///
/// ```
/// # use std::fmt::{self, Debug, Display};
/// #
/// # type T = ();
/// #
/// # impl std::error::Error for ParseError {}
/// # impl Debug for ParseError {
/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// # unimplemented!()
/// # }
/// # }
/// # impl Display for ParseError {
/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// # unimplemented!()
/// # }
/// # }
/// #
/// use eyre::Result;
/// use std::fs::File;
/// use std::path::Path;
///
/// struct ParseError {
/// line: usize,
/// column: usize,
/// }
///
/// fn parse_impl(file: File) -> Result<T, ParseError> {
/// # const IGNORE: &str = stringify! {
/// ...
/// # };
/// # unimplemented!()
/// }
///
/// pub fn parse(path: impl AsRef<Path>) -> Result<T> {
/// let file = File::open(&path)?;
/// parse_impl(file).map_err(|error| {
/// let message = format!(
/// "only the first {} lines of {} are valid",
/// error.line, path.as_ref().display(),
/// );
/// eyre::Report::new(error).wrap_err(message)
/// })
/// }
/// ```
pub fn wrap_err<D>(mut self, msg: D) -> Self
where
D: Display + Send + Sync + 'static,
{
// Safety: this access a `ErrorImpl<unknown>` as a valid reference to a `ErrorImpl<()>`
//
// As the generic is at the end of the struct and the struct is `repr(C)` this reference
// will be within bounds of the original pointer, and the field will have the same offset
let handler = header_mut(self.inner.as_mut()).handler.take();
let error: ContextError<D, Report> = ContextError { msg, error: self };
let vtable = &ErrorVTable {
object_drop: object_drop::<ContextError<D, Report>>,
object_ref: object_ref::<ContextError<D, Report>>,
object_mut: object_mut::<ContextError<D, Report>>,
object_boxed: object_boxed::<ContextError<D, Report>>,
object_downcast: context_chain_downcast::<D>,
object_downcast_mut: context_chain_downcast_mut::<D>,
object_drop_rest: context_chain_drop_rest::<D>,
};
// Safety: passing vtable that operates on the right type.
unsafe { Report::construct(error, vtable, handler) }
}
/// Access the vtable for the current error object.
fn vtable(&self) -> &'static ErrorVTable {
header(self.inner.as_ref()).vtable
}
/// An iterator of the chain of source errors contained by this Report.
///
/// This iterator will visit every error in the cause chain of this error
/// object, beginning with the error that this error object was created
/// from.
///
/// # Example
///
/// ```
/// use eyre::Report;
/// use std::io;
///
/// pub fn underlying_io_error_kind(error: &Report) -> Option<io::ErrorKind> {
/// for cause in error.chain() {
/// if let Some(io_error) = cause.downcast_ref::<io::Error>() {
/// return Some(io_error.kind());
/// }
/// }
/// None
/// }
/// ```
pub fn chain(&self) -> Chain<'_> {
ErrorImpl::chain(self.inner.as_ref())
}
/// The lowest level cause of this error — this error's cause's
/// cause's cause etc.
///
/// The root cause is the last error in the iterator produced by
/// [`chain()`][Report::chain].
pub fn root_cause(&self) -> &(dyn StdError + 'static) {
let mut chain = self.chain();
let mut root_cause = chain.next().unwrap();
for cause in chain {
root_cause = cause;
}
root_cause
}
/// Returns true if `E` is the type held by this error object.
///
/// For errors constructed from messages, this method returns true if `E` matches the type of
/// the message `D` **or** the type of the error on which the message has been attached. For
/// details about the interaction between message and downcasting, [see here].
///
/// [see here]: trait.WrapErr.html#effect-on-downcasting
pub fn is<E>(&self) -> bool
where
E: Display + Debug + Send + Sync + 'static,
{
self.downcast_ref::<E>().is_some()
}
/// Attempt to downcast the error object to a concrete type.
pub fn downcast<E>(self) -> Result<E, Self>
where
E: Display + Debug + Send + Sync + 'static,
{
let target = TypeId::of::<E>();
unsafe {
// Use vtable to find NonNull<()> which points to a value of type E
// somewhere inside the data structure.
let addr = match (self.vtable().object_downcast)(self.inner.as_ref(), target) {
Some(addr) => addr,
None => return Err(self),
};
// Prepare to read E out of the data structure. We'll drop the rest
// of the data structure separately so that E is not dropped.
let outer = ManuallyDrop::new(self);
// Read E from where the vtable found it.
let error = ptr::read(addr.cast::<E>().as_ptr());
// Read Box<ErrorImpl<()>> from self. Can't move it out because
// Report has a Drop impl which we want to not run.
let inner = ptr::read(&outer.inner);
// Drop rest of the data structure outside of E.
(outer.vtable().object_drop_rest)(inner, target);
Ok(error)
}
}
/// Downcast this error object by reference.
///
/// # Example
///
/// ```
/// # use eyre::{Report, eyre};
/// # use std::fmt::{self, Display};
/// # use std::task::Poll;
/// #
/// # #[derive(Debug)]
/// # enum DataStoreError {
/// # Censored(()),
/// # }
/// #
/// # impl Display for DataStoreError {
/// # fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// # unimplemented!()
/// # }
/// # }
/// #
/// # impl std::error::Error for DataStoreError {}
/// #
/// # const REDACTED_CONTENT: () = ();
/// #
/// # #[cfg(not(feature = "auto-install"))]
/// # eyre::set_hook(Box::new(eyre::DefaultHandler::default_with)).unwrap();
/// #
/// # let error: Report = eyre!("...");
/// # let root_cause = &error;
/// #
/// # let ret =
/// // If the error was caused by redaction, then return a tombstone instead
/// // of the content.
/// match root_cause.downcast_ref::<DataStoreError>() {
/// Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
/// None => Err(error),
/// }
/// # ;
/// ```
pub fn downcast_ref<E>(&self) -> Option<&E>
where
E: Display + Debug + Send + Sync + 'static,
{
let target = TypeId::of::<E>();
unsafe {
// Use vtable to find NonNull<()> which points to a value of type E
// somewhere inside the data structure.
let addr = (self.vtable().object_downcast)(self.inner.as_ref(), target)?;
Some(addr.cast::<E>().as_ref())
}
}
/// Downcast this error object by mutable reference.
pub fn downcast_mut<E>(&mut self) -> Option<&mut E>
where
E: Display + Debug + Send + Sync + 'static,
{
let target = TypeId::of::<E>();
unsafe {
// Use vtable to find NonNull<()> which points to a value of type E
// somewhere inside the data structure.
let addr = (self.vtable().object_downcast_mut)(self.inner.as_mut(), target)?;
Some(addr.cast::<E>().as_mut())
}
}
/// Get a reference to the Handler for this Report.
pub fn handler(&self) -> &dyn EyreHandler {
header(self.inner.as_ref())
.handler
.as_ref()
.unwrap()
.as_ref()
}
/// Get a mutable reference to the Handler for this Report.
pub fn handler_mut(&mut self) -> &mut dyn EyreHandler {
header_mut(self.inner.as_mut())
.handler
.as_mut()
.unwrap()
.as_mut()
}
/// Get a reference to the Handler for this Report.
#[doc(hidden)]
pub fn context(&self) -> &dyn EyreHandler {
header(self.inner.as_ref())
.handler
.as_ref()
.unwrap()
.as_ref()
}
/// Get a mutable reference to the Handler for this Report.
#[doc(hidden)]
pub fn context_mut(&mut self) -> &mut dyn EyreHandler {
header_mut(self.inner.as_mut())
.handler
.as_mut()
.unwrap()
.as_mut()
}
}
impl<E> From<E> for Report
where
E: StdError + Send + Sync + 'static,
{
#[cfg_attr(track_caller, track_caller)]
fn from(error: E) -> Self {
Report::from_std(error)
}
}
impl Deref for Report {
type Target = dyn StdError + Send + Sync + 'static;
fn deref(&self) -> &Self::Target {
ErrorImpl::error(self.inner.as_ref())
}
}
impl DerefMut for Report {
fn deref_mut(&mut self) -> &mut Self::Target {
ErrorImpl::error_mut(self.inner.as_mut())
}
}
impl Display for Report {
fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
ErrorImpl::display(self.inner.as_ref(), formatter)
}
}
impl Debug for Report {
fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
ErrorImpl::debug(self.inner.as_ref(), formatter)
}
}
impl Drop for Report {
fn drop(&mut self) {
unsafe {
// Read Box<ErrorImpl<()>> from self.
(self.vtable().object_drop)(self.inner);
}
}
}
struct ErrorVTable {
object_drop: unsafe fn(OwnedPtr<ErrorImpl<()>>),
object_ref: unsafe fn(RefPtr<'_, ErrorImpl<()>>) -> &(dyn StdError + Send + Sync + 'static),
object_mut: unsafe fn(MutPtr<'_, ErrorImpl<()>>) -> &mut (dyn StdError + Send + Sync + 'static),
#[allow(clippy::type_complexity)]
object_boxed: unsafe fn(OwnedPtr<ErrorImpl<()>>) -> Box<dyn StdError + Send + Sync + 'static>,
object_downcast: unsafe fn(RefPtr<'_, ErrorImpl<()>>, TypeId) -> Option<NonNull<()>>,
object_downcast_mut: unsafe fn(MutPtr<'_, ErrorImpl<()>>, TypeId) -> Option<NonNull<()>>,
object_drop_rest: unsafe fn(OwnedPtr<ErrorImpl<()>>, TypeId),
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_drop<E>(e: OwnedPtr<ErrorImpl<()>>) {
// Cast to a context type and drop the Box allocation.
let unerased = unsafe { e.cast::<ErrorImpl<E>>().into_box() };
drop(unerased);
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_drop_front<E>(e: OwnedPtr<ErrorImpl<()>>, target: TypeId) {
// Drop the fields of ErrorImpl other than E as well as the Box allocation,
// without dropping E itself. This is used by downcast after doing a
// ptr::read to take ownership of the E.
let _ = target;
// Note: This must not use `mem::transmute` because it tries to reborrow the `Unique`
// contained in `Box`, which must not be done. In practice this probably won't make any
// difference by now, but technically it's unsound.
// see: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.m
let unerased = unsafe { e.cast::<ErrorImpl<E>>().into_box() };
mem::forget(unerased._object)
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_ref<E>(e: RefPtr<'_, ErrorImpl<()>>) -> &(dyn StdError + Send + Sync + 'static)
where
E: StdError + Send + Sync + 'static,
{
// Attach E's native StdError vtable onto a pointer to self._object.
&unsafe { e.cast::<ErrorImpl<E>>().as_ref() }._object
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_mut<E>(e: MutPtr<'_, ErrorImpl<()>>) -> &mut (dyn StdError + Send + Sync + 'static)
where
E: StdError + Send + Sync + 'static,
{
// Attach E's native StdError vtable onto a pointer to self._object.
&mut unsafe { e.cast::<ErrorImpl<E>>().into_mut() }._object
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_boxed<E>(e: OwnedPtr<ErrorImpl<()>>) -> Box<dyn StdError + Send + Sync + 'static>
where
E: StdError + Send + Sync + 'static,
{
// Attach ErrorImpl<E>'s native StdError vtable. The StdError impl is below.
unsafe { e.cast::<ErrorImpl<E>>().into_box() }
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_downcast<E>(e: RefPtr<'_, ErrorImpl<()>>, target: TypeId) -> Option<NonNull<()>>
where
E: 'static,
{
if TypeId::of::<E>() == target {
// Caller is looking for an E pointer and e is ErrorImpl<E>, take a
// pointer to its E field.
let unerased = unsafe { e.cast::<ErrorImpl<E>>().as_ref() };
Some(NonNull::from(&(unerased._object)).cast::<()>())
} else {
None
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<E>.
unsafe fn object_downcast_mut<E>(
e: MutPtr<'_, ErrorImpl<()>>,
target: TypeId,
) -> Option<NonNull<()>>
where
E: 'static,
{
if TypeId::of::<E>() == target {
// Caller is looking for an E pointer and e is ErrorImpl<E>, take a
// pointer to its E field.
let unerased = unsafe { e.cast::<ErrorImpl<E>>().into_mut() };
Some(NonNull::from(&mut (unerased._object)).cast::<()>())
} else {
None
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, E>>.
unsafe fn context_downcast<D, E>(
e: RefPtr<'_, ErrorImpl<()>>,
target: TypeId,
) -> Option<NonNull<()>>
where
D: 'static,
E: 'static,
{
if TypeId::of::<D>() == target {
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, E>>>().as_ref() };
let addr = NonNull::from(&unerased._object.msg).cast::<()>();
Some(addr)
} else if TypeId::of::<E>() == target {
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, E>>>().as_ref() };
let addr = NonNull::from(&unerased._object.error).cast::<()>();
Some(addr)
} else {
None
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, E>>.
unsafe fn context_downcast_mut<D, E>(
e: MutPtr<'_, ErrorImpl<()>>,
target: TypeId,
) -> Option<NonNull<()>>
where
D: 'static,
E: 'static,
{
if TypeId::of::<D>() == target {
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, E>>>().into_mut() };
let addr = NonNull::from(&unerased._object.msg).cast::<()>();
Some(addr)
} else if TypeId::of::<E>() == target {
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, E>>>().into_mut() };
let addr = NonNull::from(&mut unerased._object.error).cast::<()>();
Some(addr)
} else {
None
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, E>>.
unsafe fn context_drop_rest<D, E>(e: OwnedPtr<ErrorImpl<()>>, target: TypeId)
where
D: 'static,
E: 'static,
{
// Called after downcasting by value to either the D or the E and doing a
// ptr::read to take ownership of that value.
if TypeId::of::<D>() == target {
unsafe {
e.cast::<ErrorImpl<ContextError<ManuallyDrop<D>, E>>>()
.into_box()
};
} else {
debug_assert_eq!(TypeId::of::<E>(), target);
unsafe {
e.cast::<ErrorImpl<ContextError<D, ManuallyDrop<E>>>>()
.into_box()
};
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, Report>>.
unsafe fn context_chain_downcast<D>(
e: RefPtr<'_, ErrorImpl<()>>,
target: TypeId,
) -> Option<NonNull<()>>
where
D: 'static,
{
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, Report>>>().as_ref() };
if TypeId::of::<D>() == target {
let addr = NonNull::from(&unerased._object.msg).cast::<()>();
Some(addr)
} else {
// Recurse down the context chain per the inner error's vtable.
let source = &unerased._object.error;
unsafe { (source.vtable().object_downcast)(source.inner.as_ref(), target) }
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, Report>>.
unsafe fn context_chain_downcast_mut<D>(
e: MutPtr<'_, ErrorImpl<()>>,
target: TypeId,
) -> Option<NonNull<()>>
where
D: 'static,
{
let unerased = unsafe { e.cast::<ErrorImpl<ContextError<D, Report>>>().into_mut() };
if TypeId::of::<D>() == target {
let addr = NonNull::from(&unerased._object.msg).cast::<()>();
Some(addr)
} else {
// Recurse down the context chain per the inner error's vtable.
let source = &mut unerased._object.error;
unsafe { (source.vtable().object_downcast_mut)(source.inner.as_mut(), target) }
}
}
/// # Safety
///
/// Requires layout of *e to match ErrorImpl<ContextError<D, Report>>.
unsafe fn context_chain_drop_rest<D>(e: OwnedPtr<ErrorImpl<()>>, target: TypeId)
where
D: 'static,
{
// Called after downcasting by value to either the D or one of the causes
// and doing a ptr::read to take ownership of that value.
if TypeId::of::<D>() == target {
let unerased = unsafe {
e.cast::<ErrorImpl<ContextError<ManuallyDrop<D>, Report>>>()
.into_box()
};
// Drop the entire rest of the data structure rooted in the next Report.
drop(unerased);
} else {
unsafe {
let unerased = e
.cast::<ErrorImpl<ContextError<D, ManuallyDrop<Report>>>>()
.into_box();
// Read out a ManuallyDrop<Box<ErrorImpl<()>>> from the next error.
let inner = ptr::read(&unerased.as_ref()._object.error.inner);
drop(unerased);
// Recursively drop the next error using the same target typeid.
(header(inner.as_ref()).vtable.object_drop_rest)(inner, target);
}
}
}
#[repr(C)]
pub(crate) struct ErrorHeader {
vtable: &'static ErrorVTable,
pub(crate) handler: Option<Box<dyn EyreHandler>>,
}
// repr C to ensure that E remains in the final position.
#[repr(C)]
pub(crate) struct ErrorImpl<E = ()> {
header: ErrorHeader,
// NOTE: Don't use directly. Use only through vtable. Erased type may have
// different alignment.
_object: E,
}
// repr C to ensure that ContextError<D, E> has the same layout as
// ContextError<ManuallyDrop<D>, E> and ContextError<D, ManuallyDrop<E>>.
#[repr(C)]
pub(crate) struct ContextError<D, E> {
pub(crate) msg: D,
pub(crate) error: E,
}
impl<E> ErrorImpl<E> {
/// Returns a type erased Error
fn erase(&self) -> RefPtr<'_, ErrorImpl<()>> {
// Erase the concrete type of E but preserve the vtable in self.vtable
// for manipulating the resulting thin pointer. This is analogous to an
// unsize coersion.
RefPtr::new(self).cast()
}
}
// Reads the header out of `p`. This is the same as `p.as_ref().header`, but
// avoids converting `p` into a reference of a shrunk provenance with a type different than the
// allocation.
fn header(p: RefPtr<'_, ErrorImpl<()>>) -> &'_ ErrorHeader {
// Safety: `ErrorHeader` is the first field of repr(C) `ErrorImpl`
unsafe { p.cast().as_ref() }
}
fn header_mut(p: MutPtr<'_, ErrorImpl<()>>) -> &mut ErrorHeader {
// Safety: `ErrorHeader` is the first field of repr(C) `ErrorImpl`
unsafe { p.cast().into_mut() }
}
impl ErrorImpl<()> {
pub(crate) fn error(this: RefPtr<'_, Self>) -> &(dyn StdError + Send + Sync + 'static) {
// Use vtable to attach E's native StdError vtable for the right
// original type E.
unsafe { (header(this).vtable.object_ref)(this) }
}
pub(crate) fn error_mut(this: MutPtr<'_, Self>) -> &mut (dyn StdError + Send + Sync + 'static) {
// Use vtable to attach E's native StdError vtable for the right
// original type E.
unsafe { (header_mut(this).vtable.object_mut)(this) }
}
pub(crate) fn chain(this: RefPtr<'_, Self>) -> Chain<'_> {
Chain::new(Self::error(this))
}
pub(crate) fn header(this: RefPtr<'_, ErrorImpl>) -> &ErrorHeader {
header(this)
}
}
impl<E> StdError for ErrorImpl<E>
where
E: StdError,
{
fn source(&self) -> Option<&(dyn StdError + 'static)> {
ErrorImpl::<()>::error(self.erase()).source()
}
}
impl<E> Debug for ErrorImpl<E>
where
E: Debug,
{
fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
ErrorImpl::debug(self.erase(), formatter)
}
}
impl<E> Display for ErrorImpl<E>
where
E: Display,
{
fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
Display::fmt(ErrorImpl::error(self.erase()), formatter)
}
}
impl From<Report> for Box<dyn StdError + Send + Sync + 'static> {
fn from(error: Report) -> Self {
let outer = ManuallyDrop::new(error);
unsafe {
// Read Box<ErrorImpl<()>> from error. Can't move it out because
// Report has a Drop impl which we want to not run.
// Use vtable to attach ErrorImpl<E>'s native StdError vtable for
// the right original type E.
(header(outer.inner.as_ref()).vtable.object_boxed)(outer.inner)
}
}
}
impl From<Report> for Box<dyn StdError + 'static> {
fn from(error: Report) -> Self {
Box::<dyn StdError + Send + Sync>::from(error)
}
}
impl AsRef<dyn StdError + Send + Sync> for Report {
fn as_ref(&self) -> &(dyn StdError + Send + Sync + 'static) {
&**self
}
}
impl AsRef<dyn StdError> for Report {
fn as_ref(&self) -> &(dyn StdError + 'static) {
&**self
}
}
#[cfg(feature = "pyo3")]
mod pyo3_compat;