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use crate::backtrace::Backtrace;
use crate::chain::Chain;
#[cfg(any(feature = "std", anyhow_no_ptr_addr_of))]
use crate::ptr::Mut;
use crate::ptr::{Own, Ref};
use crate::{Error, StdError};
use alloc::boxed::Box;
#[cfg(backtrace)]
use core::any::Demand;
use core::any::TypeId;
use core::fmt::{self, Debug, Display};
use core::mem::ManuallyDrop;
#[cfg(not(anyhow_no_ptr_addr_of))]
use core::ptr;
use core::ptr::NonNull;
#[cfg(feature = "std")]
use core::ops::{Deref, DerefMut};
impl Error {
/// Create a new error object from any error type.
///
/// The error type must be threadsafe and `'static`, so that the `Error`
/// 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(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
#[cold]
#[must_use]
pub fn new<E>(error: E) -> Self
where
E: StdError + Send + Sync + 'static,
{
let backtrace = backtrace_if_absent!(&error);
Error::from_std(error, backtrace)
}
/// Create a new error object from a printable error message.
///
/// If the argument implements std::error::Error, prefer `Error::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 `anyhow!(err)` which handles either way
/// correctly.
///
/// `Error::msg("...")` is equivalent to `anyhow!("...")` 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 anyhow::{Error, 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(Error::msg)
/// .try_collect()
/// .await
/// }
/// ```
#[cold]
#[must_use]
pub fn msg<M>(message: M) -> Self
where
M: Display + Debug + Send + Sync + 'static,
{
Error::from_adhoc(message, backtrace!())
}
#[cfg(feature = "std")]
#[cold]
pub(crate) fn from_std<E>(error: E, backtrace: Option<Backtrace>) -> Self
where
E: StdError + Send + Sync + 'static,
{
let vtable = &ErrorVTable {
object_drop: object_drop::<E>,
object_ref: object_ref::<E>,
#[cfg(anyhow_no_ptr_addr_of)]
object_mut: object_mut::<E>,
object_boxed: object_boxed::<E>,
object_downcast: object_downcast::<E>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: object_downcast_mut::<E>,
object_drop_rest: object_drop_front::<E>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: no_backtrace,
};
// Safety: passing vtable that operates on the right type E.
unsafe { Error::construct(error, vtable, backtrace) }
}
#[cold]
pub(crate) fn from_adhoc<M>(message: M, backtrace: Option<Backtrace>) -> 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>>,
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
object_mut: object_mut::<MessageError<M>>,
object_boxed: object_boxed::<MessageError<M>>,
object_downcast: object_downcast::<M>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: object_downcast_mut::<M>,
object_drop_rest: object_drop_front::<M>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: no_backtrace,
};
// Safety: MessageError is repr(transparent) so it is okay for the
// vtable to allow casting the MessageError<M> to M.
unsafe { Error::construct(error, vtable, backtrace) }
}
#[cold]
pub(crate) fn from_display<M>(message: M, backtrace: Option<Backtrace>) -> Self
where
M: Display + Send + Sync + 'static,
{
use crate::wrapper::DisplayError;
let error: DisplayError<M> = DisplayError(message);
let vtable = &ErrorVTable {
object_drop: object_drop::<DisplayError<M>>,
object_ref: object_ref::<DisplayError<M>>,
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
object_mut: object_mut::<DisplayError<M>>,
object_boxed: object_boxed::<DisplayError<M>>,
object_downcast: object_downcast::<M>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: object_downcast_mut::<M>,
object_drop_rest: object_drop_front::<M>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: no_backtrace,
};
// Safety: DisplayError is repr(transparent) so it is okay for the
// vtable to allow casting the DisplayError<M> to M.
unsafe { Error::construct(error, vtable, backtrace) }
}
#[cfg(feature = "std")]
#[cold]
pub(crate) fn from_context<C, E>(context: C, error: E, backtrace: Option<Backtrace>) -> Self
where
C: Display + Send + Sync + 'static,
E: StdError + Send + Sync + 'static,
{
let error: ContextError<C, E> = ContextError { context, error };
let vtable = &ErrorVTable {
object_drop: object_drop::<ContextError<C, E>>,
object_ref: object_ref::<ContextError<C, E>>,
#[cfg(anyhow_no_ptr_addr_of)]
object_mut: object_mut::<ContextError<C, E>>,
object_boxed: object_boxed::<ContextError<C, E>>,
object_downcast: context_downcast::<C, E>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: context_downcast_mut::<C, E>,
object_drop_rest: context_drop_rest::<C, E>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: no_backtrace,
};
// Safety: passing vtable that operates on the right type.
unsafe { Error::construct(error, vtable, backtrace) }
}
#[cfg(feature = "std")]
#[cold]
pub(crate) fn from_boxed(
error: Box<dyn StdError + Send + Sync>,
backtrace: Option<Backtrace>,
) -> Self {
use crate::wrapper::BoxedError;
let error = BoxedError(error);
let vtable = &ErrorVTable {
object_drop: object_drop::<BoxedError>,
object_ref: object_ref::<BoxedError>,
#[cfg(anyhow_no_ptr_addr_of)]
object_mut: object_mut::<BoxedError>,
object_boxed: object_boxed::<BoxedError>,
object_downcast: object_downcast::<Box<dyn StdError + Send + Sync>>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: object_downcast_mut::<Box<dyn StdError + Send + Sync>>,
object_drop_rest: object_drop_front::<Box<dyn StdError + Send + Sync>>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: no_backtrace,
};
// Safety: BoxedError is repr(transparent) so it is okay for the vtable
// to allow casting to Box<dyn StdError + Send + Sync>.
unsafe { Error::construct(error, vtable, backtrace) }
}
// 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.
#[cold]
unsafe fn construct<E>(
error: E,
vtable: &'static ErrorVTable,
backtrace: Option<Backtrace>,
) -> Self
where
E: StdError + Send + Sync + 'static,
{
let inner: Box<ErrorImpl<E>> = Box::new(ErrorImpl {
vtable,
backtrace,
_object: error,
});
// Erase the concrete type of E from the compile-time type system. This
// is equivalent to the safe unsize coercion from Box<ErrorImpl<E>> to
// Box<ErrorImpl<dyn StdError + Send + Sync + 'static>> except that the
// result is a thin pointer. The necessary behavior for manipulating the
// underlying ErrorImpl<E> is preserved in the vtable provided by the
// caller rather than a builtin fat pointer vtable.
let inner = Own::new(inner).cast::<ErrorImpl>();
Error { inner }
}
/// Wrap the error value with additional context.
///
/// For attaching context to a `Result` as it is propagated, the
/// [`Context`][crate::Context] extension trait may be more convenient than
/// this function.
///
/// The primary reason to use `error.context(...)` instead of
/// `result.context(...)` via the `Context` trait would be if the context
/// 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 anyhow::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 context = format!(
/// "only the first {} lines of {} are valid",
/// error.line, path.as_ref().display(),
/// );
/// anyhow::Error::new(error).context(context)
/// })
/// }
/// ```
#[cold]
#[must_use]
pub fn context<C>(self, context: C) -> Self
where
C: Display + Send + Sync + 'static,
{
let error: ContextError<C, Error> = ContextError {
context,
error: self,
};
let vtable = &ErrorVTable {
object_drop: object_drop::<ContextError<C, Error>>,
object_ref: object_ref::<ContextError<C, Error>>,
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
object_mut: object_mut::<ContextError<C, Error>>,
object_boxed: object_boxed::<ContextError<C, Error>>,
object_downcast: context_chain_downcast::<C>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: context_chain_downcast_mut::<C>,
object_drop_rest: context_chain_drop_rest::<C>,
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: context_backtrace::<C>,
};
// As the cause is anyhow::Error, we already have a backtrace for it.
let backtrace = None;
// Safety: passing vtable that operates on the right type.
unsafe { Error::construct(error, vtable, backtrace) }
}
/// Get the backtrace for this Error.
///
/// In order for the backtrace to be meaningful, one of the two environment
/// variables `RUST_LIB_BACKTRACE=1` or `RUST_BACKTRACE=1` must be defined
/// and `RUST_LIB_BACKTRACE` must not be `0`. Backtraces are somewhat
/// expensive to capture in Rust, so we don't necessarily want to be
/// capturing them all over the place all the time.
///
/// - If you want panics and errors to both have backtraces, set
/// `RUST_BACKTRACE=1`;
/// - If you want only errors to have backtraces, set
/// `RUST_LIB_BACKTRACE=1`;
/// - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
/// `RUST_LIB_BACKTRACE=0`.
///
/// # Stability
///
/// Standard library backtraces are only available on the nightly channel.
/// Tracking issue: [rust-lang/rust#53487][tracking].
///
/// On stable compilers, this function is only available if the crate's
/// "backtrace" feature is enabled, and will use the `backtrace` crate as
/// the underlying backtrace implementation.
///
/// ```toml
/// [dependencies]
/// anyhow = { version = "1.0", features = ["backtrace"] }
/// ```
///
#[cfg(any(backtrace, feature = "backtrace"))]
#[cfg_attr(doc_cfg, doc(cfg(any(nightly, feature = "backtrace"))))]
pub fn backtrace(&self) -> &impl_backtrace!() {
unsafe { ErrorImpl::backtrace(self.inner.by_ref()) }
}
/// An iterator of the chain of source errors contained by this Error.
///
/// 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 anyhow::Error;
/// use std::io;
///
/// pub fn underlying_io_error_kind(error: &Error) -> Option<io::ErrorKind> {
/// for cause in error.chain() {
/// if let Some(io_error) = cause.downcast_ref::<io::Error>() {
/// return Some(io_error.kind());
/// }
/// }
/// None
/// }
/// ```
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
#[cold]
pub fn chain(&self) -> Chain {
unsafe { ErrorImpl::chain(self.inner.by_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()`][Error::chain].
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
pub fn root_cause(&self) -> &(dyn StdError + 'static) {
self.chain().last().unwrap()
}
/// Returns true if `E` is the type held by this error object.
///
/// For errors with context, this method returns true if `E` matches the
/// type of the context `C` **or** the type of the error on which the
/// context has been attached. For details about the interaction between
/// context and downcasting, [see here].
///
/// [see here]: trait.Context.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>(mut self) -> Result<E, Self>
where
E: Display + Debug + Send + Sync + 'static,
{
let target = TypeId::of::<E>();
let inner = self.inner.by_mut();
unsafe {
// Use vtable to find NonNull<()> which points to a value of type E
// somewhere inside the data structure.
#[cfg(not(anyhow_no_ptr_addr_of))]
let addr = match (vtable(inner.ptr).object_downcast)(inner.by_ref(), target) {
Some(addr) => addr.by_mut().extend(),
None => return Err(self),
};
#[cfg(anyhow_no_ptr_addr_of)]
let addr = match (vtable(inner.ptr).object_downcast_mut)(inner, target) {
Some(addr) => addr.extend(),
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 = addr.cast::<E>().read();
// Drop rest of the data structure outside of E.
(vtable(outer.inner.ptr).object_drop_rest)(outer.inner, target);
Ok(error)
}
}
/// Downcast this error object by reference.
///
/// # Example
///
/// ```
/// # use anyhow::anyhow;
/// # 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: () = ();
/// #
/// # let error = anyhow!("...");
/// # 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 = (vtable(self.inner.ptr).object_downcast)(self.inner.by_ref(), target)?;
Some(addr.cast::<E>().deref())
}
}
/// 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.
#[cfg(not(anyhow_no_ptr_addr_of))]
let addr =
(vtable(self.inner.ptr).object_downcast)(self.inner.by_ref(), target)?.by_mut();
#[cfg(anyhow_no_ptr_addr_of)]
let addr = (vtable(self.inner.ptr).object_downcast_mut)(self.inner.by_mut(), target)?;
Some(addr.cast::<E>().deref_mut())
}
}
}
#[cfg(backtrace)]
impl std::any::Provider for Error {
// Called by thiserror when you have `#[source] anyhow::Error`. This provide
// implementation includes the anyhow::Error's Backtrace if any, unlike
// deref'ing to dyn Error where the provide implementation would include
// only the original error's Backtrace from before it got wrapped into an
// anyhow::Error.
fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
unsafe { ErrorImpl::provide(self.inner.by_ref(), demand) }
}
}
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
impl<E> From<E> for Error
where
E: StdError + Send + Sync + 'static,
{
#[cold]
fn from(error: E) -> Self {
let backtrace = backtrace_if_absent!(&error);
Error::from_std(error, backtrace)
}
}
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
impl Deref for Error {
type Target = dyn StdError + Send + Sync + 'static;
fn deref(&self) -> &Self::Target {
unsafe { ErrorImpl::error(self.inner.by_ref()) }
}
}
#[cfg(feature = "std")]
#[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
impl DerefMut for Error {
fn deref_mut(&mut self) -> &mut Self::Target {
unsafe { ErrorImpl::error_mut(self.inner.by_mut()) }
}
}
impl Display for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
unsafe { ErrorImpl::display(self.inner.by_ref(), formatter) }
}
}
impl Debug for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
unsafe { ErrorImpl::debug(self.inner.by_ref(), formatter) }
}
}
impl Drop for Error {
fn drop(&mut self) {
unsafe {
// Invoke the vtable's drop behavior.
(vtable(self.inner.ptr).object_drop)(self.inner);
}
}
}
struct ErrorVTable {
object_drop: unsafe fn(Own<ErrorImpl>),
object_ref: unsafe fn(Ref<ErrorImpl>) -> Ref<dyn StdError + Send + Sync + 'static>,
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
object_mut: unsafe fn(Mut<ErrorImpl>) -> &mut (dyn StdError + Send + Sync + 'static),
object_boxed: unsafe fn(Own<ErrorImpl>) -> Box<dyn StdError + Send + Sync + 'static>,
object_downcast: unsafe fn(Ref<ErrorImpl>, TypeId) -> Option<Ref<()>>,
#[cfg(anyhow_no_ptr_addr_of)]
object_downcast_mut: unsafe fn(Mut<ErrorImpl>, TypeId) -> Option<Mut<()>>,
object_drop_rest: unsafe fn(Own<ErrorImpl>, TypeId),
#[cfg(all(not(backtrace), feature = "backtrace"))]
object_backtrace: unsafe fn(Ref<ErrorImpl>) -> Option<&Backtrace>,
}
// Safety: requires layout of *e to match ErrorImpl<E>.
unsafe fn object_drop<E>(e: Own<ErrorImpl>) {
// Cast back to ErrorImpl<E> so that the allocator receives the correct
// Layout to deallocate the Box's memory.
let unerased = e.cast::<ErrorImpl<E>>().boxed();
drop(unerased);
}
// Safety: requires layout of *e to match ErrorImpl<E>.
unsafe fn object_drop_front<E>(e: Own<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;
let unerased = e.cast::<ErrorImpl<ManuallyDrop<E>>>().boxed();
drop(unerased);
}
// Safety: requires layout of *e to match ErrorImpl<E>.
unsafe fn object_ref<E>(e: Ref<ErrorImpl>) -> Ref<dyn StdError + Send + Sync + 'static>
where
E: StdError + Send + Sync + 'static,
{
// Attach E's native StdError vtable onto a pointer to self._object.
let unerased = e.cast::<ErrorImpl<E>>();
#[cfg(not(anyhow_no_ptr_addr_of))]
return Ref::from_raw(NonNull::new_unchecked(
ptr::addr_of!((*unerased.as_ptr())._object) as *mut E,
));
#[cfg(anyhow_no_ptr_addr_of)]
return Ref::new(&unerased.deref()._object);
}
// Safety: requires layout of *e to match ErrorImpl<E>, and for `e` to be derived
// from a `&mut`
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
unsafe fn object_mut<E>(e: Mut<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 e.cast::<ErrorImpl<E>>().deref_mut()._object
}
// Safety: requires layout of *e to match ErrorImpl<E>.
unsafe fn object_boxed<E>(e: Own<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.
e.cast::<ErrorImpl<E>>().boxed()
}
// Safety: requires layout of *e to match ErrorImpl<E>.
unsafe fn object_downcast<E>(e: Ref<ErrorImpl>, target: TypeId) -> Option<Ref<()>>
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 = e.cast::<ErrorImpl<E>>();
#[cfg(not(anyhow_no_ptr_addr_of))]
return Some(
Ref::from_raw(NonNull::new_unchecked(
ptr::addr_of!((*unerased.as_ptr())._object) as *mut E,
))
.cast::<()>(),
);
#[cfg(anyhow_no_ptr_addr_of)]
return Some(Ref::new(&unerased.deref()._object).cast::<()>());
} else {
None
}
}
// Safety: requires layout of *e to match ErrorImpl<E>.
#[cfg(anyhow_no_ptr_addr_of)]
unsafe fn object_downcast_mut<E>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
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 = e.cast::<ErrorImpl<E>>().deref_mut();
Some(Mut::new(&mut unerased._object).cast::<()>())
} else {
None
}
}
#[cfg(all(not(backtrace), feature = "backtrace"))]
fn no_backtrace(e: Ref<ErrorImpl>) -> Option<&Backtrace> {
let _ = e;
None
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, E>>.
#[cfg(feature = "std")]
unsafe fn context_downcast<C, E>(e: Ref<ErrorImpl>, target: TypeId) -> Option<Ref<()>>
where
C: 'static,
E: 'static,
{
if TypeId::of::<C>() == target {
let unerased = e.cast::<ErrorImpl<ContextError<C, E>>>().deref();
Some(Ref::new(&unerased._object.context).cast::<()>())
} else if TypeId::of::<E>() == target {
let unerased = e.cast::<ErrorImpl<ContextError<C, E>>>().deref();
Some(Ref::new(&unerased._object.error).cast::<()>())
} else {
None
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, E>>.
#[cfg(all(feature = "std", anyhow_no_ptr_addr_of))]
unsafe fn context_downcast_mut<C, E>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
where
C: 'static,
E: 'static,
{
if TypeId::of::<C>() == target {
let unerased = e.cast::<ErrorImpl<ContextError<C, E>>>().deref_mut();
Some(Mut::new(&mut unerased._object.context).cast::<()>())
} else if TypeId::of::<E>() == target {
let unerased = e.cast::<ErrorImpl<ContextError<C, E>>>().deref_mut();
Some(Mut::new(&mut unerased._object.error).cast::<()>())
} else {
None
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, E>>.
#[cfg(feature = "std")]
unsafe fn context_drop_rest<C, E>(e: Own<ErrorImpl>, target: TypeId)
where
C: 'static,
E: 'static,
{
// Called after downcasting by value to either the C or the E and doing a
// ptr::read to take ownership of that value.
if TypeId::of::<C>() == target {
let unerased = e
.cast::<ErrorImpl<ContextError<ManuallyDrop<C>, E>>>()
.boxed();
drop(unerased);
} else {
let unerased = e
.cast::<ErrorImpl<ContextError<C, ManuallyDrop<E>>>>()
.boxed();
drop(unerased);
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, Error>>.
unsafe fn context_chain_downcast<C>(e: Ref<ErrorImpl>, target: TypeId) -> Option<Ref<()>>
where
C: 'static,
{
let unerased = e.cast::<ErrorImpl<ContextError<C, Error>>>().deref();
if TypeId::of::<C>() == target {
Some(Ref::new(&unerased._object.context).cast::<()>())
} else {
// Recurse down the context chain per the inner error's vtable.
let source = &unerased._object.error;
(vtable(source.inner.ptr).object_downcast)(source.inner.by_ref(), target)
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, Error>>.
#[cfg(anyhow_no_ptr_addr_of)]
unsafe fn context_chain_downcast_mut<C>(e: Mut<ErrorImpl>, target: TypeId) -> Option<Mut<()>>
where
C: 'static,
{
let unerased = e.cast::<ErrorImpl<ContextError<C, Error>>>().deref_mut();
if TypeId::of::<C>() == target {
Some(Mut::new(&mut unerased._object.context).cast::<()>())
} else {
// Recurse down the context chain per the inner error's vtable.
let source = &mut unerased._object.error;
(vtable(source.inner.ptr).object_downcast_mut)(source.inner.by_mut(), target)
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, Error>>.
unsafe fn context_chain_drop_rest<C>(e: Own<ErrorImpl>, target: TypeId)
where
C: 'static,
{
// Called after downcasting by value to either the C or one of the causes
// and doing a ptr::read to take ownership of that value.
if TypeId::of::<C>() == target {
let unerased = e
.cast::<ErrorImpl<ContextError<ManuallyDrop<C>, Error>>>()
.boxed();
// Drop the entire rest of the data structure rooted in the next Error.
drop(unerased);
} else {
let unerased = e
.cast::<ErrorImpl<ContextError<C, ManuallyDrop<Error>>>>()
.boxed();
// Read the Own<ErrorImpl> from the next error.
let inner = unerased._object.error.inner;
drop(unerased);
let vtable = vtable(inner.ptr);
// Recursively drop the next error using the same target typeid.
(vtable.object_drop_rest)(inner, target);
}
}
// Safety: requires layout of *e to match ErrorImpl<ContextError<C, Error>>.
#[cfg(all(not(backtrace), feature = "backtrace"))]
#[allow(clippy::unnecessary_wraps)]
unsafe fn context_backtrace<C>(e: Ref<ErrorImpl>) -> Option<&Backtrace>
where
C: 'static,
{
let unerased = e.cast::<ErrorImpl<ContextError<C, Error>>>().deref();
let backtrace = ErrorImpl::backtrace(unerased._object.error.inner.by_ref());
Some(backtrace)
}
// NOTE: If working with `ErrorImpl<()>`, references should be avoided in favor
// of raw pointers and `NonNull`.
// repr C to ensure that E remains in the final position.
#[repr(C)]
pub(crate) struct ErrorImpl<E = ()> {
vtable: &'static ErrorVTable,
backtrace: Option<Backtrace>,
// NOTE: Don't use directly. Use only through vtable. Erased type may have
// different alignment.
_object: E,
}
// Reads the vtable out of `p`. This is the same as `p.as_ref().vtable`, but
// avoids converting `p` into a reference.
unsafe fn vtable(p: NonNull<ErrorImpl>) -> &'static ErrorVTable {
// NOTE: This assumes that `ErrorVTable` is the first field of ErrorImpl.
*(p.as_ptr() as *const &'static ErrorVTable)
}
// repr C to ensure that ContextError<C, E> has the same layout as
// ContextError<ManuallyDrop<C>, E> and ContextError<C, ManuallyDrop<E>>.
#[repr(C)]
pub(crate) struct ContextError<C, E> {
pub context: C,
pub error: E,
}
impl<E> ErrorImpl<E> {
fn erase(&self) -> Ref<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 coercion.
Ref::new(self).cast::<ErrorImpl>()
}
}
impl ErrorImpl {
pub(crate) unsafe fn error(this: Ref<Self>) -> &(dyn StdError + Send + Sync + 'static) {
// Use vtable to attach E's native StdError vtable for the right
// original type E.
(vtable(this.ptr).object_ref)(this).deref()
}
#[cfg(feature = "std")]
pub(crate) unsafe fn error_mut(this: Mut<Self>) -> &mut (dyn StdError + Send + Sync + 'static) {
// Use vtable to attach E's native StdError vtable for the right
// original type E.
#[cfg(not(anyhow_no_ptr_addr_of))]
return (vtable(this.ptr).object_ref)(this.by_ref())
.by_mut()
.deref_mut();
#[cfg(anyhow_no_ptr_addr_of)]
return (vtable(this.ptr).object_mut)(this);
}
#[cfg(any(backtrace, feature = "backtrace"))]
pub(crate) unsafe fn backtrace(this: Ref<Self>) -> &Backtrace {
// This unwrap can only panic if the underlying error's backtrace method
// is nondeterministic, which would only happen in maliciously
// constructed code.
this.deref()
.backtrace
.as_ref()
.or_else(|| {
#[cfg(backtrace)]
return Self::error(this).request_ref::<Backtrace>();
#[cfg(not(backtrace))]
return (vtable(this.ptr).object_backtrace)(this);
})
.expect("backtrace capture failed")
}
#[cfg(backtrace)]
unsafe fn provide<'a>(this: Ref<'a, Self>, demand: &mut Demand<'a>) {
if let Some(backtrace) = &this.deref().backtrace {
demand.provide_ref(backtrace);
}
Self::error(this).provide(demand);
}
#[cold]
pub(crate) unsafe fn chain(this: Ref<Self>) -> Chain {
Chain::new(Self::error(this))
}
}
impl<E> StdError for ErrorImpl<E>
where
E: StdError,
{
fn source(&self) -> Option<&(dyn StdError + 'static)> {
unsafe { ErrorImpl::error(self.erase()).source() }
}
#[cfg(backtrace)]
fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
unsafe { ErrorImpl::provide(self.erase(), demand) }
}
}
impl<E> Debug for ErrorImpl<E>
where
E: Debug,
{
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
unsafe { ErrorImpl::debug(self.erase(), formatter) }
}
}
impl<E> Display for ErrorImpl<E>
where
E: Display,
{
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
unsafe { Display::fmt(ErrorImpl::error(self.erase()), formatter) }
}
}
impl From<Error> for Box<dyn StdError + Send + Sync + 'static> {
#[cold]
fn from(error: Error) -> Self {
let outer = ManuallyDrop::new(error);
unsafe {
// Use vtable to attach ErrorImpl<E>'s native StdError vtable for
// the right original type E.
(vtable(outer.inner.ptr).object_boxed)(outer.inner)
}
}
}
impl From<Error> for Box<dyn StdError + Send + 'static> {
fn from(error: Error) -> Self {
Box::<dyn StdError + Send + Sync>::from(error)
}
}
impl From<Error> for Box<dyn StdError + 'static> {
fn from(error: Error) -> Self {
Box::<dyn StdError + Send + Sync>::from(error)
}
}
#[cfg(feature = "std")]
impl AsRef<dyn StdError + Send + Sync> for Error {
fn as_ref(&self) -> &(dyn StdError + Send + Sync + 'static) {
&**self
}
}
#[cfg(feature = "std")]
impl AsRef<dyn StdError> for Error {
fn as_ref(&self) -> &(dyn StdError + 'static) {
&**self
}
}