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use crate::backtrace::Backtrace;
use crate::context::ContextError;
use std::any::TypeId;
use std::error::Error as StdError;
use std::fmt::{self, Debug, Display};
use std::mem;
use std::ops::{Deref, DerefMut};
use std::ptr;
pub struct Error {
inner: Box<ErrorImpl<()>>,
}
impl Error {
pub fn new<E>(error: E) -> Self
where
E: StdError + Send + Sync + 'static,
{
let backtrace = backtrace_if_absent!(error);
Error::from_std(error, backtrace)
}
pub(crate) fn from_std<E>(error: E, backtrace: Option<Backtrace>) -> Self
where
E: StdError + Send + Sync + 'static,
{
let type_id = TypeId::of::<E>();
unsafe { Error::construct(error, type_id, backtrace) }
}
pub(crate) fn from_adhoc<M>(message: M, backtrace: Option<Backtrace>) -> Self
where
M: Display + Debug + Send + Sync + 'static,
{
let error = MessageError(message);
let type_id = TypeId::of::<M>();
unsafe { Error::construct(error, type_id, backtrace) }
}
pub(crate) fn from_display<M>(message: M, backtrace: Option<Backtrace>) -> Self
where
M: Display + Send + Sync + 'static,
{
let error = DisplayError(message);
let type_id = TypeId::of::<M>();
unsafe { Error::construct(error, type_id, backtrace) }
}
unsafe fn construct<E>(error: E, type_id: TypeId, backtrace: Option<Backtrace>) -> Self
where
E: StdError + Send + Sync + 'static,
{
let vtable = &ErrorVTable {
object: object_raw::<E>,
object_mut: object_mut_raw::<E>,
};
let inner = Box::new(ErrorImpl {
vtable,
type_id,
backtrace,
error,
});
Error {
inner: mem::transmute::<Box<ErrorImpl<E>>, Box<ErrorImpl<()>>>(inner),
}
}
pub fn context<C>(self, context: C) -> Self
where
C: Display + Send + Sync + 'static,
{
Error::new(ContextError {
error: self,
context,
})
}
#[cfg(backtrace)]
pub fn backtrace(&self) -> &Backtrace {
self.inner
.backtrace
.as_ref()
.or_else(|| self.inner.error().backtrace())
.expect("backtrace capture failed")
}
pub fn chain(&self) -> Chain {
Chain {
next: Some(self.inner.error()),
}
}
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
}
pub fn is<E>(&self) -> bool
where
E: Display + Debug + Send + Sync + 'static,
{
TypeId::of::<E>() == self.inner.type_id
}
pub fn downcast<E>(self) -> Result<E, Self>
where
E: Display + Debug + Send + Sync + 'static,
{
if let Some(error) = self.downcast_ref::<E>() {
unsafe {
let error = ptr::read(error);
drop(ptr::read(&self.inner));
mem::forget(self);
Ok(error)
}
} else {
Err(self)
}
}
pub fn downcast_ref<E>(&self) -> Option<&E>
where
E: Display + Debug + Send + Sync + 'static,
{
if self.is::<E>() {
unsafe { Some(&*(self.inner.error() as *const dyn StdError as *const E)) }
} else {
None
}
}
pub fn downcast_mut<E>(&mut self) -> Option<&mut E>
where
E: Display + Debug + Send + Sync + 'static,
{
if self.is::<E>() {
unsafe { Some(&mut *(self.inner.error_mut() as *mut dyn StdError as *mut E)) }
} else {
None
}
}
}
impl<E> From<E> for Error
where
E: StdError + Send + Sync + 'static,
{
fn from(error: E) -> Self {
let backtrace = backtrace_if_absent!(error);
Error::from_std(error, backtrace)
}
}
impl Deref for Error {
type Target = dyn StdError + Send + Sync + 'static;
fn deref(&self) -> &Self::Target {
self.inner.error()
}
}
impl DerefMut for Error {
fn deref_mut(&mut self) -> &mut Self::Target {
self.inner.error_mut()
}
}
impl Debug for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
writeln!(f, "{}", self.inner.error())?;
let mut chain = self.chain().skip(1).enumerate().peekable();
if let Some((n, error)) = chain.next() {
write!(f, "\nCaused by:\n ")?;
if chain.peek().is_some() {
write!(f, "{}: ", n)?;
}
writeln!(f, "{}", error)?;
for (n, error) in chain {
writeln!(f, " {}: {}", n, error)?;
}
}
#[cfg(backtrace)]
{
use std::backtrace::BacktraceStatus;
let backtrace = self.backtrace();
match backtrace.status() {
BacktraceStatus::Captured => {
writeln!(f, "\n{}", backtrace)?;
}
BacktraceStatus::Disabled => {
writeln!(
f,
"\nBacktrace disabled; run with RUST_LIB_BACKTRACE=1 environment variable to display a backtrace"
)?;
}
_ => {}
}
}
Ok(())
}
}
impl Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{}", self.inner.error())
}
}
unsafe impl Send for Error {}
unsafe impl Sync for Error {}
impl Drop for Error {
fn drop(&mut self) {
unsafe { ptr::drop_in_place(self.inner.error_mut()) }
}
}
struct ErrorVTable {
object: fn(*const ()) -> *const (dyn StdError + Send + Sync + 'static),
object_mut: fn(*mut ()) -> *mut (dyn StdError + Send + Sync + 'static),
}
fn object_raw<E>(e: *const ()) -> *const (dyn StdError + Send + Sync + 'static)
where
E: StdError + Send + Sync + 'static,
{
e as *const E
}
fn object_mut_raw<E>(e: *mut ()) -> *mut (dyn StdError + Send + Sync + 'static)
where
E: StdError + Send + Sync + 'static,
{
e as *mut E
}
#[repr(C)]
struct ErrorImpl<E> {
vtable: &'static ErrorVTable,
type_id: TypeId,
backtrace: Option<Backtrace>,
error: E,
}
#[repr(transparent)]
struct MessageError<M>(M);
impl<M> Debug for MessageError<M>
where
M: Display + Debug,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Debug::fmt(&self.0, f)
}
}
impl<M> Display for MessageError<M>
where
M: Display + Debug,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt(&self.0, f)
}
}
impl<M> StdError for MessageError<M> where M: Display + Debug + 'static {}
#[repr(transparent)]
struct DisplayError<M>(M);
impl<M> Debug for DisplayError<M>
where
M: Display,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt(&self.0, f)
}
}
impl<M> Display for DisplayError<M>
where
M: Display,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt(&self.0, f)
}
}
impl<M> StdError for DisplayError<M> where M: Display + 'static {}
impl ErrorImpl<()> {
fn error(&self) -> &(dyn StdError + Send + Sync + 'static) {
unsafe { &*(self.vtable.object)(&self.error) }
}
fn error_mut(&mut self) -> &mut (dyn StdError + Send + Sync + 'static) {
unsafe { &mut *(self.vtable.object_mut)(&mut self.error) }
}
}
pub struct Chain<'a> {
next: Option<&'a (dyn StdError + 'static)>,
}
impl<'a> Iterator for Chain<'a> {
type Item = &'a (dyn StdError + 'static);
fn next(&mut self) -> Option<Self::Item> {
let next = self.next.take()?;
self.next = next.source();
Some(next)
}
}
#[cfg(test)]
mod repr_correctness {
use super::*;
use std::marker::Unpin;
use std::mem;
use std::sync::atomic::AtomicBool;
use std::sync::atomic::Ordering::SeqCst;
use std::sync::Arc;
#[test]
fn size_of_error() {
assert_eq!(mem::size_of::<Error>(), mem::size_of::<usize>());
}
#[test]
fn error_autotraits() {
fn assert<E: Unpin + Send + Sync + 'static>() {}
assert::<Error>();
}
#[test]
fn drop_works() {
#[derive(Debug)]
struct DetectDrop {
has_dropped: Arc<AtomicBool>,
}
impl StdError for DetectDrop {}
impl Display for DetectDrop {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "does something")
}
}
impl Drop for DetectDrop {
fn drop(&mut self) {
let already_dropped = self.has_dropped.swap(true, SeqCst);
assert!(!already_dropped);
}
}
let has_dropped = Arc::new(AtomicBool::new(false));
drop(Error::new(DetectDrop {
has_dropped: has_dropped.clone(),
}));
assert!(has_dropped.load(SeqCst));
}
}