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Auto merge of rust-lang#99917 - yaahc:error-in-core-move, r=thomcc
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Move Error trait into core

This PR moves the error trait from the standard library into a new unstable `error` module within the core library. The goal of this PR is to help unify error reporting across the std and no_std ecosystems, as well as open the door to integrating the error trait into the panic reporting system when reporting panics whose source is an errors (such as via `expect`).

This PR is a rewrite of rust-lang#90328 using new compiler features that have been added to support error in core.
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bors committed Aug 23, 2022
2 parents a1bea15 + bf7611d commit 060e47f
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Showing 25 changed files with 1,264 additions and 226 deletions.
306 changes: 306 additions & 0 deletions library/alloc/src/boxed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,8 @@ use core::async_iter::AsyncIterator;
use core::borrow;
use core::cmp::Ordering;
use core::convert::{From, TryFrom};
#[cfg(not(bootstrap))]
use core::error::Error;
use core::fmt;
use core::future::Future;
use core::hash::{Hash, Hasher};
Expand All @@ -174,6 +176,9 @@ use crate::borrow::Cow;
use crate::raw_vec::RawVec;
#[cfg(not(no_global_oom_handling))]
use crate::str::from_boxed_utf8_unchecked;
#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
use crate::string::String;
#[cfg(not(no_global_oom_handling))]
use crate::vec::Vec;

Expand Down Expand Up @@ -2085,3 +2090,304 @@ impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S> {
(**self).size_hint()
}
}

#[cfg(not(bootstrap))]
impl dyn Error {
#[inline]
#[stable(feature = "error_downcast", since = "1.3.0")]
#[rustc_allow_incoherent_impl]
/// Attempts to downcast the box to a concrete type.
pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> {
if self.is::<T>() {
unsafe {
let raw: *mut dyn Error = Box::into_raw(self);
Ok(Box::from_raw(raw as *mut T))
}
} else {
Err(self)
}
}
}

#[cfg(not(bootstrap))]
impl dyn Error + Send {
#[inline]
#[stable(feature = "error_downcast", since = "1.3.0")]
#[rustc_allow_incoherent_impl]
/// Attempts to downcast the box to a concrete type.
pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error + Send>> {
let err: Box<dyn Error> = self;
<dyn Error>::downcast(err).map_err(|s| unsafe {
// Reapply the `Send` marker.
mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
})
}
}

#[cfg(not(bootstrap))]
impl dyn Error + Send + Sync {
#[inline]
#[stable(feature = "error_downcast", since = "1.3.0")]
#[rustc_allow_incoherent_impl]
/// Attempts to downcast the box to a concrete type.
pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
let err: Box<dyn Error> = self;
<dyn Error>::downcast(err).map_err(|s| unsafe {
// Reapply the `Send + Sync` marker.
mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
})
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
/// Converts a type of [`Error`] into a box of dyn [`Error`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::fmt;
/// use std::mem;
///
/// #[derive(Debug)]
/// struct AnError;
///
/// impl fmt::Display for AnError {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "An error")
/// }
/// }
///
/// impl Error for AnError {}
///
/// let an_error = AnError;
/// assert!(0 == mem::size_of_val(&an_error));
/// let a_boxed_error = Box::<dyn Error>::from(an_error);
/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(err: E) -> Box<dyn Error + 'a> {
Box::new(err)
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
/// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
/// dyn [`Error`] + [`Send`] + [`Sync`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::fmt;
/// use std::mem;
///
/// #[derive(Debug)]
/// struct AnError;
///
/// impl fmt::Display for AnError {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "An error")
/// }
/// }
///
/// impl Error for AnError {}
///
/// unsafe impl Send for AnError {}
///
/// unsafe impl Sync for AnError {}
///
/// let an_error = AnError;
/// assert!(0 == mem::size_of_val(&an_error));
/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
/// assert!(
/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
Box::new(err)
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl From<String> for Box<dyn Error + Send + Sync> {
/// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
///
/// let a_string_error = "a string error".to_string();
/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
/// assert!(
/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
/// ```
#[inline]
fn from(err: String) -> Box<dyn Error + Send + Sync> {
struct StringError(String);

impl Error for StringError {
#[allow(deprecated)]
fn description(&self) -> &str {
&self.0
}
}

impl fmt::Display for StringError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
}
}

// Purposefully skip printing "StringError(..)"
impl fmt::Debug for StringError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&self.0, f)
}
}

Box::new(StringError(err))
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "string_box_error", since = "1.6.0")]
impl From<String> for Box<dyn Error> {
/// Converts a [`String`] into a box of dyn [`Error`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
///
/// let a_string_error = "a string error".to_string();
/// let a_boxed_error = Box::<dyn Error>::from(a_string_error);
/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(str_err: String) -> Box<dyn Error> {
let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
let err2: Box<dyn Error> = err1;
err2
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "rust1", since = "1.0.0")]
impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
/// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
///
/// [`str`]: prim@str
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
///
/// let a_str_error = "a str error";
/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
/// assert!(
/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
/// ```
#[inline]
fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> {
From::from(String::from(err))
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "string_box_error", since = "1.6.0")]
impl From<&str> for Box<dyn Error> {
/// Converts a [`str`] into a box of dyn [`Error`].
///
/// [`str`]: prim@str
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
///
/// let a_str_error = "a str error";
/// let a_boxed_error = Box::<dyn Error>::from(a_str_error);
/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(err: &str) -> Box<dyn Error> {
From::from(String::from(err))
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_box_error", since = "1.22.0")]
impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
/// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
/// use std::borrow::Cow;
///
/// let a_cow_str_error = Cow::from("a str error");
/// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
/// assert!(
/// mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
From::from(String::from(err))
}
}

#[cfg(not(bootstrap))]
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_box_error", since = "1.22.0")]
impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
/// Converts a [`Cow`] into a box of dyn [`Error`].
///
/// # Examples
///
/// ```
/// use std::error::Error;
/// use std::mem;
/// use std::borrow::Cow;
///
/// let a_cow_str_error = Cow::from("a str error");
/// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
/// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
/// ```
fn from(err: Cow<'a, str>) -> Box<dyn Error> {
From::from(String::from(err))
}
}

#[cfg(not(bootstrap))]
#[stable(feature = "box_error", since = "1.8.0")]
impl<T: core::error::Error> core::error::Error for Box<T> {
#[allow(deprecated, deprecated_in_future)]
fn description(&self) -> &str {
core::error::Error::description(&**self)
}

#[allow(deprecated)]
fn cause(&self) -> Option<&dyn core::error::Error> {
core::error::Error::cause(&**self)
}

fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
core::error::Error::source(&**self)
}
}
10 changes: 10 additions & 0 deletions library/alloc/src/boxed/thin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@
// https://github.com/matthieu-m/rfc2580/blob/b58d1d3cba0d4b5e859d3617ea2d0943aaa31329/examples/thin.rs
// by matthieu-m
use crate::alloc::{self, Layout, LayoutError};
#[cfg(not(bootstrap))]
use core::error::Error;
use core::fmt::{self, Debug, Display, Formatter};
use core::marker::PhantomData;
#[cfg(not(no_global_oom_handling))]
Expand Down Expand Up @@ -271,3 +273,11 @@ impl<H> WithHeader<H> {
Layout::new::<H>().extend(value_layout)
}
}

#[cfg(not(bootstrap))]
#[unstable(feature = "thin_box", issue = "92791")]
impl<T: ?Sized + Error> Error for ThinBox<T> {
fn source(&self) -> Option<&(dyn Error + 'static)> {
self.deref().source()
}
}
11 changes: 11 additions & 0 deletions library/alloc/src/collections/btree/map/entry.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -133,6 +133,17 @@ impl<'a, K: Debug + Ord, V: Debug, A: Allocator + Clone> fmt::Display
}
}

#[cfg(not(bootstrap))]
#[unstable(feature = "map_try_insert", issue = "82766")]
impl<'a, K: core::fmt::Debug + Ord, V: core::fmt::Debug> core::error::Error
for crate::collections::btree_map::OccupiedError<'a, K, V>
{
#[allow(deprecated)]
fn description(&self) -> &str {
"key already exists"
}
}

impl<'a, K: Ord, V, A: Allocator + Clone> Entry<'a, K, V, A> {
/// Ensures a value is in the entry by inserting the default if empty, and returns
/// a mutable reference to the value in the entry.
Expand Down
4 changes: 4 additions & 0 deletions library/alloc/src/collections/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,3 +152,7 @@ trait SpecExtend<I: IntoIterator> {
/// Extends `self` with the contents of the given iterator.
fn spec_extend(&mut self, iter: I);
}

#[cfg(not(bootstrap))]
#[stable(feature = "try_reserve", since = "1.57.0")]
impl core::error::Error for TryReserveError {}
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