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/// Implements [`Error`] for structs and forwards the `source` implementation to one of its fields.
///
/// Emitted code is not compatible with `#[no_std]`.
///
/// Newtype structs can omit the field identifier.
///
/// # Examples
///
/// For newtype struct:
///
/// ```
/// use std::error::Error as _;
///
/// #[derive(Debug)]
/// struct MyError(eyre::Report);
///
/// impl_more::forward_display!(MyError);
/// impl_more::forward_error!(MyError);
///
/// let err = MyError(eyre::eyre!("something went wrong"));
/// assert_eq!(err.source().unwrap().to_string(), "something went wrong");
/// ```
///
/// For struct with named field:
///
/// ```
/// use std::error::Error as _;
///
/// #[derive(Debug)]
/// struct MyError {
/// cause: eyre::Report,
/// }
///
/// impl_more::forward_display!(MyError => cause);
/// impl_more::forward_error!(MyError => cause);
///
/// let err = MyError { cause: eyre::eyre!("something went wrong") };
/// assert_eq!(err.source().unwrap().to_string(), "something went wrong");
/// ```
///
/// This macro does not yet support use with generic error wrappers.
///
/// [`Error`]: std::error::Error
#[macro_export]
macro_rules! forward_error {
($ty:ty) => {
impl ::std::error::Error for $ty {
fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)> {
Some(::core::ops::Deref::deref(&self.0))
}
}
};
($ty:ty => $field:ident) => {
impl ::std::error::Error for $ty {
fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)> {
Some(::core::ops::Deref::deref(&self.$field))
}
}
};
}
/// Implements [`Error`] for enums.
///
/// Emitted code is not compatible with `#[no_std]`.
///
/// # Examples
///
/// ```
/// # extern crate alloc;
/// use std::error::Error as _;
///
/// #[derive(Debug)]
/// enum Err {
/// Io(std::io::Error),
/// Generic(String),
/// }
///
/// impl_more::impl_display_enum!(Err, Io(err) => "{err}", Generic(msg) => "{msg}");
/// impl_more::impl_error_enum!(Err, Io(err) => err);
///
/// # let io_err = std::io::Error::new(std::io::ErrorKind::Other, "test");
/// assert!(Err::Io(io_err).source().is_some());
/// assert!(Err::Generic("oops".to_owned()).source().is_none());
/// ```
///
/// [`Error`]: std::error::Error
#[macro_export]
macro_rules! impl_error_enum {
($ty:ty, $($variant:ident ($($inner:ident),+) => $source:expr),+ ,) => {
impl ::std::error::Error for $ty {
fn source(&self) -> ::core::option::Option<&(dyn ::std::error::Error + 'static)> {
match self {
$(
Self::$variant($($inner),+) => ::core::option::Option::Some($source),
)*
_ => ::core::option::Option::None,
}
}
}
};
($ty:ty, $($variant:ident ($($inner:ident),+) => $source:expr),+) => {
$crate::impl_error_enum!($ty, $($variant ($($inner),+) => $source),+ ,);
};
($ty:ty, $($variant:ident { $($inner:ident),+ } => $source:expr),+ ,) => {
impl ::std::error::Error for $ty {
fn source(&self) -> ::core::option::Option<&(dyn ::std::error::Error + 'static)> {
match self {
$(
Self::$variant($($inner),+) => ::core::option::Option::Some($source),
)*
_ => ::core::option::Option::None,
}
}
}
};
($ty:ty, $($variant:ident { $($inner:ident),+ } => $source:expr),+) => {
$crate::impl_error_enum!($ty, $($variant { $($inner),+ } => $source),+ ,);
};
($ty:ty,) => {
impl ::std::error::Error for $ty {}
};
($ty:ty) => {
$crate::impl_error_enum!($ty,);
};
}
#[cfg(test)]
mod tests {
use alloc::string::String;
use std::error::Error as _;
#[test]
fn with_trailing_comma() {
#![allow(unused)]
#[derive(Debug)]
enum Foo {
Bar,
}
impl_display_enum!(Foo, Bar => "bar");
impl_error_enum!(Foo,);
}
#[test]
fn no_inner_data() {
#[derive(Debug)]
enum Foo {
Bar,
Baz,
}
impl_display_enum!(Foo, Bar => "bar", Baz => "qux");
impl_error_enum!(Foo);
assert!(Foo::Bar.source().is_none());
assert!(Foo::Baz.source().is_none());
}
#[test]
fn uniform_enum() {
#[derive(Debug)]
enum Foo {
Bar(String),
Baz(std::io::Error),
Qux(String, std::io::Error),
}
impl_display_enum!(
Foo,
Bar(desc) => "{desc}",
Baz(err) => "{err}",
Qux(desc, err) => "{desc}: {err}"
);
impl_error_enum!(Foo, Baz(err) => err, Qux(_desc, err) => err);
assert!(Foo::Bar(String::new()).source().is_none());
let io_err = std::io::Error::new(std::io::ErrorKind::Other, "test");
assert!(Foo::Baz(io_err).source().is_some());
let io_err = std::io::Error::new(std::io::ErrorKind::Other, "test");
assert!(Foo::Qux(String::new(), io_err).source().is_some());
}
}