# The source() of Errors - chainerror
A tutorial for the chainerror rust crate.

# The source() of Errors

Sometimes you want to inspect the `source()` of an `Error`. `chainerror` implements `std::error::Error::source()`, so you can get the cause of an error.

    use chainerror::Context as _;

    use std::error::Error;
    use std::io;

    fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
        Err(io::Error::from(io::ErrorKind::NotFound))?;
        Ok(())
    }

    fn func2() -> Result<(), Box<dyn Error + Send + Sync>> {
        let filename = "foo.txt";
        do_some_io().context(format!("Error reading '{}'", filename))?;
        Ok(())
    }

    fn func1() -> Result<(), Box<dyn Error + Send + Sync>> {
        if let Err(e) = func2() {
            if let Some(s) = e.source() {
                eprintln!("func2 failed because of '{}'", s);
                Err(e).context("func1 error")?;
            }
        }
        Ok(())
    }

    fn main() -> Result<(), Box<dyn Error + Send + Sync>> {
        if let Err(e) = func1() {
            eprintln!("{}", e);
            std::process::exit(1);
        }
        Ok(())
    }
    #[allow(dead_code)]
    mod chainerror {
    #![doc = include_str!("../README.md")]
    #![deny(clippy::all)]
    #![allow(clippy::needless_doctest_main)]
    #![deny(missing_docs)]

    use std::any::TypeId;
    use std::error::Error as StdError;
    use std::fmt::{Debug, Display, Formatter};
    use std::panic::Location;

    /// chains an inner error kind `T` with a causing error
    pub struct Error<T> {
        occurrence: Option<String>,
        kind: T,
        error_cause: Option<Box<dyn StdError + 'static + Send + Sync>>,
    }

    /// convenience type alias
    pub type Result<O, E> = std::result::Result<O, Error<E>>;

    impl<T: 'static + Display + Debug> Error<T> {
        /// Use the `context()` or `map_context()` Result methods instead of calling this directly
        #[inline]
        pub fn new(
            kind: T,
            error_cause: Option<Box<dyn StdError + 'static + Send + Sync>>,
            occurrence: Option<String>,
        ) -> Self {
            Self {
                occurrence,
                kind,
                error_cause,
            }
        }

        /// return the root cause of the error chain, if any exists
        pub fn root_cause(&self) -> Option<&(dyn StdError + 'static)> {
            self.iter().last()
        }

        /// Find the first error cause of type U, if any exists
        ///
        /// # Examples
        ///
        /// ```rust
        /// use chainerror::Context as _;
        /// use chainerror::ErrorDown as _;
        /// use std::error::Error;
        /// use std::io;
        ///
        /// fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
        ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
        ///     Ok(())
        /// }
        ///
        /// chainerror::str_context!(Func2Error);
        ///
        /// fn func2() -> Result<(), Box<dyn Error + Send + Sync>> {
        ///     let filename = "foo.txt";
        ///     do_some_io().context(Func2Error(format!("Error reading '{}'", filename)))?;
        ///     Ok(())
        /// }
        ///
        /// chainerror::str_context!(Func1Error);
        ///
        /// fn func1() -> Result<(), Box<dyn Error + Send + Sync>> {
        ///     func2().context(Func1Error::new("func1 error"))?;
        ///     Ok(())
        /// }
        ///
        /// if let Err(e) = func1() {
        ///     if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
        ///         assert!(f1err.find_cause::<io::Error>().is_some());
        ///
        ///         assert!(f1err.find_chain_cause::<Func2Error>().is_some());
        ///     }
        /// #        else {
        /// #            panic!();
        /// #        }
        /// }
        /// #    else {
        /// #         unreachable!();
        /// #    }
        /// ```
        #[inline]
        pub fn find_cause<U: StdError + 'static>(&self) -> Option<&U> {
            self.iter()
                .filter_map(<dyn StdError>::downcast_ref::<U>)
                .next()
        }

        /// Find the first error cause of type [`Error<U>`](Error), if any exists
        ///
        /// Same as `find_cause`, but hides the [`Error<U>`](Error) implementation internals
        ///
        /// # Examples
        ///
        /// ```rust
        /// # chainerror::str_context!(FooError);
        /// # let err = chainerror::Error::new(String::new(), None, None);
        /// // Instead of writing
        /// err.find_cause::<chainerror::Error<FooError>>();
        ///
        /// // leave out the chainerror::Error<FooError> implementation detail
        /// err.find_chain_cause::<FooError>();
        /// ```
        #[inline]
        pub fn find_chain_cause<U: StdError + 'static>(&self) -> Option<&Error<U>> {
            self.iter()
                .filter_map(<dyn StdError>::downcast_ref::<Error<U>>)
                .next()
        }

        /// Find the first error cause of type [`Error<U>`](Error) or `U`, if any exists and return `U`
        ///
        /// Same as `find_cause` and `find_chain_cause`, but hides the [`Error<U>`](Error) implementation internals
        ///
        /// # Examples
        ///
        /// ```rust
        /// # chainerror::str_context!(FooErrorKind);
        /// # let err = chainerror::Error::new(String::new(), None, None);
        /// // Instead of writing
        /// err.find_cause::<chainerror::Error<FooErrorKind>>();
        /// // and/or
        /// err.find_chain_cause::<FooErrorKind>();
        /// // and/or
        /// err.find_cause::<FooErrorKind>();
        ///
        /// // leave out the chainerror::Error<FooErrorKind> implementation detail
        /// err.find_kind_or_cause::<FooErrorKind>();
        /// ```
        #[inline]
        pub fn find_kind_or_cause<U: StdError + 'static>(&self) -> Option<&U> {
            self.iter()
                .filter_map(|e| {
                    e.downcast_ref::<Error<U>>()
                        .map(|e| e.kind())
                        .or_else(|| e.downcast_ref::<U>())
                })
                .next()
        }

        /// Return a reference to T of [`Error<T>`](Error)
        ///
        /// # Examples
        ///
        /// ```rust
        /// use chainerror::Context as _;
        /// use std::error::Error;
        /// use std::io;
        ///
        /// fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
        ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
        ///     Ok(())
        /// }
        ///
        /// chainerror::str_context!(Func2Error);
        ///
        /// fn func2() -> Result<(), Box<dyn Error + Send + Sync>> {
        ///     let filename = "foo.txt";
        ///     do_some_io().context(Func2Error(format!("Error reading '{}'", filename)))?;
        ///     Ok(())
        /// }
        ///
        /// #[derive(Debug)]
        /// enum Func1ErrorKind {
        ///     Func2,
        ///     IO(String),
        /// }
        ///
        /// /// impl ::std::fmt::Display for Func1ErrorKind {…}
        /// # impl ::std::fmt::Display for Func1ErrorKind {
        /// #     fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        /// #         match self {
        /// #             Func1ErrorKind::Func2 => write!(f, "func1 error calling func2"),
        /// #             Func1ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
        /// #         }
        /// #     }
        /// # }
        ///
        /// fn func1() -> chainerror::Result<(), Func1ErrorKind> {
        ///     func2().context(Func1ErrorKind::Func2)?;
        ///     do_some_io().context(Func1ErrorKind::IO("bar.txt".into()))?;
        ///     Ok(())
        /// }
        ///
        /// if let Err(e) = func1() {
        ///     match e.kind() {
        ///         Func1ErrorKind::Func2 => {}
        ///         Func1ErrorKind::IO(filename) => panic!(),
        ///     }
        /// }
        /// #    else {
        /// #         unreachable!();
        /// #    }
        /// ```
        #[inline]
        pub fn kind(&self) -> &T {
            &self.kind
        }

        /// Returns an Iterator over all error causes/sources
        ///
        /// # Example
        #[inline]
        pub fn iter(&self) -> impl Iterator<Item = &(dyn StdError + 'static)> {
            ErrorIter {
                current: Some(self),
            }
        }
    }

    /// Convenience methods for `Result<>` to turn the error into a decorated [`Error`](Error)
    pub trait Context<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> {
        /// Decorate the error with a `kind` of type `T` and the source `Location`
        fn context<T: 'static + Display + Debug>(self, kind: T) -> std::result::Result<O, Error<T>>;

        /// Decorate the error just with the source `Location`
        fn annotate(self) -> std::result::Result<O, Error<AnnotatedError>>;

        /// Decorate the `error` with a `kind` of type `T` produced with a `FnOnce(&error)` and the source `Location`
        fn map_context<T: 'static + Display + Debug, F: FnOnce(&E) -> T>(
            self,
            op: F,
        ) -> std::result::Result<O, Error<T>>;
    }

    /// Convenience type to just decorate the error with the source `Location`
    pub struct AnnotatedError(());

    impl Display for AnnotatedError {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            write!(f, "(passed error)")
        }
    }

    impl Debug for AnnotatedError {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            write!(f, "(passed error)")
        }
    }

    impl<O, E: Into<Box<dyn StdError + 'static + Send + Sync>>> Context<O, E>
        for std::result::Result<O, E>
    {
        #[track_caller]
        #[inline]
        fn context<T: 'static + Display + Debug>(self, kind: T) -> std::result::Result<O, Error<T>> {
            match self {
                Ok(t) => Ok(t),
                Err(error_cause) => Err(Error::new(
                    kind,
                    Some(error_cause.into()),
                    Some(Location::caller().to_string()),
                )),
            }
        }

        #[track_caller]
        #[inline]
        fn annotate(self) -> std::result::Result<O, Error<AnnotatedError>> {
            match self {
                Ok(t) => Ok(t),
                Err(error_cause) => Err(Error::new(
                    AnnotatedError(()),
                    Some(error_cause.into()),
                    Some(Location::caller().to_string()),
                )),
            }
        }

        #[track_caller]
        #[inline]
        fn map_context<T: 'static + Display + Debug, F: FnOnce(&E) -> T>(
            self,
            op: F,
        ) -> std::result::Result<O, Error<T>> {
            match self {
                Ok(t) => Ok(t),
                Err(error_cause) => {
                    let kind = op(&error_cause);
                    Err(Error::new(
                        kind,
                        Some(error_cause.into()),
                        Some(Location::caller().to_string()),
                    ))
                }
            }
        }
    }

    /// An iterator over all error causes/sources
    pub struct ErrorIter<'a> {
        current: Option<&'a (dyn StdError + 'static)>,
    }

    impl<'a> Iterator for ErrorIter<'a> {
        type Item = &'a (dyn StdError + 'static);

        #[inline]
        fn next(&mut self) -> Option<Self::Item> {
            let current = self.current;
            self.current = self.current.and_then(StdError::source);
            current
        }
    }

    impl<T: 'static + Display + Debug> std::ops::Deref for Error<T> {
        type Target = T;

        #[inline]
        fn deref(&self) -> &Self::Target {
            &self.kind
        }
    }

    /// Convenience trait to hide the [`Error<T>`](Error) implementation internals
    pub trait ErrorDown {
        /// Test if of type `Error<T>`
        fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
        /// Downcast to a reference of `Error<T>`
        fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&Error<T>>;
        /// Downcast to a mutable reference of `Error<T>`
        fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut Error<T>>;
        /// Downcast to T of `Error<T>`
        fn downcast_inner_ref<T: 'static + StdError>(&self) -> Option<&T>;
        /// Downcast to T mutable reference of `Error<T>`
        fn downcast_inner_mut<T: 'static + StdError>(&mut self) -> Option<&mut T>;
    }

    impl<U: 'static + Display + Debug> ErrorDown for Error<U> {
        #[inline]
        fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
            TypeId::of::<T>() == TypeId::of::<U>()
        }

        #[inline]
        fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&Error<T>> {
            if self.is_chain::<T>() {
                #[allow(clippy::cast_ptr_alignment)]
                unsafe {
                    #[allow(trivial_casts)]
                    Some(*(self as *const dyn StdError as *const &Error<T>))
                }
            } else {
                None
            }
        }

        #[inline]
        fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut Error<T>> {
            if self.is_chain::<T>() {
                #[allow(clippy::cast_ptr_alignment)]
                unsafe {
                    #[allow(trivial_casts)]
                    Some(&mut *(self as *mut dyn StdError as *mut &mut Error<T>))
                }
            } else {
                None
            }
        }
        #[inline]
        fn downcast_inner_ref<T: 'static + StdError>(&self) -> Option<&T> {
            if self.is_chain::<T>() {
                #[allow(clippy::cast_ptr_alignment)]
                unsafe {
                    #[allow(trivial_casts)]
                    Some(&(*(self as *const dyn StdError as *const &Error<T>)).kind)
                }
            } else {
                None
            }
        }

        #[inline]
        fn downcast_inner_mut<T: 'static + StdError>(&mut self) -> Option<&mut T> {
            if self.is_chain::<T>() {
                #[allow(clippy::cast_ptr_alignment)]
                unsafe {
                    #[allow(trivial_casts)]
                    Some(&mut (*(self as *mut dyn StdError as *mut &mut Error<T>)).kind)
                }
            } else {
                None
            }
        }
    }

    impl ErrorDown for dyn StdError + 'static {
        #[inline]
        fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
            self.is::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&Error<T>> {
            self.downcast_ref::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut Error<T>> {
            self.downcast_mut::<Error<T>>()
        }

        #[inline]
        fn downcast_inner_ref<T: 'static + StdError>(&self) -> Option<&T> {
            self.downcast_ref::<T>()
                .or_else(|| self.downcast_ref::<Error<T>>().map(|e| e.kind()))
        }

        #[inline]
        fn downcast_inner_mut<T: 'static + StdError>(&mut self) -> Option<&mut T> {
            if self.is::<T>() {
                return self.downcast_mut::<T>();
            }

            self.downcast_mut::<Error<T>>()
                .and_then(|e| e.downcast_inner_mut::<T>())
        }
    }

    impl ErrorDown for dyn StdError + 'static + Send {
        #[inline]
        fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
            self.is::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&Error<T>> {
            self.downcast_ref::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut Error<T>> {
            self.downcast_mut::<Error<T>>()
        }

        #[inline]
        fn downcast_inner_ref<T: 'static + StdError>(&self) -> Option<&T> {
            self.downcast_ref::<T>()
                .or_else(|| self.downcast_ref::<Error<T>>().map(|e| e.kind()))
        }

        #[inline]
        fn downcast_inner_mut<T: 'static + StdError>(&mut self) -> Option<&mut T> {
            if self.is::<T>() {
                return self.downcast_mut::<T>();
            }

            self.downcast_mut::<Error<T>>()
                .and_then(|e| e.downcast_inner_mut::<T>())
        }
    }

    impl ErrorDown for dyn StdError + 'static + Send + Sync {
        #[inline]
        fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
            self.is::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&Error<T>> {
            self.downcast_ref::<Error<T>>()
        }

        #[inline]
        fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut Error<T>> {
            self.downcast_mut::<Error<T>>()
        }

        #[inline]
        fn downcast_inner_ref<T: 'static + StdError>(&self) -> Option<&T> {
            self.downcast_ref::<T>()
                .or_else(|| self.downcast_ref::<Error<T>>().map(|e| e.kind()))
        }

        #[inline]
        fn downcast_inner_mut<T: 'static + StdError>(&mut self) -> Option<&mut T> {
            if self.is::<T>() {
                return self.downcast_mut::<T>();
            }

            self.downcast_mut::<Error<T>>()
                .and_then(|e| e.downcast_inner_mut::<T>())
        }
    }

    impl<T: 'static + Display + Debug> StdError for Error<T> {
        #[inline]
        fn source(&self) -> Option<&(dyn StdError + 'static)> {
            self.error_cause
                .as_ref()
                .map(|e| e.as_ref() as &(dyn StdError + 'static))
        }
    }

    impl<T: 'static + Display + Debug> StdError for &mut Error<T> {
        #[inline]
        fn source(&self) -> Option<&(dyn StdError + 'static)> {
            self.error_cause
                .as_ref()
                .map(|e| e.as_ref() as &(dyn StdError + 'static))
        }
    }

    impl<T: 'static + Display + Debug> Display for Error<T> {
        #[inline]
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            write!(f, "{}", self.kind)?;

            if f.alternate() {
                if let Some(e) = self.source() {
                    write!(f, "\nCaused by:\n  {:#}", &e)?;
                }
            }

            Ok(())
        }
    }

    impl<T: 'static + Display + Debug> Debug for Error<T> {
        #[inline]
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            if f.alternate() {
                let mut f = f.debug_struct(&format!("Error<{}>", std::any::type_name::<T>()));

                let f = f
                    .field("occurrence", &self.occurrence)
                    .field("kind", &self.kind)
                    .field("source", &self.source());

                f.finish()
            } else {
                if let Some(ref o) = self.occurrence {
                    write!(f, "{}: ", o)?;
                }

                if TypeId::of::<String>() == TypeId::of::<T>()
                    || TypeId::of::<&str>() == TypeId::of::<T>()
                {
                    Display::fmt(&self.kind, f)?;
                } else {
                    Debug::fmt(&self.kind, f)?;
                }

                if let Some(e) = self.source() {
                    write!(f, "\nCaused by:\n{:?}", &e)?;
                }
                Ok(())
            }
        }
    }

    impl<T> From<T> for Error<T>
    where
        T: 'static + Display + Debug,
    {
        #[track_caller]
        #[inline]
        fn from(e: T) -> Error<T> {
            Error::new(e, None, Some(Location::caller().to_string()))
        }
    }
    /// Convenience macro to create a "new type" T(String) and implement Display + Debug for T
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use chainerror::Context as _;
    /// # use chainerror::ErrorDown as _;
    /// # use std::error::Error;
    /// # use std::io;
    /// # use std::result::Result;
    /// # fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
    /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
    /// #     Ok(())
    /// # }
    /// chainerror::str_context!(Func2Error);
    ///
    /// fn func2() -> chainerror::Result<(), Func2Error> {
    ///     let filename = "foo.txt";
    ///     do_some_io().context(Func2Error(format!("Error reading '{}'", filename)))?;
    ///     Ok(())
    /// }
    ///
    /// chainerror::str_context!(Func1Error);
    ///
    /// fn func1() -> Result<(), Box<dyn Error>> {
    ///     func2().context(Func1Error::new("func1 error"))?;
    ///     Ok(())
    /// }
    /// #     if let Err(e) = func1() {
    /// #         if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
    /// #             assert!(f1err.find_cause::<chainerror::Error<Func2Error>>().is_some());
    /// #             assert!(f1err.find_chain_cause::<Func2Error>().is_some());
    /// #         } else {
    /// #             panic!();
    /// #         }
    /// #     } else {
    /// #         unreachable!();
    /// #     }
    /// ```
    #[macro_export]
    macro_rules! str_context {
        ($e:ident) => {
            #[derive(Clone)]
            pub struct $e(pub String);
            impl $e {
                pub fn new<S: Into<String>>(s: S) -> Self {
                    $e(s.into())
                }
            }
            impl ::std::fmt::Display for $e {
                fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
                    write!(f, "{}", self.0)
                }
            }
            impl ::std::fmt::Debug for $e {
                fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
                    write!(f, "{}({})", stringify!($e), self.0)
                }
            }
            impl ::std::error::Error for $e {}
        };
    }

    /// Derive an Error for an ErrorKind, which wraps a [`Error`](Error) and implements a `kind()` method
    ///
    /// It basically hides [`Error`](Error) to the outside and only exposes the [`kind()`](Error::kind)
    /// method.
    ///
    /// Error::kind() returns the ErrorKind
    /// Error::source() returns the parent error
    ///
    /// # Examples
    ///
    /// ```rust
    /// use chainerror::Context as _;
    /// use std::io;
    ///
    /// fn do_some_io(_f: &str) -> std::result::Result<(), io::Error> {
    ///     return Err(io::Error::from(io::ErrorKind::NotFound));
    /// }
    ///
    /// #[derive(Debug, Clone)]
    /// pub enum ErrorKind {
    ///     IO(String),
    ///     FatalError(String),
    ///     Unknown,
    /// }
    ///
    /// chainerror::err_kind!(Error, ErrorKind);
    ///
    /// impl std::fmt::Display for ErrorKind {
    ///     fn fmt(&self, f: &mut ::std::fmt::Formatter) -> std::fmt::Result {
    ///         match self {
    ///             ErrorKind::FatalError(e) => write!(f, "fatal error {}", e),
    ///             ErrorKind::Unknown => write!(f, "unknown error"),
    ///             ErrorKind::IO(filename) => write!(f, "Error reading '{}'", filename),
    ///         }
    ///     }
    /// }
    ///
    /// impl ErrorKind {
    ///     fn from_io_error(e: &io::Error, f: String) -> Self {
    ///         match e.kind() {
    ///             io::ErrorKind::BrokenPipe => panic!("Should not happen"),
    ///             io::ErrorKind::ConnectionReset => {
    ///                 ErrorKind::FatalError(format!("While reading `{}`: {}", f, e))
    ///             }
    ///             _ => ErrorKind::IO(f),
    ///         }
    ///     }
    /// }
    ///
    /// impl From<&io::Error> for ErrorKind {
    ///     fn from(e: &io::Error) -> Self {
    ///         ErrorKind::IO(format!("{}", e))
    ///     }
    /// }
    ///
    /// pub fn func1() -> std::result::Result<(), Error> {
    ///     let filename = "bar.txt";
    ///
    ///     do_some_io(filename).map_context(|e| ErrorKind::from_io_error(e, filename.into()))?;
    ///     do_some_io(filename).map_context(|e| ErrorKind::IO(filename.into()))?;
    ///     do_some_io(filename).map_context(|e| ErrorKind::from(e))?;
    ///     Ok(())
    /// }
    /// ```
    #[macro_export]
    macro_rules! err_kind {
        ($e:ident, $k:ident) => {
            pub struct $e($crate::Error<$k>);

            impl $e {
                pub fn kind(&self) -> &$k {
                    self.0.kind()
                }
            }

            impl From<$k> for $e {
                fn from(e: $k) -> Self {
                    $e($crate::Error::new(e, None, None))
                }
            }

            impl From<$crate::Error<$k>> for $e {
                fn from(e: $crate::Error<$k>) -> Self {
                    $e(e)
                }
            }

            impl From<&$e> for $k
            where
                $k: Clone,
            {
                fn from(e: &$e) -> Self {
                    e.kind().clone()
                }
            }

            impl std::error::Error for $e {
                fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
                    self.0.source()
                }
            }

            impl std::fmt::Display for $e {
                fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                    std::fmt::Display::fmt(&self.0, f)
                }
            }

            impl std::fmt::Debug for $e {
                fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                    std::fmt::Debug::fmt(&self.0, f)
                }
            }
        };
    }
    }

Note, that because we changed the output of the error in `main()` from `Debug` to `Display`, we don't see the error backtrace with filename and line number.

To use the `Display` backtrace, you have to use the alternative display format output `{:#}`.