chainerror

use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;

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

derive_str_cherr!(Func2Error);

fn func2() -> Result<(), Box<Error>> {
    let filename = "foo.txt";
    do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
    Ok(())
}

derive_str_cherr!(Func1Error);

fn func1() -> Result<(), Box<Error>> {
    func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
    Ok(())
}

fn main() -> Result<(), Box<Error>> {
    if let Err(e) = func1() {
        if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
            eprintln!("Func1Error: {}", f1err);

            if let Some(f2err) = f1err.find_cause::<ChainError<Func2Error>>() {
                eprintln!("Func2Error: {}", f2err);
            }

            if let Some(f2err) = f1err.find_chain_cause::<Func2Error>() {
                eprintln!("Debug Func2Error:\n{:?}", f2err);
            }
        }
    }
    Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
# 
# pub struct ChainError<T> {
#     #[cfg(not(feature = "no-fileline"))]
#     occurrence: Option<(u32, &'static str)>,
#     kind: T,
#     error_cause: Option<Box<dyn Error + 'static>>,
# }
# 
# pub type ChainResult<O, E> = StdResult<O, ChainError<E>>;
# 
# impl<T: 'static + Display + Debug> ChainError<T> {
#     #[cfg(not(feature = "no-fileline"))]
#     pub fn new(
#         kind: T,
#         error_cause: Option<Box<dyn Error + 'static>>,
#         occurrence: Option<(u32, &'static str)>,
#     ) -> Self {
#         Self {
#             occurrence,
#             kind,
#             error_cause,
#         }
#     }
# 
#     #[cfg(feature = "no-fileline")]
#     pub fn new(
#         kind: T,
#         error_cause: Option<Box<dyn Error + 'static>>,
#         _occurrence: Option<(u32, &'static str)>,
#     ) -> Self {
#         Self { kind, error_cause }
#     }
# 
#     pub fn root_cause(&self) -> Option<&(dyn Error + 'static)> {
#         let mut cause = self as &(dyn Error + 'static);
#         while let Some(c) = cause.source() {
#             cause = c;
#         }
#         Some(cause)
#     }
# 
#     pub fn find_cause<U: Error + 'static>(&self) -> Option<&U> {
#         let mut cause = self as &(dyn Error + 'static);
#         loop {
#             if cause.is::<U>() {
#                 return cause.downcast_ref::<U>();
#             }
# 
#             match cause.source() {
#                 Some(c) => cause = c,
#                 None => return None,
#             }
#         }
#     }
# 
#     pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
#         let mut cause = self as &(dyn Error + 'static);
#         loop {
#             if cause.is::<ChainError<U>>() {
#                 return cause.downcast_ref::<ChainError<U>>();
#             }
# 
#             match cause.source() {
#                 Some(c) => cause = c,
#                 None => return None,
#             }
#         }
#     }
# 
#     pub fn kind<'a>(&'a self) -> &'a T {
#         &self.kind
#     }
# }
# 
# pub trait ChainErrorDown {
#     fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
#     fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
#     fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>>;
# }
# 
# use std::any::TypeId;
# 
# impl<U: 'static + Display + Debug> ChainErrorDown for ChainError<U> {
#     fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
#         TypeId::of::<T>() == TypeId::of::<U>()
#     }
# 
#     fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
#         if self.is_chain::<T>() {
#             unsafe { Some(&*(self as *const dyn Error as *const &ChainError<T>)) }
#         } else {
#             None
#         }
#     }
# 
#     fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
#         if self.is_chain::<T>() {
#             unsafe { Some(&mut *(self as *mut dyn Error as *mut &mut ChainError<T>)) }
#         } else {
#             None
#         }
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static {
#     fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
#         self.is::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
#         self.downcast_ref::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
#         self.downcast_mut::<ChainError<T>>()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send {
#     fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
#         self.is::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
#         self.downcast_ref::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
#         self.downcast_mut::<ChainError<T>>()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
#     fn is_chain<T: 'static + Display + Debug>(&self) -> bool {
#         self.is::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>> {
#         self.downcast_ref::<ChainError<T>>()
#     }
# 
#     fn downcast_chain_mut<T: 'static + Display + Debug>(&mut self) -> Option<&mut ChainError<T>> {
#         self.downcast_mut::<ChainError<T>>()
#     }
# }
# 
# impl<T: 'static + Display + Debug> Error for ChainError<T> {
#     fn source(&self) -> Option<&(dyn Error + 'static)> {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl<T: 'static + Display + Debug> Error for &ChainError<T> {
#     fn source(&self) -> Option<&(dyn Error + 'static)> {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
#     fn source(&self) -> Option<&(dyn Error + 'static)> {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl<T: 'static + Display + Debug> Display for ChainError<T> {
#     fn fmt(&self, f: &mut Formatter) -> Result {
#         write!(f, "{}", self.kind)?;
# 
#         #[cfg(feature = "display-cause")]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, "\nCaused by:")?;
#                 Display::fmt(&e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# impl<T: 'static + Display + Debug> Debug for ChainError<T> {
#     fn fmt(&self, f: &mut Formatter) -> Result {
#         #[cfg(not(feature = "no-fileline"))]
#         {
#             if let Some(o) = self.occurrence {
#                 write!(f, "{}:{}: ", o.1, o.0)?;
#             }
#         }
# 
#         Debug::fmt(&self.kind, f)?;
# 
#         #[cfg(not(feature = "no-debug-cause"))]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, "\nCaused by:")?;
#                 Debug::fmt(&e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# #[macro_export]
# macro_rules! cherr {
#     ( $k:expr ) => {
#         ChainError::<_>::new($k, None, Some((line!(), file!())))
#     };
#     ( $e:expr, $k:expr ) => {
#         ChainError::<_>::new($k, Some(Box::from($e)), Some((line!(), file!())))
#     };
# }
# 
# #[macro_export]
# macro_rules! mstrerr {
#     ( $t:ident, $v:expr $(, $more:expr)* ) => {
#         |e| cherr!(e, $t (format!($v, $( $more , )* )))
#     };
#     ( $t:path, $v:expr $(, $more:expr)* ) => {
#         |e| cherr!(e, $t (format!($v, $( $more , )* )))
#     };
#     ( $v:expr $(, $more:expr)* ) => {
#         |e| cherr!(e, format!($v, $( $more , )* ))
#     };
# }
# 
# #[macro_export]
# macro_rules! derive_str_cherr {
#     ($e:ident) => {
#         struct $e(String);
#         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 {}
#     };
# }
# 
# #[macro_export]
# macro_rules! try_cherr_ref {
#     ( $e:expr, $t:ident ) => {
#         $e.downcast_ref::<ChainError<$t>>()
#     };
#     ( $e:expr, $t:path ) => {
#         $e.downcast_ref::<ChainError<$t>>()
#     };
# }
# 
# #[macro_export]
# macro_rules! try_cherr_mut {
#     ( $e:expr, $t:ident ) => {
#         $e.downcast_mut::<ChainError<$t>>()
#     };
#     ( $e:expr, $t:path ) => {
#         $e.downcast_mut::<ChainError<$t>>()
#     };
# }
# }