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< ol class = "chapter" > < li class = "affix" > < a href = "index.html" > chainerror< / a > < / li > < li > < a href = "tutorial1.html" > < strong aria-hidden = "true" > 1.< / strong > Simple String Errors< / a > < / li > < li > < a href = "tutorial2.html" > < strong aria-hidden = "true" > 2.< / strong > Simple Chained String Errors< / a > < / li > < li > < a href = "tutorial3.html" > < strong aria-hidden = "true" > 3.< / strong > Mapping Errors< / a > < / li > < li > < a href = "tutorial4.html" > < strong aria-hidden = "true" > 4.< / strong > Saving coding chars< / a > < / li > < li > < a href = "tutorial5.html" > < strong aria-hidden = "true" > 5.< / strong > The source() of Errors< / a > < / li > < li > < a href = "tutorial6.html" > < strong aria-hidden = "true" > 6.< / strong > Downcast the Errors< / a > < / li > < li > < a href = "tutorial7.html" > < strong aria-hidden = "true" > 7.< / strong > The root cause of all Errors< / a > < / li > < li > < a href = "tutorial8.html" > < strong aria-hidden = "true" > 8.< / strong > Finding an Error cause< / a > < / li > < li > < a href = "tutorial9.html" > < strong aria-hidden = "true" > 9.< / strong > Selective Error Handling< / a > < / li > < li > < a href = "tutorial10.html" > < strong aria-hidden = "true" > 10.< / strong > ErrorKind to the rescue< / a > < / li > < li > < a href = "tutorial11.html" > < strong aria-hidden = "true" > 11.< / strong > Debug for the ErrorKind< / a > < / li > < li class = "affix" > < a href = "end.html" > The End< / a > < / li > < / ol >
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< main >
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< a class = "header" href = "#chainerror" id = "chainerror" > < h1 > chainerror< / h1 > < / a >
< p > < code > chainerror< / code > provides an error backtrace like < code > failure< / code > without doing a real backtrace, so even after you < code > strip< / code > your
binaries, you still have the error backtrace.< / p >
< p > < code > chainerror< / code > has no dependencies!< / p >
< p > < code > chainerror< / code > uses < code > .source()< / code > of < code > std::error::Error< / code > along with < code > line()!< / code > and < code > file()!< / code > to provide a nice debug error backtrace.
It encapsulates all types, which have < code > Display + Debug< / code > and can store the error cause internally.< / p >
< p > Along with the < code > ChainError< T> < / code > struct, < code > chainerror< / code > comes with some useful helper macros to save a lot of typing.< / p >
< p > Debug information is worth it!< / p >
< p > Now continue reading the
< a href = "https://haraldh.github.io/chainerror/tutorial1.html" > Tutorial< / a > < / p >
< a class = "header" href = "#example" id = "example" > < h2 > Example:< / h2 > < / a >
< p > Output:< / p >
< pre > < code > $ cargo run -q --example example
Main Error Report: func1 error calling func2
Error reported by Func2Error: func2 error: calling func3
The root cause was: std::io::Error: Kind(
NotFound
)
Debug Error:
examples/example.rs:45: func1 error calling func2
Caused by:
examples/example.rs:20: Func2Error(func2 error: calling func3)
Caused by:
examples/example.rs:13: Error reading 'foo.txt'
Caused by:
Kind(NotFound)
< / code > < / pre >
< pre > < code class = "language-rust ignore" > use 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(())
}
fn func3() -> Result< (), Box< Error> > {
let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
Ok(())
}
derive_str_cherr!(Func2Error);
fn func2() -> ChainResult< (), Func2Error> {
func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
Ok(())
}
enum Func1Error {
Func2,
IO(String),
}
impl ::std::fmt::Display for Func1Error {
fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match self {
Func1Error::Func2 => write!(f, " func1 error calling func2" ),
Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
}
}
}
impl ::std::fmt::Debug for Func1Error {
fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, " {}" , self)
}
}
fn func1() -> ChainResult< (), Func1Error> {
func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
let filename = String::from(" bar.txt" );
do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
Ok(())
}
fn main() {
if let Err(e) = func1() {
match e.kind() {
Func1Error::Func2 => eprintln!(" Main Error Report: func1 error calling func2" ),
Func1Error::IO(filename) => {
eprintln!(" Main Error Report: func1 error reading '{}'" , filename)
}
}
if let Some(e) = e.find_chain_cause::< Func2Error> () {
eprintln!(" \nError reported by Func2Error: {}" , e)
}
if let Some(e) = e.root_cause() {
let ioerror = e.downcast_ref::< io::Error> ().unwrap();
eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
}
eprintln!(" \nDebug Error:\n{:?}" , e);
}
}
< / code > < / pre >
< a class = "header" href = "#features" id = "features" > < h2 > Features< / h2 > < / a >
< p > < code > no-fileline< / code >
: completely turn off storing filename and line< / p >
< p > < code > display-cause< / code >
: turn on printing a backtrace of the errors in < code > Display< / code > < / p >
< p > < code > no-debug-cause< / code >
: turn off printing a backtrace of the errors in < code > Debug< / code > < / p >
< a class = "header" href = "#simple-string-errors" id = "simple-string-errors" > < h1 > Simple String Errors< / h1 > < / a >
< p > An easy way of doing error handling in rust is by returning < code > String< / code > as a < code > Box< std::error::Error> < / code > .< / p >
< p > If the rust < code > main< / code > function returns an < code > Err()< / code > , this < code > Err()< / code > will be displayed with < code > std::fmt::Debug< / code > .< / p >
< p > As you can see by running the example (by pressing the " Play" button in upper right of the code block),
this only
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prints out the last < code > Error< / code > .< / p >
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< pre > < code > Error: StringError(" func1 error" )
< / code > < / pre >
< p > The next chapters of this tutorial show how < code > chainerror< / code > adds more information
and improves inspecting the sources of an error.< / p >
< p > You can also run the tutorial examples in the checked out
< a href = "https://github.com/haraldh/chainerror" > chainerror git repo< / a > .< / p >
< pre > < code > $ cargo run -q --example tutorial1
< / code > < / pre >
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< pre > < pre class = "playpen" > < code class = "language-rust" > use std::error::Error;
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use std::io;
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use std::result::Result;
fn do_some_io() -> Result< (), Box< Error> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
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Ok(())
}
fn func2() -> Result< (), Box< Error> > {
if let Err(_) = do_some_io() {
Err(" func2 error" )?;
}
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
if let Err(_) = func2() {
Err(" func1 error" )?;
}
Ok(())
}
fn main() -> Result< (), Box< Error> > {
func1()
}
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< / code > < / pre > < / pre >
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< a class = "header" href = "#simple-chained-string-errors" id = "simple-chained-string-errors" > < h1 > Simple Chained String Errors< / h1 > < / a >
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< p > With relatively small changes and the help of the < code > cherr!< / code > macro of the < code > chainerror< / code > crate
the < code > String< / code > errors are now chained together.< / p >
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< p > Press the play button in the upper right corner and see the nice debug output.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > use crate::chainerror::*;
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use std::error::Error;
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use std::io;
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use std::result::Result;
fn do_some_io() -> Result< (), Box< Error> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
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Ok(())
}
fn func2() -> Result< (), Box< Error> > {
if let Err(e) = do_some_io() {
Err(cherr!(e, " func2 error" ))?;
}
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
if let Err(e) = func2() {
Err(cherr!(e, " func1 error" ))?;
}
Ok(())
}
fn main() -> Result< (), Box< Error> > {
func1()
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#what-did-we-do-here" id = "what-did-we-do-here" > < h3 > What did we do here?< / h3 > < / a >
< pre > < code class = "language-rust ignore" > if let Err(e) = do_some_io() {
Err(cherr!(e, " func2 error" ))?;
}
< / code > < / pre >
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< p > The macro < code > cherr!(olderror, newerror)< / code > stores < code > olderror< / code > as the source/cause of < code > newerror< / code >
along with the filename (< code > file!()< / code > ) and line number (< code > line!()< / code > )
and returns < code > newerror< / code > .< / p >
< p > < code > Err()?< / code > then returns the inner error applying < code > .into()< / code > , so that we
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again have a < code > Err(Box< Error> )< / code > as a result.< / p >
< p > The < code > Debug< / code > implementation of < code > ChainError< T> < / code > (which is returned by < code > cherr!()< / code > )
prints the < code > Debug< / code > of < code > T< / code > prefixed with the stored filename and line number.< / p >
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< p > < code > ChainError< T> < / code > in our case is < code > ChainError< String> < / code > .< / p >
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< a class = "header" href = "#mapping-errors" id = "mapping-errors" > < h1 > Mapping Errors< / h1 > < / a >
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< p > Now let's get more rust idiomatic by using < code > .map_err()< / code > .< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > use crate::chainerror::*;
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use std::error::Error;
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use std::io;
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use std::result::Result;
fn do_some_io() -> Result< (), Box< Error> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
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Ok(())
}
fn func2() -> Result< (), Box< Error> > {
do_some_io().map_err(|e| cherr!(e, " func2 error" ))?;
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
func2().map_err(|e| cherr!(e, " func1 error" ))?;
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
eprintln!(" {:?}" , e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< p > If you compare the output to the previous example, you will see,
that:< / p >
< pre > < code > Error: src/main.rs:19: " func1 error"
< / code > < / pre >
< p > changed to just:< / p >
< pre > < code > src/main.rs:16: " func1 error"
< / code > < / pre >
< p > This is, because we caught the error of < code > func1()< / code > in < code > main()< / code > and print it out ourselves.< / p >
< p > We can now control, whether to output in < code > Debug< / code > or < code > Display< / code > mode.
Maybe depending on < code > --debug< / code > as a CLI argument.< / p >
2018-12-20 16:37:43 +01:00
< a class = "header" href = "#saving-coding-chars" id = "saving-coding-chars" > < h1 > Saving coding chars< / h1 > < / a >
2018-12-20 16:02:24 +01:00
< p > Because decorating an error with more information should not
let you jump through hoops, < code > chainerror< / code > has a quick macro for that.< / p >
< p > < code > mstrerror!()< / code > fits right into < code > .map_err()< / code > letting you quickly add
more debug strings.< / p >
< p > < code > mstrerror!()< / code > even understands < code > format!()< / code > syntax like < code > println!()< / code > .< / p >
2018-12-20 14:55:19 +01:00
< pre > < pre class = "playpen" > < code class = "language-rust" > use crate::chainerror::*;
use std::error::Error;
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use std::io;
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use std::result::Result;
fn do_some_io() -> Result< (), Box< Error> > {
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Err(io::Error::from(io::ErrorKind::NotFound))?;
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Ok(())
}
fn func2() -> Result< (), Box< Error> > {
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let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
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Ok(())
}
fn func1() -> Result< (), Box< Error> > {
func2().map_err(mstrerr!(" func1 error" ))?;
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
eprintln!(" {:?}" , e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#the-source-of-errors" id = "the-source-of-errors" > < h1 > The source() of Errors< / h1 > < / a >
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< p > Sometimes you want to inspect the < code > source()< / code > of an < code > Error< / code > .
< code > chainerror< / code > implements < code > std::error::Error::source()< / code > , so you can get the cause of an error.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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(())
}
fn func2() -> Result< (), Box< Error> > {
let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
if let Err(e) = func2() {
if let Some(s) = e.source() {
eprintln!(" func2 failed because of '{}'" , s);
Err(e).map_err(mstrerr!(" func1 error" ))?;
}
}
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
eprintln!(" {}" , e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< p > Note, that because we changed the output of the error in < code > main()< / code > from
< code > Debug< / code > to < code > Display< / code > , we don't see the error backtrace with filename and line number.< / p >
2018-12-20 16:02:24 +01:00
< p > To enable the < code > Display< / code > backtrace, you have to enable the feature < code > display-cause< / code > for < code > chainerror< / code > .< / p >
2018-12-20 16:37:43 +01:00
< a class = "header" href = "#downcast-the-errors" id = "downcast-the-errors" > < h1 > Downcast the Errors< / h1 > < / a >
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< p > < code > std::error::Error< / code > comes with some helper methods to get to the original object of the
< code > & (dyn Error + 'static)< / code > returned by < code > .source()< / code > .< / p >
< pre > < code class = "language-rust ignore" > pub fn downcast_ref< T: Error + 'static> (& self) -> Option< & T>
pub fn downcast_mut< T: Error + 'static> (& mut self) -> Option< & mut T>
< / code > < / pre >
< p > This is how it looks like, when using those:< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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(())
}
fn func2() -> Result< (), Box< Error> > {
let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
func2().map_err(mstrerr!(" func1 error" ))?;
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
eprintln!(" Error: {}" , e);
let mut s = e.as_ref();
while let Some(c) = s.source() {
if let Some(ioerror) = c.downcast_ref::< io::Error> () {
eprintln!(" caused by: std::io::Error: {}" , ioerror);
match ioerror.kind() {
io::ErrorKind::NotFound => eprintln!(" of kind: std::io::ErrorKind::NotFound" ),
_ => {}
}
} else {
eprintln!(" caused by: {}" , c);
}
s = c;
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#the-root-cause-of-all-errors" id = "the-root-cause-of-all-errors" > < h1 > The root cause of all Errors< / h1 > < / a >
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< p > < code > chainerror< / code > also has some helper methods:< / p >
< pre > < code class = "language-rust ignore" > 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> >
fn root_cause(& self) -> Option< & (dyn Error + 'static)>
fn find_cause< U: Error + 'static> (& self) -> Option< & U>
fn find_chain_cause< U: Error + 'static> (& self) -> Option< & ChainError< U> >
fn kind< 'a> (& 'a self) -> & 'a T
< / code > < / pre >
< p > Using < code > downcast_chain_ref::< String> ()< / code > gives a < code > ChainError< String> < / code > , which can be used
to call < code > .find_cause::< io::Error> ()< / code > .< / p >
< pre > < code class = "language-rust ignore" > if let Some(s) = e.downcast_chain_ref::< String> () {
if let Some(ioerror) = s.find_cause::< io::Error> () {
< / code > < / pre >
< p > or to use < code > .root_cause()< / code > , which of course can be of any type implementing < code > std::error::Error< / code > .< / p >
< pre > < code class = "language-rust ignore" > if let Some(e) = s.root_cause() {
< / code > < / pre >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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(())
}
fn func2() -> Result< (), Box< Error> > {
let filename = " foo.txt" ;
do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
Ok(())
}
fn func1() -> Result< (), Box< Error> > {
func2().map_err(mstrerr!(" func1 error" ))?;
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
eprintln!(" Error: {}" , e);
if let Some(s) = e.downcast_chain_ref::< String> () {
if let Some(ioerror) = s.find_cause::< io::Error> () {
eprintln!(" caused by: std::io::Error: {}" , ioerror);
match ioerror.kind() {
io::ErrorKind::NotFound => eprintln!(" of kind: std::io::ErrorKind::NotFound" ),
_ => {}
}
}
if let Some(e) = s.root_cause() {
let ioerror = e.downcast_ref::< io::Error> ().unwrap();
eprintln!(" The root cause was: std::io::Error: {:#?}" , ioerror);
}
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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;
# }
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# Some(cause)
# }
#
# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
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# }
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# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#finding-an-error-cause" id = "finding-an-error-cause" > < h1 > Finding an Error cause< / h1 > < / a >
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< p > To distinguish the errors occuring in various places, we can define named string errors with the
" new type" pattern.< / p >
< pre > < code class = "language-rust ignore" > derive_str_cherr!(Func2Error);
derive_str_cherr!(Func1Error);
< / code > < / pre >
< p > Instead of < code > ChainError< String> < / code > we now have < code > struct Func1Error(String)< / code > and < code > ChainError< Func1Error> < / code > .< / p >
< p > In the < code > main< / code > function you can see, how we can match the different errors.< / p >
< p > Also see:< / p >
< pre > < code class = "language-rust ignore" > if let Some(f2err) = f1err.find_chain_cause::< Func2Error> () {
< / code > < / pre >
< p > as a shortcut to< / p >
< pre > < code class = "language-rust ignore" > if let Some(f2err) = f1err.find_cause::< ChainError< Func2Error> > () {
< / code > < / pre >
< p > hiding the < code > ChainError< T> < / code > implementation detail.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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 {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#selective-error-handling" id = "selective-error-handling" > < h1 > Selective Error Handling< / h1 > < / a >
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< p > What about functions returning different Error types?< / p >
< p > In this example < code > func1()< / code > can return either < code > Func1ErrorFunc2< / code > or < code > Func1ErrorIO< / code > .< / p >
< p > We might want to < code > match< / code > on < code > func1()< / code > with something like:< / p >
< pre > < code class = "language-rust ignore" > fn main() -> Result< (), Box< Error> > {
match func1() {
Err(e) if let Some(s) = e.downcast_chain_ref::< Func1ErrorIO> () =>
eprintln!(" Func1ErrorIO:\n{:?}" , s),
Err(e) if let Some(s) = e.downcast_chain_ref::< Func1ErrorFunc2> () =>
eprintln!(" Func1ErrorFunc2:\n{:?}" , s),
Ok(_) => {},
}
Ok(())
}
< / code > < / pre >
< p > but this is not valid rust code, so we end up doing it the hard way.
In the next chapter, we will see, how to solve this more elegantly.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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!(Func1ErrorFunc2);
derive_str_cherr!(Func1ErrorIO);
fn func1() -> Result< (), Box< Error> > {
func2().map_err(mstrerr!(Func1ErrorFunc2, " func1 error calling func2" ))?;
let filename = " bar.txt" ;
do_some_io().map_err(mstrerr!(Func1ErrorIO, " Error reading '{}'" , filename))?;
Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
if let Some(s) = e.downcast_ref::< ChainError< Func1ErrorIO> > () {
eprintln!(" Func1ErrorIO:\n{:?}" , s);
}
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if let Some(s) = e.downcast_chain_ref::< Func1ErrorFunc2> () {
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eprintln!(" Func1ErrorFunc2:\n{:?}" , s);
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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> > ();
# }
#
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# match cause.source() {
# Some(c) => cause = c,
# None => return None,
# }
# }
# }
#
# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
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# }
# }
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# # else {
# # unreachable!();
# # }
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# }
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# ~~~
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#
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# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#errorkind-to-the-rescue" id = "errorkind-to-the-rescue" > < h1 > ErrorKind to the rescue< / h1 > < / a >
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< p > To cope with different kind of errors, we introduce the kind of an error < code > Func1ErrorKind< / code > with an enum.< / p >
< p > Because we derive < code > Debug< / code > and implement < code > Display< / code > our < code > Func1ErrorKind< / code > enum, this enum can be used as
a < code > std::error::Error< / code > .< / p >
< p > Not using < code > String< / code > errors anymore, the < code > cherr!()< / code > macro seen in the beginning of
the tutorial has to be used again.< / p >
< p > Only returning < code > Func1ErrorKind< / code > in < code > func1()< / code > now let us get rid of < code > Result< (), Box< Error> > < / code > and we can
use < code > ChainResult< (), Func1ErrorKind> < / code > .< / p >
< p > In < code > main< / code > we can now directly use the methods of < code > ChainError< T> < / code > without downcasting the error first.< / p >
< p > Also a nice < code > match< / code > on < code > ChainError< T> .kind()< / code > is now possible, which returns < code > & T< / code > , meaning
< code > & Func1ErrorKind< / code > here.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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(Debug)]
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enum Func1ErrorKind {
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Func2,
IO(String),
}
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impl ::std::fmt::Display for Func1ErrorKind {
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fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match self {
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Func1ErrorKind::Func2 => write!(f, " func1 error calling func2" ),
Func1ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
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}
}
}
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fn func1() -> ChainResult< (), Func1ErrorKind> {
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
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let filename = String::from(" bar.txt" );
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do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
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Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
match e.kind() {
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Func1ErrorKind::Func2 => eprintln!(" Main Error Report: func1 error calling func2" ),
Func1ErrorKind::IO(filename) => {
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eprintln!(" Main Error Report: func1 error reading '{}'" , filename)
}
}
if let Some(e) = e.find_chain_cause::< Func2Error> () {
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eprintln!(" \nError reported by Func2Error: {}" , e)
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}
eprintln!(" \nDebug Error:\n{:?}" , e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
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< a class = "header" href = "#debug-for-the-errorkind" id = "debug-for-the-errorkind" > < h1 > Debug for the ErrorKind< / h1 > < / a >
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< p > One small improvement at the end of the tutorial is to fix the debug output of
< code > Func1ErrorKind< / code > . As you probably noticed, the output doesn't say much of the enum.< / p >
< pre > < code > Debug Error:
src/main.rs:35: Func2
[…]
< / code > < / pre >
< p > As a lazy shortcut, we implement < code > Debug< / code > by calling < code > Display< / code > and end up with< / p >
< pre > < code > Debug Error:
src/main.rs:40: func1 error calling func2
[…}
< / code > < / pre >
< p > which gives us a lot more detail.< / p >
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< pre > < pre class = "playpen" > < code class = "language-rust" > 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(())
}
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enum Func1ErrorKind {
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Func2,
IO(String),
}
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impl ::std::fmt::Display for Func1ErrorKind {
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fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match self {
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Func1ErrorKind::Func2 => write!(f, " func1 error calling func2" ),
Func1ErrorKind::IO(filename) => write!(f, " Error reading '{}'" , filename),
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}
}
}
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impl ::std::fmt::Debug for Func1ErrorKind {
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fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, " {}" , self)
}
}
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fn func1() -> ChainResult< (), Func1ErrorKind> {
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
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let filename = String::from(" bar.txt" );
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do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
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Ok(())
}
fn main() -> Result< (), Box< Error> > {
if let Err(e) = func1() {
match e.kind() {
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Func1ErrorKind::Func2 => eprintln!(" Main Error Report: func1 error calling func2" ),
Func1ErrorKind::IO(filename) => {
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eprintln!(" Main Error Report: func1 error reading '{}'" , filename)
}
}
if let Some(e) = e.find_chain_cause::< Func2Error> () {
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eprintln!(" \nError reported by Func2Error: {}" , e)
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}
eprintln!(" \nDebug Error:\n{:?}" , e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
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# /*!
#
# `chainerror` provides an error backtrace without doing a real backtrace, so even after you `strip` your
# binaries, you still have the error backtrace.
#
# `chainerror` has no dependencies!
#
# `chainerror` uses `.source()` of `std::error::Error` along with `line()!` and `file()!` to provide a nice debug error backtrace.
# It encapsulates all types, which have `Display + Debug` and can store the error cause internally.
#
# Along with the `ChainError< T> ` struct, `chainerror` comes with some useful helper macros to save a lot of typing.
#
# # Examples
#
# ~~~rust
# use 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(())
# }
#
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:20: func1 error
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
#
# ~~~rust
# use 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(())
# }
#
# fn func3() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# func3().map_err(mstrerr!(Func2Error, " func2 error: calling func3" ))?;
# Ok(())
# }
#
# enum Func1Error {
# Func2,
# IO(String),
# }
#
# impl ::std::fmt::Display for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# match self {
# Func1Error::Func2 => write!(f, " func1 error calling func2" ),
# Func1Error::IO(filename) => write!(f, " Error reading '{}'" , filename),
# }
# }
# }
#
# impl ::std::fmt::Debug for Func1Error {
# fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# write!(f, " {}" , self)
# }
# }
#
# fn func1() -> ChainResult< (), Func1Error> {
# func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# let filename = String::from(" bar.txt" );
# do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# assert!(
# match e.kind() {
# Func1Error::Func2 => {
# eprintln!(" Main Error Report: func1 error calling func2" );
# true
# }
# Func1Error::IO(filename) => {
# eprintln!(" Main Error Report: func1 error reading '{}'" , filename);
# false
# }
# }
# );
#
# assert!(e.find_chain_cause::< Func2Error> ().is_some());
#
# if let Some(e) = e.find_chain_cause::< Func2Error> () {
# eprintln!(" \nError reported by Func2Error: {}" , e)
# }
#
#
# assert!(e.root_cause().is_some());
#
# if let Some(e) = e.root_cause() {
# let ioerror = e.downcast_ref::< io::Error> ().unwrap();
# eprintln!(" \nThe root cause was: std::io::Error: {:#?}" , ioerror);
# }
#
# assert_eq!(
# format!(" \n{:?}\n" , e), r#"
# src/lib.rs:47: func1 error calling func2
# Caused by:
# src/lib.rs:22: Func2Error(func2 error: calling func3)
# Caused by:
# src/lib.rs:15: Error reading 'foo.txt'
# Caused by:
# Kind(NotFound)
# " #
# );
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# !*/
#
# use std::any::TypeId;
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# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
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# /** chains an inner error kind `T` with a causing error
# **/
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# pub struct ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
# occurrence: Option< (u32, & 'static str)> ,
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# }
#
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# /// convenience type alias
# pub type ChainResult< O, E> = std::result::Result< O, ChainError< E> > ;
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#
# impl< T: 'static + Display + Debug> ChainError< T> {
# #[cfg(not(feature = " no-fileline" ))]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# 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" )]
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# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
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# pub fn new(
# kind: T,
# error_cause: Option< Box< dyn Error + 'static> > ,
# _occurrence: Option< (u32, & 'static str)> ,
# ) -> Self {
# Self { kind, error_cause }
# }
#
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# /// return the root cause of the error chain, if any exists
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# 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)
# }
#
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# /** find the first error cause of type U, if any exists
#
# # Examples
#
# ~~~rust
# # 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() {
# 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!();
# # }
# }
# ~~~
# **/
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# 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,
# }
# }
# }
#
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# /** find the first error cause of type ChainError< U> , if any exists
#
# Same as `find_cause`, but hides the `ChainError< U> ` implementation internals
#
# # Examples
#
# ~~~rust,ignore
# /// Instead of writing
# err.find_cause::< ChainError< FooError> > ();
#
# /// leave out the ChainError< T> implementation detail
# err.find_chain_cause::< FooError> ();
# ~~~
#
# **/
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# 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,
# }
# }
# }
#
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# /** return a reference to T of `ChainError< T> `
#
# # Examples
#
# ~~~rust
# # 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(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() -> ChainResult< (), Func1ErrorKind> {
# func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
# do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(" bar.txt" .into())))?;
# Ok(())
# }
#
# fn main() {
# if let Err(e) = func1() {
# match e.kind() {
# Func1ErrorKind::Func2 => {},
# Func1ErrorKind::IO(filename) => panic!(),
# }
# }
# # else {
# # unreachable!();
# # }
# }
# ~~~
#
# **/
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# pub fn kind< 'a> (& 'a self) -> & 'a T {
# & self.kind
# }
# }
#
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# /** convenience trait to hide the `ChainError< T> ` implementation internals
# **/
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# pub trait ChainErrorDown {
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# /** test if of type `ChainError< T> `
# **/
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# fn is_chain< T: 'static + Display + Debug> (& self) -> bool;
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# /** downcast to a reference of `ChainError< T> `
# **/
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# fn downcast_chain_ref< T: 'static + Display + Debug> (& self) -> Option< & ChainError< T> > ;
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# /** downcast to a mutable reference of `ChainError< T> `
# **/
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# fn downcast_chain_mut< T: 'static + Display + Debug> (& mut self) -> Option< & mut ChainError< T> > ;
# }
#
# 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)?;
# }
# }
#
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# if self.is_chain::< String> () {
# Display::fmt(& self.kind, f)?;
# } else {
# Debug::fmt(& self.kind, f)?;
# }
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#
# #[cfg(not(feature = " no-debug-cause" ))]
# {
# if let Some(e) = self.source() {
# writeln!(f, " \nCaused by:" )?;
# Debug::fmt(& e, f)?;
# }
# }
# Ok(())
# }
# }
#
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# /** creates a new `ChainError< T> `
#
# # Examples
#
# Create a new ChainError< FooError> , where `FooError` must implement `Display` and `Debug`.
# ~~~rust
# # use chainerror::*;
# #
# # #[derive(Debug)]
# enum FooError {
# Bar,
# Baz(& 'static str),
# }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
#
# // impl ::std::fmt::Display for FooError
#
# fn do_some_stuff() -> bool {
# false
# }
#
# fn func() -> ChainResult< (), FooError> {
# if ! do_some_stuff() {
# Err(cherr!(FooError::Baz(" Error" )))?;
# }
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# Additionally an error cause can be added.
#
# ~~~rust
# # use chainerror::*;
# # use std::io;
# # use std::error::Error;
# #
# # #[derive(Debug)]
# # enum FooError {
# # Bar,
# # Baz(& 'static str),
# # }
# #
# # impl ::std::fmt::Display for FooError {
# # fn fmt(& self, f: & mut ::std::fmt::Formatter) -> ::std::fmt::Result {
# # match self {
# # FooError::Bar => write!(f, " Bar Error" ),
# # FooError::Baz(s) => write!(f, " Baz Error: '{}'" , s),
# # }
# # }
# # }
# #
# fn do_some_stuff() -> Result< (), Box< Error> > {
# Err(io::Error::from(io::ErrorKind::NotFound))?;
# Ok(())
# }
#
# fn func() -> ChainResult< (), FooError> {
# do_some_stuff().map_err(
# |e| cherr!(e, FooError::Baz(" Error" ))
# )?;
# Ok(())
# }
# #
# # pub fn main() {
# # match func().unwrap_err().kind() {
# # FooError::Baz(s) if s == & " Error" => {},
# # _ => panic!(),
# # }
# # }
# ~~~
#
# **/
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# #[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!())))
# };
# }
#
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# /** convenience macro for |e| cherr!(e, format!(…))
#
# # Examples
#
# ~~~rust
# # 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(())
# # }
# #
# fn func2() -> Result< (), Box< Error> > {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(" Error reading '{}'" , filename))?;
# Ok(())
# }
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(" func1 error" ))?;
# Ok(())
# }
#
# # fn main() {
# # if let Err(e) = func1() {
# # assert_eq!(
# # format!(" \n{:?}\n" , e), r#"
# # src/lib.rs:20: func1 error
# # Caused by:
# # src/lib.rs:15: Error reading 'foo.txt'
# # Caused by:
# # Kind(NotFound)
# # " #
# # );
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# `mstrerr!()` can also be used to map a new `ChainError< T> `, where T was defined with
# `derive_str_cherr!(T)`
#
# ~~~rust
# # 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() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
# **/
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# #[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, $( $more , )* ))
# };
# }
#
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# /** convenience macro to create a " new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result< (), Box< Error> > {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult< (), Func2Error> {
# let filename = " foo.txt" ;
# do_some_io().map_err(mstrerr!(Func2Error, " Error reading '{}'" , filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result< (), Box< Error> > {
# func2().map_err(mstrerr!(Func1Error, " func1 error" ))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::< Func1Error> () {
# # assert!(f1err.find_cause::< ChainError< Func2Error> > ().is_some());
# # assert!(f1err.find_chain_cause::< Func2Error> ().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
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# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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 {}
# };
# }
# }
< / code > < / pre > < / pre >
2018-12-21 13:55:46 +01:00
< a class = "header" href = "#the-end" id = "the-end" > < h1 > The End< / h1 > < / a >
< p > That's it for now…< / p >
< p > Happy error handling!< / p >
2018-12-20 14:55:19 +01:00
< / main >
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<!-- Mobile navigation buttons -->
< div style = "clear: both" > < / div >
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