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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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<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
prints out the last <code>Error</code>.</p>
<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>
<pre><pre class="playpen"><code class="language-rust">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>> {
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()
}
</code></pre></pre>
<a class="header" href="#simple-chained-string-errors" id="simple-chained-string-errors"><h1>Simple Chained String Errors</h1></a>
<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>
<p>Press the play button in the upper right corner and see the nice debug output.</p>
<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>> {
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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<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>
<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
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>
<p><code>ChainError<T></code> in our case is <code>ChainError<String></code>.</p>
<a class="header" href="#mapping-errors" id="mapping-errors"><h1>Mapping Errors</h1></a>
<p>Now let's get more rust idiomatic by using <code>.map_err()</code>.</p>
<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>> {
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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<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>
<a class="header" href="#saving-coding-chars" id="saving-coding-chars"><h1>Saving coding chars</h1></a>
<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>
<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!("{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<a class="header" href="#the-source-of-errors" id="the-source-of-errors"><h1>The source() of Errors</h1></a>
<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>
<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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<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>
<p>To enable the <code>Display</code> backtrace, you have to enable the feature <code>display-cause</code> for <code>chainerror</code>.</p>
<a class="header" href="#downcast-the-errors" id="downcast-the-errors"><h1>Downcast the Errors</h1></a>
<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>
<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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<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>
<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>
<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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<a class="header" href="#finding-an-error-cause" id="finding-an-error-cause"><h1>Finding an Error cause</h1></a>
<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>
<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 {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<a class="header" href="#selective-error-handling" id="selective-error-handling"><h1>Selective Error Handling</h1></a>
<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>
<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);
}
if let Some(s) = e.downcast_chain_ref::<Func1ErrorFunc2>() {
eprintln!("Func1ErrorFunc2:\n{:?}", s);
}
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<a class="header" href="#errorkind-to-the-rescue" id="errorkind-to-the-rescue"><h1>ErrorKind to the rescue</h1></a>
<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>
<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)]
enum Func1ErrorKind {
Func2,
IO(String),
}
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))?;
let filename = String::from("bar.txt");
do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
match e.kind() {
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
Func1ErrorKind::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)
}
eprintln!("\nDebug Error:\n{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<a class="header" href="#debug-for-the-errorkind" id="debug-for-the-errorkind"><h1>Debug for the ErrorKind</h1></a>
<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>
<p>To create your own Errors, you might find <a href="https://crates.io">crates</a> which create enum <code>Display+Debug</code> via derive macros.</p>
<p>Also noteworthy is <a href="https://crates.io/crates/custom_error">custom_error</a> to define your custom errors,
which can then be used with <code>chainerror</code>.</p>
<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(())
}
enum Func1ErrorKind {
Func2,
IO(String),
}
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),
}
}
}
impl ::std::fmt::Debug for Func1ErrorKind {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "{}", self)
}
}
fn func1() -> ChainResult<(), Func1ErrorKind> {
func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
let filename = String::from("bar.txt");
do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(filename)))?;
Ok(())
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
match e.kind() {
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
Func1ErrorKind::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)
}
eprintln!("\nDebug Error:\n{:?}", e);
}
Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# /*!
#
# `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.
#
# ## Features
#
# `no-fileline`
# : completely turn off storing filename and line
#
# `display-cause`
# : turn on printing a backtrace of the errors in `Display`
#
# `no-debug-cause`
# : turn off printing a backtrace of the errors in `Debug`
#
#
# # Tutorial
#
# Read the [Tutorial](https://haraldh.github.io/chainerror/tutorial1.html)
#
# # 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;
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
#
# /** chains an inner error kind `T` with a causing error
# **/
# pub struct ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# occurrence: Option<(u32, &'static str)>,
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# }
#
# /// convenience type alias
# pub type ChainResult<O, E> = std::result::Result<O, ChainError<E>>;
#
# impl<T: 'static + Display + Debug> ChainError<T> {
# #[cfg(not(feature = "no-fileline"))]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# 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")]
# /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
# pub fn new(
# kind: T,
# error_cause: Option<Box<dyn Error + 'static>>,
# _occurrence: Option<(u32, &'static str)>,
# ) -> Self {
# Self { kind, error_cause }
# }
#
# /// return the root cause of the error chain, if any exists
# 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)
# }
#
# /** 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!();
# # }
# }
# ~~~
# **/
# 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,
# }
# }
# }
#
# /** 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>();
# ~~~
#
# **/
# 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,
# }
# }
# }
#
# /** 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!();
# # }
# }
# ~~~
#
# **/
# pub fn kind<'a>(&'a self) -> &'a T {
# &self.kind
# }
# }
#
# /** convenience trait to hide the `ChainError<T>` implementation internals
# **/
# pub trait ChainErrorDown {
# /** test if of type `ChainError<T>`
# **/
# fn is_chain<T: 'static + Display + Debug>(&self) -> bool;
# /** downcast to a reference of `ChainError<T>`
# **/
# fn downcast_chain_ref<T: 'static + Display + Debug>(&self) -> Option<&ChainError<T>>;
# /** downcast to a mutable reference of `ChainError<T>`
# **/
# 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)?;
# }
# }
#
# if self.is_chain::<String>() {
# Display::fmt(&self.kind, f)?;
# } else {
# Debug::fmt(&self.kind, f)?;
# }
#
# #[cfg(not(feature = "no-debug-cause"))]
# {
# if let Some(e) = self.source() {
# writeln!(f, "\nCaused by:")?;
# Debug::fmt(&e, f)?;
# }
# }
# Ok(())
# }
# }
#
# /** 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!(),
# # }
# # }
# ~~~
#
# **/
# #[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!())))
# };
# }
#
# /** 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!();
# # }
# # }
# ~~~
# **/
# #[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, $( $more , )* ))
# };
# }
#
# /** convenience macro to create a "new type" T(String) and implement Display + Debug for T
#
# ~~~rust
# # use crate::chainerror::*;
# # use std::error::Error;
# # use std::io;
# # use std::result::Result;
# #
# # fn do_some_io() -> Result<(), Box<Error>> {
# # Err(io::Error::from(io::ErrorKind::NotFound))?;
# # Ok(())
# # }
# #
# derive_str_cherr!(Func2Error);
#
# fn func2() -> ChainResult<(), Func2Error> {
# let filename = "foo.txt";
# do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
# Ok(())
# }
#
# derive_str_cherr!(Func1Error);
#
# fn func1() -> Result<(), Box<Error>> {
# func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
# Ok(())
# }
# #
# # fn main() {
# # if let Err(e) = func1() {
# # if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
# # assert!(f1err.find_cause::<ChainError<Func2Error>>().is_some());
# # assert!(f1err.find_chain_cause::<Func2Error>().is_some());
# # } else {
# # panic!();
# # }
# # } else {
# # unreachable!();
# # }
# # }
# ~~~
#
# **/
# #[macro_export]
# macro_rules! derive_str_cherr {
# ($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>
<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>
<p>To report issues, submit pull request or for the source code, examples and the book source, visit
the <a href="https://github.com/haraldh/chainerror">Git Repo</a>.</p>
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