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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" class="active"><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><a href="tutorial12.html"><strong aria-hidden="true">12.</strong> Deref for the ErrorKind</a></li><li><a href="tutorial13.html"><strong aria-hidden="true">13.</strong> Writing a library</a></li><li class="affix"><a href="end.html">The End</a></li></ol>
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                    <main>
                        <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 chainerror::*;

use std::error::Error;
use std::io;
use std::result::Result;

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

fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    if let Err(e) = do_some_io() {
        Err(cherr!(e, &quot;func2 error&quot;))?;
    }
    Ok(())
}

fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    if let Err(e) = func2() {
        Err(cherr!(e, &quot;func1 error&quot;))?;
    }
    Ok(())
}

fn main() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    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&lt;T&gt;` 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() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# //!     Err(io::Error::from(io::ErrorKind::NotFound))?;
# //!     Ok(())
# //! }
# //!
# //! fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# //!     let filename = &quot;foo.txt&quot;;
# //!     do_some_io().map_err(mstrerr!(&quot;Error reading '{}'&quot;, filename))?;
# //!     Ok(())
# //! }
# //!
# //! fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# //!     func2().map_err(mstrerr!(&quot;func1 error&quot;))?;
# //!     Ok(())
# //! }
# //!
# //! fn main() {
# //!     if let Err(e) = func1() {
# //!         #[cfg(not(windows))]
# //!         assert_eq!(
# //!             format!(&quot;\n{:?}\n&quot;, e), r#&quot;
# //! src/lib.rs:20: func1 error
# //! Caused by:
# //! src/lib.rs:15: Error reading 'foo.txt'
# //! Caused by:
# //! Kind(NotFound)
# //! &quot;#
# //!         );
# //!     }
# //! #    else {
# //! #        unreachable!();
# //! #    }
# //! }
# //! ~~~
# //!
# //!
# //! ~~~rust
# //! use chainerror::*;
# //! use std::error::Error;
# //! use std::io;
# //! use std::result::Result;
# //!
# //! fn do_some_io() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# //!     Err(io::Error::from(io::ErrorKind::NotFound))?;
# //!     Ok(())
# //! }
# //!
# //! fn func3() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# //!     let filename = &quot;foo.txt&quot;;
# //!     do_some_io().map_err(mstrerr!(&quot;Error reading '{}'&quot;, filename))?;
# //!     Ok(())
# //! }
# //!
# //! derive_str_cherr!(Func2Error);
# //!
# //! fn func2() -&gt; ChainResult&lt;(), Func2Error&gt; {
# //!     func3().map_err(mstrerr!(Func2Error, &quot;func2 error: calling func3&quot;))?;
# //!     Ok(())
# //! }
# //!
# //! enum Func1Error {
# //!     Func2,
# //!     IO(String),
# //! }
# //!
# //! impl ::std::fmt::Display for Func1Error {
# //!     fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
# //!         match self {
# //!             Func1Error::Func2 =&gt; write!(f, &quot;func1 error calling func2&quot;),
# //!             Func1Error::IO(filename) =&gt; write!(f, &quot;Error reading '{}'&quot;, filename),
# //!         }
# //!     }
# //! }
# //!
# //! impl ::std::fmt::Debug for Func1Error {
# //!     fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
# //!         write!(f, &quot;{}&quot;, self)
# //!     }
# //! }
# //!
# //! fn func1() -&gt; ChainResult&lt;(), Func1Error&gt; {
# //!     func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
# //!     let filename = String::from(&quot;bar.txt&quot;);
# //!     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 =&gt; {
# //!                     eprintln!(&quot;Main Error Report: func1 error calling func2&quot;);
# //!                     true
# //!                 }
# //!                 Func1Error::IO(filename) =&gt; {
# //!                     eprintln!(&quot;Main Error Report: func1 error reading '{}'&quot;, filename);
# //!                     false
# //!                 }
# //!             }
# //!         );
# //!
# //!         assert!(e.find_chain_cause::&lt;Func2Error&gt;().is_some());
# //!
# //!         if let Some(e) = e.find_chain_cause::&lt;Func2Error&gt;() {
# //!             eprintln!(&quot;\nError reported by Func2Error: {}&quot;, e)
# //!         }
# //!
# //!
# //!         assert!(e.root_cause().is_some());
# //!
# //!         if let Some(e) = e.root_cause() {
# //!             let ioerror = e.downcast_ref::&lt;io::Error&gt;().unwrap();
# //!             eprintln!(&quot;\nThe root cause was: std::io::Error: {:#?}&quot;, ioerror);
# //!         }
# //!
# //!         #[cfg(not(windows))]
# //!         assert_eq!(
# //!             format!(&quot;\n{:?}\n&quot;, e), r#&quot;
# //! 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)
# //! &quot;#
# //!         );
# //!     }
# //! #    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&lt;T&gt; {
#     #[cfg(not(feature = &quot;no-fileline&quot;))]
#     occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     kind: T,
#     error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
# }
# 
# /// convenience type alias
# pub type ChainResult&lt;O, E&gt; = std::result::Result&lt;O, ChainError&lt;E&gt;&gt;;
# 
# impl&lt;T: 'static + Display + Debug&gt; ChainError&lt;T&gt; {
#     #[cfg(not(feature = &quot;no-fileline&quot;))]
#     /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
#     pub fn new(
#         kind: T,
#         error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
#         occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     ) -&gt; Self {
#         Self {
#             occurrence,
#             kind,
#             error_cause,
#         }
#     }
# 
#     #[cfg(feature = &quot;no-fileline&quot;)]
#     /// Use the `cherr!()` or `mstrerr!()` macro instead of calling this directly
#     pub fn new(
#         kind: T,
#         error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
#         _occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     ) -&gt; Self {
#         Self { kind, error_cause }
#     }
# 
#     /// return the root cause of the error chain, if any exists
#     pub fn root_cause(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         self.iter().last()
#     }
# 
#     /// 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() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
#     ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// derive_str_cherr!(Func2Error);
#     ///
#     /// fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
#     ///     let filename = &quot;foo.txt&quot;;
#     ///     do_some_io().map_err(mstrerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// derive_str_cherr!(Func1Error);
#     ///
#     /// fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
#     ///     func2().map_err(mstrerr!(Func1Error, &quot;func1 error&quot;))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// fn main() {
#     ///     if let Err(e) = func1() {
#     ///         if let Some(f1err) = e.downcast_chain_ref::&lt;Func1Error&gt;() {
#     ///
#     ///             assert!(f1err.find_cause::&lt;io::Error&gt;().is_some());
#     ///
#     ///             assert!(f1err.find_chain_cause::&lt;Func2Error&gt;().is_some());
#     ///         }
#     /// #        else {
#     /// #            panic!();
#     /// #        }
#     ///     }
#     /// #    else {
#     /// #         unreachable!();
#     /// #    }
#     /// }
#     /// ~~~
#     pub fn find_cause&lt;U: Error + 'static&gt;(&amp;self) -&gt; Option&lt;&amp;U&gt; {
#         self.iter().filter_map(Error::downcast_ref::&lt;U&gt;).next()
#     }
# 
#     /// Find the first error cause of type `ChainError&lt;U&gt;`, if any exists
#     ///
#     /// Same as `find_cause`, but hides the `ChainError&lt;U&gt;` implementation internals
#     ///
#     /// # Examples
#     ///
#     /// ~~~rust,ignore
#     /// // Instead of writing
#     /// err.find_cause::&lt;ChainError&lt;FooError&gt;&gt;();
#     ///
#     /// // leave out the ChainError&lt;FooError&gt; implementation detail
#     /// err.find_chain_cause::&lt;FooError&gt;();
#     /// ~~~
#     pub fn find_chain_cause&lt;U: Error + 'static&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;U&gt;&gt; {
#         self.iter()
#             .filter_map(Error::downcast_ref::&lt;ChainError&lt;U&gt;&gt;)
#             .next()
#     }
# 
#     /// Find the first error cause of type `ChainError&lt;U&gt;` or `U`, if any exists and return `U`
#     ///
#     /// Same as `find_cause` and `find_chain_cause`, but hides the `ChainError&lt;U&gt;` implementation internals
#     ///
#     /// # Examples
#     ///
#     /// ~~~rust,ignore
#     /// // Instead of writing
#     /// err.find_cause::&lt;ChainError&lt;FooErrorKind&gt;&gt;();
#     /// // and/or
#     /// err.find_chain_cause::&lt;FooErrorKind&gt;();
#     /// // and/or
#     /// err.find_cause::&lt;FooErrorKind&gt;();
#     ///
#     /// // leave out the ChainError&lt;FooErrorKind&gt; implementation detail
#     /// err.find_chain_or_kind::&lt;FooErrorKind&gt;();
#     /// ~~~
#     pub fn find_kind_or_cause&lt;U: Error + 'static&gt;(&amp;self) -&gt; Option&lt;&amp;U&gt; {
#         self.iter()
#             .filter_map(|e| {
#                 e.downcast_ref::&lt;ChainError&lt;U&gt;&gt;()
#                     .map(|e| e.kind())
#                     .or_else(|| e.downcast_ref::&lt;U&gt;())
#             })
#             .next()
#     }
# 
#     /// Return a reference to T of `ChainError&lt;T&gt;`
#     ///
#     /// # Examples
#     ///
#     /// ~~~rust
#     /// # use crate::chainerror::*;
#     /// # use std::error::Error;
#     /// # use std::io;
#     /// # use std::result::Result;
#     /// #
#     /// fn do_some_io() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
#     ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// derive_str_cherr!(Func2Error);
#     ///
#     /// fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
#     ///     let filename = &quot;foo.txt&quot;;
#     ///     do_some_io().map_err(mstrerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// #[derive(Debug)]
#     /// enum Func1ErrorKind {
#     ///     Func2,
#     ///     IO(String),
#     /// }
#     ///
#     /// /// impl ::std::fmt::Display for Func1ErrorKind {…}
#     /// # impl ::std::fmt::Display for Func1ErrorKind {
#     /// #     fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
#     /// #         match self {
#     /// #             Func1ErrorKind::Func2 =&gt; write!(f, &quot;func1 error calling func2&quot;),
#     /// #             Func1ErrorKind::IO(filename) =&gt; write!(f, &quot;Error reading '{}'&quot;, filename),
#     /// #         }
#     /// #     }
#     /// # }
#     ///
#     /// fn func1() -&gt; ChainResult&lt;(), Func1ErrorKind&gt; {
#     ///     func2().map_err(|e| cherr!(e, Func1ErrorKind::Func2))?;
#     ///     do_some_io().map_err(|e| cherr!(e, Func1ErrorKind::IO(&quot;bar.txt&quot;.into())))?;
#     ///     Ok(())
#     /// }
#     ///
#     /// fn main() {
#     ///     if let Err(e) = func1() {
#     ///         match e.kind() {
#     ///             Func1ErrorKind::Func2 =&gt; {},
#     ///             Func1ErrorKind::IO(filename) =&gt; panic!(),
#     ///         }
#     ///     }
#     /// #    else {
#     /// #         unreachable!();
#     /// #    }
#     /// }
#     /// ~~~
#     pub fn kind(&amp;self) -&gt; &amp;T {
#         &amp;self.kind
#     }
# 
#     /// Returns an Iterator over all error causes/sources
#     ///
#     /// # Example
#     ///
#     ///
#     pub fn iter(&amp;self) -&gt; impl Iterator&lt;Item = &amp;(dyn Error + 'static)&gt; {
#         ErrorIter {
#             current: Some(self),
#         }
#     }
# }
# 
# struct ErrorIter&lt;'a&gt; {
#     current: Option&lt;&amp;'a (dyn Error + 'static)&gt;,
# }
# 
# impl&lt;'a&gt; Iterator for ErrorIter&lt;'a&gt; {
#     type Item = &amp;'a (dyn Error + 'static);
# 
#     fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
#         let current = self.current;
#         self.current = self.current.and_then(Error::source);
#         current
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; std::ops::Deref for ChainError&lt;T&gt; {
#     type Target = T;
# 
#     fn deref(&amp;self) -&gt; &amp;Self::Target {
#         &amp;self.kind
#     }
# }
# 
# /// Convenience trait to hide the `ChainError&lt;T&gt;` implementation internals
# pub trait ChainErrorDown {
#     /// Test if of type `ChainError&lt;T&gt;`
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool;
#     /// Downcast to a reference of `ChainError&lt;T&gt;`
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt;;
#     /// Downcast to a mutable reference of `ChainError&lt;T&gt;`
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt;;
# }
# 
# impl&lt;U: 'static + Display + Debug&gt; ChainErrorDown for ChainError&lt;U&gt; {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         TypeId::of::&lt;T&gt;() == TypeId::of::&lt;U&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         if self.is_chain::&lt;T&gt;() {
#             #[allow(clippy::cast_ptr_alignment)]
#             unsafe {
#                 Some(&amp;*(self as *const dyn Error as *const &amp;ChainError&lt;T&gt;))
#             }
#         } else {
#             None
#         }
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         if self.is_chain::&lt;T&gt;() {
#             #[allow(clippy::cast_ptr_alignment)]
#             unsafe {
#                 Some(&amp;mut *(self as *mut dyn Error as *mut &amp;mut ChainError&lt;T&gt;))
#             }
#         } else {
#             None
#         }
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         self.error_cause.as_ref().map(|e| e.as_ref())
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for &amp;ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         self.error_cause.as_ref().map(|e| e.as_ref())
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for &amp;mut ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         self.error_cause.as_ref().map(|e| e.as_ref())
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Display for ChainError&lt;T&gt; {
#     fn fmt(&amp;self, f: &amp;mut Formatter) -&gt; Result {
#         write!(f, &quot;{}&quot;, self.kind)?;
# 
#         #[cfg(feature = &quot;display-cause&quot;)]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, &quot;\nCaused by:&quot;)?;
#                 Display::fmt(&amp;e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Debug for ChainError&lt;T&gt; {
#     fn fmt(&amp;self, f: &amp;mut Formatter) -&gt; Result {
#         #[cfg(not(feature = &quot;no-fileline&quot;))]
#         {
#             if let Some(o) = self.occurrence {
#                 write!(f, &quot;{}:{}: &quot;, o.1, o.0)?;
#             }
#         }
# 
#         if self.is_chain::&lt;String&gt;() {
#             Display::fmt(&amp;self.kind, f)?;
#         } else {
#             Debug::fmt(&amp;self.kind, f)?;
#         }
# 
#         #[cfg(not(feature = &quot;no-debug-cause&quot;))]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, &quot;\nCaused by:&quot;)?;
#                 Debug::fmt(&amp;e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# pub trait ChainErrorFrom&lt;T&gt;: Sized {
#     fn chain_error_from(_: T, line_filename: Option&lt;(u32, &amp;'static str)&gt;) -&gt; ChainError&lt;Self&gt;;
# }
# 
# pub trait IntoChainError&lt;T&gt;: Sized {
#     fn into_chain_error(self, line_filename: Option&lt;(u32, &amp;'static str)&gt;) -&gt; ChainError&lt;T&gt;;
# }
# 
# impl&lt;T, U&gt; IntoChainError&lt;U&gt; for T
# where
#     U: ChainErrorFrom&lt;T&gt;,
# {
#     fn into_chain_error(self, line_filename: Option&lt;(u32, &amp;'static str)&gt;) -&gt; ChainError&lt;U&gt; {
#         U::chain_error_from(self, line_filename)
#     }
# }
# 
# impl&lt;T, U&gt; ChainErrorFrom&lt;T&gt; for U
# where
#     T: Into&lt;U&gt;,
#     U: 'static + Display + Debug,
# {
#     fn chain_error_from(t: T, line_filename: Option&lt;(u32, &amp;'static str)&gt;) -&gt; ChainError&lt;Self&gt; {
#         let e: U = t.into();
#         ChainError::&lt;_&gt;::new(e, None, line_filename)
#     }
# }
# 
# #[macro_export]
# macro_rules! minto_cherr {
#     ( ) =&gt; {
#         |e| e.into_chain_error(Some((line!(), file!())))
#     };
# }
# 
# #[macro_export]
# macro_rules! into_cherr {
#     ( $t:expr ) =&gt; {
#         $t.into_chain_error(Some((line!(), file!())))
#     };
# }
# 
# /// Creates a new `ChainError&lt;T&gt;`
# ///
# /// # Examples
# ///
# /// Create a new ChainError&lt;FooError&gt;, where `FooError` must implement `Display` and `Debug`.
# /// ~~~rust
# /// # use chainerror::*;
# /// #
# /// # #[derive(Debug)]
# /// enum FooError {
# ///     Bar,
# ///     Baz(&amp;'static str),
# /// }
# /// #
# /// # impl ::std::fmt::Display for FooError {
# /// #     fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
# /// #         match self {
# /// #             FooError::Bar =&gt; write!(f, &quot;Bar Error&quot;),
# /// #             FooError::Baz(s) =&gt; write!(f, &quot;Baz Error: '{}'&quot;, s),
# /// #         }
# /// #     }
# /// # }
# ///
# /// //  impl ::std::fmt::Display for FooError
# ///
# /// fn do_some_stuff() -&gt; bool {
# ///     false
# /// }
# ///
# /// fn func() -&gt; ChainResult&lt;(), FooError&gt; {
# ///     if ! do_some_stuff() {
# ///         Err(cherr!(FooError::Baz(&quot;Error&quot;)))?;
# ///     }
# ///     Ok(())
# /// }
# /// #
# /// # pub fn main() {
# /// #     match func().unwrap_err().kind() {
# /// #         FooError::Baz(s) if s == &amp;&quot;Error&quot; =&gt; {},
# /// #         _ =&gt; panic!(),
# /// #     }
# /// # }
# /// ~~~
# ///
# /// Additionally an error cause can be added.
# ///
# /// ~~~rust
# /// # use chainerror::*;
# /// # use std::io;
# /// # use std::error::Error;
# /// #
# /// # #[derive(Debug)]
# /// # enum FooError {
# /// #     Bar,
# /// #     Baz(&amp;'static str),
# /// # }
# /// #
# /// # impl ::std::fmt::Display for FooError {
# /// #     fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
# /// #         match self {
# /// #             FooError::Bar =&gt; write!(f, &quot;Bar Error&quot;),
# /// #             FooError::Baz(s) =&gt; write!(f, &quot;Baz Error: '{}'&quot;, s),
# /// #         }
# /// #     }
# /// # }
# /// #
# /// fn do_some_stuff() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
# ///     Ok(())
# /// }
# ///
# /// fn func() -&gt; ChainResult&lt;(), FooError&gt; {
# ///     do_some_stuff().map_err(
# ///         |e| cherr!(e, FooError::Baz(&quot;Error&quot;))
# ///     )?;
# ///     Ok(())
# /// }
# /// #
# /// # pub fn main() {
# /// #     match func().unwrap_err().kind() {
# /// #         FooError::Baz(s) if s == &amp;&quot;Error&quot; =&gt; {},
# /// #         _ =&gt; panic!(),
# /// #     }
# /// # }
# /// ~~~
# #[macro_export]
# macro_rules! cherr {
#     ( $k:expr ) =&gt; ({
#         ChainError::&lt;_&gt;::new($k, None, Some((line!(), file!())))
#     });
#     ( None, $k:expr ) =&gt; ({
#         ChainError::&lt;_&gt;::new($k, None, Some((line!(), file!())))
#     });
#     ( None, $fmt:expr, $($arg:tt)+ ) =&gt; ({
#         cherr!(None, format!($fmt, $($arg)+ ))
#     });
#     ( None, $fmt:expr, $($arg:tt)+ ) =&gt; ({
#         cherr!(None, format!($fmt, $($arg)+ ))
#     });
#     ( $e:path, $k:expr ) =&gt; ({
#         ChainError::&lt;_&gt;::new($k, Some(Box::from($e)), Some((line!(), file!())))
#     });
#     ( $e:path, $fmt:expr, $($arg:tt)+ ) =&gt; ({
#         cherr!($e, format!($fmt, $($arg)+ ))
#     });
# 
# }
# 
# /// 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() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
# /// #     Ok(())
# /// # }
# /// #
# /// fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     let filename = &quot;foo.txt&quot;;
# ///     do_some_io().map_err(mstrerr!(&quot;Error reading '{}'&quot;, filename))?;
# ///     Ok(())
# /// }
# ///
# /// fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     func2().map_err(mstrerr!(&quot;func1 error&quot;))?;
# ///     Ok(())
# /// }
# ///
# /// # fn main() {
# /// #     if let Err(e) = func1() {
# /// #         #[cfg(not(windows))]
# /// #         assert_eq!(
# /// #             format!(&quot;\n{:?}\n&quot;, e), r#&quot;
# /// # src/lib.rs:20: func1 error
# /// # Caused by:
# /// # src/lib.rs:15: Error reading 'foo.txt'
# /// # Caused by:
# /// # Kind(NotFound)
# /// # &quot;#
# /// #         );
# /// #     } else {
# /// #         unreachable!();
# /// #     }
# /// # }
# /// ~~~
# ///
# /// `mstrerr!()` can also be used to map a new `ChainError&lt;T&gt;`, 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() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
# /// #     Ok(())
# /// # }
# /// #
# /// derive_str_cherr!(Func2Error);
# ///
# /// fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     let filename = &quot;foo.txt&quot;;
# ///     do_some_io().map_err(mstrerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))?;
# ///     Ok(())
# /// }
# ///
# /// derive_str_cherr!(Func1Error);
# ///
# /// fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     func2().map_err(mstrerr!(Func1Error, &quot;func1 error&quot;))?;
# ///     Ok(())
# /// }
# /// #
# /// # fn main() {
# /// #     if let Err(e) = func1() {
# /// #         if let Some(f1err) = e.downcast_chain_ref::&lt;Func1Error&gt;() {
# /// #             assert!(f1err.find_cause::&lt;ChainError&lt;Func2Error&gt;&gt;().is_some());
# /// #             assert!(f1err.find_chain_cause::&lt;Func2Error&gt;().is_some());
# /// #         } else {
# /// #             panic!();
# /// #         }
# /// #     } else {
# /// #         unreachable!();
# /// #     }
# /// # }
# /// ~~~
# #[macro_export]
# macro_rules! mstrerr {
#     ( $t:path, $msg:expr ) =&gt; ({
#         |e| cherr!(e, $t ($msg.to_string()))
#     });
#     ( $t:path, $msg:expr, ) =&gt; ({
#         |e| cherr!(e, $t ($msg.to_string()))
#     });
#     ( $t:path, $fmt:expr, $($arg:tt)+ ) =&gt; ({
#         |e| cherr!(e, $t (format!($fmt, $($arg)+ )))
#     });
#     ($msg:expr) =&gt; ({
#         |e| cherr!(e, $msg.to_string())
#     });
#     ($msg:expr, ) =&gt; ({
#         |e| cherr!(e, $msg.to_string())
#     });
#     ($fmt:expr, $($arg:tt)+) =&gt; ({
#         |e| cherr!(e, format!($fmt, $($arg)+ ))
#     });
# }
# 
# /// Convenience macro for `cherr!(T(format!(…)))` where `T(String)`
# ///
# /// # Examples
# ///
# /// ~~~rust
# /// # use crate::chainerror::*;
# /// # use std::error::Error;
# /// # use std::result::Result;
# /// #
# /// derive_str_cherr!(Func2Error);
# ///
# /// fn func2() -&gt; ChainResult&lt;(), Func2Error&gt; {
# ///     let filename = &quot;foo.txt&quot;;
# ///     Err(strerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))
# /// }
# ///
# /// derive_str_cherr!(Func1Error);
# ///
# /// fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     func2().map_err(mstrerr!(Func1Error, &quot;func1 error&quot;))?;
# ///     Ok(())
# /// }
# /// #
# /// # fn main() {
# /// #     if let Err(e) = func1() {
# /// #         if let Some(f1err) = e.downcast_chain_ref::&lt;Func1Error&gt;() {
# /// #             assert!(f1err.find_cause::&lt;ChainError&lt;Func2Error&gt;&gt;().is_some());
# /// #             assert!(f1err.find_chain_cause::&lt;Func2Error&gt;().is_some());
# /// #         } else {
# /// #             panic!();
# /// #         }
# /// #     } else {
# /// #         unreachable!();
# /// #     }
# /// # }
# /// ~~~
# #[macro_export]
# macro_rules! strerr {
#     ( $t:path, $msg:expr ) =&gt; ({
#         cherr!($t ($msg.to_string()))
#     });
#     ( $t:path, $msg:expr, ) =&gt; ({
#         cherr!($t ($msg.to_string()))
#     });
#     ( $t:path, $fmt:expr, $($arg:tt)+ ) =&gt; ({
#         cherr!($t (format!($fmt, $($arg)+ )))
#     });
#     ($msg:expr) =&gt; ({
#         cherr!($msg.to_string())
#     });
#     ($msg:expr, ) =&gt; ({
#         cherr!($msg.to_string())
#     });
#     ($fmt:expr, $($arg:tt)+) =&gt; ({
#         cherr!(format!($fmt, $($arg)+ ))
#     });
# }
# 
# /// Convenience macro to create a &quot;new type&quot; T(String) and implement Display + Debug for T
# ///
# /// # Examples
# ///
# /// ~~~rust
# /// # use crate::chainerror::*;
# /// # use std::error::Error;
# /// # use std::io;
# /// # use std::result::Result;
# /// #
# /// # fn do_some_io() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
# /// #     Ok(())
# /// # }
# /// #
# /// derive_str_cherr!(Func2Error);
# ///
# /// fn func2() -&gt; ChainResult&lt;(), Func2Error&gt; {
# ///     let filename = &quot;foo.txt&quot;;
# ///     do_some_io().map_err(mstrerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))?;
# ///     Ok(())
# /// }
# ///
# /// derive_str_cherr!(Func1Error);
# ///
# /// fn func1() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
# ///     func2().map_err(mstrerr!(Func1Error, &quot;func1 error&quot;))?;
# ///     Ok(())
# /// }
# /// #
# /// # fn main() {
# /// #     if let Err(e) = func1() {
# /// #         if let Some(f1err) = e.downcast_chain_ref::&lt;Func1Error&gt;() {
# /// #             assert!(f1err.find_cause::&lt;ChainError&lt;Func2Error&gt;&gt;().is_some());
# /// #             assert!(f1err.find_chain_cause::&lt;Func2Error&gt;().is_some());
# /// #         } else {
# /// #             panic!();
# /// #         }
# /// #     } else {
# /// #         unreachable!();
# /// #     }
# /// # }
# /// ~~~
# #[macro_export]
# macro_rules! derive_str_cherr {
#     ($e:ident) =&gt; {
#         pub struct $e(pub String);
#         impl ::std::fmt::Display for $e {
#             fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
#                 write!(f, &quot;{}&quot;, self.0)
#             }
#         }
#         impl ::std::fmt::Debug for $e {
#             fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
#                 write!(f, &quot;{}({})&quot;, stringify!($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, &quot;func2 error&quot;))?;
    }
</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&lt;Error&gt;)</code> as a result.</p>
<p>The <code>Debug</code> implementation of <code>ChainError&lt;T&gt;</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&lt;T&gt;</code> in our case is <code>ChainError&lt;String&gt;</code>.</p>

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