Debug for the ErrorKind
One small improvement at the end of the tutorial is to fix the debug output of
Func1ErrorKind. As you probably noticed, the output doesn't say much of the enum.
Debug Error:
src/main.rs:35: Func2
[…]
As a lazy shortcut, we implement Debug by calling Display and end up with
Debug Error:
src/main.rs:40: func1 error calling func2
[…}
which gives us a lot more detail.
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 {} # }; # } # }