Macro trace

macro_rules! trace {
    (struct $trace:ident; $($a:ty => $b:ty,)*) => { ... };
    (struct $name:ident; $($a:ty => $b:ty),*) => { ... };
    (struct $name:ident) => { ... };
    ($($a:ty => $b:ty,)*) => { ... };
    ($($a:ty => $b:ty),*) => { ... };
}

Helper macro for defining a Trace struct, and instances of From<Trace<B>> for Trace<A>.

Example use

#[macro_use] extern crate stacktrace;

pub struct Error1(usize);
pub struct Error2(String);

impl From<Error1> for Error2 {
    fn from(err: Error1) -> Error2 {
        Error2(format!("{}", err.0))
    }
}

trace!{Error1 => Error2}

fn makes_a_traced_error() -> Result<(), Trace<Error1>> {
    try!(Err(Error1(1337))); // Uses generic instance of "From<Err>" for "Trace<Err>"
    Ok(())
}

fn propagates_a_traced_error() -> Result<(), Trace<Error2>> {
    try!(makes_a_traced_error()); // Uses the macro-generated instance of "From<Trace<Error1>>" for "Trace<Error2>"
    Ok(())
}

Advanced use

The trace macro takes an optional initial ‘name’ parameter: trace!{struct MyTrace} will define a struct named Example that behaves exactly like the default Trace struct.

#[macro_use] extern crate stacktrace;

pub struct Error1(usize);
pub struct Error2(String);

impl From<Error1> for Error2 {
    fn from(err: Error1) -> Error2 {
        Error2(format!("{}", err.0))
    }
}

trace!{struct MyTrace; Error1 => Error2}

fn makes_a_traced_error() -> Result<(), MyTrace<Error1>> {
    try!(Err(Error1(1337))); // Uses generic instance of "From<Err>" for "MyTrace<Err>"
    Ok(())
}

fn propagates_a_traced_error() -> Result<(), MyTrace<Error2>> {
    try!(makes_a_traced_error()); // Uses the macro-generated instance of "From<MyTrace<Error1>>" for "MyTrace<Error2>"
    Ok(())
}