Macro err

macro_rules! err {
    (@accum $body:tt $(,)?) => { ... };
    (@accum ($($body:tt)*), source($src:expr) $($tail:tt)*) => { ... };
    (@accum ($($body:tt)*), msg($format:expr) $($tail:tt)*) => { ... };
    (@accum ($($body:tt)*), msg($format:expr, $($args:tt)*) $($tail:tt)*) => { ... };
    ($builder:expr $(, $($tail:tt)*)? ) => { ... };
}

Constructs an Error, tersely.

This is a shorthand way to use ErrorBuilder.

The first argument is an Into<ErrorBuilder>, such as the following:

• an ErrorKind enum variant name like Unauthenticated. There’s an implicit use ::coded::ErrorKind::* to allow the bare variant names just within this restrictive scope where you’re unlikely to have conflicts with other identifiers.
• an std::io::Error as a source, which sets the new Error’s ErrorKind based on the std::io::Error.
• an Error as a source, which similarly copies the ErrorKind.
• an existing ErrorBuilder, which does not create a new source link.

Following arguments may be of these forms:

• msg(...), which expands to .msg(format!(...)). See ErrorBuilder::msg.
• source(...), which simply expands to .source($src). See ErrorBuilder::source.

Examples

Simplest:

let e = err!(InvalidArgument);
let e = err!(InvalidArgument,); // trailing commas are allowed
assert_eq!(e.kind(), coded::ErrorKind::InvalidArgument);

Constructing with a fixed error variant name:

let input = "a12";
let src = i32::from_str_radix(input, 10).unwrap_err();

let e = err!(InvalidArgument, source(src.clone()), msg("bad argument {:?}", input));
// The line above is equivalent to:
let e2 = ::coded::ErrorBuilder::from(::coded::ErrorKind::InvalidArgument)
    .source(src.clone())
    .msg(format!("bad argument {:?}", input))
    .build();

assert_eq!(e.kind(), coded::ErrorKind::InvalidArgument);
assert_eq!(e.source().unwrap().downcast_ref::<ParseIntError>().unwrap(), &src);

Constructing from an std::io::Error:

let e = std::io::Error::new(std::io::ErrorKind::NotFound, "file not found");
let e = err!(e, msg("path {} not found", "foo"));
assert_eq!(e.kind(), coded::ErrorKind::NotFound);