derive-error-chain 0.1.2

A Macros 1.1 implementation of https://crates.io/crates/error-chain

The error-chain example

error_chain {
    types { Error, ErrorKind, ChainErr, Result; }

    links {
    	rustup_dist::Error, rustup_dist::ErrorKind, Dist;
    	rustup_utils::Error, rustup_utils::ErrorKind, Utils, #[cfg(unix)];
    }

    foreign_links {
    	temp::Error, Temp;
    }

    errors {
    	InvalidToolchainName(t: String) {
    		description("invalid toolchain name")
    		display("invalid toolchain name: '{}'", t)
    	}
    }
}

becomes

#[derive(Debug, error_chain)]
// This attribute is optional if using the default names "Error", "Result" and "ChainErr"
#[error_chain(error = "Error", result = "Result", chain_err = "ChainErr")]
pub enum ErrorKind {
    Msg(String), // A special variant that must always be present.

    Dist(rustup_dist::Error, rustup_dist::ErrorKind),

    #[cfg(unix)]
    Utils(rustup_utils::Error, rustup_utils::ErrorKind),

    #[error_chain(foreign)]
    Temp(temp::Error),

    #[error_chain(custom, description = "invalid_toolchain_name_description", display = "invalid_toolchain_name_display")]
    InvalidToolchainName(String),
}

// A description function receives refs to all the variant constituents, and should return a &str
fn invalid_toolchain_name_description(_: &str) -> &str {
    "invalid toolchain name"
}

// A display function receives a formatter and refs to all the variant constituents, and should return a ::std::fmt::Result
fn invalid_toolchain_name_display(f: &mut ::std::fmt::Formatter, t: &str) -> ::std::fmt::Result {
    write!(f, "invalid toolchain name: '{}'", t)
}

Notes:

• This library requires the nightly compiler to be able to use the proc_macro and conservative_impl_trait rust features.
• The macro output can be used with #[deny(missing_docs)] since it allows doc comments on the ErrorKind variants.
• The macro output uses ::backtrace::Backtrace unlike error-chain which uses $crate::Backtrace. Thus you need to link to backtrace in your own crate.
• The backtrace type can be overridden from ::backtrace::Backtrace by setting backtrace = "SomeOtherPath". It can be disabled completely by setting it to an empty string.
• The enum must always have a special Msg(String) member. Unlike error_chain which adds this member implicitly, this macro requires it explicitly.