Replace error-chain

[niklasad1]

error-chain is not maintained anymore and depends on Error::cause which will be deprecated in Rust 1.33.

I don't know what the best solution to this but what I can think of:

• Manually implement it
• Migrate to failure

[ascjones]

In #10510 I manually implemented Error and the From impls, but used the derive_more Display derive for that boilerplate. @niklasad1 let me know what you think of this approach and we could apply to other errors.

Here's one of the regexes I used for the variants inside error_chain {} for future use:

\#\[doc = \"(.+)\"]\n\s+(.*) \{\n.*\n.*display\(\"(.*)\".*\n.*\}\n

/// $1\n\t\t#[display(fmt = "$3", _0)]\n\t\t$2,

[niklasad1]

nice work, yeah looks good to me.

could make sense to write a macro for the fn source impl:

impl error::Error for Error {
	fn source(&self) -> Option<&(error::Error + 'static)> {
		match self {
			Error::Io(e) => Some(e),
	                // more patterns
			_ => None,
		}
	}
}

[ascjones]

At first I converted to using err-derive which has essentially just copied failure macros and allows annotating nested errors with #[cause] for this purpose.

However I decided to user the more general and popular derive_more, rather than introducing another error library.

So we could just copy that macro from there or consider adding a dependency to it. In the meantime I figured it's not that bad to implement source manually.

[niklasad1]

Ok, I see.

Let's go with a manual implementation for now and see how much extra code it will require.