Using a `failure::Error` as a cause / `Error::into_fail()`

[Diggory Blake]

It's difficult to allow arbitrary causes when deriving Fail, because failure::Error does not implement Fail, and so cannot be used as a cause.

At the moment, you can use error.compat() to turn it into a type implementing Fail, but this results in the backtrace and further cause information being thrown away.

I think a better solution would be for failure::Error to provide an into_fail() method which returns a Box<Fail>. Now custom types can store a Box<Fail> as their cause and still derive Fail (because Box<Fail> implements Fail).

[Kevin M Granger]

Would AsFail handle your use case?

[Diggory Blake]

Yes, it would!