Error Display implementation contains source display impl as well

[faern]

Feature Request

When printing a connection refused error and all its source errors you currently end up with:

Error: Client: error trying to connect: tcp connect error: Connection refused (os error 111)
Caused by: error trying to connect: tcp connect error: Connection refused (os error 111)
Caused by: tcp connect error: Connection refused (os error 111)
Caused by: Connection refused (os error 111)

That is very redundant and not very nice to read. A good rule is to not include the Display implementation of your source error in your error. Or if you do, don't return it from source(). Never do both.

I created a forum post on this topic a while back: https://users.rust-lang.org/t/do-people-not-care-about-printable-error-chains-a-k-a-how-to-nicely-implement-display-for-an-error/35362

I see the stack of errors here is not only tonic specific, but the problem exists in hyper as well.

Proposal

Change some error type implementations. Especially if there are errors which are basically just combinations of sub-errors, then make them "transparent". Meaning their Display impl just proxies to the Display of the sub-error and source() become something like:

fn source() -> Option<dyn Error> {
    match self {
        Io(error) => error.source(),
        Something(error) => error.source(),
        ...
    }
}

[LucioFranco]

@faern hi! I agree the current error situation with the transport errors is a bit funky. I plan on improving them but am lacking some time right now to get there. I think what you're suggesting seems good! If you're open to PRing it I would love that and I'm happy to help out :)

[faern]

With the submitted PR, #217, The output of printing the error chain is now reduced to:

Error: error trying to connect: tcp connect error: Connection refused (os error 111)
Caused by: tcp connect error: Connection refused (os error 111)
Caused by: Connection refused (os error 111)

The remaining problems exist in layers outside of tonic. I will have to do something similar to hyper later.