[#1035] Create ZcashError.unknown

[LukasKorba]

Closes #1035

• new ZcashError.unknown that wraps and handles any Error added

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[Chlup]

My main objection to this is that it defeats the purpose of errors having locality and being pin pointed to there they occurred.

Even a more local but yet generic error has some value of providing clients some code location.

Being reported an unknown error would be undesirable to us, because: 1- our app throws unknown errors. 2- we don't get any information beforehand that the user can capture to fix it.

I agree. Problem is that our SDK emits and throws Error type. Not ZcashError. It may be possible to change error types in streams. But it's impossible to specify error type when throwing error from method. So we need some easy way how to convert Error type to ZcashError. Because in fact all the errors generated by the SDK are ZcashError. Without unknown error there will be some Optional handling when doing Error -> ZcashError conversion. unknown is there to not need to handle Optionals when doing that conversion. And it should never be used directly. Like no function should explicitly throw ZcashError.unknown. It will be used only in case that we made a mistake and somewhere is thrown something else than ZcashError. And it will be used only in case that client uses toZcashError() function.

I checked the PR and toZcashError() is wrongly implemented due to misunderstanding. Implementation should looks like this:

func toZcashError() -> ZcashError {
        if let zcashError = self as? ZcashError {
            return zcashError
        } else {
            return ZcashError.unknown(self)
        }
    }

[LukasKorba]

Main reason we added this is to use TCA actions

case someFailure(ZcashError)

so we need to ensure ZcashError is possible to pass from a throwing function. If it's not a ZcashError, we don't have a tool to wrap it from the app side.

[pacu]

I guess we don't have much wiggle room here and will have to live with it.