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https://web.archive.org/web/20190508021859/https://twitter.com/davecheney/status/942593128355192832
This one works.

Go doesn't have covariance/contravariance or auto casting between identical interfaces.
What it means in context of using interfaces in the package of invocation is that if you have a local interface Handler that uses another local interface, Message it cannot be implemented without importing the Message, and different callers cannot have different interfaces.

type Message interface {
    GetText() string
}
type Handler interface  {
    Handle(msg Message)
}

More to that, if the local interface if not exported (i.e. message, lowercase) it cannot be implemented at all outside of the package.

The only solution I see is to have a common "interface" package and use it in both places, which this article is against.
So the question is – what would you propose in that case?