[Issue 12247] in contract in interfaces is not checked

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=12247

--- Comment #3 from Simon Naarmann <eiderdaus at gmail.com> ---
Ah, I wouldn't have guessed that absence of contract means an always-passing
contract. Thanks!

I agree to close it as a duplicate of 6856.

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