omochimetaru

@swift-5.6.3 @swift-5.7.3

protocol P {} protocol Q {} struct S: P {} extension Q { func p() -> some P { return S() } } func foo(q: Q) -> some P { return q.p() }

exit status: 1 with stderr:

<stdin>:8:10: error: member 'p' cannot be used on value of protocol type 'Q'; use a generic constraint instead return q.p() ^ ~