protocol P {}
protocol Q : P {}
protocol R : P {}

struct X<T> {}
extension X: P where T: Q {}
extension X: Q where T: Q {}
extension X: R where T: R {}

confusing_error.swift:8:1: error: type 'T' does not conform to protocol 'Q'
extension X: R where T: R {}
^
confusing_error.swift:8:1: error: 'R' requires that 'T' conform to 'Q'
extension X: R where T: R {}
^
confusing_error.swift:8:1: note: requirement specified as 'T' : 'Q'
extension X: R where T: R {}
^
confusing_error.swift:8:1: note: requirement from conditional conformance of 'X<T>' to 'P'
extension X: R where T: R {}
^

error: Type `X<T>` doesn't conform to inherited protocol `P` with the requirement `T` : `R`
extension X: R where T: R {}
error Type `X<T> : P` requirement specified as `T` : `Q`
extension X: P where T: Q {}