test/decl/protocol/req/unsatisfiable.swift

// RUN: %target-typecheck-verify-swift -swift-version 4

protocol P {
  associatedtype A
  associatedtype B

  func f<T: P>(_: T) where T.A == Self.A, T.A == Self.B // expected-error{{instance method requirement 'f' cannot add constraint 'Self.A == Self.B' on 'Self'}}
}

extension P {
  func f<T: P>(_: T) where T.A == Self.A, T.A == Self.B { }
}

struct X : P {
  typealias A = X
  typealias B = Int
}

protocol P2 {
  associatedtype A

  func f<T: P2>(_: T) where T.A == Self.A, T.A: P2 // expected-error{{instance method requirement 'f' cannot add constraint 'Self.A: P2' on 'Self'}}
}

class C { }

protocol P3 {
  associatedtype A

  func f<T: P3>(_: T) where T.A == Self.A, T.A: C // expected-error{{instance method requirement 'f' cannot add constraint 'Self.A: C' on 'Self'}}
  func g<T: P3>(_: T) where T.A: C, T.A == Self.A  // expected-error{{instance method requirement 'g' cannot add constraint 'Self.A: C' on 'Self'}}
}

protocol Base {
  associatedtype Assoc
}

// FIXME: The first error is redundant, isn't correct in what it states, and
// also should be emitted on the inheritance clause.
// FIXME: This used to /not/ error in Swift 3. It didn't impose any statically-
// enforced requirements, but the compiler crashed if you used anything but the
// same type.
protocol Sub1: Base { // expected-error {{first type 'Self.Assoc' in conformance requirement does not refer to a generic parameter or associated type}}
  associatedtype SubAssoc: Assoc // expected-error {{inheritance from non-protocol, non-class type 'Self.Assoc'}}
}
// FIXME: This error is incorrect in what it states and should be emitted on
// the where-clause.
protocol Sub2: Base { // expected-error {{first type 'Self.Assoc' in conformance requirement does not refer to a generic parameter or associated type}}
  associatedtype SubAssoc where SubAssoc: Assoc
}