protocol P {
    typealias T
    var env: T { get }
    func f(a: Int);
}

struct IgnoreInt: P {
    typealias T = Int
    var env: T
    func f(a: Int) { }
}

class IntBox {
    var value: Int
    init(value: Int) { self.value = value; }
}

struct AssignIntBox: P {
    typealias T = IntBox
    var env: T
    func f(a: Int) { env.value = a }
}

var a: P = IgnoreInt(env: 0)
var b: P = AssignIntBox(env: IntBox(value: 0))
b = a
b.f(1);

foo.swift:24:8: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var a: P = IgnoreInt(env: 0)
       ^
foo.swift:25:8: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var b: P = AssignIntBox(env: IntBox(value: 0))
       ^

foo.swift:24:8: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var a: P = IgnoreInt(env: 0)
       ^
foo.swift:24:5: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var a: P = IgnoreInt(env: 0)
    ^
foo.swift:25:8: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var b: P = AssignIntBox(env: IntBox(value: 0))
       ^
foo.swift:25:5: error: protocol 'P' can only be used as a generic constraint because it has Self or associated type requirements
var b: P = AssignIntBox(env: IntBox(value: 0))
    ^