test/Constraints/collection-mutablecollection-order-dependency-2.swift

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

// rdar://problem/29954938 -- A bug in associated type inference exposed an
// order dependency where, if a type conformed to Collection in one extension
// then conformed to MutableCollection in a later extension, it would fail
// to type-check. This regression test ensures that a "working" order,
// where MutableCollection comes first, remains working.

struct Butz { }

extension Butz: MutableCollection {
    public var startIndex: Int { return 0 }
    public var endIndex: Int { return 0 }
}

extension Butz: Collection {
    public subscript (_ position: Int) -> Int {
        get { return 0 }
        set {  }
    }
    public func index(after i: Int) -> Int { return 0 }
}