duplicates:

• SR-9760 Can't add @escaping to an argument of generic function having typealiased function type

Issue Description:

Using a function-type type alias as an escaping parameter type fails to compile:

protocol Foo
{
    associatedtype Bar
    typealias Callback = (Bar) -> Void

    var currentValue: Bar { get }
}

// Error: @escaping attribute only applies to function types
func callBroken<T: Foo>(foo: T, callback: @escaping T.Callback) {
    DispatchQueue.main.async { callback(foo.currentValue) }
}

// Spelling it out works (of course).
func callWorks<T: Foo>(foo: T, callback: @escaping (T.Bar) -> Void) {
    DispatchQueue.main.async { callback(foo.currentValue) }
}

I know there is SR-2316 and several duplicates. Especially the comment by Jordan Rose addresses what I think is still broken:

The actual behavior we want here is that @escaping is a property of the parameter, not the function type, but we don't currently allow you to write @escaping on typealiases.

Later in the comments, David Grove added "fix confirmed" but he was probably referring to something else.

I tested this with swift-3.1-RELEASE.xctoolchain and swift-DEVELOPMENT-SNAPSHOT-2017-05-12-a.xctoolchain.