Issue Description:

I wanted to ask if founded by me strange behaviour of compiler/parser is bug or it is 'feature' and 'by design' :
(Swift version 3.0-dev (LLVM b010debd0e, Clang 3e4d01d89b, Swift 7182c58))
(IBM Swift Sandbox)

1. I was not expecting this will compile :

let ft1 : (Int,Int) -> Void = { x in print(x.0, x.1)}
ft1(1, 2)

the type of ft1 is definitely not the same as closure

2. The same. But this generates error in runtime :

let ft2 : (Int,Int) -> Void = { x in print(x)}
ft2(1, 2)

3. Could you describe why this compile, as types of closures are not the same

func z1(block: (Int,Int) -> Void) {
    block(1,2)
}

z1 { x, y in print(x,y)}
z1 { x in print(x.0, x.1)}
z1 { (x, y) in print(x, y)}

func z2(block: ((Int,Int)) -> Void) {
    block((1,2))
}

z2 { x, y in print(x,y)}
z2 { x in print(x.0, x.1)}
z2 { (x, y) in print(x, y)}
//z2 { ((x, y)) in print(x, y)}  // compilation error ???

Thank you for your description and comments.