=== tests/cases/compiler/multiCallOverloads.ts ===
interface ICallback {
>ICallback : ICallback

    (x?: string):void;
>x : string
}

function load(f: ICallback) {}
>load : (f: ICallback) => void
>f : ICallback
>ICallback : ICallback

var f1: ICallback = function(z?) {}
>f1 : ICallback
>ICallback : ICallback
>function(z?) {} : (z?: string) => void
>z : string

var f2: ICallback = function(z?) {}
>f2 : ICallback
>ICallback : ICallback
>function(z?) {} : (z?: string) => void
>z : string

load(f1) // ok
>load(f1) : void
>load : (f: ICallback) => void
>f1 : ICallback

load(f2) // ok
>load(f2) : void
>load : (f: ICallback) => void
>f2 : ICallback

load(function() {}) // this shouldn’t be an error
>load(function() {}) : void
>load : (f: ICallback) => void
>function() {} : () => void

load(function(z?) {}) // this shouldn't be an error
>load(function(z?) {}) : void
>load : (f: ICallback) => void
>function(z?) {} : (z?: string) => void
>z : string