=== tests/cases/compiler/multiCallOverloads.ts ===
interface ICallback {
>ICallback : Symbol(ICallback, Decl(multiCallOverloads.ts, 0, 0))

    (x?: string):void;
>x : Symbol(x, Decl(multiCallOverloads.ts, 1, 5))
}

function load(f: ICallback) {}
>load : Symbol(load, Decl(multiCallOverloads.ts, 2, 1))
>f : Symbol(f, Decl(multiCallOverloads.ts, 4, 14))
>ICallback : Symbol(ICallback, Decl(multiCallOverloads.ts, 0, 0))

var f1: ICallback = function(z?) {}
>f1 : Symbol(f1, Decl(multiCallOverloads.ts, 6, 3))
>ICallback : Symbol(ICallback, Decl(multiCallOverloads.ts, 0, 0))
>z : Symbol(z, Decl(multiCallOverloads.ts, 6, 29))

var f2: ICallback = function(z?) {}
>f2 : Symbol(f2, Decl(multiCallOverloads.ts, 7, 3))
>ICallback : Symbol(ICallback, Decl(multiCallOverloads.ts, 0, 0))
>z : Symbol(z, Decl(multiCallOverloads.ts, 7, 29))

load(f1) // ok
>load : Symbol(load, Decl(multiCallOverloads.ts, 2, 1))
>f1 : Symbol(f1, Decl(multiCallOverloads.ts, 6, 3))

load(f2) // ok
>load : Symbol(load, Decl(multiCallOverloads.ts, 2, 1))
>f2 : Symbol(f2, Decl(multiCallOverloads.ts, 7, 3))

load(function() {}) // this shouldn’t be an error
>load : Symbol(load, Decl(multiCallOverloads.ts, 2, 1))

load(function(z?) {}) // this shouldn't be an error
>load : Symbol(load, Decl(multiCallOverloads.ts, 2, 1))
>z : Symbol(z, Decl(multiCallOverloads.ts, 11, 14))