=== tests/cases/compiler/functionOverloads15.ts ===
function foo(foo:{a:string; b:number;}):string;
>foo : Symbol(foo, Decl(functionOverloads15.ts, 0, 0), Decl(functionOverloads15.ts, 0, 47), Decl(functionOverloads15.ts, 1, 47))
>foo : Symbol(foo, Decl(functionOverloads15.ts, 0, 13))
>a : Symbol(a, Decl(functionOverloads15.ts, 0, 18))
>b : Symbol(b, Decl(functionOverloads15.ts, 0, 27))

function foo(foo:{a:string; b:number;}):number;
>foo : Symbol(foo, Decl(functionOverloads15.ts, 0, 0), Decl(functionOverloads15.ts, 0, 47), Decl(functionOverloads15.ts, 1, 47))
>foo : Symbol(foo, Decl(functionOverloads15.ts, 1, 13))
>a : Symbol(a, Decl(functionOverloads15.ts, 1, 18))
>b : Symbol(b, Decl(functionOverloads15.ts, 1, 27))

function foo(foo:{a:string; b?:number;}):any { return "" }
>foo : Symbol(foo, Decl(functionOverloads15.ts, 0, 0), Decl(functionOverloads15.ts, 0, 47), Decl(functionOverloads15.ts, 1, 47))
>foo : Symbol(foo, Decl(functionOverloads15.ts, 2, 13))
>a : Symbol(a, Decl(functionOverloads15.ts, 2, 18))
>b : Symbol(b, Decl(functionOverloads15.ts, 2, 27))