==== tests/cases/compiler/functionOverloads15.ts (1 errors) ====
    function foo(foo:{a:string; b:number;}):string;
    function foo(foo:{a:string; b:number;}):number;
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! functionOverloads15.ts(2,1): error TS2175: Overloads cannot differ only by return type.
    function foo(foo:{a:string; b?:number;}):any { return "" }
    