QML code model should understand function return values and function arguments

The following examples show a fundamental limitation of the current code model:

function foo() { return new Date }
var x = foo()
x.<complete fails>

function foo(a) { 
    a.<complete fails>
}
foo(new Date)

To offer useful completion in these cases we either need to annotate functions with information about return and argument types or implement intricate static analysis.