Thanks for writing it out, but you've actually illustrated exactly my complaint. When you call oldMethod console.warn will spit out the line number of the wherever in your framework you have the

    var deprecated = function(fn) {
       console.warn("Deprecated!");
       fn.apply(this, arguments);
    };

declared... but you (as the user of a framework) still have no real idea where the actual function you shouldn't be calling (the fn) lives in your code (especially since the function can be anonymous)... you just know that the framework is telling you you're using a deprecated function somewhere in the code you wrote.

What I really want, and what can't be achieved with your purely in-language solution (and it really is a great solution considering the constraints), is a special form for things like @deprecated such that it straight-up can capture not only the function it's decorating, but also meta-data about the function (e.g. where it's declared, the caller / callee, etc.)