Object.defineProperties: "Index Signature is missing in type {}"

[felixrieseberg]

The following is valid ES5.1 JavaScript, but yields an error when used in TypeScript. TS2345: Argument of type '{}' is not assignable to parameter of type 'PropertyDescriptorMap'. Index signature is missing in type '{}'. A side effect is that Code's IntelliSense considers this JavaScript to be invalid.

var source = {get name() { return 'source'}};
var target = {};

var map = Object.keys(source).reduce(function (descriptors, key) {
    descriptors[key] = Object.getOwnPropertyDescriptor(source, key);
    return descriptors;
}, {});

Object.defineProperties(target, map);

I'd love to fix this, but I'm not sure where to look. Any suggestions?

(Debug info: Tested with Version 1.8.0-dev.20160119)

[RyanCavanaugh]

Same root cause as #6041