__assign polyfill is emitted even when targeting ES6

[billti]

Using the release-2.1 branch, with target: "es6", this code:

const init = {a: 10, b: true};
let newObj = {...init, c: null};

Generates the below emit, which contains the unnecessary helper __assign, as Object.assign is part of ES6 (see http://www.ecma-international.org/ecma-262/6.0/#sec-object.assign ).

var __assign = (this && this.__assign) || Object.assign || function(t) {
    for (var s, i = 1, n = arguments.length; i < n; i++) {
        s = arguments[i];
        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
            t[p] = s[p];
    }
    return t;
};
const init = { a: 10, b: true };
let newObj = __assign({}, init, { c: null });

[sandersn]

What emit would you like to see? I think it's best to keep the expression emit as __assign({}, init, { c: null }) instead of Object.assign({}, init, { c: null }), which means that some kind of helper emit is needed. @rbuckton, can you provide an opinion on how the ES6 emit should look for spread?

[mhegazy]

why not just call Object.assign, like we do with Math.pow for instance?

[rbuckton]

I concur with @mhegazy, we can special case Object.assign if we know we aren't further transforming the file to ES5/3.