Bug in the __rest helper function for numeric properties

[evanw]

TypeScript Version: Nightly

Search Terms: namespace rest export number numeric object destructuring pattern

Code

namespace Foo { 
    export let { 0: a, ...b } = [0, 1]
    console.log(JSON.stringify({a, b}))
}

Expected behavior:

I expect this to log {"a":0,"b":{"1":1}} because that's what you get when you run the following JavaScript natively:

let { 0: a, ...b } = [0, 1];
console.log(JSON.stringify({a, b}))

Actual behavior:

This actually logs {"a":0,"b":{"0":0,"1":1}}.

I'm working on my own TypeScript parser for esbuild, a JavaScript bundler, and I noticed that the code TypeScript generates for destructuring object properties has this bug. The generated code for the sample above looks like this:

"use strict";
var __rest = (this && this.__rest) || function (s, e) {
    var t = {};
    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
        t[p] = s[p];
    if (s != null && typeof Object.getOwnPropertySymbols === "function")
        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) {
            if (e.indexOf(p[i]) < 0 && Object.prototype.propertyIsEnumerable.call(s, p[i]))
                t[p[i]] = s[p[i]];
        }
    return t;
};
var Foo;
(function (Foo) {
    var _a;
    _a = [0, 1], Foo.a = _a[0], Foo.b = __rest(_a, [0]);
    console.log(JSON.stringify({ a: Foo.a, b: Foo.b }));
})(Foo || (Foo = {}));

The problem is that the numeric property is passed to __rest as a number, not as a string, but __rest is implemented using indexOf which doesn't consider 0 and "0" to be equal.

I think the most straightforward fix would be for the compiler to emit __rest(_a, ["0"]) instead of __rest(_a, [0]).

Playground Link: https://www.typescriptlang.org/play/?ts=Nightly#code/HYQwtgpgzgDiDGEAEAxA9mpBvJAoJBSEAHjGgE4AuSANhNTgAwBcSIANEgHQ8BGSAXyQBeJAG1GnAIwBdfIXhpgUNHS400AcwAUAKQDKAeQByXKJXIBLYJssAzAJ7asHJLwEBKD7gG4gA

Related Issues: I couldn't find any existing issues about this.